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?
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.
Inevitable problems if you use a roofing material on the wrong roof.
Every roofing material is manufactured to performed certain tasks and behave a certain way. For example, steep-sloped roofing materials are meant to allow quickly moving water to move in one direction – down. Low-sloped roofing materials are meant to allow water to move in all directions and at a much slower pace. When you use something in a manner in which it wasn’t meant to be used, something is bound to go wrong and cost a lot of money to fix.
Before I explain why you shouldn’t 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 or slow moving water. And, although the bottom of one row of asphalt shingles are somewhat adhered to the below row, it’s not strong enough to keep standing water from moving underneath it. 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.
What’s more, steep slope roofing materials use fewer fasteners per square, if any. If used on a steep slope, it’s not enough to hold the membrane up and on the roof. Single-ply membranes were designed to almost lay flat and use fewer fasteners. They were not designed to withstand the weight of itself on a steep incline. Steep-sloped roofing materials were designed to be installed onto steep sloped and with more fasteners. As Kevin of Huuso points out, “Potential issues with installing EDPM/TPO membrane roofs on steep slopes is the lack of reinforcements and shrinkage. The weight would pull on the fasteners causing potential wrinkles, tears, and damage to the membrane.”
Also, no roofing material manufacturer, such as Mule Hide or Owens Corning, is going to warranty the roofing product if it was installed in an inappropriate manner or onto an inappropriate roof.
Although some single-ply membranes come in different colors, they aren’t nearly as appealing as shingles or tile. Most low-slope roofing material is either white, grey, or black. As a result, these have very low curb appeal. Ami of Feller Roofing says “Putting low slope products on a steep roof looks strange.”
No professional roofer is going to install a steep-slope roofing material, such as asphalt shingles, onto a low-sloped roof, or a low-slope roofing material, such as EPDM, onto a steep-sloped roof. If you find a so-called ‘professional’ roofer that will, you should find a better roofer 🙂
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:
.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