Double Coverage shingles?
The roof wil be between 2/12 and 3/12. I have heard I need double coverage shingles. Does anyone know what this means?
Double coverage: Application of asphalt roofing such that the lapped portion is at least two inches wider than the exposed portion, resulting in two layers of roofing material over the deck.
Take 2 shingles. Over-lap them so that the top-to-bottom 'part' of the TOP shingle measures 2" LONGER that the LOWER shingle that you can see.
If the part of the shingle that 'laps' is, say, 5", it would cover the UNDER shingle in such a way that you only see at least 3" of the UNDER shingle.
If you still can't picture it, bring the definition w/you to any Home Center and the folks in the building materials dept. will help you. My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!
All shingles provide a double layer as they are installed but some manufactureres allow that for a low pitch installation (normally shingles are not used below a 3/12 pitch) You can decrease the exposure and increase the headlap. For instance a typical shingle 12" high will have a five inch exposure with a 2" headlap. Decreasing the exposure to four inches will give a four inch headlap and actuall triple coverage, in terms of number of layers. The same specs would require a double ply of tarpaper as well.
A good way of insuring against leaks if you need to use shingles for appearance is to apply ice and water shield membrane under the shingles. It is commonly called Bituthyne