Another issue is that when you add in the second layer it can add extra weight to your roof.
Second layer of roof shingles.
The second layer of shingles will trap heat which can result in the decomposition of both roof layers.
However there are good reasons it doesn t really cut down much on the amount of work.
Examine the existing roof.
You will get what you pay.
In fact the extra layer can reduce your roof s lifespan by up to 40.
How to shingle over existing shingles and how to shingle a roof how to install roof shingles shingle layout lines h.
I don t know if a precise formula like that exists but the second layer does have less firm foundation than the first and it would be logical to expect shorter life span.
It forces more oil to evaporate out of it and more of the materials that make it pliable and watertight.
Roofing second layer of shingles roofing.
I think you ve got a good life out of it.
This will force you to replace your roof earlier than expected.
A second layer is more difficult to install properly.
That can be either architectural shingles or conventional 3 tab shingles.
I won t speak to a haphazardly done job.
That second layer of shingles won t last as long.
And shingles have started to separate.
Because the first layer holds a lot of heat and that can over the long haul wear out the second layer because that heat is the enemy of the asphalt shingle.
And so second layers generally don t last as long as the first layers.
Still you ve got no less than 17 years from it already.
But check the shingle warranty from your shingle manufacturer.
How to put on a second layer of shingles evaluate the job.
Before you start hefting shingles to the roof consider whether or not the project is worth doing.
That in itself eats away at the.