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Technical Note (National Research Council of Canada. Division of Building Research), 1966-11-01
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475
PREPARED BY H B Di k
• • c ens CHECKED BY APPROVED BY RFL
ｾ November 1966
PREPARED FOR
SUBJECT
Presentation to the 1966 Fall Conference of the Canadian Wood Council, Harrison Hot Springs, B.C., October 17, 1966
DBR/NRC STUDIES OF INTEREST TO THE WOOD INDUSTRY
I am very pleased to be able to be with you today to report on the research activities of DBRfNRC. I understand that this Fall meeting is of more than usual significance in that it was here in 1959 that your organization, the Canadian Wood
Council, was founded. I am sure that all in the industry, particularly those who participated in that founding meeting, must be very gratified by the a.ccomplishments of CWC and the
stature it has achieved in this relatively short space of time. We in the Division of Building Research vaiue very highly our
contacts with your Association, particularly the usefu.l working liaison that has developed with the Council staff and with the Executive Director, Mr. Bob DeGrace.
The National Research Council is also celebrating an anniversary this year, its Fiftieth, having been formed in 1916. At that time NRC had no laboratories of its own. In fact laboratory work on a significant scale did not begin until 1932 when a central laboratory was opened on Sussex Drive in Ottawa. The laboratory operation is now centered mainly on a 450acre site on the Montreal Road and comprises ten Divisions -four engineering and six scientific, of which Building Research is one. We in DBRfNRC will be completing twenty years of
operation next year, haVing been established in 1947.
At that time we were assigned three main tasks. These are to provide:
(1) a research service to the construction industry of Canada;
2
-(2) technical support to Central Mortgage and Housing Corporation; and
(3)
secretarial and technical assistance to the Associate Committee on the National Building Code.As you might expect from this, our stu.dies have encompassed many different areas ranging all the way from structural, fire, and materials research through the thermal performance of building enclosures to ice lensing in soils. Much of this work relates to wood and its use in building and
in this brief report I hope to give you at least the essentials of what we are doing. I shall do this by discussing our work in the context of housing technology, an area in which my own Section has a particular interest.
First let me explain briefly the facilities at our disposal and the way we are organized. We have a total staff of 220 of which about one-third are research officers and the remainder supporting personnel. Most of the staff are located at the Building Research Centre in Ottawa but we also have small Regional Stations in Vancouver, Saskatoon and Halifax to serve the needs of these areas.
Our research studies are broadly organized into two main groups - "Building ScienceTl and "Building Practice". The
former comprises sections concerned with specialized disciplines such as materials, fire, acoustics, structures and soils (eight in all), while the latter has two research sections
-Construction and Housing - which are concerned more with the building process as a whole and the application of research results within the industry. We are not a testing agency nor have we any responsibility for "approving" materials used in construction. We may, however, .undertaketests for industry in those areas where commercial facilities are not available. Technical Studies Relating to Residential Standards
Turning now to our technical studies, several of the$e have been concerned with the efficient use of wood in frame
construction and a number have been the basis for refining the requirements of "Residential Standards". In all such work we maintain close liaison with the ForestProdu.cts Laboratories of the Department of Forestry and Rural Development and several projects have been carried out jointly with them.
Most of you will be familiar with our program of ｲｯｯｾ truss research which has led to much wider use of trusses in house building. In this program many types of conventiona.l
roof frames and trusses were load tested to failure to gain an overall picture of their strength and deflection characteristics.
These tests showed that trusses designed by normal engineering methods provide load factors of 3 to
5,
whereas mos t conventional roofs, mainly because of the nailing system, support only 1 to 2 times the design load before failure.Since even these weaker roofs had been satisfactory in service it was decided that trusses need only be designed with a load factor of 2 to provide acceptable performance. This approach was used to prepare the performance criteria now inoorpora ted in the Residential Standards. These require a full-scale load test and form the basis for the acceptance of practically all residential roof truss systems used in this country. Recently we have developed a method of predicting the deflection
characteristics of wood roof trusses based on simple joint tests which should greatly aid the truss developer by reducing the amount of prototype testing he needs to do during the
initial design stage.
You will appreciate that the test approach was an important depar.ture from standard engineering practice since it implied an increase in the permissible wood stresses and nail loads. It raises the question whether a similar load factor should also be applied to other elements of house
co nstruction such as floors and walls, or more broadly speak-ing, whether houses should be designed with lower safety margins than larger "engineered" structures. Such questions require careful consideration and also raise other important matters' such as the magnitune of design loads and how these relate to actual loads in service.
