Curl at architectural shingles

[Jon mackay]

This roof appears to be a 2 layer job 20 or so years old.

Has anyone seen this curling at the bottom portion of all the shingles before and does the condition have a name? Cupping?

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[Mike Moser]

From the photo it appears that the 2nd layer was not nested ( butted against 1st layer). This caused the lifted lower edges of the shingles as the shingles will not lat flat. This makes them very suceptible to the damage as shown and shortens the life of the roof. The "scuffing " was probably caused from foot traffic. It appears to be a glass mat but I can not be sure from photo.
A comment "The lack of nesting as shown in the manufacturers installation instructions ,ARMA and NRCA appears to be leading to a pre mature roof failure. Suggest having the roof checked out by a Lisc contractor. Monitor and repair / replace as needed."
Remember the IRC no longer allows any overlays on shingles.

[Brandon Whitmore]

The shingles were bridged instead of nested-- not ideal in my opinion. See here: http://www.asphaltroofing.org/pdf/tb_203.pdf

Remember the IRC no longer allows any overlays on shingles.

Which version is that from? 2006 IRC still allows it--- Check out R907 "reroofing"

[Mike Moser]

Slight mistake in source . Minnesota when adopted 2006 stated no overlays allowed.
many local cities as well as most states (mainly in snow belt) do not allow any overlays. They used to allow up to 2 overlays = 3 total layers.

Check City and State where you live or inspect.

[Brandon Whitmore]

Slight mistake in source . Minnesota when adopted 2006 stated no overlays allowed.

I figured that to be the case. That, or I figured it was wishful thinking. Oregon still allows 3 total layers, and the number of defects builds with the number of layers installed.

[Fred Weck]

Slight mistake in source . Minnesota when adopted 2006 stated no overlays allowed.
many local cities as well as most states (mainly in snow belt) do not allow any overlays. They used to allow up to 2 overlays = 3 total layers.

Check City and State where you live or inspect.

The whole state of Minnesota is not effected, only those counties that are shown in figure 903.5 cannot have an overlay. Figure 903.5 is what changed between the 2000 & 2006 IRC's (2003 was skipped). In Minnesota local cities cannot amend the State Building Code.