# How to properly ventilate a Mansard Roof?



## Shaitan00 (Feb 3, 2015)

Seems like my terminology might have been bad - when I say "finished" I mean it needs to be replaced immediately - the previous owner block all the soffits (thought they were mistakes) - so now I need to tear it down - while I am doing that I am going to improve the ventilation and thus my questions.

The roof is NOT flat (small pitch, not sure how many degrees), and there is an attic that I can get to and almost stand-up in (so pretty large).

Right now the roof top is the same as the sides, shingles (falling apart), and I plan to put new IKO 50 year fiberglass shingles on - would have loved metal but can't afford it.


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## PatChap (Nov 17, 2012)

Where are you located. Mansards are a bear to ventilate, budget for a large amount of plywood replacement.
A roofside intake vent is a good idea, I'm not to familiar with the maximum products, but an intake vent like smartvent by DCI would work well.


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## Shaitan00 (Feb 3, 2015)

@PatChap - Quebec/Canada - get it nice and hot in the summer and nice and cold in the winter ...

By roof in-take you mean (1) option I listed, why that over (2)? Curious.


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## PatChap (Nov 17, 2012)

I think it would be more effective and less likely to leak when an ice dam occurs, as it is below the roof line.

On your shingle choice, IKO make a decent product these days, but only offer a 12yr warranty when installed on a 3:12, which is likely what your top is.
Other manufacturers offer full warranty on 3:12 pitch.

If your curious, this is right from their limited warranty package.


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## Shaitan00 (Feb 3, 2015)

Like who? I only say IKO because the only other options I am aware of is BP and I am tired of getting their defective stuff ... do you know someone else?


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## PatChap (Nov 17, 2012)

It looks like your in a city, so I imagine you have access to the american brands. Certainteed and Owens corning, GAF. See what's available where you live and read the warranty limitations.
BP is also not what they once were, they're product is actually pretty good these days though in not sure how they warranty low slope shingle roofs.
Iko and bp had the same problems, as they both put out a lot of organic shingles.


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## Windows on Wash (Aug 30, 2011)

The dreaded Mansard venting issue. 

You ever considered just yanking the front roof and spray foaming?


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## derekbrian (Oct 12, 2015)

First of all make up your mind, whether you want to remain that roof or not. Don't go for friend's opinion and take the advice of your family members. Although this type of roof is very good for passing of ventilation and moreover it has its own beauty.


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## carpdad (Oct 11, 2010)

If it's that hard to ventilate, how about installing a second layer of sheathing with a spacer? Since reroofing, and if the rafters can take the load.


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## Gary in WA (Mar 11, 2009)

Only need to ventilate the top, mainly. Side walls are usually closed-off from the top and convective loops in double walls with space is not insulated/air sealed properly, it acts as a wall not a roof. Vent the top roof with intake/exhaust, leave the walls for another day...

Gary
PS. Thanks Joe! see what you started with an old post...


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