Letters to the Editor 01/18/2017

To the Editor:

Perhaps because I am a builder, I've been asked by several people if I thought it necessary to have snow shoveled off their roof. My initial response was "look: I'm not an engineer, I have no idea." Then I asked them how many residential structures they know of in the past 50 years that have failed due to snow loads? This may have relieved their minds, but I continued to fret if I was giving out poor advice.

We've all heard about the gym roof failure in Bend, and some of you may be aware of the horse arena collapse on Goodrich Rd. These were long-span structures with no pitch or shallow-pitched roofs. But it got me thinking-and talking to my structural engineer.

Residential structures in Deschutes County are required by code to have a minimum live/snow load capacity of 25 pounds per square foot. But how much does a one-square-foot-column of snow actually weigh? Obviously the answer depends on depth and moisture content.

Turns out that as of Saturday, in Tollgate, on undisturbed ground the snow measured 30 inches deep. When melted down a one-foot-square column of snow 30 inches high produced 3.4 gallons of water. That water weighed 28.5 pounds - several pounds over code design load.

But aren't there safety factors built into the design load? (I was searching for an excuse not to shovel my roof). Yes, there are, but this was my engineers response:

"The safety factor is a tricky deal and there is no specific number we use. If you can get weight off your roof down to the design snow load, that is the best option."

So I decided to shovel snow off the roof over my garage and kitchen, as those are the areas that rely on longer span trusses. I'm not worrying about the rest of the house because interior walls keep the simple-beam spans more "reasonable."

I hope this helps some of you decide what might be needed on your homes to increase the margin of safety - or simply sleep better at night.

Kris Calvin