How many layers of shingles can a house hold?

[esch]

Just thought I'd share my findings

This is the most layers I have found yet. (asphalt)

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8 Layers on this 1960 house.

How common is it to find this many layers?

The house shows NO settlement other then on one wall theres a vertical crack close to corner on brick outside, but unable to be found inside.

Its around a 4 pitch roof with 2x6 rafters and 1x6 ridge board.

Very sound house.

[Tom Raymond]

It would be with all that weight holding it down. Typical 3 tabs are about 70 pounds per bundle, that translates to 168 pounds per square foot or 1680 pounds per square. That's more than four times the design snow load here in snow country [:-bigeyes

Tom

[Neal Lewis]

If that house was built in the 1960's, why would there be 8 layers of shingles? Doesn't make sense.

[Mike Lamb]

If you counted 8 layers at the eave, you are likely looking at 4 roof jobs. That's alot over a 50 year period. I put the third roof cover on my house (1962) in 2004. I'll leave Tom to the math but that's a heavy roof.

[Jerry Simon]

If that house was built in the 1960's, why would there be 8 layers of shingles? Doesn't make sense.

I agree. 20 bucks says there are three layers (each layer *looks* like three layers).

[Marc]

A plantation home here in south Louisiana built near the turn of the century had six layers of asphalt shingle roofing over the original cedar shingles on spaced decking. During the demolition phase, I had access to a cross section of it and measured the total thickness at 2 1/4 inches. The roofing nails on the top few layers didn't even hit any wood. A lot of dump fees. The framing held surprisingly well and was undamaged.

This was 7 years ago before I became an inspector.

Marc

[esch19]

There is only 2 shingles on edges, they stripped them over the eves but left the rest

I've heard a rule of thumb is every layer is a half life, is this a common theory?

Assuming they were 30 year shingles...

1-30

2-15

3-10

4-5

Maybe I some how miscounted and theres 4 layers, but there is about 2 inches of shingles at cut-outs for the turbine vents in the attic.

Still yet, I could have sworn there was 8 layers, as odd as it would be, I'll look one day if I get the chance, I know the owner.

Matt

[kurt]

I agree with Mike. I bet it's 4 roof layers; there's probably some starter strips or underlayment applied that's making it look like 8.

8 layers doesn't make any sense at all.

[Phillip]

5 layers on top of wood shingles. They had used 16 penny nails on the top layer.

[Mike Lamb]

I've heard a rule of thumb is every layer is a half life, is this a common theory?

Matt

I believe that's a common myth. No shingle manufacturer I know of mentions the number of roofs in their warranty.

[RobC]

The most layers I've seen is 4, one more than the allowable according to our code.

If what you say is correct "...but there is about 2 inches of shingles at cut-outs for the turbine vents in the attic." then there might very well be 8 layers (1/4" per layer x although I find it difficult to believe.

An average asphalt shingle roof weighs between 210psq. and 235psq. (100 sq feet) or 2.1psf. and 2.35psf. If you add the 8 layers, between 16.8 and 18.8sqf. to your design snow load you'll find you're well over your maximum allowable.

I'd make my client aware that once the roof is relieved it could spring back and cause interior cracking.

Next time you're over, take a close up picture of the turbine.

[RickSab]

I swear I heard my house sigh when I removed the 5 (maybe 6) layers of roof on it. It was about 1.75 inches thick. I bought an old bungalow that was first titled in 1917. It has the typical 2x4 framing, even the roof. The ridge has that sag in the middle that try as I may I could not get out. The sag has been there longer than I have been alive. The stucco showed the normas stress cracks but nothing big. If I had not enlarged the dormer on it to put bedrooms upstairs I may not have even roofed it when I did.

[hausdok]

I once had a 1920's Tudor in Seattle with six actual full layers over a layer of original cedar shingles. I called the city to ask how many were allowed. "As many as they want," said the code guy, "We've never adopted any restriction on the number of layers. If a homeowner wants to put that many layers on, it's up to the homeowner." I couldn't believe my ears; and the client, having used option B, couldn't get out of the deal based on the roof thanks to the city.

Thankfully, since then they've changed their policy and they do now restrict the number of layers to two; however, they still allow the old cedar shingle decks to be used as a roof base. That's an issue around here since most roofers here aren't old enough to know that when they do that they're supposed to cut back the first ten inches of material around the perimeter and replace it with one-by before they start applying the new deck.

