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Question DetailsAsked on 12/2/2015

on shingle garage roof, can metal roof be used effectively

Roof replacement. I want to install a sheet metal roof onmy garage. I would like to install it over a shingle roof.wii this be satisfactory

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Some contractors will put it over shingles, some will not. Personally, I consider it bad practice for several reasons -


1) you are not replacing the water barrier (tarpaper or synthetic membrane), so you are counting on THAT lasting another 30-50 years - a bad bet when that is your protection against water infiltration in the event of roof leakage, especially a flashing, valley, or ice damming infiltration


2) because you are not tearing off down to the sheathing, you do not know what its condition is - so you could be locking in decay and deteriorated sheathing that should have been replaced, plus if in poor shape the fasteners for the new metal roofing might not hold like they are supposed to in high winds


3) putting metal roofing over old shingles (or any other roofing) commonly results in distortions and ripples in the finished product that just plain look bad


4) could affect your warranty on the metal roofing - and even if not stated so in print, it gives the roofing manufacturer and contractor a VERY easy out in the event of a claim, by blaming any failure on problems in the underlying roofing, whether that is true or not.


5) if not taking off old roofing, you cannot do a proper flashing job at valleys and adjacent walls and chimneys and such, and cannot add effective ice and water shield at the eave areas, because those should go on the water barrier/sheathing, not on top of existing shingles or jimmied in under them.


For the maybe $$0.50-$1.50/SF difference in price for the tearoff and disposal, depending on your area, I wouldl not be pennywise and pound foolish. If it is worth doing, it is worth doing right. And several other truisms. Course, on a garage, if there is no living space above it or it is unfinished, the cost factor may weigh more than the possibility of leaks or appearance issues - your call, obviously.

Answered 3 years ago by LCD




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