In this connection the Division has been conducting a long-term survey of snow loads on roofs across the country with the assistance of part-time observers. These observations have already had tangible results by permitting a reduction in the roof design loads for houses from 80 per cent to 60 per ｾ･ｮｴ of the ground load.
Another area where research studies have allowed the "Standards" to be more liberal is in relation to wall sheathing and bracing. It has been traditional in the construction of exterior walls to require corner bracing or sheathing to resist racking forces due to wind. In the current "Standards" these requirements have been eliminated and sheathing is only specified where needed for the support or attachment of the siding material. This has resulted in part from racking tests on wall panels which indicated that in most cases the cladding materials alone provide as much, and frequently more, racking resistance than traditional sheathing or bracing.
Other examples of cost-saving changes to the "StandardsIl
include the elimination of cross-bridging in floors, wider stud spacing for parti tions, reduction in thickness of subflooring and under certain conditions the elimination of subflooring.
4
-Prefabrication and Productivity
Thus far I have been talking about the product; now I would like to discuss the methods of production. These too have been changing. The Divisionis studies of prefabrication indicate significant gains in overall productivity by trans-ferring to the shop even a small proportion of the site labour content of the average house. There are no official statistics available but our studies suggest that leading builders have nearly doubled their labour productivity since the early 1950's by turning increasingly to components and to fabricating the basic wood shell in the shop. There is little doubt that these moves have aided the builder in holding the line on construction
costs in the face of rising prices. They have also helped him to build in winter and thus put his construction program on a year-round basis.
Our prefabrication study has attempted an assessment of these trends. The report of this study, which is available from the Division, considers the effects of such factors as financing, codes, distribution, and labour, and also discusses production methods, factory equipment, and shop layout.
Inquiries received on these practices suggest that this trend to shop fabrication is continuing not only among builders but also among many building supply dealers. The study also showed, however, that the point is soon reached with wood frame where further stages of prefabrication do not automatically reduce total labour. This appears to occur with shop content repre-senting only 15 per cent to 30 per cent of total labour and is the stage which most of our project prefabricators have now reached. This is likely to be of some significance in the developing competition from other materials.
Fire and Sound
Another significant trend in. Canada in recent years has been the increased emphasis on multi-family housing. Until recently Canadian housing has consisted chiefly of single-family dwellings. In 1961 apartments and flats represented about 30 per cent of all completions. These rose to 40 per cent in 1963 and to approximately 50 per cent in 1965. In the light of these trends builders previously concerned almost solely with single-family houses are now adapting their wood-frame production to row housing and other low-rise multi-family designs.
This has led to increased emphasis on fire and sound separations in wood-frame constructions, and these are also areas in which DBRfNRC has several studies underway. Much of our work on fire is aimed at providing improved information on the fire endurance of wall and floor assemblies. Recently it
Ratings" (Supplement Noo 2 to the National Building Code), which now offers the designer a method of calculating the fire resistance of different construction systems where no test information is available o Currently the Division is under-taking studies to evaluate the effect of fastenings sunh as nails, screws, staples, and glue on the stability of the interior finish when exposed to fire. The effect of mineral wool insulation on the fire endurance of a wood-frame wall is also being examined and full-scale fire tests are planned on staggered stud constructions which have been ､･ｶ･ｬｯｾ･､ to meet the sound insulation requirements of the "Standards '.
Considerable laboratory and field testing has been done by DBRfNRC on the airborne sound insulation aspects of wood-frame construction including a test to develop a partition w:Qich would satisfy the British requirements. This test was carried out to aid the Canadian Government in its promotion of the timber frame system in the United Kingdom. Currently, detailed investigations are being conducted on the effect of gypsum board cladding and its method of attachment on the airborne sound rating of frame walls.
Recent work has also included studies of impact noise through wood joist floors. Attempts are being made to correlate the sound transmission rating produced by a machine-induced
tapping noise with subjective reactions to actual footsteps. Initial results indicate that the machine rating, which it is hoped can form the basis for standard tests, is fairly
con-sistent with the SUbjective rating except for floors with very poor impact values. Earlier this year we presented a seminar on Noise Control in Residential Construction to the National House Builders Association annual meeting and this material will shortly be available in our Technical Paper series. Work with National House Builders Association
In addition to these studies the Division has assisted the NHBA with their research house program in which several items of interest to your industry have been under investigation.
These include the use of wood in basement construction and the application of kraft paper as a low-cost interior and also exterior finish. I unDerstand the observations by the FPL on the wood foundations in these houses indicate generally satis-factory performance to date. The kraft paper has also work quite well on the interior as a substitute for conventional drywall but has been less successful on the outside due mainly to difficulties of field application involving large sheets. It is worth noting, however, that the paper itself weathered quite well with only a paint treatment and we are now interested in its possiblities as a cheap factory-applied coating over a wood substrate to proVide an improved base for painting.
