Want To Install A Metal Roof Over Shingles? Know These 3 Things

Adding a metal roof to your home can be a great way to give some longevity to your roofing material. However, you may have asphalt shingles on your home and are wondering if you need to rip those off prior to installing the metal roofing material. Here are a few things to know about this unique metal roof installation.

Underlayment Material Is Necessary

If you will be placing metal roofing material over asphalt shingles, know that a layer of underlayment material is necessary for the installation to work. The goal will be to create some separation between the two materials so that the back of the metal panels are not touching the shingles. If the two materials touch, the granules of the asphalt shingles can actually scratch the surface of the metal material. 

While you may not think this is a problem since the underside of the metal roofing material is not seen by others, it does make the metal more vulnerable to rusting. If moisture did get underneath the metal panels, it can rust from the bottom and cause significant damage. 

Uneven Roof Decks Can Cause Oil Canning

Oil canning is an issue that affects how a metal roof looks from the ground, where it may look like it is wavy or uneven. This problem can be amplified even more when you have a metal roof installed on top of an existing roof with asphalt shingles. If there are issues with the evenness of the roof due to the roof deck, you are not going to be able to rip off all of the old material to fix the deck. Your roofing contractor will then have to get more creative to make the metal roofing level. 

One solution is to use the snaplock style of roofing panels, which is due to how the installation method puts less pressure on the seams and reduces the unevenness. Ask your roofing contractor how they plan to minimize potential oil canning issues before the first panel is placed on the roof. Even a perfectly flat panel that looks fine on the ground can have the oil canning effect if the roof's surface is not level.

Insulation Can Reduce Heat Transfer And Smooth Unevenness

While a metal roof is known to reflect the heat from the sun, the roofing material can still get quite hot. Having a layer of insulation underneath the roofing material can prevent that heat transfer from happening, making your home cooler overall. In addition, that layer of insulation can help smooth out imperfections with the roof surface not being level and reduce oil canning.