This paper is submitted in accordance with formal requirements for the course: EVDS 611: BUILDING SCIENCE AND TECHNOLOGY II, in the Faculty of Environmental Design, The University of Calgary. The purpose of this report is strictly an academic exercise. As such neither the authors, the instructor, nor the University assumes responsibility if the content of this report is used for any other purpose.
We will investigate traditional and new products used as structural components of floors in small buildings. Products included in this study are laminated veneer and strand lumber, prefabricated wood I-joists, and flat trusses where they are used to support floors. We compare these products against traditional fir dimensional lumber in terms of various concerns such as performance, ease of handling and construction, health and environment, fire resistance and safety, and consumer acceptance. We determine that there are significant advantages to the new systems in terms of performance and environmental impact, but that they require extra consideration from traditional systems in terms of fire resistance and sound attenuation. Costs and difficulties in handling are not significant enough to advise against their use.
When we think of a building, often the walls and roof are the first components that come to mind. These elements effectively define an enclosure and determine our relationship with it. However, except in the most primitive structures, a very important structural and spatial component is the floor. The simplest floors are laid directly on or in the ground, and provide various barriers to the outside environment. These floors, such as flagstone or poured concrete slab, rely on their contact with the ground for their structure and load bearing properties. More complex floors can span between the walls and columns of a building allowing for multiple stories in buildings. These spanning floors have to be designed and built such that they can carry their own dead weight, which is called the dead load, and the weight of anything placed or moving upon them, the live load. As well, all the weight must usually be borne entirely by the floor's edges.
Such a floor of any considerable size must be constructed from a number of components. In small buildings these components normally include a floor deck, or subfloor, supported by evenly spaced structural members. These members can be either flat trusses or joists, each in concert with beams where lengthy spans require them.
Like all trusses, flat trusses are made from three components. These include the top chord, bottom chord and the webbing. (figure 5) The top chord is a horizontal member that establishes the upper edge of the truss. It is subjected to the stresses of compression and bending. The bottom chord defines the lower edge of a truss. This member is subject to both tensile and bending stresses. The web is the structure that joins the top and bottom chords together. In flat trusses, the web is made of boards arranged in a triangular pattern and connected together with metal connector plates. These members are subject to the stresses of pure compression and tension only. This arrangement transfers stresses along the truss to the bearing walls or foundations.
Joists are usually made from a solid material, such as fir, but have more recently been manufactured from wood materials laminated and bonded together with glue. (slide 1) Prefabricated wood I-joists are similar to trusses in the way they manage stresses and in the terminology used to describe them. I-joists, like trusses, have a top and a bottom chord, but use a piece of oriented strand board (OSB) as the web. Unlike in the truss web, the joist web is subject mainly to shear stresses.
Trusses and joists fulfill the same structural role when used in a floor. They transfer downward stresses on the floor deck to the bearing walls at the ends of the span. Where the span is too long for joists or trusses to clear, beams are used as an intermediate bearing structure. Beams transfer downward stresses from joists or trusses to either the ends of the beam's span or to columns. Beams can be made of one or more solid wood members fastened together, and recently have been manufactured from laminated veneers. (figure 2) Occasionally, steel beams are used in small buildings to achieve a certain span.
It has been suggested that flat trusses, I joists, laminated lumber and their companion components represent an improvement in performance over traditional floor system materials and components. These products are being used increasingly in the construction of houses and other small buildings by both custom home builders and developers. As floor systems are a integral part of any building, we believe that making informed choices with respect to floor system materials is very important when designing or constructing a building.
In this investigation, through product analysis and comparison, we intend to recommend an approach to floor systems that is informed and practical, allowing for the readers to make choices suitable to their given construction situation.
We began our investigation with conversations with people who have built and designed floor systems, and with people who have recently made floor system choices. We then visited the Calgary based manufacturers of the new products. There are three manufacturers of prefabricated wood I-joists and flat trusses in the Calgary area. These are Nascor Incorporated, Jager Industries Inc., and Trus Joist MacMillan Limited1. The latter company also manufactures a variety of laminated lumber for use as beams or in I-joists. Information about their products was gained through both their product literature and discussions with their engineers or representatives. We also visited building sites where these products were being used and made observations.
To complete our analysis we have described how and why new floor system products are manufactured the way they are, and then assessed them in terms of various concerns that users, builders and designers have about floor systems. Through the assessment, we have determined what the problems and advantages are with each product.
I-joists are used in a floor system in the same way as dimensional lumber joists have been. As mentioned previously the joists are made of three primary components: the top chord (or flange), bottom chord and the web. These components are bonded together by a glue compound at connections of various types. The resulting member is true and will not warp or shrink in time. It is lighter than a wooden member, and can be manufactured much longer. This section will detail the primary components of the I-joist and discuss how these parts operate together to accommodate various loads and stresses.
Because a joist is in bending, it has to handle a combination of compressive and tensile forces. The top chord of the I-joist is the member responsible for resisting the compressive forces of a load, and the bottom chord is responsible for tensile forces. This puts the top chord into compression, and the bottom chord into tension. Compressive and tensile stresses are applied to the joist when an object is placed on the joist, or the floor system. The stress can come tin two ways. The first is a distributed load which distributes the load evenly throughout the member. Comparatively, a point load is concentrated on a single point on the joist. In traditional wood joist floor systems the compressive and tensile forces were handled by a single wood member. In the I-Beam system only the top chord is in compression and only the bottom chord is in tension.
Various types of products are used by the different manufacturers to form both the top and bottom chords. The most common is machine stress rated (MSR) dimensional lumber. This is wood that has been put through a rigourous process of testing and once completed the lumber is rated according to its performance. This lumber is generally considered to be superior to regular dimensional lumber. In addition to being machine stress rated some of the joist systems also laminate that lumber to give it additional strength and rigidity. The MSR chords are connected together by various methods of finger jointing in order to enable longer spans.
As with traditional wood joists the chords made of this type of wood have a tendency to shrink over time, although this may be less than the traditional joist, given the relative size of the chord. Another consideration when choosing the wood flanges is how straight they are. Wood joists have a tendency to bend in one direction over time. The MSR lumber has less of a tendency to do this but will likely bend a little over time.
