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.
Ah yes, inches worth of snow in extra weight is tooootally fine… yep, no downsides to increasing deadwwight at all, nope, nosiree, engineers all agree, dead weight needn’t factor in to calculations at all.
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.
Ah yes, inches worth of snow in extra weight is tooootally fine… yep, no downsides to increasing deadwwight at all, nope, nosiree, engineers all agree, dead weight needn’t factor in to calculations at all.
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
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.