This report summarises the work accomplished in this one-year project in which the fire performance of wood-frame buildings was to be documented. A detailed analysis of Canadian and American fire loss statistics for residential occupancies was undertaken in order to assess the impact of the choice of building materials and the nature of fire-safety provisions in building codes on the overall fire safety in buildings. It was expected that the knowledge gained would enable the wood industry to argue more effectively during deliberations of codes and standards committees.
This study demonstrated that buildings constructed in compliance with current North American building code requirements are among the safest in the world. It was found that the fire loss record of wood-frame houses is about the same as that of large apartment buildings of non-combustible construction. It was shown that the ignition of upholstered furniture or mattresses by smokers’ materials is far and away the leading cause of residential fires involving deaths. Most of these deaths occur before the structure of the building becomes damaged by or involved in fire. Enacting more stringent building code requirements is unlikely to pay a large dividend in terms of life safety. In fact, the statistics suggest that significant improvements in fire safety in buildings would be more easily achieved by limiting the flammability of upholstered furniture and mattresses.
This report summarizes the progress from Year 4 of the multi-year Lumber Properties project. All activities continue to conform to the guiding principles adopted by the Lumber Properties Steering Committee (LPSC) at the start of the program. This year support was provided to statisticians from the University of British Columbia’s Department of Statistics to meet and work with researchers and statisticians from the US Forest Products Laboratory (USFPL) in Madison, WI. All physical testing under the ongoing monitoring pilot study was also completed, allowing the UBC statisticians to continue work refining their global lumber properties simulator. Work is continuing on the collection of secondary properties for Norway spruce and on the analysis of the data collected to-date.
No activities requiring significant resources were carried out under the Resource Assessment and the Special Products Initiative. Instead, these resources were redirected to cover shortfalls in the provincial funding under the Strategic Framework Initiative, so that the statistical work with the USFPL could continue.
A new National Lumber Grades Authority (NLGA) standard for evaluating structural wood adhesives has been approved by the NLGA Board and will be available shortly for use by Canadian fingerjoined lumber manufacturers. Development of this document was in response to an urgent industry need to provide a procedure for evaluating structural wood adhesives other than phenol resorcinol formaldehyde or resorcinol formaldehyde (PRF/RF). While these adhesive have performed satisfactorily for many years, not having a means for evaluating newer adhesive technology severely limited the ability of Canadian glued wood product manufacturers to maintain the competitiveness of their products.
When adhesives offering lower overall manufacturing costs or light-coloured bond lines were made available to manufacturers of competing wood products, Canadian manufacturers were not able to take advantage of these adhesives. This forced Canadian manufacturers to use overseas or US adhesive standards. While this provided a solution, it created an awkward situation where Canadian production could not be used in Canada because the adhesive did not meet the requirements of the Canadian wood product standard and thus the Canadian building code.
The development of the new NLGA adhesive standard occurred in two stages. The first stage, which was funded under the Canadian Forest Service Value-Added program, consisted of the following: a survey of industry stakeholder needs; a review of existing North American and overseas structural wood adhesive and glued wood product standards; and drafting and verification of the proposed standard in an inter-laboratory test. Two working groups were established: an Industry Working Group (IWG) consisting of several Canadian lumber and glued lumber producers; and an adhesive manufacturers group consisting of several Canadian and US manufacturers of wood adhesives. At the completion of the planned program, it was the opinion of the project team that the proposed standard and supporting technical information could only be used to assess structural wood adhesives for dry service conditions. Although it was estimated that nearly all of the glued wood applications, especially those involving alternative adhesives, would be for dry service conditions, the IWG and the NLGA Standards Committee (NLGASC) recommended that additional effort be put into developing a standard that would be suitable for wet or exterior use.
The rationale for this request was that although most of the applications would be for dry service conditions, the need to mark the product as being only suitable for such conditions would give the end-user the appearance that the product is “inferior” to a competing product without such markings. This would be the case in the US market where a US producer using the same adhesive would not be required to mark the product as “intended for dry service conditions only”.