An alternative to the MSR lumber is laminated veneer lumber (LVL) This is manufactured by the bonding of many layers of veneers to create a sort of plywood member. This lumber offers several advantages over the MSR lumber. It is possible to have very long spans of a continuous board. In addition it is possible to have long lengths of perfectly straight lumber. Laminated lumber will not shrink over time like dimensional lumber and subsequently will provide a stiffer and quieter floor system. Recently LVL has been replaced in I-joists by laminated strand lumber (LSL) such as TimberStrand¨ from Trus Joist Macmillan. Because it is made of strands that are not always oriented parallel to the length of the member, it can handle sideways bending stresses more effectively. The TimberStrand¨ product is discussed further, along with other similar products in the section on laminated timber.
The web is the middle member which is primarily responsible for connecting the top and bottom chords together. The main force acting on the web is shearing towards the ends and along the axis of the top and bottom chords. This member helps the joist react to the forces of shearing where it bears on a supporting member, such as a wall.
There are several different types of webs used in floor joists. Some employ an open web system, somewhat like a truss. More commonly, however, the joist will have a single wood product member making up the web. The most common web material used in wood I- joists is Oriented Strand Board (OSB). (Slide 2) OSB is basically a building material composed of long strands of wood fibre, compressed and glue laminated together under pressure into three to five layers. The intentional orientation of the wood strands increases the OSB's resistance to shearing forces. OSB boards are generally stiffer and stronger than other types of non-veneered panels.2 The three Calgary manufacturers of I-joists obtain their OSB from the Weyerhaeuser, an international wood-product corporation. This product is called Sturdi-Wood¨.
The three manufacturers of floor systems in Calgary use a phenol-resorcinol waterproof glue in their I-joists. Resorcinol is a glue that is commonly used in the manufacture of wooden boats as it has proven durable below the waterline. There are three connections in an I-joist where glue is used. The first is within the OSB itself, bonding the many strands together to form the sheathing. The second bond is within the chords, bonding the various types of chords together. The third joint holds the chords and the web together.
The second bond has the most variables mainly depending on the nature of the chord. Both LVL and LSL require glue to bond the veneers or strands together. This is done with a large press and microwaves. The fibre and the glue is fed into a machine that compresses them into a space about a quarter of the dimension they entered at. The microwaves heat the glue so that when the member leaves the machine the glue is at least 90% cured. This process is the same for most laminated timber.
The other possible material for the chord is MSR lumber. Although solid wood is equally acceptable as a chord member, its length is limited by the length of available trees. Finger jointing and gluing is necessary to achieve longer lengths. Similar to the microwave process, this is done on a conveyor which pushes the wood between two electrodes. When a finger jointed glue joint passes between the electrodes a high voltage circuit is closed through the glue. The glue in turn cures to about 90%. Because phenol-resorcinol is too resistant to electricity, a straight resorcinol glue is used in this process.3
The third joint is done manually by a production line of workers.
Laminated timber is used in floor systems where dimensional lumber beams would normally be required. Laminated beams use glued plies or strands to eliminate the occurrence of knots and other wood defects; therefore, the strength of a laminated wood beam is greater than a standard wood beam4 Laminated wood is manufactured by gluing smaller pieces of wood together to form structural members. (Figure 1) This is usually done in hydraulic presses and bonded with synthetic glues. This process allows manufacturers to produce members of almost any regular size and shape. It allows for the manufacture of the members in curved shapes; it is not uncommon to see these types of beams used in architectural design.5 This laminating process also can use almost the entire volume of both large and small trees. If there are any serious defects in the wood used, they can be rejected during the process of manufacturing and subsequently discarded.
?
|
Just as with I-joist chords, laminated timber is manufactured with both veneers, strands and parallel strands. Products on the market in Calgary are TimberStrand®, ParallamTM and MicrollamTM by Trus Joist MacMillan, and TecLamTM and TemLamTM from Jager. The National Research Council of Canada, Institute for Research in Construction has evaluated all of these products and determined that they can serve as lumber with respect to structural capacity.
LVL is an engineered wood product which is used as larger beams and headers in floor systems. These include products such as MicrollamTM, TecLamTM and TemLamTM. Each of these products demonstrate a greater ability than dimensional wood to span long distances and carry greater loads. In addition they exhibit the same characteristics as other manufactured timber in that they do not shrink or deform as dimensional lumber does. This is because any tendencies of the veneers to distort are counteracted by the opposing tendencies of the adjacent veneers.
LVL is manufactured from a variety of woods. MicrollamTM is made from varies types of western species trees including Douglas fir, lodgepole pine, southern pine, western hemlock, white fir or yellow poplar.6 TecLamTM is manufactured from fir trees and TemLamTM from poplar trees. Each of these products are produced using the waterproof adhesive phenol-formaldehyde making the wood fibres resistant to moisture penetration.
?
 |
LSL is an another type of engineered wood product that can be used as larger beams and headers or as the top and bottom chord in an I-joist. TimberStrand® is manufactured by Trus Joist MacMillan for use in both instances. (figure 2) Instead of veneers, they incorporate the use of deliberately oriented long strands (appox. 300mm). The fibres are oriented in a parallel direction and formed into a large mat 2.44 m wide by 10.67 m long, in thicknesses up to 140mm.7 The fibres are bonded with isocyanurate-based adhesive. As the greatest strength of wood is along its grain, having the fibres arranged parallel maximizes the shear capacity of the material. This in turn contributes to the strength of the member.
Because they are composed by only small pieces of wood, inherent tendencies in larger dimensional lumber such as twisting, splitting or warping will not occur in time. This is because any tendencies of the smaller pieces to distort will be counteracted by other adjacent pieces tending to bend in opposing directions.
?
 |
PSL is similar to LSL except that the fibres are arranged parallel to the length of the manufactured member. ParallamTM is a PSL product made by Trus Joist MacMillan. (figure 3) Its strands are made of either Douglas fir, Western Hemlock, Southern pine or Yellow Poplar. The former two are considered "Western Species" and the latter two "Eastern Species". The strands are coated with phenol formaldehyde, an exterior type adhesive, and fed into a belt press under heat and pressure to form a continuous billet.8 ParallamTM is used for beams and columns with beam lengths of up to 60' available in dimensions ranging from 2 11/16" to 7". 9
An alternative to either the I-joist configuration or dimensional lumber is the open web truss joist system. These joists are also called flat trusses. An open web truss consists of the same members as the I-joist: a top and bottom chord and a web member. The top and bottom chords are generally made of wood or a wood product and are subjected to the same compression, tension and bending stresses as discussed in the joists. The web of the truss can have many different configurations depending upon the truss's application. The web can be made of either wood or steel depending on the desired structural capacity. As in the I-joist, the web consists of members that join the top and bottom chord together. In a truss these members form a triangular patterns that give the truss action. These members are only subjected to the forces of pure compression or tension, no bending.
