Did you know that the right roofing material for your roof depends upon the pitch, or angle, of the roof? There are other considerations, as well, such as if you're doing a lot of cooking in the building. The below chart and step-by-step info-graphic walks you through the basic process of determining what the right roofing material is for your roof.
What's your roof's pitch?
Is your roof's pitch less or more than 2/12 (9.5º)?
Less than 2/12?
If you have a flat roof; is a lot of cooking involved, such as at a hospital, restaurant, etc.?
If so, then you should choose PVC since it is resistant to animal fat and grease, and resistant to fire.
Money a concern?
If there isn't a lot of cooking involved, is money a concern?
If money is not a concern, choose TPO as it's less expensive than PVC yet still a great product.
If money is a concern, choose EPDM or modified bitumen since these are the least expensive options for a flat roof. It is interesting to note that EPDM, also known as a 'rubber roof', is also the longest lasting.
Greater than 2/12?
(If your roof's pitch is greater than 3/12, tile is also an option.)
Do you get a lot of snow? For example, more than a foot in one snow storm.
If you do, you should consider a metal roof as it sheds heavy snowfall quickly.
Looks, Longevity, or Cost?
If you don't get a lot of snow at once, do you want your roof to look good, last a long time, or cost the least?
Look Good: If you want your roof to stand out, consider a tile roof for its unique appearance.
Longevity: If you want your roof to potentially last a long time, again, consider tile since it is among the longest lasting roofing material.
Cost Less: If you want the least expensive roofing material, stick with asphalt shingles.
Installing a steep-slope roofing material onto a low-sloped roof
Before I explain why you should install a steep-slope roofing material onto a low-sloped roof, let me start by explaining how low-sloped roofing materials work.
Low-slope single-ply membranes, such as EPDM, are mechanically attached (nailed) or fully adhered (glued) to the roof's insulation or deck. Single-ply membrane roofs are installed by rolling-out the roofing material (PVC, TPO, EPDM), securing each rolled-out layer to the next one and to the roof. When fully adhered, the seams become stronger than the membrane itself. When done, you end-up having one large membrane that covers your entire roof. This is required for low-sloped roofs because rain water moves much slower on low-sloped roofs compared to steep sloped roofs. Low sloped roofs require impenetrable seams and membranes to prevent water from seeping in.
Steep slope roofing materials, such as shingles, are only mechanically attached at the tops of each shingle. The sides of shingles are completely exposed to standing water. And, although the bottom of one row of shingles are somewhat adhered to the below row of shingles, it's not strong enough to resist standing water. Roofing tiles are completely exposed to standing water on the sides and the bottom of each tile. This is one major reason you do not install steep-sloped roofing material onto a low-sloped roof.
Learn more about residential roofing material longevity, cost, etc. in our Guide to Residential Roofing.
Learn more about commercial roofing material longevity, cost, etc. in our Guide to Commercial Roofing.
Summary of roof pitch and the right roofing material for it:
Roof pitch: material option(s)
.25/12 to 2/12: EPDM, TPO, PVC, Mod-Bit
3/12 to 20/12: metal
2.5/12 to 19/12: tile. clay or cement
2.5/12 to 20/12: asphalt shingles