Still, it's probably a non-issue since I don't think one could find a roofer these days that's going to waste time tearing off and leaving an old cedar shingle deck when a new deck can be thrown on in half the time and with half the aggravation of trying to separate old layers of roofing from an old shingle deck.

ONE TEAM - ONE FIGHT!!!

Mike

[Les]

We did not have any restriction regarding the number of layers. We had a restriction on the load of 640per sq.

For many years asphalt shingles (tab and lock) weighed in at 300-325lb per sq for premium, 285 for "regular" 225 for fiberglass and 185 for B grade. So we did the math and figgered out that three layers could be ok. Now it is restricted to two layers period!

Really how you gonna bitch about a house that is 80yrs old, has four layers, completely dry interior and straight rafters? About the most important thing you can report is the tear off is going to cost more than the put-back.

BTW, I felt bad that I didn't know the exact thickness of new asphalt shingles.

[Tom Raymond]

Around here the limit is three layers (if the town set a limit), with Buffalo counting the cedar shingles as plywood. The reasoning behind this is that even when the cedar is removed, the new ply goes right on the skip. That said, the last roof I did in Buffalo had seven layers of modern asphalt shingles over a layer of T loks over the cedar shingles.

While remodeling my house I found "new" and old cedar shingles and several dated labels from the new bundles. Both the original cedar and the replacement each lasted over 60 years, the current 3 tabs are shot after only 14. In the spring I will be installing the fourth roof cover on a 140 year old house. I'm looking for a cover that will last nearly as long as the first two. I really like the Follansbee diamond shingle, but tern coated stainless steel is gonna be spendy. I'll likely go standing seam.

Tom

[Marc]

I know that I'm the odd guy out, but I always recommend that prior roof finishes be removed before applying a new one. Don't ask me for my basis. I've simply seen too many doubled up asphalt shingle roofs with widespread moisture-damaged decking to bother.

Marc

[hausdok]

Hi Marc,

I don't think you're odd man out; I think that you're doing what most of us do. We all (At least I think we all) try to serve our clients to the best of our abilities, without overstepping our bounds. I routinely tell folks that I think the best policy is to tear down to the deck and reroof with one layer, but I don't have anything I can point to that makes that mandatory except in the case of a shake roof. If a client want to follow that recommendation, they need to understand that doing so could very well be at their own expense.

Sometimes, our opinions notwithstanding, sellers have the edge over a buyer and all the common sense in the world won't help help unless the buyer can show that what the seller has done is outright illegal. That can be pretty difficult when/if the AHJ isn't on board with your own recommendation.

That's why I was so happy when Seattle finally changed their rules; I now carry a tattered copy of those rules in my clipboard for this very issue. When an agent, owner or a roofer starts arguing that Seattle doesn't prohibit more than two layers, or that they're allowed to install up to 3 layers, I love to practically shove that document down their throats.

ONE TEAM - ONE FIGHT!!!

Mike

[Erik]

If that house was built in the 1960's, why would there be 8 layers of shingles? Doesn't make sense.

He's south of me. Makes sense to me I've seen roofs replaced twice in one year. Think Hail!

[John Kogel]

I think the best policy is to tear down to the deck and reroof with one layer, but I don't have anything I can point to that makes that mandatory

The maufacturer's warranty for fiberglass shingles is void unless they start with a clean new deck. I don't know if that's true for all, (and we all know what a roof warranty is worth) but that's what I base my advice on - tear it all off, and lay a clean new roof.

My stepdad's garage had five layers of asphalt on it, 2X4 rafters with 3 rafter ties spaced about 6' apart. I know cuz it all caved in with a load of wet snow on it last winter.[:-yuck]

[Jim Katen]

The maufacturer's warranty for fiberglass shingles is void unless they start with a clean new deck. I don't know if that's true for all, (and we all know what a roof warranty is worth) but that's what I base my advice on - tear it all off, and lay a clean new roof.

Which manufacturers do you know of who void their warranty if you install their singles over a previous layer of shingles? Pabco, Certainteed, & IKO all allow it for most of their shingles.

- Jim Katen, Oregon

[Scottpat]

I belive it is FHA who has/had the no more than 2 layers of shingles on a home rule, in their appraisal guidelines.