snow sheared plumbing stacks

[srich]

I have a 32'x32' two story cabin in Western Washington. It has a 12:12 pitch metal roof and was built by the previous owner. The problem? He installed 4 different plumbing stack penetrations, 3 on one side and one on the other. All of them are at least half way down the roof and two are three quarters of the way down. Twice now, heavy wet snow has come down and sheared off two of the PVC vent stacks. There is no access via an attic, due to a cathedral ceiling of tongue and groove car decking, so repairs are done 2 stories up on a wet steep roof.

Adding metal braces uphill of the stack were supposed to cleave the snow on the way down. All they did was rip out of the roof (despite 4 one inch lags) and then give the snow leverage in breaking off the vent stacks. I've thought of trying to sleeve the PVC with galvanized or cast iron pipe as far into the roof as possible, but there is no way to easily access the inside to brace the new pipe well. I still wonder if that might work since the break is always about where the pipe comes through the roof sheathing.

Other ideas include rerouting the stacks to near the roof peak (which should have been done in the first place) and replacing the affected roof sections. An expensive option. The last thing I can think of is the snow rails or other devices that clamp onto the roof section seams. I'm afraid I'd end up with a huge roof weight load, since rain often makes our accumulated snow like wet cement. HELP! Any ideas or experience with solving this issue?

[Fischer]

Here's what I'm thinking and take it for what it's worth.

Sheet metal shop and have a little heavier guage piece of stainless formed into a steep V shape with a bottom flange at a 90 degree angle to fasten to the roof. Think of a Naval Destroyers sharp hull. The V to cut the snow and the flange to fasten to the roof deck with the gasketed screws along with a polyurethane sealant. This would be placed just above to just past the vent pipe.

The deep V shape should decrease the leading edge force of the snow which causes the shear load on the pipe.

[suemarkp]

What is used for electrical masts could work. How did you brace the pipes before -- from below (so snow pushed the brace into the roof), or from above (so snow would pull the brace out of the roof)? It sounds like you had the mast legs on the high side which is backwards -- you want to compress them under load and not pull them, because they can pull out.

Power mast guy wires go above, but you need to be sure to screw them into a rafter and not just decking (at least a 2" long 5/16 dia lag bolt). Mast legs go on the low side, and should really be screwed into a rafter also, but deck sheathing may be sufficient if it is at least 5/8 thick since these are under compression and not tension.

[Wgoodrich]

From what I am seeing on the news this state had a 6' snow then a rapid thaw causing all kinds of havoc. That much snow on a roof is causing many concern of caving in roof due to the weight. If a half frozen chunk of this broke loose and come down that roof not sure anything will survive for a stack out the roof. If no way to reroute to top of the roof then I would put a 90 where that stack passes through the roof and lay the stack down along the roof. Not really intended by the code but again who designed in the code for a 6' snow ?

Just an idea

Wg

[joed]

Here's what I'm thinking and take it for what it's worth.

Sheet metal shop and have a little heavier guage piece of stainless formed into a steep V shape with a bottom flange at a 90 degree angle to fasten to the roof. Think of a Naval Destroyers sharp hull. The V to cut the snow and the flange to fasten to the roof deck with the gasketed screws along with a polyurethane sealant. This would be placed just above to just past the vent pipe.

The deep V shape should decrease the leading edge force of the snow which causes the shear load on the pipe.


Not sure if this is the same idea. But make the V like a mini dormer, like a cricket behind a chimney to preven dirt build up. Keep it back an inch or two from the pipe but also a inch or two higher. If it doesn't split the snow around the pipe it should deflect the snow over the pipe.

[srich]

What is used for electrical masts could work. How did you brace the pipes before -- from below (so snow pushed the brace into the roof), or from above (so snow would pull the brace out of the roof)? It sounds like you had the mast legs on the high side which is backwards -- you want to compress them under load and not pull them, because they can pull out.

Power mast guy wires go above, but you need to be sure to screw them into a rafter and not just decking (at least a 2" long 5/16 dia lag bolt). Mast legs go on the low side, and should really be screwed into a rafter also, but deck sheathing may be sufficient if it is at least 5/8 thick since these are under compression and not tension.

Thanks. I felt that downhill would be correct too, based on same principles of compression vs tension. however, reread the install instructions twice, and they want them on the upslope side. Apparently to cleave the snow as it passes by. however, in our climate, I think the snow melts, locks into the brace, then tears it out once the total weight becomes too much. May have to install backwards next time. thanks!

[srich]

From what I am seeing on the news this state had a 6' snow then a rapid thaw causing all kinds of havoc. That much snow on a roof is causing many concern of caving in roof due to the weight. If a half frozen chunk of this broke loose and come down that roof not sure anything will survive for a stack out the roof. If no way to reroute to top of the roof then I would put a 90 where that stack passes through the roof and lay the stack down along the roof. Not really intended by the code but again who designed in the code for a 6' snow ?

Just an idea

That's creative! I will have to give that some thought, as it seems like it would work. No chance of trapping the gases that way due to draw issues or deep snow covering the pipe?

[srich]

Thanks for the ideas. I have a buddy with a sheet metal shop, so may go over and see how heavy he can make something like this. I would worry about it caving in on itself unless pretty rigid.

[joed]

Thanks for the ideas. I have a buddy with a sheet metal shop, so may go over and see how heavy he can make something like this. I would worry about it caving in on itself unless pretty rigid.

If you can get some of the material your roof is made of it will look like part of the roof.

[skipatroller]

Yes, heavy gauge sheet metal crickets work. I had a metal roof put on the house last September. (I am in Northern Idaho) I moved one of the vent stacks that I could easilly get to from about 3' from the bottom edge of the roof to about 3' from the ridge. The roofer put heavy gauge crickets about the other ones (not easy to get to them to move) as well as above the chimney.

We got the big dump before Christmas when the weather was in the single digits. I was somewhat disappointed in that the snow didn't slide. (it didn't even slide on the steep parts of the gambrel roof on my shop that has a 13/12 pitch). I think the snow was so light that it it just piled up. The snow got over 4 feet deep before it finally decided to slide and had settled for about 2 weeks. When it went it went in a 4' Slab (sounded like a freight train coming into the bedroom at 1:30 AM ! !) The crickets worked great (although they did get bent in a little on the sides. However the vent stack that I moved up near the ridge didn't fair so well -- snappped it off right at the roof line. (yes I will be installing a cricket above that stack as well.

I have seen other places where they have used 1-1/2 Schedule 80 PVC conduit for the vent stack instead of the schedule 40 ABS pipe and they seem to do OK as well. (I am not sure of how well this meets code though)