You want a new metal roof but the idea of tearing off the old roof leaves you exhausted. Good news! You most likely can put a metal roof over the top of the existing shingles.
Before you do anything though, check your local building codes. If they allow you to install a new roof over the old roof, go for it. It can save you the backache of tearing off the old shingles which is messy, time-consuming, and costs more if you’re not doing it yourself.
Take into consideration how many layers of roofing materials you already have on top of your house. Metal roofing materials are very lightweight, so they won’t be a problem. But if you having 2-3 layers of wood shingles up there already you might be required to remove them.
Some building codes say you can’t have more than two layers of roofing materials on top of your house. Consider the weight that puts on the trusses and you’ll understand why that rule exists.
Another consideration is the condition of the plywood underneath the shingles. Is it in good shape with no rot? When the metal roof is installed, it’s screwed into the plywood on your roof and needs to be in good condition.
It’s possible that moisture can creep under the metal roof and be trapped causing mold and mildew problems, and maybe even rot. Talk to your roofing contractor about a moisture barrier between the two roofs. They can do one of two things:
• They can install a vented metal roof that allows moisture to escape.
• They can put on the new metal roof over 1 x 3s, known as furring strips. This provides ventilation which will keep moisture at bay.
A plus for installing a metal roof over your old roof is the noise factor. The insulating quality of the old roof under the metal makes for a quiet roof. That insulating quality also increases the R-value of your roof, cutting down on heating and cooling costs.
Maybe the best reason to keep your old roof is this – fewer asphalt shingles in the landfill is always a good thing.
