We’re in the process of insulating and renovating an unfinished attic space in a 1915 home. Our assumption going into the project was that we would allow space for ventilation behind the insulation (under the roof) so that air could pass from the soffit vents to the ridge vent.
Well, it turns out that we actually don’t have soffit vents, and we don’t have a ridge vent, either. Looking up an down our street, it appears that all the homes on our street don’t have soffit vents.
So, the GC has suggested using closed cell or open cell foam to fully insulate the roof, and forget about ventilation altogether.
Because we have a slate roof, putting in a ridge vent would be very costly. I’m not really sure if it would even be useful, because it wouldn’t have anything to ventilate.
This is a pretty dramatic step, so I’m looking to collect as many opinions as possible before dramatically altering our roof in this way. We live in the NE, so avoiding ice dams is an issue.
Add a double set of gable end vents (low down near the bottom of the gable end and near the peak). Drill 2/3/4 inch holes on the soffits and add aluminum or plastic vent covers.
Partial ventilation is better than no ventilation.
T.Neyedli
www.alphahomeinspections.ca
I have seen many unvented 100+ year old attics ,they have survived this long so as the saying goes if it ain’t broke why fix it.
The slope sounds great to me to step to walk , I expect snow will not stay much.
…Cookie
Without knowing your location, site orientation and the specifics of your roof design, all bets are off as far as any of us really providing fact based info.
He’s some info from some of the most knowledgeable for general ideas on how to design your attic retrofit.
I would seal any opening in the attic floor which would allow warm/moist air into the attic area. Slate is not air tight it breathes. I would not spray foam on the underside of the roof. Bad idea.
Roof ventilation is a big issue today in the roofing industry, and it should be. Asphalt roofing shingles nailed or stapled onto plywood decks are roofs systems that will not breathe – they suffocate the roof, and proper ventilation is imperative. Otherwise the plywood will delaminate and the roof will fall apart. Slate roofs attached to board decking, on the other hand, are breathable roof systems. They are not air-tight – they’re water tight. Ventilation may be necessary to prevent condensation occurring under the roof sheathing from warm inside air leaking into the roof space. This is easily achieved with gable vents or roof vents, air spaces between the insulation and the sheathing, and ventilated soffits. However, most older residential slate roofs had no particular ventilation systems associated with them. After a century, most are still in good working order. Such is the advantage of a roof that can breathe on its own. When these older slate roofs are retrofitted with roof insulation, care must be made to ensure that warm air will not come in contact with cold roof sheathing. Aluminum ridge vents should be avoided on slate roofs. Such vents are designed to be used with asphalt shingle roofs — as such, they’re cheaply made, they do not fit the ridge of a slate roof well, and they interfere with the normal maintenance of a slate roof.
Interesting information. I definitely feel convinced that an unvented attic would be the best for my situation (Massachusetts, front gabled roof with a 12/12 pitch). Now I just need to figure out the most cost effective way of getting there.
My thought was to do a couple inches of closed cell foam, and then fill the rest of the rafter bays with spray in place cellulose. But, after talking with one insulation guy, he told me that wouldn’t be much cheaper than just doing the whole thing in cc foam. I’ll wait to see the actual prices. I’m a little wary I’m going to have significant sticker shock.
