Matthew Brown
Going to put a metal roof on my friend's house, and we are trying to keep costs down but still do a good job. I have known local roofers to put the panels directly down on the shingles, but I know a lot of times it is recommended to use 1x4s and/or tar paper. What are the pros and cons of the different methods? The roof has a pitch of 4/12.
An informed customer is our best customer.
One cons may be that you might invalidate the warranty on the roofing panel if you don't put some sort of slip layer between the shingles and the new metal. Check with the manufacturer on their recommendations first. Pros to leaving roof in place: Less trash, labor, expense, and time. Cons: More weight on the roof, inability to inspect and address the decking beneath, more attic heat is trapped in the summer
Nate Libbey
Several things to think about: In most cases, metal roofing can be installed over existing shingles, but (1) make sure there are no more than two layers of shingles there and (2) I definately recommend putting down 1x4s, tar paper, or a synthetic underlayment down. The main reason you want felt, tar pape, or synthetic underlayment down is to keep the rough surface of the shingles of the backside of the metal roofing panels. Here are the advantages/disadvantages of each: ***1x4s (a) Creates an air gap that provides some insulation value. (b) If there are eneven places in the old roof, you can shim up the 1x4s to help level it out. (c) can help strengthen weak areas of a roof BUT --- 1x4s aren't as firm of a roof as going down over solid decking. You still should be able to walk on it if installed at 2' apart or less (more if using a thicker gauge material). ***Felt (a)Cheapest method (b)Quick to install (c)Creates a firm roof BUT --- felt has no long term value as a second layer of protection as it deteriorates. It also can stick to the metal roofing, which further tears it. ***Synthetic Underlayment (a) Quick to install (b) Provides second layer of protection (c) Usually has a lifespan of 30 or more years (d) Creates a firm roof BUT --- synthetic underlayment usually cost somewhat more than felt, and slightly more than 1x4s.
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