Snow Load & Roof Slope (Oxford, Penobscot: houses, calculator, camps)

[gcberry]

How do I determine snow load amount, so I can figure out the necessary roof slope when building a house? (metal roof, house to be vacant much of the time so there won't be anyone to clean snow off roof)
This would be in White Mts. area of Oxford County (western ME)

[7th generation]

Originally Posted by gcberry

How do I determine snow load amount, so I can figure out the necessary roof slope when building a house? (metal roof, house to be vacant much of the time so there won't be anyone to clean snow off roof)
This would be in White Mts. area of Oxford County (western ME)

Metal roof-no maintenance= 8" on 12".

[Submariner]

Each county in Maine has it's own building code 'snow load' numbers. You can check with the county to find it's required minimum Snow Load numbers.

In this area, it seems like everyone is falling in love with metal roofs.

We have a metal roof, though it's slope is very shallow, nearly flat, 1' of vertical drop for every 10' horizontal.

I do see a lot of very steep roofs too.

Our building was pre-engineered so they set the Snow Load numbers at 50% higher than Penobscot county requires.

Steel buildings tend to be cheaper than woodstick, and allow for large open rooms without interior loading bearing supports.

[woxyroxme]

Weight/sq.ft. X cos(roof angle)

Flat roof - 0° - !0lbs./sq.ft. snow exerts 10 lbs./sq.ft. force

30° - 10lbs./sq.ft. snow exerts 8.66lbs./sq.ft. force

45° - 10lbs./sq.ft. snow exerts 7.07lbs./sq.ft. force

That is why houses in the north have steeper roofs than houses in Florida, building codes will require roofs to support several times more weight than would actually ever be placed on it.

[Maineah]

We have a 12-12 pitch on our house and a 10-12 pitch on the barn and garage. With those angles we do not need to shovel the roof off. Anything below 8-12 you will most likely have to shovel off heavy loads. Chalets and "A" frame camps in snow country (White Mointains are in this snow belt) will have very steep pitches. These roofs see much higher than normal snow loads so the steep pitch is essential in unoccupied buildings

[AliceT]

I can't begin to tell you what the pitch of this roof is, but can tell you that this shingled roof has held its own with the snowfall of the last two years as it sat vacant and unattended through three winters.

[island mermaid]

Doesn't a metal roof stand a better chance of less snow build up? I'm just thinking unless it was sitting in a completely shaded area, the heat of the daylight sun might allow for it to melt faster and run off? Especially with a 10 - 10 or higher pitch?

[Submariner]

Our metal roof builds up a fairly thick layer of snow and ice. Being nearly flat it does slide off, but slowly. Huge sheets of snow will slide out 2 or 3 feet from the eave and break off.

Anything up against the exterior walls needs to be protected. Like water faucets that stick out through the walls, propane lines, and stuff.

[Nor'Eastah]

Originally Posted by AliceT

I can't begin to tell you what the pitch of this roof is, but can tell you that this shingled roof has held its own with the snowfall of the last two years as it sat vacant and unattended through three winters.

Alice's roof looks like an 8-12 pitch, not unusual for these small cabins sold ready-made in Maine. This looks to be about a 12' wide building, judging by the T1-11 siding on the gable.

If you only need to span 12' it doesn't much matter what the pitch is. If you're spanning 28' or 32', you need a steeper pitch. There's a limit to what dimensional lumber will support, and a limit to the sizes available in dimensional lumber. You might want to look into roof trusses, which are engineered for the footage they span, as well as snow loads.

Always ask a professional. Just a suggestion.

[kellysmith]

Originally Posted by Nor'Eastah

Alice's roof looks like an 8-12 pitch, not unusual for these small cabins sold ready-made in Maine. This looks to be about a 12' wide building, judging by the T1-11 siding on the gable.

If you only need to span 12' it doesn't much matter what the pitch is. If you're spanning 28' or 32', you need a steeper pitch. There's a limit to what dimensional lumber will support, and a limit to the sizes available in dimensional lumber. You might want to look into roof trusses, which are engineered for the footage they span, as well as snow loads.

Always ask a professional. Just a suggestion.

The photo is definitely not an 8/12 pitch. Looks more like a 5/12 pitch to me. That means 5 inch vertical for every 12 inch of horizontal. A 6/12 pitch is a 45 degree angle, the photo is closer to 30 degrees which is about what a 5/12 pitch gives you.
The part about professional advice is the right answer. You need to consider the material of the rafter, whether pine, spruce, engineered, etc. Also the length of the rafter, the spacing whether 16 inches on center or 2 ft, as well as the width of the rafter. Here's a link to a handy calculator. I think 40 lbs/sq ft snow load is fairly normal, but again check with a professional in the area you are planning to build in.

Maximum Span Calculator for Joists & Rafters