# Venting Question in Attic With Mansard Roof



## Nealtw (Jun 22, 2017)

No the holes should have been much bigger on a normal house we would remove that material, but it might be structural in your house.
The other thing to check and some have found is no common space from that cavity to the attic so baffles don't help.


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## JiggsDinner (Jul 15, 2017)

So you're saying in BC you would remove the plywood behind the soffits vents altogether and allow the wind to blow up the wall cavity portion of the mansard roof where it would then be channeled through the baffles and into the roof portion/out the roof vents? I imagine you get some strong winds there but I can't help but think the plywood serves some structural purpose here. 

Good point about checking the opening between the wall cavity and the roof portion - I'll have to check it out. I just assumed when the fella put in baffles he would have told me that. But you know what they say about assumptions........


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## Nealtw (Jun 22, 2017)

JiggsDinner said:


> So you're saying in BC you would remove the plywood behind the soffits vents altogether and allow the wind to blow up the wall cavity portion of the mansard roof where it would then be channeled through the baffles and into the roof portion/out the roof vents? I imagine you get some strong winds there but I can't help but think the plywood serves some structural purpose here.
> 
> Good point about checking the opening between the wall cavity and the roof portion - I'll have to check it out. I just assumed when the fella put in baffles he would have told me that. But you know what they say about assumptions........


I haven't worked on a mansard so not familiar with the structure it looks like that plywood could be flooring but I don't know that but bigger hole should have been cut.

The plus here tho is that vented soffet is easy to work with so it can be re and re fairly easily .

Baffles go from the attic into the over hang and as you have no over hang???


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## JiggsDinner (Jul 15, 2017)

Well the way I see it the whole shingled wall portion of my roof is the overhang. So air should shoot through the soffit vents, up the wall portion, and though the baffles into the attic. Thought I'd attach this pic to help clarify. 

Basically the picture above (of the wall cavity portion of my mansard roof) is on the other side of the shingles to the right of the window. Normally the homeowner would never see this but I had access to it as I had to rip open the wall behind the chimney in the master bedroom due to water damage. 

I think I will check that the attic and the wall portion of my roof are not blocked first. If they aren't blocked I will have to take down the soffit vents on the outside and cut bigger holes in the plywood to allow air through. The only reason I'm hesitant to cut bigger holes is I feel like more air flowing through the wall portion will make the 2nd story of my house colder. That and the fact we regularly get 80/90 kph gusts here. 

Anyways, I'm likely not going to go up in the attic until we get a really cool day, so might be a few weeks left. I'll let you know what I find out!


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## Nealtw (Jun 22, 2017)

If that wall has a top plate and the rafters sit on that?????????

It could be built with venting in mind, in the attic you would hope that the wall continues above the ceiling.


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## carpdad (Oct 11, 2010)

Venting is 98% for ice dam problem.:smile: It doesn't keep the space cooler and doesn't help with shingle life. For your kind of roof, do you get ice dam? If you do, you'd see lot of stains on 1st floor ceiling, being in your area. If you have water stains, where? I would expect more problems with flat roof above and flashing around the windows. Also, your rafter is also your wall. Venting the wall, even if insulated, would keep it cold. 
Some roofing pros may tell you, but dense packing the bay space may work better. You'd remove the soffit vents, sheath and air seal, then blow in dense pack newspaper insulation (name?). Remove ridge vent, air seal and reroof.


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## JiggsDinner (Jul 15, 2017)

Sorry about the slow response, I was out of town the last few days. Interesting point about venting not helping with keeping the space cooler. I would've thought lack of air flow through the soffits would keep the attic warmer and, because the attic is warmer, shingle life would be lessened. 

As for your ice dam question, no, we don't have an issue with ice dams. So perhaps ventilation isn't something I have an issue with. Maybe the stained sheeting that I see in the attic is due entirely to the fact that the piece of cardboard we had covering our attic hatch was letting a lot of warm air up there which was creating condensation and over time it created discolouration. Also I forgot to mention below the 2 bathroom fans were also venting hot air into the attic (which I corrected) so this might've contributed as well. 

Back to my original post/question, *I couldn't feel a draft when I put my hand up to the baffle. Is this normal? * It wasn't a particularly windy day outside but I still thought you would feel some sort of draft even on a calm day


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## Nealtw (Jun 22, 2017)

I doubt you ever feel the air flow like that.


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## Bud9051 (Nov 11, 2015)

Ventilation is also necessary to remove any moisture that seeps into the attic via air leakage or diffusion. The staining on the inside, as you suspect, is probably due to condensation and a leaky attic hatch would be a major contributor.

As for shingle life the Florida State University has done a lot of work researching that issue, specifically in relation to unvented attics where the temp rise has no relief from venting below. As it turns out, the resulting temp rise is within the limits the shingles can handle and they were testing in Florida. Here's their link.
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

Bud


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## JiggsDinner (Jul 15, 2017)

Thanks for the feedback Nealtw and Bud9051! I plan on double checking that the attic is properly air sealed (I haven't checked around light fixtures and bathroom vents) but am thinking my ventilation isn't as bad as originally thought. Will reply back next time I'm up there on my findings


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