6
-Speaking of painting, one of my colleagues was in Norway recently ann was impressed at the apparent absence of paint problems in that country despite their extensive use of wood siding. One difference is that all their lumber siding is rough sawn and is not dressed. Another is their general use of linseed oil paint. In any event the rough siding pro-vides an economical and apparently trouble-free cladding which may be worthy of more extensive use here.
Another feature of interest in Norway is their u,se of factory-made plank flooring laid directly over the floor
joists without any subflooring. The planks which are 6 ft long,
5
lr4 in. wide and7r8
in. thick consist of threelaminations with the centre ply at right angles to the outer layers. The top layer is lrB-in.-thick factory-finished oak strips about 2
)r8
in. wide and 12 in. long. The bottom andmiddle layers are
3r8
in. thiok layers of kiln-dried softwood. The planks are both end- and side-matohed and are blind nailed to the joists so that when laid the overall effect is that of a well finished high quality oak floor. The system allows the finish floor to be installed in one applioation eliminating the need for subflooring and subsequent sanding, sealing and varn-ishing. The material oost is reported to be55
to 60 oents per square foot.Developments such as these whioh offer the possibility of more rapid finishing at lower cost are likely to receive
increased attention from builders as the pressures for improved productivi ty oontinue to mount. In the past these pressures have been met by the steady evolution of wood-frame oonstruction
itself and it is obviously important to those concerned with this market to encourage any fu.rther developments leading to its more efficient use.
I know you are already doing much in this direction, both individually and through CWC. May I suggest, however, that "one of the biggest road blocks to the use of lumber is the complexity of the grading rules." In case you think this presumptuous may I explain that these remarks did not originate with me but are a direct quote from an article by your Executive Director, Bob DeGrace, in an earlier issue of the CWC News
Bulletin. Mr. DeGrace went on to say that "many Canadian species with different nomenclature and variety of grade stamps add to the confusion and that the system as a whole may satisfy the producer but it frustrates the user."
I feel certain that the plea he made in that article, for the development of simple lumber standards in Canada in tune with what the consumer needs and wants, will prove of increasing significance in the years ahead.
May I turn now to a brief mention of some recent innovations in technology which some believe may lead to new building systems capable of challenging the position of
wood-frame construction. Some of these are already under development
and show promise for low buildings. Compared with wood frame,
these systems are characterized by fewer pieces to be handled, fewer processes and more controllable operations, all favouring
optimum machine production. Several involve wood but in reduced
or reconstituted form. Of these the I1formable wood-plastics"
consisting of wood fibre bonded with phenolic or other plastic resins have aroused much interest.
The extruded particle boards are perhaps the best
current example of this concept. They can be produced at costs
between raw lumber and plywood and are very versatile, being formable in hollowed-out shapes that offer good dimensional
stability. They use far more of the tree than can lumber or
plywood. When bonded to suitable skins these extruded boards
form strong, smooth composite panels which offer potential as
prefinished floor, roof, wall, or partition systems. The cores
in the panels provide space for insulation or for plumbing and
wiring. To meet the rising interest in such materials we have
undertaken some small study projects in this area and will shortly be completing the preparation of a detailed report on the related field of sandwich panel design and development. ;As a further step in this study of new building methods we have recently arranged for one of our staff to spend several months in Europe examining developments and assessing the potential
of Eu.ropean systems for Canadian use. The future of all such
systems will depend not only on their technical adequacy and cost but also on their ability to satisfy consumer taste and
local building codes. Whatever the outcome there is little
doubt that wood construction will remain a most difficult
yardstick of cost and quality against which proposed innovations must be measured.
In concluding I should like to mention an important
new program we have just begun. It is concerned with the
application of work study techniques in ｢ｵｾｬ､ｩｮｧ and involves
the systematic measurement of labour and materials in the
building operation. The first study is being carried out with
the assistance of a local Ottawa builder and with the support of the Research Committee of the National House Builders
Association. It involves determining the labour and material
content of two houses. The first is a typical project house
and the second is one that is similar in appearance but has been redesigned to take full advantage of the minimum technical
requirements of the "Standards". The observations will show the
savings to be expected in man hours and materials. We shall be
presenting the highlights of our findings to the NHBA annual meeting in Toronto in January next, following which we expect to
8
-include the full report in our pub1ication series., The work study technique can bea most useful tool in research and offers oon.siderable potential to the builder in improving his
own
operations. It is our intention t6 e'xtend its use' in the f'utu,r:e to a wide variety of building studies.', It, has been a pleasure to present' this report.
