Older Roof Ventilation
I live in Ottawa, Canada where the winters are cold and the summers hot. My roof needs reshingling again and its the third time in 23 years. I believe the problem is caused by the manner in which the attic was finished. There is insulation between the rafters, a vapor barrier and then T&G knotty pine. I don’t believe there is any ventilation to let the heat out of the insulation in the summertime, but don’t know how to rectify the problem. I don’t want to have to rip out the finished T&G and start over. Instead, I am looking for a solution from the out/topside. I am considering strapping the roof (after stripping the shingles) with 1x4s, adding a layer of sheathing, and then reshingling. My thinking is that with ridge and hip vents and ventilting soffits, there would be an air space between the shingles and the roof itself that would allow air to circulate and heat to escape rather than build up in the insulation and bake the shingles to a premature death. Am also wondering if a layer of Tyvek house wrap on the original sheathing boards (the house is 80 years old) but underneath the strapping would be a good idea to reduce air infiltration and loss in the winter time. The roof has about a 6/12 slope so working up there won’t be much fun.
Would this work? Is/are there better solutions I should consider??
I live in Montreal, Where the winters are colder and the summers hotter, You know the competition.
Kidding aside: Yes that would work. Just make sure the soffits are open to the new airspace that you will create. If you go with a ridge vent, then I would worry about ice damming in the winter as the roof will heat up and melt the snow. Then the water will freeze at the soffit. My parents have the same slope of roof in the eastern townships and have had large ice dams over the last two winters. Suggest you put a layer of ice membrain along the overhang.
With regular vents, I would leave the strapping short of the ridge (about 1 foot) and run strapping along the ridge. Then install your vents.
As for the house wrap, I don't know about that.
Good Luck Bruce
Edited 7/13/2002 11:11:00 PM ET by weekendwarrior
You guys have nothing on Winnipeg. :-)
Had the same problem a few years ago. Was refurbishing an old storey & a half. R12 fg between the 2x4 rafters with R12 SM sheeted underneath w/vapour barrier poly & drywall. R24 ceilings! 20 years ago that was better then new construction. You wouldn't beleive the amount of water I had running down the inside walls the following spring. I've never seen such ice dams.
I was living in the downstairs & luckily hadn't taped the drywall. So, down comes all the drywall, SM, & fg. I nailed up 1x2 spacers along both sides of the upper edge of all rafters & ripped some old paneling to nail accross the bottom edge of all those spacers, creating a 1 1/2" air space from eave up into the attic in each rafter space. After nailing up a 2x2 on the bottom of each rafter to make up for the lost space for ventilation, I replaced the FG, the SM, the Poly & drywall. Never had another problem with ice dams.
I Suspect ( now where did those damned Italics come from?) the method you propose using would do the same thing, but I wonder if you wouldn't be better off using 2x2s for strapping to create a more effecient ( IMHO) air space to provide for better flow. The purpose of the ventilation space is to allow cold air to flow through, keeping the roof deck below freezing to keep snow from melting and then reforming as ice dams.
I also suppose that using Tyvek on the existing deck, below the new strapping, would do no harm & would probably provide some extra protection against roof leaks. HOWEVER, one mistep & can you say slippery slide? Be careful up there!
It's 35c in Winnipeg today. Those tabs will really seal.
I heard you guys are going to make the mosquitoe the provincial "BIRD".
Rainning and 18 c in YUL.
Adding space between the sheating and the insulation would maybe and a stress maybe have a 1 year effect on the life expectancy of your shingled roof.
You have another problem if your shingles are having to be replaced that often. What are you shingling with and who did the shingling would be a good place to start.
There are 10's of thousands of homes in Ottawa without ventilation in some part of the roof and replacing roofs has not made it to the regional games as yet, so it would be highly likely that you have a unique situation caused by something else.