Can Metal Roofs Be Installed Over an Asphalt Roof?

Installation Process

• If you're outfitting an already-roofed building with a new metal roof, you likely will not have to remove the previous asphalt roof before attaching this new one. As long as your roof has no more than two layers of prior roofing material stacked on it, you can simply place your metal roof over the existing roofing material, even if it's asphalt.

Considerations

• In some situations, you may have to do a bit more than just pile another layer of roofing on top of what you already have. If your existing asphalt roof is heavily damaged, you should remove loose pieces prior to adding your metal roofing material. Because these pieces are not attached, they will not serve as a strong base upon which to place your new roofing.

Issues to Address

• Before you start layering your new metallic roofing atop your asphalt roof, you need to address a few issues. First, look for the source of ventilation in your existing roofing. With an asphalt roof, particularly one topped with shingles, finding this ventilation can require a careful eye. Walk the length of the roof looking for this vent or vents. When you locate the ventilation sources, make note of them and install necessary venting in your metal roof. Laying a moisture barrier between your old roof and the new metal one is also an important step in the process, as a buildup of moisture could lead to leakage.

Benefits

• While it may seem easier simply to replace your current asphalt roofing with a new layer of asphalt or -- cheaper yet -- patch the existing roof, you should carefully weigh the benefits of metal roofing. This roofing is often more durable than asphalt, making it an option that is likely to survive more severe weather. It is also more energy-efficient. While dark asphalt absorbs heat, metal roofing reflects the sun's rays, making it an ideal option for warmer climates.