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Overlaying roof shingles


Fixit4u
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The topic keeps coming up about overlaying roof shingles. For those who may not know what overlaying is, it is simply applying new shingles over top of existing shingles without stripping the roof.

For the roofer he has a substantial savings on labour for preparation of the roof , no disposal fees, very little mess to deal with, no labour or transportation fees related to the disposal of the old shingles.

The homeowner gets a couple hundred dollars off, and sometimes not that, he has no idea of the condition of the sheathing or other structural related problems, and has a roof that will not last as long.Estimates are 20% shorter lifespan.

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Estimates are 20% shorter lifespan.

That sounds good but is there any credible data to support that statement? Is there any roof shingle manufacturer which reduces its warranty because it is a second roof cover?

I'd like to know because I used to tell people the very same thing, along with a darker roof won't last as long, but I stopped saying that hearsay stuff a long time ago.

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That sounds good but is there any credible data to support that statement? Is there any roof shingle manufacturer which reduces its warranty because it is a second roof cover?

I'd like to know because I used to tell people the very same thing, along with a darker roof won't last as long, but I stopped saying that hearsay stuff a long time ago.

I did roofing replacement for years. The only time I came close to falling thru rotted decking was when I was removing two layers of 3-tabs. The older layer retains any moisture that happens to get thru the top layer and rots large areas of the deck.

It ain't heresay for me.

Marc

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The older layer retains any moisture that happens to get thru the top layer and rots large areas of the deck.

Marc

Without trying to sound harsh...

How does moisture "happen" to get through the second layer? Then, how does that moisture "happen" to get through the first layer as well? Then, how does that same moisture get under the roofing felt?

Sounds like magic moisture.

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Without trying to sound harsh...

How does moisture "happen" to get through the second layer? Then, how does that moisture "happen" to get through the first layer as well? Then, how does that same moisture get under the roofing felt?

Sounds like magic moisture.

From the top down, as in a roof leak. Leaks through the top layer, gets absorbed by the second layer. Asphalt degrades quite rapidly if kept moist.

I shoulda explained better.

Marc

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OP Mike Lamb

That sounds good but is there any credible data to support that statement? Is there any roof shingle manufacturer which reduces its warranty because it is a second roof cove

Marc's experience notwithstanding, is there any credible manufacturer's data regarding reduced warranty? Of course its tough to reduce a roof warranty (read: zero real value) even further.[:-monkeyd

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Hi Greg,

Certainteed will not allow roof overs for their Integrity Roof System (extended warranty program). This is because there is an increased risk for workmanship errors. That , and defects to the decking/ framing be not be discovered when there is a roof over.

I am not aware of any manufacturers that lower their standard warranty for roof overs, but would not doubt that some do so.

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Without trying to sound harsh...

How does moisture "happen" to get through the second layer? Then, how does that moisture "happen" to get through the first layer as well? Then, how does that same moisture get under the roofing felt?

Sounds like magic moisture.

From the top down, as in a roof leak. Leaks through the top layer, gets absorbed by the second layer. Asphalt degrades quite rapidly if kept moist.

I shoulda explained better.

Marc

A roof leak through 2 layers will degrade what's beneath faster because it is harder for it to dry out? Maybe. Will a single cover with the same leak allow more water to the sheathing over and over, more so than 2 covers and accelerate sheathing decay? Falling through 2 roof covers because of rot would be something you might anticipate just looking at it.

Someone credible needs to come out with a study on the 2 roof theory, otherwise it is still hearsay. Does a second roof cover have 20% less roof life compared to the original as originally posted?

If there are two layers

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