It’s time for Minnesotans to consider removing snow from their roofs because of the weight.
Just two weeks ago I wrote a blog saying not to worry. At that time, roof snow loads were somewhere in the neighborhood of 15 pounds per square foot (psf), but that has changed dramatically over the weekend. With all of the rain and wet snow that we received, the weight of snow has gone way up.
I measured another section of undisturbed snow in my back yard just yesterday to see how we’re doing. The weight of the snow was somewhere in the neighborhood of 35 – 40 psf. Yikes! That’s quite a jump. With modern roofs having a design load of 35 psf, I’m no longer comfortable telling people not to worry about snow loads.
Roofs at risk
If you have large areas where a lot of snow drifts, you’re going to have a lot of weight concentrated in these areas. If you have a flat roof or a low-sloped roof, you have a greater potential for problems. You probably don’t need to worry about collapse… yet… but we have a lot more rain in the forecast for the rest of the week. Given the additional weight that this will add to roofs, it might be a good idea to remove snow. Today.
As I mentioned in my blog post on ice dams, using a roof rake is a good way to remove snow from the ground. Don’t risk your life walking around on your roof to shovel the snow off. If you can’t remove snow with a roof rake, hire a professional to remove the snow.
On the other hand, if you look up at your roof and you see a lot of bare shingles, or you have a very steep roof, you probably don’t have much to worry about.
Here’s a short clip from a story that I just did with WCCO News on this topic last night: https://youtu.be/LY-EkNAhCuo
Author: Reuben Saltzman, Structure Tech Home Inspections
Dominic
April 2, 2019, 9:57 pm
Rueben, I had ice dams this winter on my 110 year old in Minneapolis. I’m planning on upgrading the attic insulation this summer. I’m going with your gold standard of 2 inch closed cell foam covered with blown in cellulose to an R50. BUT, my attic has an old floor covering most joists, wondering if I can spray a foam “lid” right over the subfloor and then add cellulose??? I’d love to avoid tearing up 1200 square feet of wood. The current cavity between ceiling and subfloor is empty (no insulation). I’m also upgrading some old knob/tube beforehand but leaving subfloor seems a little insurance against any unseen exposed knob/tube in between joists.
Reuben Saltzman
April 3, 2019, 4:37 am
Hi Dominic,
You should talk to your insulation professional about your idea and get their take on it, but I can’t think of any reason why your idea wouldn’t work. That sounds like a good plan to me. The only concern I’d have is that you’re making it pretty much impossible to access any of the old knob & tube wiring in the ceiling. If it were me, I’d get all of the knob & tube replaced before taking on the attic insulation.
Rob Cooper
April 6, 2019, 8:09 am
With all this talk of snow buildup on the roof, I’m sure glad I live in Alabama. Just out of curiosity, what’s the highest PSF you’ve measured up there in MN?
Reuben Saltzman
April 7, 2019, 4:52 am
Hi Rob,
This was the highest I’ve ever personally measured.