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 even where it’s a factor, local code will (slowly) reflect actual capability.
Ive lived in several states, a few which get snow, even the heavy wet kind. Even there code permits up to 3 layers, depending on how the roof is constructed.
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.
I mean snow’s only a factor in some places
And even where it’s a factor, local code will (slowly) reflect actual capability.
Ive lived in several states, a few which get snow, even the heavy wet kind. Even there code permits up to 3 layers, depending on how the roof is constructed.