Yes, in some cases, you can install a metal roof over asphalt shingles. Always check with your local building code officials first. Some codes don’t allow this at all and some only allow 2 layers of roofing in total, so if you already have 2 layers, the code will not allow going over it again with metal. If allowed, per your local code, there are still a few things to consider before proceeding.
You will want to make sure the plywood under the existing shingle roof is in good shape, meaning it has no soft spots. It is important to have a solid deck for the fasteners to attach to. You wouldn’t want to rely on rotten wood to hold your metal roof on in a windstorm.
You will need to confirm with the metal roof manufacturer, their recommendations for installing metal roofing over shingles. Some products are approved to go straight over non-compromised asphalt shingles. Others will require a new layer of underlayment over the entire roof. And some may require both underlayment and wood strapping secured to the roof deck. Be sure to follow the manufacturer instructions accordingly.
Metal roofing installed onto a wood strapping system provides certain benefits when going over top of asphalt shingles. The strapping gives the installer a flat surface to install the metal roofing panels onto without the old roofs’ irregularities. The metal securely attaches to the strapping which securely fastens to the deck, making the overall roofing system stronger. Also, the air space created directly under the metal roof with this type of installation provides added airflow. This allows for the old roof to dry out properly and it acts as a buffer to keep the hot metal from directly transferring heat to the old asphalt during hot weather.
Disclaimer: This article intends to offer general knowledge on this topic. While every caution has been taken to provide accurate information, it does not intend as professional advice. Please consult with an industry professional in your area to obtain proper advice based on your unique circumstances. Rare Mfg. Inc. will not be held liable in any way should you suffer any loss/damage because of the information in this blog.