Trusses offer a great deal of flexibility because they can be manufactured to the exact specifications of the designer. There are some limitations with the flat trusses as the deflection considerations are more critical than with pitched trusses. The span to depth ratio is limited by the desired depth of the floor and consequently the spanning distances of flat trusses are limited, although they can outspan all but the deepest I-joists.
Trusses are manufactured by Jager Industries and Trus Joist MacMillan in Calgary. Both of these companies produce wood and steel web trusses for all applications. The primary use of these trusses are for flat roofs with large spans as they tend to be more expensive than I-joists or dimensional wood systems when used in residential applications. However, in our investigation we found them being used in the new townhouses and condominiums at MacKenzie Towne.
Generally, new products that intend to satisfy existing demands are not acceptable unless they perform at least as well as materials currently available. In terms of our analysis, there would be no point discussing new products in small building floor systems if they did not suggest an improvement in performance over traditional dimensional wood systems. To be specific, new systems should be durable, predictable, and able to span distances, all in a manner similar to traditional systems. Dimensional wood lumber has been used in floor systems for centuries. For this reason, we will consider it a benchmark by which to judge new products.
Dimensional lumber has long been the material of choice in the Canadian home-building industry. It is readily available in all practical dimensions and is relatively inexpensive. Fir is the most common type of wood to be used for framing and floor systems. Fir is a workable softwood that has a good capacity for spanning and resisting loads when used as a joist. The two sizes normally used are 2" x 10" and 2" x 12". These are commonly available in lengths up to about 18 feet.
As with all but the highest grade dimensional lumber there are inherent flaws in the makeup of a fir joist. As the wood dries it tends to shrink and distort. This shrinkage and distortion can lead to squeaky floors as the joists pull away from the subfloor and other adjacent members of the structure. This can also lead to other problems within the structure, such as cracked ceiling drywall and a reduced load bearing capacity of the floor. In addition there are other flaws within each board such as knots and cracks which reduce the structural strength of a piece of lumber, make it harder to shape and are sometimes considered undesirable in appearance. Decay and insect damage will occur over the life of the tree and can affect the useful properties of its wood. Organisms may still be alive in the piece of lumber and will continue to contribute to its decay. There are also characteristics which arise largely from the changes that take place during the seasoning process of the wood. These arise because of different rates of shrinkage in the wood with respect to the orientation of the grain. Bowing, crooking, cupping, and twisting all happen because of non uniform shrinkage. (figure 4) 10
?
 |
Despite the inherent problems with dimensional lumber it continues to be a versatile and relatively inexpensive building material that is still very popular for use in floor systems. However, as new products develop and the availability of good lumber declines there will be an increasing demand for alternative products to dimensional lumber. Concerns with Engineered Alternatives
The Calgary manufacturers of premanufactured wood I-joist systems claim they are superior to dimensional lumber floor systems. The 'I' shape of the joist uses wood fibres more effectively than traditional dimensional lumber joists. The joists create a more rigid and sturdy floor which is capable of spanning greater distances than dimensional lumber.11
There are many variables involved in determining the distance that a particular joist can span. In general the larger the chords and deeper the web, the longer the spanning ability of the member. This is true of both the I-joists and dimensional lumber. The I-joist system, in general, has the capability to span longer distances with similar size members to that of dimensional lumber.
A span is the distance between supports that a joist or other horizontal member is able to bridge and effectively carry a load.12 When placing this in the context of a floor system there are some additional considerations. The floor must be able to carry both a live load and a dead load. (for definitions refer to glossary)
There are several types and sizes of I-joists on the market and it is not within the scope of this analyses to compare each one. Refer to Appendix 3 for span charts of the various types and sizes of I-joists. In general the I-joists obtained results greater than those specified by the Canadian Building Code in all respects.
There is a clear advantage, in terms of spanning, with the I-joist systems over traditional wood systems. With the diverse range in I-joist products available almost any residential and small commercial spanning requirements can be met. The I-joists offer the consumer the potential for longer continuous spans and allow for more open spaces within the structure. This can result in a cost savings within the scope of the overall system because the use of additional beams, teleposts and other structural members are not required.
Joist spacing is more flexible with manufactured I-joists than with dimensional lumber joists. The use of deeper joists can allow for wider spacing. This flexibility allows the floor system designer to use the best configuration for the job in terms of both structural adequacy and cost.
I-Beam joists are a durable alternative to traditional dimensional lumber. They exhibit a resistance to water and moisture penetration that traditional lumber does not. This is largely due to the use of a waterproof glue that is used to bond the members together and to produce the OSB web member. The service life of the joist depends on the environment it is in as well as the material it is made of. If the I-Beam is constructed of laminated materials it will have a greater resistance to moisture penetration and will have a longer service life. When installed according to the company specifications the I-Beam joist can be expected to function for the life of the structure.
The I-Joists manufactured in Calgary are designed to serve as floor or roof joists. They can be used in these capacities in either simple or continuous spans which support uniform loads only. Just as the Building Code's tables must be adhered to when spanning with wood, it is critical that the installation of I-joists be in accordance with the span tables and the erection and installation details provided in the manufacturers specifiers guide. Here are some additional recommendations made in Trus Joist MacMillan's specifier guide13:
It is possible for these joists to have applications outside of the scope of the manufacturers specifications but only if the specifications have been approved by a professionally licensed engineer.
All of the design details, fabrication, handling and installation should be in accordance with the manufacturer's instructions. Specifically with respect to loads and spans, bracing, bearing and web-hole drilling. Any damaged or defective joists should not be used unless it has been properly repaired and approved by the manufacturer. This is important because any damage to either of the top or bottom chord can result in a lower load bearing capacity for the joist. This is particularly true of the bottom chord. Any damage to this chord could result in the entire joist being discarded or the application of another joist beside the damaged one. Tests by a recognized agency of the National Research Council of Canada confirmed the manufacturer's claims that the I-joists exceed the standards set forth in the National Building Code. The tests performed were in accordance with the Standard Specification for Establishing and Monitoring Structural Capacities of Wood I-Joists.14 In terms of shearing and moment capacity the I-joists consistently exceeded the design values by an acceptable margin. The allowable deflection for a joist by code is 1/360. This means if a member were divided into 360 equal parts, the deflection in the centre of the member could be equal to one of those parts. The standard that I joists meet is at least 1/450.
