The Trials Of Personal Snow Removal.

[neufox47]

It seems like almost all the new construction in Tahoe has flat roofs now. What’s up with that? Is it somehow easier to build to hold the snow than to shed it?


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[climberevan]

Roof load is calculated independent of pitch, so it has to be just as strong at 8/12 as it does when flat. Even metal won't reliably shed below about 8/12, so the engineering assumes no shedding at all.

I have a pic of one of my guys with a snowblower inside of a living room a few years ago, and I fully expect we'll be able to refresh that photo in a couple of weeks.

I've shoveled my whole roof twice this winter. El Chup, fingers crossed for you but I would not be a bit surprised if you had an... incident. That shit is heavier than you think and the rain will really rapidly add to the load.

[::: :::]

Roof load is calculated independent of pitch, so it has to be just as strong at 8/12 as it does when flat.

I don’t know if it’s local, but this isn’t correct for OR anyway

[climberevan]

I don’t know if it’s local, but this isn’t correct for OR anyway

Huh. That was how it was explained to me by engineers in CO and Tahoe. I have to build it like they specify.

But certainly it's true that low to mid pitch roofs don't shed snow anyway.

[old goat]

I'm no engineer so feel free to correct or ignore me, but my understanding--having pulled a bunch of permits here involving roofs and engineers, is that the snow load in psf is the same regardless of pitch but the size of the rafters to support said load varies with pitch.

[Alpinord]

Here there is a percentage reduction based on pitch.


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[El Chupacabra]

My house roof has never slid snow, though seems steep ish - 8/12 maybe? Heavy concrete tile, not light weight - roofer from last summer who did some repairs said it's the older style you don't have to be as careful about as far as where you walk on it.

Just walked around the house looking closely at the ceiling, windows, and door jambs. There's some hairline cracking along drywall seams, but only in straight lines where the drywall pieces come together). Some of those cracks were already there, not sure if there are any new ones. No doors are sticking.

[John_B]

I'm no engineer so feel free to correct or ignore me, but my understanding--having pulled a bunch of permits here involving roofs and engineers, is that the snow load in psf is the same regardless of pitch but the size of the rafters to support said load varies with pitch.

I'm not sure what it is locally but my neighbors just had an interesting problem this winter. They've got a steep pitched garage roof that slides multiple times every winter. Last summer they installed solar panels which provided enough anchoring that the roof stopped shedding. After a large amount of snow early this winter they had multiple cracked trusses and rafters and were quite lucky to not have lost the entire structure and the cars/gear inside.

Based upon this it seems like it would make more sense to require roof loads to be more standardized due to the uncertainty of what future landowners may do.

Like I said I'm not familiar with the local code requirements but it was an eye-opening issue to me that I'd never thought of.

[old goat]

I don't know where you are but it certainly seems weird that the roof woudn't be engineered for the snow load on a non-siding roof.
Around here some roofs aren't sliding because the snow on the ground is up to the roof.

[John_B]

I don't know where you are but it certainly seems weird that the roof woudn't be engineered for the snow load on a non-siding roof.
Around here some roofs aren't sliding because the snow on the ground is up to the roof.

I'm on the east side of the Cascades in Washington. We get enough snow that homes need to be built to 80 lbf. The garage very well could have not been built to code, but the structure is about 20 years old and large enough that it should have been permitted.

I was more commenting about how allowing lower snowload on sliding roofs could have issues later in time.

[riser4]

Attachment 450996


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Oh shit. Hang-fire.

[dan_pdx]

I was kind of cranky that I had to shovel plow berms from our 150 feet of sidewalk a few times this winter, but after reading this thread I'm counting my blessings.

[ticketchecker]

Oh shit. Hang-fire.

She slid out about two more feet over the last couple days and finally lest loose tonight.

Now I can let the dog out alone again


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[zion zig zag]

I get the ice overhang too. This was last year, its bigger and thicker this year.

[Alpinord]

Here there is a percentage reduction based on pitch.

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FWIW and to follow up on the above ‘chairlift comment’…..

