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mlysell 08-30-2010 10:28 AM

removal / insulation
if you have one layer of shingle roofing, do you have to remove the old roof before putting on a new one? can you leave the old roof as an insulating layer? or, what are other materials to use if you want a layer of insulation of some kind under the new shingles?

federer 08-30-2010 11:04 AM

shingles are not insulation. you can put down a 1/2in board insulation over the decking first

epson 08-30-2010 11:19 AM

That is actually a great and very straight-forward question, with an equally great and straight-forward answer. You can generally lay a new roof over the old without any problems as long as:

1) You only have one layer of asphalt shingles on the roof. Most roof frames can support two layers of asphalt shingles, rarely three this all depends on the framing, of course.

2) The shingles lay fairly flat. The new shingles will take on the shape of the old, so if the old shingles are very curled, twisted, or buckled, the new roof will eventually look the same AND the life span of the new shingles may be decreased. This may also void the manufacturer's shingle warranty.

3) There are no existing leaks from undetermined sources. Just putting a new roof over an old roof will not necessarily fix underlying problems, such as with flashing or roof vents. These leaks will most likely recur unless they are properly repaired prior to installation of the new roof.

4) You were satisfied with the performance of the old roof... e.g. no occasional leaks during rainstorms, etc. This refers back to item (3)... new roof over old roof may not guarantee elimination of leaks.

5) An examination of the roof deck or underlayment shows it to be solid. If there is any widespread warping or softness, repair will necessitate the stripping of old shingles. If the area is large enough, it makes sense to restore the entire roof to new condition.

Ideally, your or your contractor should repair, reseat, or (ideally) replace all flashing around chimneys, valleys, vents, etc. He should also cut off or replace any curling shingles so the new ones lay flat. If you have had ice dam leakage, he should also remove the bottom few feet of old shingles and install an ice and water shield right against the roof sheathing plywood.
You can then be assured that your roof will have a long and healthy life!

OldNBroken 08-30-2010 03:49 PM

Well put epson. It's always ideal to tear off the existing to be able to inspect the soundness underneath as well as having a clean slate to start with. There is nothing wrong with going over existing as long as it is still relatively smooth and flat. Federer, sorry, recovery board has no business on a shingle roof, it is used for low-slope roof applications.

epson 08-30-2010 04:29 PM

Thank you OldNBroken...

Gary in WA 08-30-2010 07:04 PM

Check locally, you may have something as this:
16. Section R907.3, #4 does not allow an overlay of asphalt shingles on re-roofing since
Broomfield is considered a “moderate” hail damage area per Figure R903.5.
Therefore all re-roof permits will require a complete removal of old roofing.


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