Laminated timber is an alternative to traditional dimensional timber. The manufacturers of these products maintain that these products perform as well or better than dimensional lumber. In terms of spanning these members are capable of equaling or bettering the abilities of wood because of the way they are constructed. Certain types of Laminated timber is designed to perform specific tasks. TimberStrand®, for example, is used either as a header or as the chords in I-joists. ParallamTM can be used wither as a beam or a column because of its ability to respond to compressive loads. As with other laminated products, laminated timber is able to resist moisture better than traditional lumber because the glue used has water resistant properties. Laminated timber has a distinct advantage over traditional lumber because it will not shrink over time. One concern when using laminated timber is the glue used in the laminating process. This has implications on both health and fire safety which is discussed later in this analysis. In general laminated timber is an excellent building material that can be used almost anywhere that traditional lumber is used.
?
 |
These trusses are used on occasions where the structural demands exceed the capacity of the I-Joist or dimensional wood. Another occasion why this system might be chosen over the other systems is when flexibility is required for routing ductwork and other services within the floor. They employ a system of triangulations which give the truss actions. This system provides the structural strength required to span relatively long distances.?
Each of these new products, when used according to the manufacturers specifications, outperforms dimensional wood lumber. Engineered members can either span longer distances, accommodate greater loads, or have more inherent flexibility in the way they can be configured to fit in any given project.
Fire resistance and safety are primary concerns when considering any building material. This is especially true when considering systems that are primarily made of a combustible material such as wood. New systems must exhibit an ability to resist fire comparable to existing systems. Of course, all systems must meet or beat the fire code. In terms of a floor system these requirements are critical because the floor is a structural member of the building. The floor must be able to support the structure in a fire long enough to allow the occupants to safely evacuate the building.
I-Joists are constructed primarily of wood and wood products and are therefore combustible. I-Joists have less mass than a traditional board of lumber and will therefore be consumed more rapidly by fire. The I-joists meet the required criteria for a one hour fire resistance rating when they compose part of a complete floor system. This complete systems requires that there be bridging of the members, the installation of mineral wool blankets between the joists and galvanized sheet steel furring channels. In addition 5/8" thick gypsum wallboards should be attached to the underside of the furring channels. (figure 6) In order to achieve a two hour fire rating the joists must be further protected from flame by adding a second layer of gypsum board. These criteria for fire safety need only be executed when the I-joists are used in a commercial or industrial setting that requires a one or two hour fire rating. The additional components are not required for residential use of the system.
?
 |
Even thought the I-joist when used as a complete floor system pass the minimum requirements, they do so by a very slim margin. A representative at Jager Industries informed us that the I-joist lasted just seconds past the minimum burning time required to achieve the one hour resistance criteria.15
The other variable in the I-joist is the glue used in bonding the components together. This glue, resorcinol and phenol-resorcinol is moderately flammable and remains so even after it has cured. It is not certain to us whether the wood or the glue is more combustible. As well there is a certain threat to both the occupants and the firefighters when this glue is burning which will be discussed further in the section n health and environment.
One of the requirements of any construction system is that it be buildable. Even when a new system demonstrates remarkable performance when tested or used in a pilot project, if the components are difficult to transport, put together or configure to most circumstances, it will not be feasible. In terms of floor systems, new systems should not only be easily transported and constructed, but be able to accommodate plumbing, ductwork, and electrical services in a manner similar to traditional systems.
We will not present an involved description or analysis of wood handling and construction. For our purposes it is enough that we understand that there is an existing process whereby timber is obtained, processed, transported and used in floor systems which in terms of handling and construction is highly developed and successful. We will use this process as a benchmark by which to judge new products in terms of handling and construction.
It can be assumed that the manufacturers of engineered floor system products have no more difficulty in obtaining their raw materials than any consumer in the market for wood. Indeed, their demand for large volumes of wood and wood fibres may actually decrease their costs. That said, the handling of engineered floor system alternatives can be divided into two areas each of which has implications on feasibility. The first area includes all the processes that occur from when a material is manufactured to when it arrives on the work site. The second is the process of building erection. If either one proves too difficult or expensive, the usefulness of the product is minimized.
In the Nascor manufacturing facility we observed the completion of the last I-joist batch of the day. They were stacked bottom chord down so that the webs were vertical, and then each layer of joists was separated by spacers. They were then wrapped in a plastic tarp. We were told by the Nascor representative that they had to remain inside overnight as the glue cured, but that they would be stored outside in the morning. Just as with dimensional lumber, when I-joists are outside contact with water is generally not a problem, but they should be protected from the weather. Jager provides the following specifications:
The Jager Super ITM (JSI) joists must be carefully handled at all times to prevent damage. The JSITM joists must be stored in a vertical position and protected from the weather.16
When handled according to the manufacturers specifications, I-joists are no more or less susceptible to damage during storage and transportation than dimensional lumber is, but unlike lumber, damage to I-joists may cause the material to become unusable. For example, if one of the chords of an I-joist is partially crushed by the tine of a forklift, the joist must be repaired or more likely replaced.
Transportation becomes an issue when joists and laminated lumber are available at lengths in excess of 18 feet. Special transportation that can accommodate very long joists or beams may effectively increase the costs of the material.
The manufacturers we spoke to believed that framing with I-joists was no more difficult than framing with dimensional lumber. Jager makes the following claim in their product literature on their Super Floor SystemTM: No special tools are required. If you can frame with 2 x 10 or 2 x 12, then you can frame with Jager Super I'sTM.
We spoke to a number of house framers as they were constructing an I-joist floor in the new suburb of MacKenzie Towne. Because of the design of the house which had large rooms and resulting large spans, the joists were as long as fifty feet. We observed that it took three men to feed these members to the second floor, one to lift an end to the top of the wall and two to pull it across to the opposite wall of the house. On the other hand, foot by foot the I-joists are much lighter than 2 x 10's. A 30' joist can weigh as little as 60 pounds.17
Prior to visiting this site, we had spoken to one framer who disliked I-joists because they were difficult to cross cut with a Skil saw. He had difficulties with the saw skipping down to the web when cutting. The resulting cut tended to be messy which could cause problems when attaching a rim joist or web stiffener. The framers at the MacKenzie Towne site had solved this by using a small plank of OSB that fit against the web between the chords, that was flush with the edge of the chords when in position. (slide 3) They lined up the edge of the plank with their cut, tacked the plank in position with a nail, and proceeded. They told us that they preferred to frame with dimensional lumber because it is easier to cut, but their solution seemed to be a workable one.