The research program was subsequently extended, which is the subject of this report.
Lumber trusses are an essential part of residential and other light frame building construction. The use of metal plate connectors has been an accepted form of connecting wood members to build up the trusses for these constructions. Wood trusses are a potentially viable application for fingerjoined structural lumber. However, little information is available on the strength of the fingerjoined member when truss plates are applied on or in the vicinity of a fingerjoint. This project deals with issues that may arise from the use of fingerjoined lumber in metal plate-connected truss applications aimed at optimizing the use of wood to meet end-user expectations in terms of structural performance. To meet the objective, a phased approach was taken involving representatives from both the lumber producing and wood truss industries. Phases included: (i) creation of an Industry Working Group (IWG) to discuss the issues that may arise from the widespread use of fingerjoined lumber in truss applications and identify relevant studies, (ii) carrying out the identified priority studies, (iii) and identification of issues that would need additional research. The IWG was composed of 12 members representing truss fabricators, truss plate manufacturers, and lumber producers. The industrial partners in the project are Canadian Forest Products Ltd., Jager Building Systems, Inc., and Weyerhaeuser Canada Ltd. The members of the IWG convened last year, and discussed potential research items for the project. As a result of the meeting, two basic studies were identified as priorities, namely: (i) effect of fingerjoint offset on truss plate capacity, and (ii) effect of truss plate over-pressing on plate capacity. These two studies have been completed and results are reported.
In Eastern Canada, black spruce (Picea mariana (mill.)) lumber is often used by companies producing engineered wood products. Since it has only recently been utilized for finger-jointing, there is a need to examine this species with a view to optimizing the manufacturing parameters that influence the finger-jointing process. Key parameters influencing the finger-jointing process for softwoods such as black spruce were identified following visits to five finger-jointing plants in the Québec region.
The key parameters selected for study included: finger-joint geometry, curing time, pressure, machining parameters and moisture content and temperature of the jointed wood. Bending and tension tests were used to evaluate the finger-joints as per NLGA-SPS1-2000. Test results indicated a strong influence of finger-joint geometry on bending strength and, to a lesser extent, on tensile strength of finger-jointed black spruce. Optimum pressure was achieved at about 500 psi. Results on curing time of isocyanate adhesive indicated that mean tensile strength increased slightly with curing time until it stabilised at around 24 hours following joint assembly. More than 90% of finger-joint mean tensile strength was achieved after 5 hours of curing time at room temperature.
Results on the influence of machining parameters on the performance of finger-joints indicated no significant influence of cutting speed on tensile strength. Chip-load, however, was found to have some effect following a parabolic trend where the optimum value was achieved at 0.034 inch and at a feed speed of 60 feet/min. No clear trend on the influence of moisture content and temperature conditioning was observed for the combinations tested. However, the two combinations tested at -5oC exhibited the lowest mean tensile strength among all other combinations. There is a need to expand on this study to include more combinations of moisture content and temperature before concrete conclusions can be made.
Sound-transmission-class (STC) and fire-resistance (FR) ratings for many of the generic construction assemblies traditionally used in construction of Canadian housing and small buildings have been published in the National Building Code of Canada (NBCC) since 1950. While some of those ratings were updated over the intervening years, many of them had not been revised since 1965. Therefore, in 1992 the Canadian Commission for Building and Fire Codes decided to delete from the 1995 edition of the NBCC, every STC and FR ratings that could not be supported by contemporary data.
