The maximum layers of shingles allowed to be on the roof according to most building codes are two.
How to remove shingles off a roof.
When you rip the old shingles off your roof they are not likely to come off like a clean and neat old carpet but in various sized patches there will be bits of broken shingles everywhere.
And try as you might to get every bit into that trash bin some scraps are likely to slip and slide off in different directions.
Push the shingles down to the roof jacks.
Hose off and brush all moss loose from your roof shingles.
Always work from the top of the roof downward to ensure water pours off the roof and so the water or tools won t lift and break shingles and tiles.
Examine the roof for remaining bits of shingle and loose roofing nails.
Chances are the nails that will be securely seated in the wood so a bit of force will be needed with a twisting motion of the roofing shovel or spade.
Carefully place a ladder near the area of moss growth and don slip resistant shoes old clothes rubber gloves and eye protection.
Remove the shingles in layers as you work your way up the roof.
Remove shingles in a 2 to 3 ft wide section as you work down the roof.
By removing the old roof you keep the opportunity to double up roof layers during your next roof replacement.
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Scrub shingles before applying a moss remover cleaner use a scrub brush 3 15 the home depot or a long handled soft bristle brush to gently scrape or pluck moss from the roof shingles.
Continue tearing off the shingles and underlayment until you reach the roof jacks then start over at the top of the roof.
Use a rip claw hammer to remove nails holding down bits of shingle and push the debris off the roof.
So once you use this strategy you must tear off both roof surfaces during your next roof replacement.