Another complaint made about I-joists by a framer was regarding the metal joist hangers which some configurations of I-joist floor systems rely upon. These hangers must be nailed in place by hand as a framer cannot not reliably aim a nail through the provided holes with a power nailer.
We were told by the Jager representative that plumbers often drill holes for sewer services without regard to the floor structure18. This negligence can easily cause damage to the chords of an I-joist, if not the web itself. Because the top chord of an I-joist is in compression, if it is damaged, a repair may be possible. A knowledgeable representative of the manufacturer must visit the site, assess the situation, and approve any required repairs before those repairs can be undertaken. In the case of damage to a bottom chord, which is in tension, the whole joist usually must be replaced. Dimensional lumber is much more resistant to this sort of negligence given that holes and notches can be inserted in a number of (reasonable) places without significant effect to its performance.?
?
 |
However, unlike dimensional lumber, there are many situations where one can cut a hole in an I-joist that is as wide and tall as the whole web without compromising the member's structure. (figure 7) This means that most services, including ventilation, can be concealed within the floor itself, potentially eliminating the necessity for awkward boxes and low ceilings in some areas of a building. There are strict limitations as to where these holes can be located in an I-joist. Jager provides the following formula for calculating allowable hole size and location: Distance from Support (feet) + 1 = Diameter (inches)20 As well, other there are other restrictions. Holes that remove the web from chord to chord must be within the centre third of the span. Multiple holes in a small area must fit into an encompassing imaginary hole as determined by the above formula. (figure 8) Where a square opening is required, it must not remove any of the web within 1 /12" of a chord. An exception is that in some of Jager's products the entire web can be removed. In the JSI 20 and 30 Series, 15" of the web can be removed entirely within the center third of the span. In the JSI 40 you can take out 24" of the web.21
?
 |
Despite the possibilities this feature allows, at the sites we visited, virtually all the services were hung below the bottom chord in residential basements.
The floor systems that use prefabricated wooden I-joists tend to be more labour intensive. Special cutting procedures and hand nailing of joist hangers adds time to the project and therefore increases expenses. I-joists offer some excellent opportunities for concealing services, with some limitations on locations. These limitations are not significant with electrical services or most plumbing.
In cases where there are disadvantages in handling, they are often compensated by increased performance. Longer spans may prove worth the extra costs involved in transportation and labour.
The impact of building systems on people's health and the environment has been realized over the last few decades. People have been exposed to buildings with inadequate ventilation systems, materials that outgas toxic vapours, and the undesirable side effects of unmanaged interior humidity. We have also experienced the environmental cost of clearcutting for timber, and as a part of a larger air-quality problem, the pollution from building component manufacturing. It has been evidenced that material choice and composition has implications on both health and environment.
With declining lumber resources due to long term and worldwide overharvesting of trees, wood of any dimension has become scarce and expensive. Even common wood members such as 2 x 4 have risen sharply in cost within the last five years. Despite this, solid wood remains a versatile and relatively inexpensive building material that is still very commonly used. This includes its common use in most residential and small building floor systems.
For example, even though the solid wood tongue and groove subfloor of twenty years ago has been universally replaced by the plywood subfloor, the remainder of the residential floor system is still commonly made with fir dimensional lumber. There are a number of reasons for this, including costs and the lack of awareness of the engineered alternatives, each of which we shall discuss later. What concerns us here is the relative environmental and health impact between using solid wood members and using premanufactured wood I-joists or laminated veneer and strand lumber in floor systems.
Wood has traditionally been used in floor systems without adverse environmental or health effects. For this reason, we will consider it a benchmark by which to judge new products. There are two issues with regards to wood and its derivative products, one being environmental and the other concerning health.
The primary environmental concern with regards to wood is its increasing scarcity. Because it is a traditional material, remains relatively inexpensive, and continues to perform well in all its common applications (including floor systems), we have been harvesting it to the point that the sustainability of the industry, and the future ready availability of wood is in question. It is clear that there is less room for overbuilding and waste when using wood products in building.
In terms of health, wood generally has no adverse effects on the occupants of buildings made with it. The exception is that when wood gets wet, organisms such as fungus can use it as food. While people have a certain resistance to spores in the air, if there is enough fungus growing within a building, people will become ill. It is therefore important to prevent wood from getting wet when it is used in building construction.
The Calgary manufacturers of both Laminated Lumber and I-joists claim that their products are environmentally friendly. This demonstration of environmental concern is evident in their product literature23 A Nascor pamphlet on their I-joists reads:
Not only are we improving on Mother Nature but we are helping to preserve her as well. Old fashioned 2 x 10 joists are cut from mature forests. It is in everyone's best interest to preserve these pristine forests for future generations to enjoy. In an effort to be environmentally responsible, your NASCOR floor will be designed with less than half the wood used in a conventional floor system.24
This concern could be legitimized by the fact that their products either use less wood to perform the same tasks as wood, or waste less wood in their manufacturing process.
The former way of reducing materials is accomplished in prefabricated wood I-joists. This is done through the elimination of excess material near the axis of the member. Because a joist it is in bending, most of the forces are transferred only through the top and bottom of a joist. The material near the axis of a joist primarily holds the top and the bottom together. It also handles both the vertical and horizontal shear forces in the joist. All that is required to perform these two functions is a thin material with a good resistance to shear, such as oriented strand board. An I-joist with its two chords and an OSB web uses less wood than the dimensional lumber member that would be used to perform the same task. The latter way of reducing material is accomplished in laminated lumber. In order to produce dimensional timber, one must fall a tree that at it's narrowest is as deep as the desired timber. When the squared lumber is cut from a tree, there is significant waste as the tree is round. Because lamination allows many smaller wood pieces to be put together as one, all the wood in a tree can be used. Therefore less trees need be used to make the same amount of lumber.
However, some of the manufacturers claims are dubious. One environmental benefit of lamination that was mentioned by the Jager representative was that fast-growing, "inferior" woods such as poplar and aspen can be used in structural members, such as in Jager's SelecTemTM product. This was seen by this manufacturer as a way to reduce the amount of quality timber being consumed. Rather than protecting the environment, this seems to open up the possibility of harvesting formerly untouched soft hardwood forests. It is not clear that the increased use of soft hardwoods would offset the demand for quality timber in such a way that there would be an overall reduction in the amount of wood used, or that quality timber would be effectively conserved. While the faster growth rate of these woods may allow for some sustainability, the application of soft hardwoods in structural members primarily appears to be a way for the manufacturer to cut their costs.
