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1995 Building Code: trend towards performance codes
Desserud, R. J.
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1995 Building Code: trend
towards performance codes
Desserud, R.J.
NRCC-35019
A version of this document is published in
Building Owner and Property Manager, 7, (1), pp. 10, February-92
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TREND TOWARDS
PERFORMANCE CODES
Work on the 1995 edition of the National Building Code began long before the 1990 edition even went to press. It's always that way.
T
here is a feeling of accomplishmentwhen a new edition of the National
Building Code (NBC) comes off the press, but there is never time to put one's feet up and contemplate the end of the job.
So, by now 1 a head start has been made on the 1995 edition, although one cannot predict what changes it might contain until at least the first round of public comment. Two guesses are safe, however. The 1995 edition
will
continue the trend toward ｰ･ｲｾ＠fotmance·oriented codes. And there defi· nitely will be an energy code.
The growth of international trade and
free,trade agreements between countries makes the development of ｰ･ｲｦｯｲｭ｡ｮ｣･ｾ＠
oriented codes more important than ever. New and different products, designs and techniques may not fit standards and codes
written in prescriptive terms, but might
well do the job specified in a perfonnance code. ln fact, that is the key to perfonnance codes.
A criticism of building codes written in
prescriptive terms is that they can stifle innovation and prevent cost,reducing
shortcuts. These are codes that specify exactly how things are to be done -how the building is to be put together.
In contrast, performance codes specify just what the materials, components and equipment are required to do instead of specifying a particular kind or brand. This opens the door for more competition and innovation resulting, finally, in more effi; cient (and cheaper) construction.
To a certain extent, the 1990 NBC is already a 'perfonnance code' because of an 'equivalents clause' which allows for alter-native methods i:tnd materials if it can be shown the result will be as good as or better than that required by the code. Proving equivalence can be difficult in some cases because the intent of a requirement may
By
Richard Desserudnot be obvious.
It would be tempting to say that the 1995 code will be entirely perfonnance·ori· emed, but this is a long;term objective. Performance codes are not easy to write. lnstead of specifying the stud size and spac· ing for a wood-frame wall, for example, one would have to specify the vertical and hori· zontalloads that the wall must support and relate these to local snow and wind loads. This often requires evaluation procedures that take a great deal of time and money.
There are certain difficulties in writing performance codes. For instance, if we look at Part
5
of the NBC, which deals with water and vapour protection, we find it is a pure performance code as it is presently written. It takes almost three pages to say 'keep the liquid water out and the vapour water in'. But the industry finds it almost unusable.The designers really don't know what they have to do to satisfy it and the enforcers don't know what they should be looking for in the field to know whether the building satisfies those requirements.
We're trying to address that now. We're working on a commentary on Part 5 -what it means and -what it takes to satisfy it.
And we're trying to come up with some revisions, maybe some of them for the 1995 code. Fire safety provisions, including the National Fire Code and Parts 3 and 8 of the National Building Code, are another exam· ple of how easy it is for perfonnance require· ments to
be
mistaken for something else.If the NBC says a wall has to have a one; hour fire; resistance rating, some people consider that to be a specification. In fact, it's a perfonnance requirement because the NBC is not stating what materials have to be used. The code provides the criteria by which the performance can be evaluated.
The present codes lean toward perfor;
mance standards. They are probably head· ing even more in that direction as standards are referenced. Codes say 'this is the stan-dard and these are the criteria to meet it', but they don't tell you how to do it.
OLcourse, some people prefer codes written in prescriptive tenns. It makes their job easier. Such codes are cleat and easy to use. It's often easier having a requirement to tell you what to do rather than do an analysis of what you need.
The energy code coming out in 199 5 will be a separate document tided Canadi· an Code for Energy Efficiency in New Buildings. It is not the first stab at an ener; gy code in this country. An attempt was made in 1983 but, for a number of reasons, it was not widely accepted.
The new effort will be a combination of both performance and prescriptive code writing. The shape that seems to be emerg-ing is that there will be either two pam to it, or two separate publications: one for houses and one for all other buildings.
Each part will have two compliance paths. One is prescriptive, outlining such things as minimum R-values, minimum heating plant efficiency, efficiency of the water heater and so forth. The other path will relate to performance. lt will say the building can be built any way the designer wishes, as long as, in the end, it won't use more energy than if it were built to comply with the prescriptive path. And we will prescribe a computer,based method of demonstrating that.
It must be stressed that building regula· tions are a provincial responsibility. That means the national codes are models only to be accepted or rejected in whole or in part, or added to or subtracted from, by provincial authorities.To help the energy codes gain acceptance, they will, as pub, lished, contain a lot of blanks to be filled in by the adopting authorities, taking local conditions into account.
We will provide software which can
car-ry out the cost;benefit analysis to enable them to fill in those blanks. •
Richard Desserud is head of the Canadian Codes Centre of the Institute for Research in
Construction, National Research Council of Canada.
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