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Old 11-21-2009, 06:47 PM   #1
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flat roof vents

Hello all,

I would like any advice people might have regarding proper flat roof ventilation. I'm attached on one side. there are soffit vents that are aluminum that was installed over the original woodwork. So maybe it gets airflow and maybe not. It was there before I arrived BTW- this is a 100 year old house. several years ago I insulated between the rafters leaving aprox 1" between the top of the batts and the underside of the decking. Decking is old 1" planks with many gaps running between edges. I also have a vapour barrier between insulation and drywall.

What are my options for venting, as I only have one point (no in/out), or is this not such a big deal with all the gaps etc? I just had a nice modified bitumen roof torched down too

If need be, what's the best way to vent from the roof top? I was hoping that some sort of continuous long vent that could be fixed on top of the roof and sealed? Or maybe I just need a few indivdual vents ?? I could either drill lots of big holes in a row or cut the roof back and run the saw along to make an open strip.

Need some advice here, thanks.


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Old 11-21-2009, 09:11 PM   #2
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Some pics might help.A flat roof can be vented the same as a pitched roof.Exhaust without intake is useless and vice-versa.Does your roof have a peak?Do you have attic space?We need some pics


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Old 11-21-2009, 09:50 PM   #3
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It doesn't really have a peak. It's almost completely flat. I think it might be something like 2 inch over 4 feet. I will have to go and take some pics. So even though it's an isulated roof with just an air gap, I need that cross ventilation?

There is no attic. It's a full 3rd floor living space. Heated etc. The roof is insulated 2x12 rafters from the tops of the outside wall to party wall then over to my neighbor's outside wall.


Last edited by zantar; 11-21-2009 at 09:55 PM.
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Old 11-22-2009, 05:06 PM   #4
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Ideally a roof with the insulation below the decking(cold roof) should be vented as any moisture getting through can condense on the bottom of the decking.
You have got a moisture check though, so this will help a lot.
When the insulation is above the decking (warm roof) venting is not needed.
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