Do you know the right roof covering starts with the pitch, or angle, of the roof? There are other considerations, as well, such as if it’s a commercial building and you’re doing a lot of cooking in it. The below chart and step-by-step infographic walks you through the basic process of determining which is the right roof for you.
What’s your roof’s pitch/angle? Most modern homes have a roof that’s considered steep, such as between 3/12 and 12/12. Most modern homes also have a section of roof that’s low-sloped, or less than 3/12. Commercial buildings, on the other hand, often have low-sloped/flat roofs with a pitch less than 2/12.
So, is your roof’s pitch less or more than 2/12 (9.5º)? Is it basically flat (commercial) or steep (residential)?
Commercial
If your roof’s pitch is less than 2/12, it’s considered flat and your options are PVC, TPO, EPDM, and Modified Bitumen.
Is cooking involved?
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.
Residential
If your roof’s pitch is greater than 2/12, your options are asphalt shingles, stone-coated metal shingles and tiles, and metal, such as standing seam and corrugated/PBC. (If your roof’s pitch is greater than 3/12, clay and concrete tiles are also an option.)
Snow?
Do you get a lot of snow, for example, more than a foot in one snow storm? If you do, you should consider a standing seam or corrugated/PBC metal roof as it sheds heavy snowfall quickly. Even if you don’t get a lot of snow, you should still seriously consider a metal roof, such as standing seam. There are more options today than there used to be. What’s more, metal roofing is the ‘coolest’ roof as it helps to lower your Summer cooling bill. It’s also recyclable, unlike asphalt shingles. Lastly, a metal roof often costs less in the long run compared to traditional asphalt roofing shingles.
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? If you want your roof to stand out, consider a tile roof for its unique appearance. If you want your roof to last a long time, consider metal, such as stone-coated metal shingles or tiles, or standing seam, since these are among the longest lasting roofs (psst – a metal roof often costs less in the long run, because they last so long). If you want the least expensive roof initially, asphalt shingles are what you want.
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 a downward direction only. Low-sloped roofing materials, on the other hand, are manufactured 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, something is bound to go wrong and cost a lot of money to fix.
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 unrolling the roofing material (PVC, TPO, EPDM), securing each 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 the 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.
Leaks
Steep slope roofing materials, such as asphalt shingles, are mechanically attached at the top 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.
Strength
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 are 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 slopes, 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.”
Warranty Void
Also, no roofing material manufacturer, such as Mule Hide or Owens Corning, will warranty an incorrectly installed roofing product, or a roof covering installed onto an inappropriate roof.
Appearance
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:
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