As I approach four decades in this industry (!), the list of building code and design requirements that seem odd to me continues to grow. I am the first to acknowledge that the primary goal in designing a home is, and should be, occupant safety. But there are some requirements and inconsistencies that have me shaking my head. I am addressing this primarily from my Canadian background, but I am sure those of you working in the U.S. or elsewhere can find similar oddities in your codes and engineering approaches.
- Snow will always fall onto single family house roofs in a nice, uniform blanket – at least that is what the Canadian building code presumes. Of course, this is not really the case, because snow from the windward side of any peaked roof will tend to accumulate to a greater extent on the leeward side, creating an unbalanced loading condition. If exactly the same roof configuration occurred on a commercial building, we would need to address that possibility, but not when it happens on a house.
- Similarly, the depth of that snow blanket is typically assumed to be ~33% greater on the commercial building than the residential one.
- And further, with rare exceptions, wind is not considered to be a design consideration for roofs in Canada. Two years ago, a small but still significant tornado went through my hometown, destroying several homes and severely damaging others. Would designing for wind, and including hurricane clips to secure the trusses to the walls, have prevented all the damage? Of course not, but it would be foolish to think that it wouldn’t have helped. Decades of research on the effect of wind on houses has shown that keeping the roof intact is a key component of maintaining the integrity of the building and preventing a domino effect of damage. A study completed in Canada over 40 years ago, following a tornado event that resulted in many homes and cottages being lifted clean off their foundations, resulted in increased requirements to anchor the house to the foundation. However, there was a conscious decision not to address anchorage of the roof to the framing. Why not? Basically just the couple hundred extra dollars it would have added to the construction cost.
- When designing trusses, especially girders or long span trusses, bearing contact area is often a limiting factor. Essentially, we consider that under very high loading conditions the wood of either the truss bottom chord, the wall top plate, or both may be crushed somewhat. Here is my take on this – if a truss or beam member fails in bending strength, the roof could fail and people could be hurt; if that same member fails in shear strength, the roof could fail and people could be hurt; if that same member deflects too much, we could see or feel unacceptable amounts of deflection and undesirable performance. If the top plate or bottom chord get crushed a bit, it is highly unlikely that anyone will ever know. If you don’t believe me, take a piece of 2x4 framing lumber and put it in a vice. Tighten the vice until it is snug, then continue tightening. It is likely that after the wood is compressed (crushed) about 1/8” you will find it very difficult to tighten the vice further. This is essentially the concern when limiting bearing capacity.
- With apologies to my friends who work at the various truss connector companies, scissor slider brackets are a waste of time in most residential conditions. I understand that there is a need to limit the amount of horizontal movement that will theoretically occur in cathedral ceiling arrangements, especially high pitch scissor trusses, parallel chord scissors, etc. This limit is generally ~1” under total load. Brackets are available, and commonly required, to allow one end of the truss to move laterally, while simultaneously keeping the truss secured to the wall. But here is my thought. These brackets have been in common use to my knowledge for something like 35 years. In that time, literally thousands of them have been installed in roofs supplied by the various companies where I’ve worked. Now, look up at the ceiling at the outside wall of your house, and imagine that the roof and ceiling were to move outwards 1” while the wall stays where it is. What are you likely to see? Well, I would guess that you would soon see a tear in the taped joint at the ceiling. This would then soon result in an angry call from the homeowner to the builder and then on to the truss supplier. For most of my years in the industry, those calls would have almost always been directed to me. But in 35 or so years, I have yet to get one call or hear about a single case where the drywall joint failed because of horizontal movement. What that tells me is that sliding doesn’t really happen on light frame roofs in the real world.
So, those are some of the situations I have encountered at the intersection where reality and the codes meet. Are there things in your building code that seem unusual, inconsistent, or just plain silly? I’d love to hear them! Likewise, if you have any other tips to share that help with installation and bracing, please pass them along.