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One of the great benefits of metal roofing that we want homeowners in the Minneapolis metro area to know is that yes, metal roofing can often be installed over your existing asphalt shingle roof.
Standard building codes reference weight loads in conjunction with allowable roofing layers. (But we recommend you ALWAYS check your local building code to verify what's permitted in your area. Some locales actually require a tear-off of the old roof, regardless of the type.)
Often when an asphalt roof is being replaced, the old one has to be torn off. But since metal roofing is much lighter in weight than asphalt shingles, a tear-off can sometimes be avoided. No roof tear-off saves both time and money, but there is another benefit as well: that existing shingle roof will provide another layer of insulation, making your new metal roof even more energy efficient. So you save money both ways!
Do I Need Underlayment for a Metal Roof Over Shingles?
You might think that if your new metal roof is being installed over your existing asphalt shingle roof that you won't require underlayment. But the truth is, in this particular type of roof installation, having some type of underlayment between the two roofs is critical. Local building codes may require it, plus it serves as a layer of protection on your old roof while the new roof is being put on. There will be lots of foot traffic on that roof and screws and nails being put in, so that underlayment helps avoid damage to your existing roof.
But the topic of underlayment often brings up another question, and that has to do with vapor barrier. Some people assume they are the same thing.
Is Roof Underlayment the Same as Vapor Barrier?
This question isn't as simple to answer, because it depends on the type of material. There are a variety of products used as underlayment when a new roof is being installed. Some are waterproof, some are water resistant. And for areas that get extreme cold and dam formation is common, waterproof underlayment rather than simply water resistant products are highly recommended. There are also parts of a roof like eaves and valleys where waterproof underlayment should be used, even if the rest of the roof has a water-resistant product on it.
There are no hard and fast rules for metal roofing installation, because each home is different. We will work with you to come up with the absolute best solution for your new roof, whether that includes tearing off the old roof or leaving it on. And we'll suggest what we believe is the right underlayment and/or vapor barrier. We want you to be absolutely satisfied with your new metal roof, and it's our goal that it will provide exceptional performance for decades. For a free quote, please call or text us at 763-785-1472.