Eh, going over one layer is fine as long as there are no decking or other structural problems. From what I can see here the older ones are in good enough shape.
I was a roofer for a few years. In Florida, a state with some of (if not the) the most strict roof codes in the country. It’s perfectly ok to layer shingles like that and was common practice for a good while. I’ve torn off houses with 4+ layers of shingles several times and had the decking be just fine underneath them. You have no idea what you’re talking about
The weight-per-unit-area of a shingle is dwarfed by the amount of snow it takes to affect a roof.
These shingles weight 1.8lbs per square foot when installed (3 packs for 99.9sqft at 62lbs per pack). Call it 2lbs/sqft with nails. Ice (the densest form of “snow” weighs 57lbs per cubic foot. 57 divided by 2 gives us a factor of 28.5 to divide into 1ft (the height of 1 cubic foot) to find that a 1/2" layer of ice weighs more than shingles per square foot. I’m not going to worry about the weight of shingles.
And the person who found it isn’t doing a good job either, putting new shingles over old. The old should be removed.
Eh, going over one layer is fine as long as there are no decking or other structural problems. From what I can see here the older ones are in good enough shape.
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I was a roofer for a few years. In Florida, a state with some of (if not the) the most strict roof codes in the country. It’s perfectly ok to layer shingles like that and was common practice for a good while. I’ve torn off houses with 4+ layers of shingles several times and had the decking be just fine underneath them. You have no idea what you’re talking about
I can imagine he’s used to having snow, and when you’ve got 2feet of snow on your roof extra shingles definitely wouldn’t help.
If they get 2 feet of snow in Florida we have bigger problems than this guy’s roof.
As an engineer, we only ever agree on two things:
The weight-per-unit-area of a shingle is dwarfed by the amount of snow it takes to affect a roof.
These shingles weight 1.8lbs per square foot when installed (3 packs for 99.9sqft at 62lbs per pack). Call it 2lbs/sqft with nails. Ice (the densest form of “snow” weighs 57lbs per cubic foot. 57 divided by 2 gives us a factor of 28.5 to divide into 1ft (the height of 1 cubic foot) to find that a 1/2" layer of ice weighs more than shingles per square foot. I’m not going to worry about the weight of shingles.