*
I’m planning on installing a metal roof, getting estimates for both standing seam and pre-formed panel. The roofing contractor I spoke with is telling me that with either roof, there is no need to do a tear-off, just put down purlins and the new roof. On one part of the house (160 years old), there are 2-3 layers of asphalt over cedar shakes. On other parts (100 or so) just one layer of asphalt over plywood sheathing (obvious update). The contractor knows this. His reply was that I don’t want to get involved with a tear-off, it’s too much work & $$. Time for a new roofer? Frankly, I’ve never hired out any of the work on the house, and have done everything, from sill replacement on up to the soffits myself, but figured I’d pass this job onto the pros however…
Thanks,
Doc
Replies
*
Dave,
I'm a guy who believes that tearoffs are the right way to go in general. The old section with 2-3 layers has to come off. The one layer area maybe can stay. But if you do a tear off, you'll know what condition your roof deck is in, be able to deal with ventilation better, be able to see the rafters or nail pattern if it's plywood to nail the purlins into solid material instead of guessing if the nails are hitting anything besides shingles and plywood. Plus, if there are any sags, it's really easy to run stringlines to straighten the roof by shimming the purlins. With shingles on, you may not see it as well.
Then there's the weight issue. What about the extra weight from the new roof sitting on top of the old (heavy) roofing? Probably pushing the old rafters pretty hard. A lot of older houses had small rafters, and weren't tied off that well either. Something to check out.
But I'd be wary of any "roofer" who put any roof finish over "2-3 layers"...
good luck,
MD
*I agree with Mad Dog, especially on the weight issue.I like the standing seam roofing. It's expensive, but there are no exposed fasteners.We worked on a 2 year old house with a screwed down metal roof recently and they were already having some minor leaks around some vent flashings.
*Doc, i "It's too much work and $$$"?Why is he in business? Work = $$$ = business. Sounds like it's time to find a real roofer now, before this one spends a bunch of your money making a mess of your home. Your local building dept. might also have an opinion as to how many layers of old roofing material are acceptable. I'm as lazy as the next guy, but there's a limit. Joe H
*I agree with above, no way do you want to leave all that up there.
*"figured I'd pass this job onto the pros however... "Now all you need to do is find a pro.Metal on straping over old can be done but this sounds way out of line of possibility with so many layers. Bet the original sheathing hasn't seen the light of day since slavery was legal.
*I am installing a metal roof on new construction and was told by the yard that purlins were not a good idea in cold weather. He said the open space under the metal roof would cause condensation which would than drip down into the insulation. Is plywood a better route to go than purlins?
*David, I think you are talking about what we call "skip sheathing". Put the 1Xs on the trusses or rafters and fasten the roof to that. Very common in utility roofing for things like barns, sheds, etc.If you have insulation, vapor barriers, etc you must use solid sheathing like ply or osb.Over the solid sheathing lots of people use tar paper then the metal. Some just put the metal directly on the sheathing. I don't think it much matters as long as you follow the metal manufacturers instructions.Oh by the way, not your question but; for a re-roof do a complete tear off first. No metal on top of any other roofing.
*As I write, I am sitting in a nice dry house with an 8/12 roof that is metal over skip sheathing. It is an extremely humid climate.The spaces do not 'cause' condensation. Instead they allow ventilation that prevents condensation. A vapour bar inside on the living side of the insulation prevents moisture from getting out that far anyway.
*Piffin-When you installed the vapor barrier did you have to be anal about it and tape over staples, etc, and seams? Or just do a decent job of tacking it?I did a roof has no vapor barrier at all. It has a lot of thermal breaks, and it mostly is unheated space, but have not noticed any condensation. Just curious because it seems metal is getting a lot more popular.MD
*I placed kraft faced R-19 fibreglas between the rafters with the kraft down to living space. Then I used long plasticap nails to fasten foil faced thermax (inch and a half or two inch - I forget) to the underside of the rafters. I did tape the seams but didn't lose any sleep about nail holes through the foam. Then I put up strapping and screwed my sheet rock to it.I'm sure plenty of house moisture gets through the vapour bar but I'm equally sure that I've allowed a way for it to escape up and out. I've left the foaam block strips out at the ridge and eaves. used screen at ridge for insects. I'm also sure that someone who is anal about such things will tell me all about why this won't work or shouldn't be done this way.
*Piffin- If it works for you, who can argue with that. I have had to fix more than one metal roof over purlins. Maybe there was just not enough ventilation but up to a half inch of ice would form in the winter and then melt when the roof warmed up. This damaged the ceiling and got us a phone call. When we install the roof, why take a chance? I'm sure that this is more of a problem in a cold climate.
*The asphalt roofing layers under metal act as heat mass and nothing more, do a complete tear off to recieve maximum benifit from the metal roof, I go over solid deck, it makes the metal more resistant to hail damage.
*Do you need to put the 1Xs over the tar paper? Or just nail the metal directly over the paper?
*Randy, please, please read the mfg installation stuff. After that I doubt you will want to nail.Oh yes, any dealer should have a stock of installation manuals. If not just call the mfg.
*
I'm planning on installing a metal roof, getting estimates for both standing seam and pre-formed panel. The roofing contractor I spoke with is telling me that with either roof, there is no need to do a tear-off, just put down purlins and the new roof. On one part of the house (160 years old), there are 2-3 layers of asphalt over cedar shakes. On other parts (100 or so) just one layer of asphalt over plywood sheathing (obvious update). The contractor knows this. His reply was that I don't want to get involved with a tear-off, it's too much work & $$. Time for a new roofer? Frankly, I've never hired out any of the work on the house, and have done everything, from sill replacement on up to the soffits myself, but figured I'd pass this job onto the pros however...
Thanks,
Doc