Canadian architects, fire-protection engineers and building officials make extensive use of the STC and FR ratings in the NBCC when designing and approving housing and small buildings in Canada. The STC ratings are also used extensively in the design of engineered structures. Wood-frame assemblies, more than any other, are designed and constructed in accordance with the STC and FR ratings listed in the NBCC. Therefore, it was crucial for the wood industry to generate the necessary data to retain STC and FR ratings for wood-frame assemblies. No single organisation in Canada could afford to bear the costs associated with a testing program to determine STC and FR ratings for all assemblies commonly used in Canadian housing and small buildings. Therefore, a partnership of affected industries and governmental organisations was created, and the National Research Council Canada (NRC), in collaboration with those partners, commenced a research program to quantify STC and FR ratings for generic building assemblies protected by gypsum board. Forintek Canada Corp., in conjunction with the Canadian Wood Council, and a number of North American manufacturers of engineered wood products, is participating in that program on behalf of Canada’s wood products industry. This report describes progress achieved in that research program between April 1, 2000 and March 31, 2001.
A paper entitled “Observations on fire-endurance tests of wood-frame assemblies protected by gypsum board” was presented at the 4th International Wood & Fire Safety Conference in ÒrbskJ Pleso, Slovak Republic. A paper entitled “Sound-transmission-class and fire-resistance ratings for wood-frame floors” was published in Fire and Materials. A 26-page paper entitled “Thoughts and observations on fire-endurance tests of wood-frame assemblies protected by gypsum board” was submitted for publication in Fire and Materials.
The second meeting of the steering committee for the collaborative research project to assess fire and acoustical performances of floor assemblies was held on September 12, 2000. When completed, the total value of the work carried out for this part of the overall collaborative testing program will be about $2,200,000. NRC is contributing 40%. The wood industry is contributing about 20%.
There are no differences in the fire endurance times of floor assemblies constructed with nominal 2x8’s, compared to those for assemblies constructed with nominal 2x10’s, provided all other construction details are identical and applied structural loads are proportionally the same. The addition of 25-mm thick gypsum-concrete toppings (1957 kg/m3) on wood-frame floors does not reduce the fire endurance of the floor. There are no differences in the fire endurance times of wood-frame floor assemblies having ceilings constructed with two layers of gypsum board, irrespective of whether the gypsum board is fastened directly to the bottom of the joists or attached to the bottom of the joists using resilient channels.
Attempts to design wood-joist floor assemblies having 45-min fire-resistance-ratings were unsuccessful when there was no insulation between the joists and the ceiling consisted of a single layer of gypsum board. Similarly, attempts to design wood-joist floor assemblies having 1-hr fire-resistance ratings failed when the ceiling consisted of only one layer of gypsum board and rock-fibre insulation was placed between the joists.
The third meeting of the steering committee for the Phase-II collaborative research project to assess flanking sound transmission in multifamily dwellings was held on June 13, 2000. The fourth meeting was held at USG’s Research and Technology Center on October 12 and 13, 2000.
When acoustical performance is considered, and particularly impact-noise-transmission, wood-frame construction has an almost insurmountable advantage over heavy concrete.
A meeting of the steering committee for the collaborative research project to assess fire and acoustical performances of wall assemblies was held on September 13, 2000.
The results of fire tests on wood-frame walls were reported in two Internal Reports published by NRC. The first draft of a NRC Internal Report on the acoustical testing carried out for this project has been written.
A representative of Forintek attended meetings of the AF&PA Subcommittee on Fire Performance of Wood, and the AF&PA Technical Committee from August 8 to 10, 2000.
AF&PA funded a series of fire endurance tests on wood-frame walls. By selecting only the strongest studs and using specially selected Type X gypsum board, they were able to achieve greater fire resistance ratings for wood-stud walls than were observed in the collaborative project described in this report.
This research project will continue in 2001/2002. Forintek will continue to write papers for presentation at conferences, seminars and workshops and for publication in journals and other written media in order to get the message out about this project and the acoustical and fire performance of wood-frame construction. One of the major points that will be made in those papers is that wood-frame construction provides superior sound insulation, compared to concrete assemblies, and that it is less expensive to construct acoustically superior wood-frame assemblies than steel-frame ones. In addition, Forintek will work with CMHC and NRC to develop a “best-practice” guide describing construction details for party-walls separating adjacent units in multifamily dwellings.