Another concern of ours is that the ability to use smaller pieces of wood might not be used only to eliminate waste, but to justify forest clearcutting on the basis that all the material can now be used. Unfortunately in our investigation, we did not find any manufacturers using fibre other than wood in their products. If the environment was of great concern surely there would be some investigation of the use of crop fibre as a sustainable source of fibre. Hemp may be a possible candidate given its resilient nature and ease of production.
Common to all laminated wood products, whether it is laminated lumber, I-joists, OSB or plywood, is the glue. Although many glues are used to laminate wood including phenol-formaldehyde and isocyanurate-based adhesives, phenol-resorcinol and resorcinol are used in most of the products we investigated.
Because phenol-resorcinol glue is an organic chemical, it certainly must be considered in environmental and health terms. When we visited one of the Calgary manufacturing facilities, we passed the bin where they store and mix this glue. It comes in large paper sacks much as cement does, and is mixed on-site to produce the glue. We were advised not to breathe when passing this area as there were open containers of the glue and a lot of glue dust in the air. The dust may cause headaches, coughing, dizziness or difficulty breathing. As well, ventilation must be provided in addition to the use of proper protective gear including safety glasses with sideshields, a uniform, rubber gloves, and respiratory protection.25 As it is considered hazardous to work with, this must be taken into consideration both at the manufacturing site and at the worksite; one must take precautions when sanding laminated lumber as the dust produced is still toxic.
Given that the glue and its dust is so toxic in the manufacturing and construction process, we should be concerned about the occupants of buildings made with this product. It has been evidenced that outgassing of formaldehyde from particle board commonly used in millwork can be detrimental to interior air quality. We were told by the Jager representative that the glue they use in their I-joists is formaldehyde free, and that there should be no outgassing as all their products are sealed against dampness. It was his opinion that kitchen cabinets made of particle board that are unsealed on the interior represented a greater health risk than his company's products could. It is worth noting that whenever the web is pierced for services the joist's sealant is defeated. As well, many laminates are still made with formaldehyde based glues. A materials data safety sheet on resorcinol revealed that before it has cured it is a moderately combustible compound that may not be extinguished with water if ignited. Alcohol foam, dry chemical or carbon dioxide should be used by firefighters in special protective equipment and self-contained breathing apparatus with full facepiece operated in positive pressure mode.26 The other major concern for building occupants and firefighters is the effect on air quality when the cured glue is ignited. The materials safety data sheet we found listed this information as not available.
Obviously, if a material is of this much concern with regards to human health, it certainly has an environmental effect. It is yet another of the geometrically increasing number of chemicals that we produce. Although when cured phenol-resorcinol is stable in the products we have investigated, we are not in a position to predict how it will break down in the future and react to the environment. Resorcinol's US Environmental Protection Agency Hazardous Waste Number is U201 (Toxic Waste).27
Primarily, what makes open web joists different than the I-joists is their use of steel members in the web. While the use of steel has no health implications for the users of buildings made with it, the manufacture of steel has a significant environmental impact. Forintek Canada Corp. compared two 3 x 30 m non load-bearing walls, one built of 2 x4 wood studs and the other of 20 gauge steel studs. They found that the manufacture of the steel wall required about four times the energy, and ten time the water. It also produced about three times the carbon-dioxide emissions than the manufacture of the wooden wall. The steel wall also required over 25% more kilograms in raw resources and produced significantly more toxic effluents.28 One could argue that the avoidance of steel in light building construction may be the most environmentally considerate strategy there is.
It has been shown that laminated products can reduce the amount of wood needed in structural members. As well, lamination of wood fibres allows for less wood fibre waste. However, lamination also allows for the use of wood types previously unused in structural member creating a new demand for those resources. The glue used in lamination is of considerable health and environmental concern, although it is stable in the products we have investigated.
While there are many reasons for building partitions between rooms, whether they are walls or floors, one important one is certainly privacy. A floor system may function perfectly as a way to create multiple floors in a building, but it will generally not be acceptable if occupants on separate floors can hear one another. For this reason, floors need to be designed to reduce, or attenuate, the sound transmitting from one side of it to another.
The designation used for determining the allowable or acceptable sound transmission is called the sound transmission class rating(STC). This is an index of the resistance of a ceiling or partition to the passage of sound.29 The index is based on the ability of the human ear to detect sound through a partition. The following table30 shows how STC ratings relate to effective sound reduction.
| STC Rating | Effective Sound Reduction |
| 25 | Normal speech can be understood clearly |
| 30 | Loud speech can be understood fairly well |
| 35 | Loud speech audible but not intelligible |
| 42 | Loud speech audible as a murmur |
| 45 | Must strain to hear loud speech |
| 48 | Some loud speech barely audible |
| 50 | Loud speech not audible |
Sound attenuation is an issue with regards to manufactured wood I-joists as they are marketed as TMSilent Floor" systems. For example, Trus Joist Macmillan TMfeatures" the TMSilent Floor® System"31 and Nascor markets TMThe Strong Quiet TypeTM32.
The primary factor in the favour of dimensional wood floor systems is their mass. The mass law of sound dictates that the heavier a material is, the greater its sound attenuation properties. As well, because the members are solid, there is less of a tendency for them to reverberate when sound passes through them. Because most Canadians have lived in houses that use wooden floor systems, it is considered a standard by consumers. If a person were to purchase an alternative floor system, he or she would likely compare its sound attenuation properties to a standard floor system.
In terms of sound, the use of laminated timber will have no effect on the sound attenuating properties of a floor. The mass of any given laminated member is within the same general range as timber of the same dimension. For this reason, it will have the same attenuating properties.
I-Joists, on the other hand, have significantly less mass than dimensional lumber joists. This would lead one to believe that they may not attenuate sound as well. However all three manufacturers of I-Joists in Calgary market their products on their supposed quietness. In fact, wooden I-joist systems are commonly known as silent floors.
