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Question DetailsAsked on 1/22/2014

Is it ok to put new roof composition shingles over old shingles that were laid 25 years ago on new 3/4 plywood?

We need to re-roof an old seasonal vacation cabin. Looking for a budget-minded approach. The old shingles are still in fairly good shape despite being 25 years old. New 3/4 plywood underlayment was installed when the last roof was done. We have decided to redo the roof to be proactive. Since the cabin is closed in the winter, a leak during the off season could cause major damage before it would be discovered. We need to keep the cost of re-roofing down and wonder if not stripping the old shingles would create problems after the new roof is installed.

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7 Answers

Voted Best Answer
3
Votes

As long as the shingles are not cupped and would not present a flat surface two layers is not usually a problem. You mention a seasonal cabin so snow load comes to mind. The pitch and length and spacing of the rafters would have to be known to give you a good answer. Two layers is fine and even if the shingles are curled or cupped it is not often done but you could do what is called tabbing off. You may go through a few hook blades but if this is a do it yourself project it might be the way to go. You just cut the tabs off the old roof leaving the flatter upper part of the shingles to roof over. It leaves some protection while the work is done and if the cabin is hard to get to you have a bit less waste to cart away. You have to check and see if the rafters are strong enough though. If it is a steep enough roof the snow loads may not factor in as much since the snow mat slide off.


Don

Answered 5 years ago by ContractorDon

1
Vote

+1 to Don's feedback.


I would add that cutting the tabs is usually more work that stripping the roof in entirety.


Have you considered metal as well? There are some R-panel profiles that are cost effective and homeowner / DIY friendly.



Answered 5 years ago by WoWHomeSolutions

0
Votes

Don, our old seasonal cabin is not insulated -- the studs and rafters are exposed in the interior. The cabin is located in New Hampshire where there can be significant snow. The roof slopes at about a 45 degree angle (my estimate) and snow buildup on the roof generally isn't a problem. Considering these factors, would roofing over the old shingles be advisable?

Answered 5 years ago by Guest_9408712

0
Votes

WoW Home Solutions - Can you tell me more about the metal roof option? Would the metal roof go over old composition shingles? Where do you buy metal roof panels? How does the price compare to composition shingles? Thanks!


Answered 5 years ago by Guest_9408712

1
Vote

Since you are only adding about 2.5 lbs per square foot you should be OK. I can not say for sure without knowing the size,spacing and length of the rafters. I have seen a few cabins built by weekend warriors that I wondered how they stood up in my visits to the North Country. And with age your shingles do not weigh what they did when they were new.


Don

Answered 5 years ago by ContractorDon

0
Votes

Where is the home located?


Most metal roof systems can be installed directly over the top (with some sort of slip layer) or overtop of a system or purlins or battens.


Doing it in this manner will allow for some convection beneath the roof panel and therefore make the roof system considerably cooler.


http://www.bing.com/images/search?q=r+panel+metal+roof&qs=IM&form=QBIR&
amp;pq=r+panel&sc=8-7&sp=2&sk=HS1

Answered 5 years ago by WoWHomeSolutions

0
Votes

I would assume when the new 3/4 underlayment (actually sheathing) was put down, I assume underlayment (roofing felt or roof wrap / water shield) was put down over it before the shingles.

I can only tell you what I would do, being in a cold climate, heavy snow zone myself:

1) since 45 degree roof and unheated in the winter, your ice damming leak potential is way down, and you will have (hopefully) minimal melting of or rain on the snowpack in the winter to cause potential water issues.

2) Obviously, to be as safe as possible, then the $1.00-1.50/SF tearoff and new underlayment (water barrier) would be "better" than just placing a second layer, but with a 45 degree roof I would not worry as much about it anywhere as much as I would on a 3:12 or 4:12 roof. (Tearoff price high due to 12:12 pitch - about double normal pitch).

3) For the $1000-2000+ ballpark additional cost of a tearoff I would do it if feasible cost wise, but if not perhaps spend a bit of those "savings" on a couple of preventative things:

4) get someone local to check the place every week or two for maybe $15-25 (assuming you have neighbors in the winter and driveable or easy snow machine access) - just a walk-through inspection for leaks and vandalism and such (which could cause as much water damge from broken windows as a leaking roof).

5) if you can get up there every month or two, especially in spring early thawing, buy a snow rake with extension pieces, and when you visit if very heavy snow buildup (dangerous weight) or starting to ice dam, pull down the snowpack - should not be tough on that steep a roof. Just be sure to clear entire height, not just lower edge - otherwise ice damming will form at where the cleared edge is, in the "middle" of the roof from top to bottom, rather than at the overhang where leak-through is less of a problem.

6) BTW - you said you wanted to keep cost of reroofing down - so that probably rules out metal shingles, which cost roughly twice asphalt installed.

7) Cost of removing removed shingles could weight your decision toward second layer if tough access - snowmachine or boat only, say, where hauling off 10-20 cy of torn off shingles would be a hassle or take many trips.

Answered 5 years ago by LCD

0
Votes

BTW - in Contractor Don's comment, he said "would not present a flat surface" - presumably he meant "would not PREVENT a flat surface"

Answered 2 years ago by LCD




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