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April 2024 #16297 Page #86
Design Connections
Geordie Secord, Senior Recruiter TheJobLine.com – Canada
Resilient Designs Cost Less Than You Think
n last month’s article, Designing for Resiliency, I present some of my thoughts on how changing the design approach for wood trusses could aid in making future homes more resilient to the types of climate extremes that seem to be ahead of us. Whether you think that climate change is a man-made problem (I believe it largely is) or is part of a natural cycle (highly unlikely), it is very likely that no matter where you live you are looking at more extreme snow, rain, and wind conditions in the future than we have seen in the past.
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In the past, I have confidently relayed to anyone who cared to listen that I had never seen – in 35+ years now – the failure of a properly installed truss roof. In fact, the only house roof failure I was ever involved in related to a 10-year-old house with inadequate truss bearing and no bracing that experienced approximately 200% of design load due to significant snow drifting on a lower roof followed by heavy rain in mid-February. Every other truss failure I have experienced was related to a lack of adequate bracing and/or poor installation practices. Today though, I cannot be as confident looking forward 35 years. It seems entirely possible to me that my area could see 5 to 6 ft of snow in a short period of time, after all we got 3 ft in less than 24 hours around Christmas 2022. If that had been followed by several days of heavy rain, with all of the snow acting as a sponge and holding it on the roof for some time, then we could easily see roofs experience significantly higher than code-specified loads would predict. It isn’t reasonable to build our homes as bunkers – but how should we proceed? It’s true that the building codes use historical data to predict future loading, but in a rapidly changing environment, this will be less valuable. In the absence of data, looking forward into the unknown is always going to be a bit of a guessing game. So to satisfy my curiosity and expand this discussion, I decided to run some test designs. I decided to design a typical roof for a home located near me in Barrie, ON. The layout shown gives you some idea of the house I used, with a footprint of approximately 2,400 sq ft, a cathedral ceiling over the great room, and attic trusses over the garage. There are some piggybacks due to height constraints, and I’ve included lay-in gables at the hips and valleys as needed. I am sure that some of you may want to comment on the arrangement of the truss framing, but I hope you will accept that the intent is to provide relative costs. I designed the trusses essentially as I would for production, although I am sure that there are savings available in all cases. Continued next page
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