In our investigation we discovered that the manufacturers claims of floor silence are only intended to refer to the prevention of floor squeaks in their systems. The I-joists in the floor provide no special sound attenuation properties at all. We were told by the Jager representative that many people get this confused. Customers have complained that they can easily hear people on another floor through the supposed silent floor. The fact is with less mass I-joists can not attenuate sound as well as than wood. As well, because of the thinness of the web, the joists have a tendency to reverberate and therefore carry sound from one part of the building to another. In order to achieve the building code required STC ratings the floor system needs to be crossbraced, use resilient channels and a 3" sound attenuation blanket. With one layer of gypsum board on the underside this treatment will result in a STC rating of 47. The introduction of carpet, undercushions, thicker sub floors or a concrete pour on top will further reduce sound transmission and reverberation.33 The customers who complain about sound transmission generally have not taken these measures, and claim that they have been mislead by the manufacturer.
So if low sound transmission is not what the manufacturers are guaranteeing their floor on, what is it? They claim that their floors will not squeak over time because, unlike wood joists, their I-joists will not shrink. It is the shrinking of the joist away from the subfloor which usually causes floor squeaks. The resulting gap allows the floor to slide up and down on the nails causing the squeak.
Upon further investigation, we found that the manufacturers always specify that their floor systems be screwed and glued. This means that the subfloor should be glued to the tops of the joists, and then screwed in place. Yet this is common practice in conventional floor system building. The claim that the I-joist system singularly offers the consumer a silent floor that is free from squeaking is a myth. When installed correctly any floor system will not squeak, including a dimensional lumber system.
The representative at Jager Industries confirmed the myth by stating that the guarantee they offer is only applicable when the entire floor system is installed with a high degree of craftsmanship, and the correct methods of installation are employed. As well, the guarantee only applies to squeaks caused by the joists themselves, and not squeaks caused by separation of the joists from the subfloor, by ductwork hanging from them, or through faults in the installation. Jager's Homeowner Guarantee reads as follows:
...We take great pride in our products and guarantee that they are free from defects in workmanship and materials and will carry the loads specified provided they are used under normal service conditions and in accordance with the instructions and specifications as referenced in our literature. You can also be assured that floor squeaks will not occur as a result of defects in Jager Super ITM products... (our italics)34
The representative told us that the Jager Homeowner Guarantee only mentions floor squeaks because Jager's competitors do. (Jager does not call their products Silent Floors) He also concurred that traditional dimensional lumber floor systems when installed correctly will not squeak.
As with the I-joist the truss systems exhibit a greater tendency for sound reverberation than dimensional lumber, due to its smaller mass. There are several measures which can be taken to improve the sound attenuating properties of a truss. The use of sound absorptive materials placed in the floor space such as loose fill insulation. Loose fill insulation provides more sound dampening than batt insulation. The loose fill insulation will have some health considerations which should be addressed before using it. Carpet and underlay also contributes to sound dampening in the floor system. Other solutions include the use of 5/8" plywood sheathing in conjunction with 3/8" particle board, and the use of resilient channels and gypsum board.
The new floor systems we have investigated all require special consideration when sound attenuation is required. Even though the members themselves are lighter, additional materials can be used to dampen sound transmission. It should be noted that these additional materials can also be used in dimensional wood systems with the same effect, resulting in a floor with even better sound attenuation properties.
It is difficult to accurately assess the costs of the various systems as the number of variables involved are many. Certainly the continued use of dimensional lumber is largely because solid wood remains somewhat cheaper than engineered alternatives when considered on a cost per board foot basis. However, this system of comparing costs is irrelevant when one is costing an entire floor system. Differences in joist spacing directly affects costs. As well, span lengths have a direct influence on the number of costly teleposts and foundations required in the middle of the structure. When analyzing the costs of a system, the entire configuration must be considered. For this reason, without comparing a vast number of configurations, we can only generalize costs based on what the company representatives have told us.
When undertaking a floor system project, costs will be evaluated on an individual project basis because in certain instances it will be more cost effective to chose one system over another. For example it will likely be more cost effective when spanning distances outside of the capacity of dimensional lumber to chose an I-joist system. Without the use of additional costly structural members such as beams and teleposts dimensional lumber could not be used. The additional cost of adding the support structures may outweigh the costs of installing an I-joist system capable of spanning the distance without the use of any other structural members to support it .
On the other hand, there are many special considerations for in new floor system products such as fire resistance and sound attenuation. Additional products required to meet fire codes or a particular STC rating may increase cost over a traditional floor system.
The Jager representative told us that in his experience, all things being equal, I-joist floor systems cost the consumer about the same amount as traditional systems. As well, with the increasing scarcity of dimensional lumber, the increasing market share of alternative systems, and the increasing skill and familiarity of building framers with the new products, traditional systems will become universally more expensive by the end of the decade, and likely sooner.
We found while undertaking this investigation that most people in the construction industry, whether they are architects, manufacturers, builders, or retail salespeople, are aware of the new products used in floor systems. As mentioned previously, they are commonly referred to as Silent Floors by everyone but Jager. Given this general awareness, it is no surprise that the new systems are taking more of the market share every year.
The manufacturers place a lot of value in their marketing. The pamphlets and specifying guides we were given are easy to use, attractive, and show their products well. The Jager material specifically mentions consumer acceptance:
We believe that consumer acceptance and satisfaction with a Jager Super Floor SystemTM is a matter of understanding the concept and performance expectations of an engineered floor system. Since expectancy levels vary from one person to the next the design of an engineered floor system becomes subjective. This requires some choices that will ultimately reflect the sensitivity and living conditions of the occupant.35
Not only are they demonstrating concern for their customer, but all three manufacturers were willing to sit down and talk to us, photocopy material for us, or give us a tour of their manufacturing facilities.
The best report on consumer acceptance is from the consumer, though. David Ross, a furniture maker and resident of Varsity Village, recently built an addition on his 27 year old house. It was raised off the ground, so he certainly had to make a floor system product decision. After much consideration, he used TJ MacMillan I-Joists purchased through Davidson Enman Trus Joist Division. He chose them because they were straight, didn't have any knots, and he was given product support from Davidson Enman. Given that David Ross is a perfectionist and built his addition like it was a large piece of well-crafted furniture, the I-joists were, in his opinion, perfect for the job.
On the other hand, David Cormier, who recently purchased a new home in Edgemont, was happy to discover that they still made houses the way they used to: with reliable solid fir.
We believe that an informed approach is essential when making any building product decision. We have intended through this product analysis and comparison to present sound information that can help the user, builder or designer make floor system product decisions. Through the assessment, we have determined what the problems and advantages are with each product. We have concluded that there are significant advantages presented by the new products, but that these have their related costs. There are advantages new systems have in terms of performance and environmental impact, although we have reservations about the environmental and health effects of the glue. New systems require extra consideration from traditional systems in terms of fire resistance and sound attenuation. Often additional materials and labour must be undertaken to meet desired STC rating or fire codes. Costs and difficulties in handling are not significant enough to advise against their use. Indeed, costs are likely to decrease in the future as wood becomes scarcer and more framers are familiar with installations procedures.
