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I am replacing some flashing on a roof and therefore need to take up some shingles. Unfortunately, there appears to be four layers of shingles, so I will have remove quite a mass of shingling.

Is this normal to have four layers of shingles on a roof? I thought when a new roof is added they are supposed to remove the old shingling first.

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  • Different areas will have different regulations on old shingles. You can normally put a new layer right on top of the original, but 4 layers seems like too much anywhere. I think I've heard of 3 being a common limit (maybe not anymore tho)... Where is the house?
    – JPhi1618
    Oct 23, 2017 at 19:02
  • I thought 3 was the max but usually strip because old leaking shingles are not a good base to put a new roof on.
    – Ed Beal
    Oct 23, 2017 at 19:02
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    Tyler, are you sure it's 4 layers? A single installation may appear two layers deep to the unfamiliar eye. I've seen two actual layers a few times, and three once or twice, but four? That's 80 years worth of roof stacked up.
    – isherwood
    Oct 23, 2017 at 19:16
  • @isherwood, that's true. Because of the overlap, any given point on the roof will have "two layers" of shingles for one installation.
    – JPhi1618
    Oct 23, 2017 at 19:21
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    Keep in mind the OP is installing flashing. It's not uncommon for roofers to "double up" shingles near edges and other places where flashing might be installed.
    – aghast
    Oct 23, 2017 at 20:26

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It was fairly common years ago, but even then there was a right way and a wrong way. The right way was to nest the new layer into the existing layer such that there's no structural span happening--each new shingle is fully supported. When that wasn't done the new layer was sure to fail prematurely. I watched it happen across the alley--a brand new roof came completely apart after about 8 years.

In my area the practice became outlawed some years ago (and manufacturers began to specifically reject warranty claims when it was done). It's rare to come across lingering roofs with multiple layers aside from the odd neglected outbuilding, for example.

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If you visualize four layers at the eave, where the metal nosing is, it is actually the starter course and first course. If there are four separate layers at the eave that would actually be two roofs. The only variable would be if a new piece of nosing was installed OVER an existing roof, when installing another roof.

I do not recommend you recover a third time for a few reasons. One, the weight. Two, the quality of the installation will be affected by the likely deteriorated condition of the material you will be going over. Three, after this many years it would be wise to examine the roof sheathing.

Replace any broken or dry rotted sheathing and if it's one by six "solid sheathing", consider skinning over your roof deck with 1/2 in ply or oriented strand board sheathing. (You can go right over the existing 1X6 sheathing without having to remove it.) It will give you a more consistent nailing surface without the occasional "nail in the gap" effect, common when going over 1X6 solid roof sheathing, and provide the shear strength afforded by a plywood sheathed roof deck.

Was a roofer for over forty years and although you can probably get away with a third re-cover, in my experience, it is not a good idea at all.

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  • One concern with over-sheathing old plank roof decks is that they're often hand-framed, already sagging and may not like the added weight much. Good info, though the question of whether it's a common practice isn't really addressed.
    – isherwood
    Oct 23, 2017 at 21:03
  • "I do not recommend you recover a third time for a few reasons" Also, how will the nails even reach solid wood through the old shingles?
    – DJohnM
    Oct 24, 2017 at 21:45
  • Right, not sure what's meant by unaddressed Q's,or if you are referring to my input.If your referring to ply skinning an existing solid sheet deck,it's commonly done,often with 3/8's over solid sheeting, but commonly 1/2in.The weight to shear strength makes it a good consideration.Assuming a deck and framing of good condition of course.If there is any concern it can be visualized through the access hatch on most pitched roof's,or if you don't have a hatch,removing a few boards to get into the dead space and examine the framing is not as involved as it might sound.Take a couple of minutes.
    – Ralph Newton
    Oct 25, 2017 at 1:14
  • Hey,DJohnM,Grip-Tite makes 3in EG smooth shank roofing nails!.Once again,and to be clear for those,like myself,with OCD, I DO NOT recommend recovering to a third layer of roofing either asphaltic fiberglass shingles or BUR's.Have torn off BUR's in Chinatown SF,of 4in. thickness!.And do not know why these flat roof decks did not simply collapse under the weight.These were buildings built around the turn of the century with roof's that had never been torn off!.By the way, isherwood, i was referring to a ceiling,or attic not,"roof",hatch although on SF Victorians,12x12 P roof's do have hatches!.
    – Ralph Newton
    Oct 25, 2017 at 2:37
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Yes, 3 roofs is the limit. (See ICC Section R907.3.1.1 Reroofing.)

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