The international residential code says that you cannot put a new roof over two or more applications of any type of roof.
Roof patch with 2 layers of shingles.
Before you reshingle a roof read our step by step guide for adding new shingles over old ones.
Fha single family housing policy handbook cited at references.
If your roof already has two layers of shingles layering will not be an option.
Beveled wood pieces called horsefeathers must be laid along the thick edges of the shakes to make a fairly flat surface.
Push the shingles down to the roof jacks.
In fact the extra layer can reduce your roof s lifespan by up to 40.
Roofers will have to work harder and longer to remove two layers of shingles later making the savings only temporary.
Another issue is that when you add in the second layer it can add extra weight to your roof.
This is because the weight of three or more layers of shingles can compromise the structural integrity of your home.
Continue tearing off the shingles and underlayment until you reach the roof jacks then start over at the top of the roof.
Layering shingles is typically less expensive but there are many reasons to remove the old shingles before re roofing.
Laminated shingles instead of one layer laminated or architectural shingles have two or more layers with three dimensional tabs of varying sizes.
Two layers of shingles trap more heat which in turn damages the shingles and shortens the life span of the roof.
Here is a typical excerpt limiting the number of shingle layers on a residential roof to two.
Saving on the initial shingle installation doesn t solve the long term cost of adding a second layer of shingles.
That second layer of shingles won t last as long.
Most shingle warranties do not apply when shingles are layered over existing roofing according to internachi.
This will force you to replace your roof earlier than expected.
The savings you re going to see may be in the range of a modest 25.
Remove the existing shingles then roof with new shingles.
If you already have two layers shingles the decision is made for you.
Get some other roofing companies minimum of 2 to inspect the roof and give you an assessment of the roof deck shingle condition and estimate to replace the roof deck shingles.
Don t be afraid to pay up to 100 for a well documented report with photos showing what they found.
Doing a second layer right means a lot of prep work goes into the overlay anyway and flashing which remember is the most vulnerable point on your roof is harder to guarantee.
Roofs that already have two layers of 2 shingles should not be roofed again.
Asphalt shingles can be laid over cedar shakes or shingles however this is a roofing project best left to pros.
The second layer of shingles will trap heat which can result in the decomposition of both roof layers.
That in itself eats away at the savings.
