One of the biggest advantages of metal roofing is that it is light-weight – making it the perfect material to install over an existing asphalt shingle roof. However, there are some considerations you should think about before installing a new metal roof over an existing roof.
Things To Consider Before Installing Metal Over An Existing Shingle Roof
Does It Meet Local Code?
First, you will need to check in with your city, parish, or county building department to find out if it is an approved installation method in your area. Whether installing a new metal roof over shingles is a good idea – is a pointless discussion if your local building code does not allow for it.
Is Your Existing Roof in Good Shape?
Your new metal roof is only going to be as strong as the foundation it is attached to. When installing a metal roof. the screws need something to dig into. A rotting foundation underneath your existing asphalt shingles will undermine the integrity of your metal roof installation. It doesn’t generally matter if the existing shingles are faded, cracked, or crumbly, as long as the plywood structure under them is in good shape.
How Many Layers of Roofing Are in Place?
Depending on your local building code, you may be restricted about how many roofing layers you are allowed to have. Most building trusses are designed to hold a specific amount of roof weight. If you add too many layers of roofing materials onto a building, there’s a good possibility the trusses may fail. Check with your local building code enforcement administration to find out how many roof layers are permitted.
How is a Metal Roof Installed Over Shingles?
There are two basic ways to install metal roofing over an existing shingle roof. The first involves running a new underlayment over and completely covering the existing shingles. The new underlayment offers more protection against water seeping under the metal roofing and acts as a buffer between the shingle roof and the metal. Because metal expands and contracts under different weather conditions, and a shingle roof has a texture like sandpaper, the metal tends to move. Without this underlayment as a buffer, the shingles could wear down the back of the metal roofing.
The second method of installing metal roofing over pre-existing shingles is by using battens or purlins. These are nailed or screwed down into the roofing deck, and then the metal panels are secured to them. Using battens or purlins helps avoid the issue of irregular shingles, as it provides a flat surface to attach the metal panels to. Another benefit of using battens or purlins is that it creates an air gap between the new roof and the existing roof. This gap serves as a buffer and eliminates the issue of the metal roof heating up the shingle roof, and it allows for a radiant barrier installation if desired.
What’s the Best Method of Installing a Metal Roof Over Shingles?
Before you begin any roofing project, contact your local building department to find out what is and is not allowable in your construction, as well as what codes need to be followed. Every roofing project is unique. To determine the best installation method for your new metal roof, call the roofing experts at ADCO Metals today. Whether you are a DIY kind of person or need a complete installation performed, ADCO Metals has what you need.