-over a 6:12 pitch local codes may or may not allow a percentage reduction in live/snow loads. If involved, the architect/designer &/or engineer may decide to not take the reduction and even bump the loading &/or deflection criteria for the structural design. For ‘value engineering’, for instance, a truss engineer could simply meet the minimums, take the reduction and be legal. Accumulative loads (valleys, dumping onto lower roofs, etc) would need to be part of the engineering.

-the trend here for higher end projects, is to not take the allowed reduction, possibly bumping the live load and stiffen the deflection.

-for longer spans (horizontal distance between bearing), allowable deflections for both rafters and trusses (same for floor joists) could deflect ceilings noticeably when loaded. To minimize this, a stiffer deflection value could (and should) be used. This in turn might beef up the roof system relative to live load capacity.

-for the same span and different roof pitches, the rafters will have different lengths. To meet loading, span and deflection criteria, the rafter sizing, design series or layout may or may not need to be different. Part of the dead loading is the weight of the roofing material and is added to the live (snow) load to determine total design load.

-in a County where we range from 30ish to 150ish or more snow loading, a dual ‘zone’ system has been the basis for design load formulas based on elevation. Now the GIS system is incorporating more variably criteria within the same zone and elevation to account for more location specific data.


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[J. Barron DeJong]

Is it a bad sign when your ice dams are forming tiers?

[ötzi]

There must be heat coming out from under that edge.

[J. Barron DeJong]

There must be heat coming out from under that edge.

That’s over an unheated garage, and north facing. That roof section does extend over part of the living space though, so the attic space is getting heat from that.

Hoping with the snow cleared and warmer weather coming that they’ll loosen up and shed.

[bodywhomper]

No ice dams, but our garage roof was not subject to any snowload code. The side door had become hard to open/close. 6” of rain expected between tomorrow and Sunday. Hopefully this does the trick. Also spent the afternoon restoring drainage systems around the house.


Less snow on the roof of the house… I guess our insulation isn’t that great.

My friend went up to his a-frame in bear valley. Shoveling was futile. The bear valley village has now recorded over 600”, which I think is more than the ski hill over the ridge.

[::: :::]

Here there is a percentage reduction based on pitch.


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^^^Here too


I have a cabin project in Govy that has a snow load of something like 320#/sf. [need to dbl-check that with the eng, but that’s what I’m remembering atm]

[ötzi]

That’s over an unheated garage, and north facing. That roof section does extend over part of the living space though, so the attic space is getting heat from that.

Hoping with the snow cleared and warmer weather coming that they’ll loosen up and shed.

Hm. Well something is melting that down and making those icicles, I dunno.

[Alpinord]

I'm not sure what it is locally but my neighbors just had an interesting problem this winter. They've got a steep pitched garage roof that slides multiple times every winter. Last summer they installed solar panels which provided enough anchoring that the roof stopped shedding. After a large amount of snow early this winter they had multiple cracked trusses and rafters and were quite lucky to not have lost the entire structure and the cars/gear inside.

Based upon this it seems like it would make more sense to require roof loads to be more standardized due to the uncertainty of what future landowners may do.

Like I said I'm not familiar with the local code requirements but it was an eye-opening issue to me that I'd never thought of.

They did add dead load to the trusses that changed the design criteria. As noted by others, the code would have required the roof design to hold the snow load without snow sliding off. Does this roof shed one direction or two? If two, it sounds like possibly a differential loading situation compounded the loading on the panels side.


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[ötzi]

Teflon-coated roofing shingles. We'll be rich!

[Alpinord]

No ice dams, but our garage roof was not subject to any snowload code. The side door had become hard to open/close. 6” of rain expected between tomorrow and Sunday. Hopefully this does the trick. Also spent the afternoon restoring drainage systems around the house.


Less snow on the roof of the house… I guess our insulation isn’t that great.

My friend went up to his a-frame in bear valley. Shoveling was futile. The bear valley village has now recorded over 600”, which I think is more than the ski hill over the ridge.

Did you pump up a raft with survival gear? 6” of rain!


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[John_B]

They did add dead load to the trusses that changed the design criteria. As noted by others, the code would have required the roof design to hold the snow load without snow sliding off. Does this roof shed one direction or two? If two, it sounds like possibly a differential loading situation compounded the loading on the panels side.


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It's single pitch. Maybe 7/12 or 8/12. I don't have a good eye for that.