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Last year, we re-roofed out 83-year old house. We removed the 3-layer cedar/asphalt shingles and laid plywood decking, 30# paper, ice-barrier and 26-gauge metal roofing. As far as ventilation, we just figured that whatever the house already had, must have been working well, so why add anything extra? There was no mold or humidity damage. Now I am not sure. Any advice?

The attic was converted to an upstairs years ago, so the only true "attic" space is the peak and the eaves area (4'H x 6'W triangle), connected by about a foot depth of air space up the roof. The roof is a 2/3 grade, pretty steep. The insulation is foam board above the ceilings, with the interior otherwise open between insulation and plywood decking. Ventilation is two 8" roof vents and a 12" turbine set about a foot down from the peak. We declined to use a ridge vent while roofing because the winds in our area are so bad, neighbors said they had rain forced down their ridge vents. Not sure what sq. ft. our attic space is, but the lower floor is only 800ft.

If we Do need soffit vents, can they be added easily from the outside, without tearing off roofing? The metal roof, with such a steep grade, is pretty slick, and it would be a beast to redo.

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  • Is your "true attic area" actually connected to the soffits? I'm not sure if that's what you mean by "connected by about a foot depth of air space up the roof". Is that your rafter cavity? If so, then you could add soffit ventilation. As for whether you need it, your new metal roof may benefit from it if you get cold weather. Depends on how well your living space is insulated. If you have a cold winter and your space leaks warm moist air to the underside of a poorly-vented metal roof, moisture will condense on the cold metal - bad. If your insulation is really good that's not a concern.
    – Shimon Rura
    Commented Aug 7, 2014 at 21:16
  • Yes, I guess I meant the rafter space. They are definitely connected - we saw that when we were adding the new plywood decking to the roof. We do get cold weather here in the Midwest.
    – user24347
    Commented Aug 8, 2014 at 13:50

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The best and easiest solution is unfortunately no longer possible without removing and reinstalling the metal roofing: you vent above the sheathing and below the metal roof. The way you would do this is by installing the metal roof on vertical eave-to-ridge battens, with a metal ridge vent piece at the ridge. This way, all the ventilation is on the outside and you don't have to worry about complicated interactions with your finished attic.

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If my understanding is correct, you are referring to the knee wall formed when you finished the attic. This is a pain in the butt to vent; join the club.

I have a Cape Cod-style home which has the same issues. You need to vent the knee wall to the main attic above (the peak) while not losing the insulating properties for the rafter space in the sloped area. I used PVC pipes sparingly and insulated the knee wall facing the interior more.

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  • Another option it is simply fill the entire knee wall cavity with insulation.
    – Evil Elf
    Commented Aug 12, 2014 at 20:36
  • I wanted to update my answer with a brilliant solution I came up with on my own. The AEP inspector for my rebate was impressed.with how I vented the knee wall to the main attic in above the second floor. I turned the space above my stairs into a plenum that would carry the air in the knee wall area to the upper attic. I then insulated it with batts and foam board. You can hear and feel the air whipping up that shaft now.
    – Evil Elf
    Commented Nov 13, 2014 at 19:34

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