First off, if you’re at the design stage of the project, you are best served by putting the patio under the main roof of your home. Typically, that would have a sloped roofing system such as asphalt shingles. This strategy eliminates low-sloped roofing products entirely, along with their high cost and relatively short life.
If you are adding a patio, avoid the type of lightweight metal roof panels that are typically attached to manufactured homes for carports and such. Not only are these products vulnerable in high winds, they won’t withstand foot traffic. And if you can’t walk on it, you can’t service it when needed.
But there is a structural metal panel that words pretty good for patio roofing. It is a composite of polyurethane foam that is sandwiched between two layers of aluminum. The foam provides insulation and the panels can withstand some foot traffic. To be safe, I walk on plywood when working on this type of roof to distribute my weight.
Moving onto a more conventional option for your patio roofing, the most important thing to remember is that you need to have positive drainage. This can be accomplished with a slope that is as low as 1/4″ per foot. If you don’t have it in the structure, install a tapered system between the roof deck and the roofing. Almost any low sloped roofing system can succeed with proper drainage. Virtually none will succeed without it.
For over a hundred years, the traditional choice for low-sloped roofing has been a built-up roof (BUR) with gravel surfacing. The multiple layers of felt, each set in a layer of hot asphalt make for a thick, heavy-duty roof system that is tough to beat. But this type of roofing is on the decline due to the hazards associated with hot asphalt. Insurance companies are demanding outrageous deductibles for hot tar accidents, which is cooling the market for BUR, especially on small residential jobs.
A popular alternative for patio roofing is torch-applied modified bitumen, or just “modified” as it is commonly called. It is a rolled roofing product that is specially formulated to accommodate temperature changes. Unfortunately, the torch application can easily start a house fire… and often does.
There is a family of plastic and rubber roofing products called “single-ply” that can be installed without torch or kettle hazards. But the inherent problem with single-ply roofing is just as the name implies: There is just one layer of waterproof protection. Something as simple as a dropped tool or a discarded cigarette butt can cause a leak. And if there is any ponding at all, the seams must be PERFECT to prevent water intrusion. Perfection is a lot to expect from anybody, including us roofers.
Fortunately, there is an excellent option for your patio roofing. It’s a hybrid that combines the best features of two different systems. It starts with a nailed down base sheet over a tapered roof deck. Then a smooth-surfaced, self-adhering mid-ply of modified bitumen is installed. Finally a self-adhering modified cap sheet with white granular surfacing is installed.
This system gives you the back-up protection of a built-up roof and the flexibility of modified, without the dangers of torches and kettles.