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Rossland Roofs

For all the engineer-types out there in our snow globe; how do you measure the snow load on roofs and should we all be hiring shovellers asap or go for a ski instead?

1.- Take a 1' x 1' x 1' sample of undisturbed snow from near your roof and weigh it. It will be adecuate for an approximation, and safer than going up there.

2.- Measure the vertical height of roof snow in feet - at your own risk. Better to approximate by using a visual cue such as a nearby brick chimney, etc.

3.- Multiply the weight of the snow by the height. This will give you the snow load in pounds per square foot.

4.- As a rule of thumb (derived from the building code) for your average modern house you can use 160 lbs. per square foot as a worst-case scenario. For old construction ???

5.- If you want to find the total snow load on your roof: Measure the footprint of your roof. Not the actual roof surface but the plan view surface ("birds view") A  good approximation is to measure your house perimeter walls and add 1' at each corner if it is an old house, to take the overhang into account - add 2' for newer houses. Figure out the square footage by using those measurements. Multiple the square footage by the amount of pounds per square foot you found in step 3. This will give you the approximate total snow load affecting your house (read walls, footings, and possibly ceilings in poorly built/renovated houses). You need to be aware of measuring your walls if there is a possibility of the snow sliding. Safer bet, and still a good-enough approximation, is to measure from within your house taking into account the thickness of the walls that you encounter as you measure. Typically these walls are between 4.5" and 6.5" for interior walls, and 5" to 10" approximately for exterior walls.

All of the above really means nothing. Better to look for new cracks in the drywall, windows/doors that may not be opening correcly at this time, noticeable buckling of ceilings and/or walls, new cracks in the foundation walls and/or slab, etc....

In the end, if you are worried, you should just hire somebody who is insured to clear it. It is, literally, the roof over your head.

Hope this helps, cheers.

awesome and thanks

 

I am wondering if people in town have done this snow load test. I did one today , March 3, and had 4.5 ft on my roof and weighed a 1'x1'x 1' square and came up with about 11 lbs  x 4.5 ft   = roughly  50 lbs . With code in Rossland at 160 lbs per sq ft . one would think newer construction should be fine. I weighed the lower heavier snow on my roof not the fluffier top layer.  cheers

Thanks Karl Frank! I did one but obviously didn't get the decimal right (math not being my strong point lol); snow weight was close to yours, but I had figured our roof at 60 lbs/ ft. Thankfully either way, looks like we are good to go...for a while! Thanks for your efforts on this, much appreciated!

160 lbs is the ground snow load, which you can use as a very rough approximation. The actual snow load for structural calculations is the specified snow load which is roughly 90 lbs give or take for most residential buildings in Rossland. If you really wanted to know what's going on with your roof you need to take measurements everywhere to take into account uneven loading due to snow drifts, solar aspect, etc. Then your 50 lbs could end up being 70-80 lbs in the middle of your longest span...

160 lbs is the value used for 1 in 50 years worst case scenario ground snow loads. This number was taken as some kind of average over the early and mid decades of the 20th century. I don't believe it has been updated for a long time. With global warming on the rise this number does not necessarily reflect the new reality. This also applies to all the current rain/melt flooding that has been happening in the last three decades during the Spring freshet all over Canada.

Also, as I said in my OP, old and shoddy construction, and construction method - or lack thereof - are not accounted by the code.

Hope this helps.

This is a really good discussion. I've been wondering about this myself. I'm going to try to figure out what load my own roof will carry. It just seems so wasteful to do all that shovelling if it's unnecessary.