Foam insulation under a slate roof
Greetings,
We have an 1850 converted carriage house with a slate roof that was put in around the 20’s. Needless to say, the house leaks a bit. We had an energy audit and it was suggested that we have foam insulation sprayed into the rafters and the gable ends, bringing the attic into the house’s envelope and eliminating the vents. (BTW, the AC air handler and the duct work is in the attic). I’ve been reading a bit about this approach to insulation, both on this site and elsewhere, but I haven’t been able to find anything about doing this with a slate roof. Not sure if the slate roof would have any particular impact on the decision. One of my concerns is that sealing the underside of the roof would eliminate one way of tracking leaks if they were to occur.
I would appreciate any thought or insights on this.
Thanks,
Anthony
Replies
I have been looking into different insulation schemes while planning a new cottage and have come across a product called P2000. If all you are looking to insulate is the ceiling, their web site has info on retrofitting insulation on the inside. might be worth a look.
Believe about 1/10 of the information on their website. I have a letter in hand from Intertek Testing saying that P2000 broke agreements with them about how the results were to be used. I have been contacted about possibly beginning a charge of fraudulent advertising against them. Wisconsin has allowed them to advertise the product only as R5, not the " R27 performance" they claim.
Before you make up your mind on the insulation it might be wise to hire a slate contractor to give you an assesment of the roofs present condition and what it will require in 1,5, and 10 years from now.
Slateman has a good point to follow-up on.
As far as tracing leaks - I have almost never been able to pinpoint a leak source from inside. That is a minor hint at best. An experienced roofer can find it from the outside 80% of the time on first glance.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
My experiance with closed cell polyureathane spray (R-7 Per inch) has been positive with asphalt shingles. This creates a "hot roof" in a conventional sense, ie: unvented. Time will tell if the spray applied poly will have the same long term negative affect. The postive side is a well insulated roof with near zero perm and added structure from the spray applied foam.
berone,
My thoughts on spraying a foam insulation under a slate roof. First I like the concept!
But!
don't expect the foam to provide you with a leak proof roof.. water can travel all sorts of ways (including uphill!?!!!!) sprayed on foam doesn't provide a totally sealed surface. Once you foam the roof it will be harder not easier to find the source of a leak..
I shouldn't expect the slate to be impacted in any fashion by the insulation method.. if you have concerns what I would do is staple those plastic/ foam roof vents to the underside of the roof decking and that way still have a cold roof while enjoying the benefits of foam insulation.. If you are clever you can set those vents up so one tray over laps the bottom tray etc. etc right up untill you are outside of the building enevelope and rain leaks fall harmlessly onto the soffit..
If I read your posting correctly you propose to spray a coating on the inside of the roof space to try and keep out the moisture. This method has been criticised over here (Scotland) because it leads to rot in the roof timbers and makes any subsequent repairs very difficult. The problem has to be tackled from the side the water is coming from - the outside surface of the roof.
Our slated roofs have boards (called sarking) across the rafters then a covering of roofing felt (asphalt coated material) on top of that. The slates are then put on top of that. This results in a combination which is quite capable of keeping out even driving rain. The little that get through is easily taken care of by the ventilation in the roof space.
The overlap on the slates and tightness of the fit is also important in reducing water penetration.
NICK
I just re-read my post and I understand the confusion. When I said "the house leaks" I didn't mean water - I meant hot air in the winter and cold air in the summer. The slate roof does not leak (okay, mostly does not leak. When there's a driving rain some water does get in around a vent that some idiot put tar on). I am not looking to have the foam treat water leaks, only air leaks. My concern was that spraying the foam would deprive me of a way to trace a potential future roof leak and would trap the water and do real damage. Slateman has an excellent point, though. I should have the roof evaluated before taking the next step. Following that logic, I should have the work that I know needs doing to the roof done before I do the insulation. I'm sort of putting the cart before the horse - the roof doesn't leak water but the house does leak air. I'm trying to reduce the heating and cooling bills in any way I can. But it doesn't make sense to deal with the insulation if future roof work might be limited by that. Time to pony up the $300 and have the roof company come and do an evaluation and an estimate.
Edited 6/4/2006 7:34 pm ET by berone
berone,
Before you spend the money, can you evaulate it yourself? How old is it? How well was it installed? How does it look compared to new slate roofs? Now you might be ready to hire outside experts..
You see few experts are immune from creating their own work schedule. I'm a bit of a old barn fanatic, a few decades ago I saw the results of poor advice from a roofing "expert" This barn hadn't leaked but the owner knew that his grandfather had shingled it almost 80 years ago..
He allowed himself to be talked into a new roof decking of plywood to replace "all those old boards with gaps between them" and a fresh rolled asphalt roof. I saw all these beautiful hand split shakes stacked up on the ground.. none of them showing any sign of decay.. each one had a neat hole drilled in the it's corner and a carefully fit tapered peg driven flush. The deck boards were all fine white oak.. with absolutely no sign of decay! each one had carefullly drilled pegs holding it on.. The workmanship involved was simply awesome. No signs of failure or decay..
The plywood was banged on with regular steel nails which with luck and little leakage might last twenty years before they rotted thru from the tannic acid in the oak.. cheap rolled roofing was almost an embaresment, a decade later the barn was gone.
In summery, knowledge is power know what you have before you allow the "experts" to talk you out of it!
Thanks for the advice. Before I even closed on the house last year I bought a copy of Joseph Jenkin's book "The Slate Roof Bible". The contractor I've contacted I found through Jenkin's website. There are a number of broken slates on the roof, and if that was the only problem I might take a crack at it myself. But the valley's have been tarred, as has the flashing around the chimney. Overall, it's more of a project than I want to take on myself. I'll limit my work to enclosing the porch. And installing a new bathroom... finishing the basement... moving and remodelling the kitchen... turning the garage into a mudroompantry...
If you'd like a second opinion on what you hear from this roofer or slater e-mail me and I'll give you my two cents for free.
I've got a lot of Shutterfly albums of different slating situations which I would gladly send along.