In conclusion, we are satisfied that the new floor systems products of I-joists, laminated lumber and open web truss joists represent and improvement over traditional dimensional wood systems.
Nascor primarily makes the engineered wall systems that use expanded polystyrene as a stiffener and insulator which was developed by CANO Structures Inc. As they are also a custom home manufacturer, they manufacture trusses and I-joists as a complement to their walls systems. Their manufacturing facility is in Calgary.
The Nascor representative we spoke to was Roger Wiewel. We thank him for the tour of their plant, the introduction to other Nascor products, and the opportunity to see the I-joist fail.?
Jager began as a home builder and continues to operate as a developer. They manufacture trusses, I-joists, and a wide range of connectors such as joist hangers and truss connector plates. Jager also distributes laminated veneer lumber products and engineering software for use with their products.
The Jager representative we spoke to was Akrin Abougosh. We appreciate the time he spent with us in helping to understand these products. We also thank him for providing the joist for our presentation.?
TJ Macmillan is an international corporation which manufactures a wide range of I-joists, trusses, and laminated veneer and strand lumber products. TJ Macmillan also produces software for use with their products. Their nearest manufacturing facility to Calgary is in Claresholm, Alberta.
The TJ MacMillan representative we spoke to was Gary G. Yuen. We thank him for his time and the National Research Council information and for the ParallamTM samples.
Allen Edward, Fundamentals of Building Construction-Material and Methods. John Wiley & Sons, 1990, New York.
Gordon, J.E., The New Science of Strong Materials or Why You Don't Fall Through the Floor. 1991. Penguin Group. London.
Institute for Research in Constuction, National Research Council Canada.
TimberStrand® LSL, Parallam, Micro+Lam, TJI Joists Evaluation Reports. Sep 28 1994, CCMC 12627-R.
Jager Industries Inc. Jager Handling & Installation Recommendations Sheet.
Jager Industries Inc. Jager Homeowner Guarantee pamphlet.
Jager Industries Inc. Jager Specifying Catalogue.
Jager Industries Inc. Super FloorSystemTM product pamphlet (05/958000).
Materials Data Safety Sheet, Resorcinol, gopher://gopher.chem.utah.edu:70/00/MSDS/R/RESORCINOL
Nascor Incorporated. The Strong Quiet TypeTM product pamphlet (DS 120 - 2/95).
Sandaker, BjTMrn Normann & Arne Petter Eggen, The Structural Basis of Architecture, Whitney Library of Design, 1992.
Trus Joist MacMillan Limited. Trus Joist MacMillan Specifier's Guide. (TJM/JM195/7.5M Reorder: 2090)
Weyerhaeuser Canada. Materials Data Safey Sheet, Phenol Formaldehyde/M.D.I. Bonded Products,
Ross, Cormier. Woodworker
Cormier, David. Industrial Designer
1 See Appendix 1 for company descriptions.
2 Edward Allen, Fundamentals of Building Construction-Material and Methods. John Wiley & Sons, 1990, New York. pp. 77,789.
3 Information from Jager representative Bill Dyer
4 BjTMrn Normann Sandaker & Arne Petter Eggen, The Structural Basis of Architecture, Whitney Library of Design, 1992, pp. 22, 23
5 J.E. Gordon, The New Science of Strong Materials or Why You Don't Fall Through the Floor. 1991. Penguin Group. London. pp.160-162
6 Trus Joist Macmillan Specifying Guide: Microllam, p 2
7 TimberStrand® LSL Evaluation Report, Institute for Research in Constuction, National Research Council Canada, Sep 28 1994, CCMC 12627-R.
8 Parallam® PSL Evaluation Report, Institute for Research in Constuction, National Research Council Canada, Oct 19 1993, CCMC 11161-R.
9 Trus Joist Macmillan Specifying Guide: Parallam, p 2.
10 Edward Allen, Fundamentals of Building Construction-Material and Methods. John Wiley & Sons, 1990, New York. pp. 67.
11 Jager Specifying Catalogue, p 3.1.
12 Edward Allen, Fundamentals of Building Construction-Material and Methods. John Wiley & Sons, 1990, New York. p. 794.
13 Trus Joist MacMillan Specifier's Guide, p. 3. (TJM/JM195/7.5M Reorder: 2090)
14 TJI Joists Evaluation Report, Institute for Research in Constuction, National Research Council Canada, Feb 24 1994, CCMC 12460-R.
15 The reppresentative told us about a test where the joist lasted only a few seconds past the minimum required time, it was passed only after some deliberation.
16 Jager Specifying Catalogue, p 3.2.
17 Jager Specifying Catalogue, p 3.1.
18 He gave the example of a plumber who had drilled straight through a dimensional lumber joist when installing a toilet service in his brother's house.
19 Jager Handling & Installation Recommendations Sheet
20 Jager Specifying Catalogue, p
21 Jager Specifying Catalogue, p
22 Jager Handling & Installation Recommendations Sheet
23 for example: TMOur Mission", Super Floor System_ product pamphlet, Jager Industries Inc. (05/958000); 1.5E Header product pamphlet, Trus Joist MacMillan
24 The Strong Quiet TypeTM product pamphlet, Nascor Incorporated. (DS 120 - 2/95)
25 Materials Data Safety Sheet, Resorcinol, gopher://gopher.chem.utah.edu:70/00/MSDS/R/RESORCINOL
26 Ibid.
27 Ibid.
28 Wood vs Steel, Some quick facts!, Canadian Wood Council pamphlet.
29 Edward Allen, Fundamentals of Building Construction-Material and Methods. John Wiley & Sons, 1990, New York. p. 794.
30 Jager Specifying Catalogue, p 3.20
31 Trus Joist MacMillan Specifier's Guide, front cover, (TJM/JM195/7.5M Reorder: 2090)
32 The Strong Quiet TypeTM product pamphlet, Nascor Incorporated. (DS 120 - 2/95)
33 Jager Specifying Catalogue, p 3.20
34 Jager Homeowner Guarantee pamphlet.
35 Super Floor SystemTM product pamphlet, Jager Industries Inc. (05/958000)
36 The definitions of chards and webs have partly been paraphrased from the Jager Specifying Catalogue, p 2.3.