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.
Best Answer
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.