“Slope” is the amount of incline in a roof surface. It is usually expressed as a ratio of “rise over run.” For example, a 5:12 slope rises 5 vertical inches for every 12 inches of horizontal distance. A 12:12 would be steeper because it rises 12 inches over the same horizontal distance.
Virtually all of your options for new roofing can be divided into two categories:
Roofing Types for Steep Slopes
“Steep-slope” roofing is available for roofs with a slope of 2:12 and up. That is the kind you find on most homes and many other structures as well.
It’s usually “water-resistant” rather than “water-proof”. By that, I mean it sheds water fine, as long as there is enough slope for it to do so. However, it can leak if it has a buildup off ice, leaves or pine needles that causes the roof system to be submerged.
Your five major steep-sloped choices are:
1. Asphalt shingles, which are typically the three-tab or the architectural variety.
2. Metal panels, metal tile and metal shingles.
3. Clay and concrete tile.
4. Wood shingles and wood shakes.
Roofing Types for Low Slopes
“Low-slope” systems are typically used on slopes less than 2:12. Just a quarter inch rise per foot is usually sufficient for these types of systems.
They are typically “waterproof” rather than “water resistant.” That means they could be submerged and not leak. However, good roofing practice, along with building codes and warranties dictate at least some slope to provide positive drainage. A roof that is constantly wet can absorb water and deteriorate prematurely.
Your major low-sloped options include:
1. Modified Bitumen (pronounced buy-TOO-men). There are different varieties which are applied by various methods such as torch, hot asphalt, cold adhesives or self-adhering.
2. Built-up Roofing (hot asphalt and layers of roofing felt).
3. Single-ply (typically either plastic or rubber).
4. Spray Polyurethane Foam