Roof repair question

So my house needs a new roof. Pretty standard asphalt shingle job (no flat roof) and I've gotten a few quotes. My question concerns removing prior layers of shingles rather than re-shingling on top. Most guys quoted between $8k and $12k to remove two (maybe even three) older layers of shingles before nailing in the new roofing. One guy wants only $3,500 to lay new shingles on top of the old ones. My house is about 80-90 yrs old and the roof is made with 1" thick planks rather the 3/8" sheets of plywood they use today. This guy, who was recommended by a friend who's used him and has done other houses in the neighborhood, assures me that nailing new shigles on top of the old ones is not a problem in my case.

I am usually sceptical of cutting corners with these things but even if laying new shingles on the old one reduces the life of the shingles from the stated 25 yrs to 15 yrs, I may be willing to forego the additional expense for that time.

So anyone know about roofing or has experience with this type of repair? Thanks

I'd be concerned if the number of layers existing exceeds what the manufacturer recommends it may not just limit the lifespan but could impact the warrantee as well. Something to check on...

I may also be concerned that the roof won't have as uniform a look.

But at the least I'd get several opinions, I don't even trust the contractors that I know

-spence

+1 on number/thickness of old layers. Putting down over old shingles is not a problem if there are no critical issues with the old roof.

Originally Posted by Cary Grant

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+1 on number/thickness of old layers. Putting down over old shingles is not a problem if there are no critical issues with the old roof.
Putting shingles on top of layers of old shingles could be against code in your area.

I have done plenty of paid work as a carpenter and while I am not an expert, I never got a contractors license, I have NEVER EVER heard of doing it this way. Not to say it would not work for a while but in my experience it was just taken for granted that you would strip first. Doing it this way is just half assed and you can likely expect half assed results.

Good points about building code and warranties - thanks.

Originally Posted by Cary Grant

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Putting down over old shingles is not a problem if there are no critical issues with the old roof.

This is what this roofer claims but

Originally Posted by NorCal

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I have done plenty of paid work as a carpenter and while I am not an expert, I never got a contractors license, I have NEVER EVER heard of doing it this way. Not to say it would not work for a while but in my experience it was just taken for granted that you would strip first. Doing it this way is just half assed and you can likely expect half assed results.

My gut feeling also says that it's a half-assed way to do it but I need something some concrete before I spend another $4-5K to strip away the old shingles. If it will be reduce the life of the roof by a few years, I can live with that in order to defer the added expense. Wouldn't most contractors want to strip away old roofing because it makes the job that much bigger and they can charge more?

Anyone else care to weigh in?

Roofing over existing shingles is usually fine structurally. However, the roof may look like **** (lumpy, uneven, etc) depending on what all is underneath.

In these parts there is a limit to how many layers are allowed by the building code.

My roof was redone a few years ago. I had a complete tear off as my roof had multiple layers including the original layer of cedar shingles from 1889.

Originally Posted by JayJay

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In these parts there is a limit to how many layers are allowed by the building code.

My roof was redone a few years ago. I had a complete tear off as my roof had multiple layers including the original layer of cedar shingles from 1889.

Agreed- sounds like that was silly- but also proves the point that new over old is sound. Up to about three layers.

also, check with your insurance company. even if it is not against code (which anything over 2 layers most likely is) it may negate your coverage in the event of a fire.

Originally Posted by dave

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also, check with your insurance company. even if it is not against code (which anything over 2 layers most likely is) it may negate your coverage in the event of a fire.
Very true. This was the case with my cedar shake shingles. If I had shingled over them, then my insurance would have been negated in the event of fire.

Ok so I talked to a friend of mine who is a contractor and worked for years and years as a builder and he agreed with what I already said. Its kind of a ol' timer, half assed way of doing it. Potential problems include not having a good surface to nail to and having to nail through too many shingles. In the valleys (where two roof lines meet) this might be a particular problem. Valleys are also where water gathers to run off your roof so this would make the problem worse. Also shingles are asphalt, they will melt and settle and if they are over an uneven surface (like an old roof) they will crack sooner and look like ****. Finally anyone who builds this way is not going to stand by his product and if he told you that this is a fine way of doing things then you already know he is a bit fly by night. ( or full of ****, take your pick)
Bottom line is if you can afford to do it right do so. A ****** roof will keep rain out over the winter but it will cost you money in the long run, potentially a **** load if, say, the shingles fly off in mid Dec because the nails were barely able to grip or your insurance company won't cover you in the case of a fire.

I would not put new shingles over old, and have never done so on my houses. YMMV

Originally Posted by weeks

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Roofing over existing shingles is usually fine structurally. However, the roof may look like **** (lumpy, uneven, etc) depending on what all is underneath.

Agreed on both points. How many layers do you currently have on your roof?

It doesn't matter if it's a code violation or not. Strip the old roof off and make sure the sub layer isn't rotten etc. What most people fail to remember is something called a snow load and you're in Canada, the less weight on the roof the more accumulated snow it can take before failure.