Flat Roof vs. Pitched Roof: What’s the Difference?

Flat roof

We have covered pitched roofs and asphalt shingles on our blog, but as that’s not the only thing we do, I wanted to talk about the difference between a flat roof and a pitched roof – which is more typical for residential applications. There are obvious differences and not so obvious.

Flat roofs are more common for commercial buildings and, while not as architecturally beautiful as a pitched roof, can also be used for residential buildings. It’s all in what you want from your roof.

Is a flat roof going to cause me problems?

First of all, a “flat” nay or may not be actually flat. Many “flat” roofs are sloped to drain water and become “low Slope” roofs. Many “flat” roofs are actually low sloped roofs in order to provide drainage. The way we measure the slope is to measure the roof’s rise over 12 inches. If a roof rises one inch over 12 inches, it’s called a 1 in 12 and it would be a low slope. Anything pitched 3 and 12 or less is considered a low sloped roof. Pitched roofs are anything 4 and 12 or above.

When we roof a “flat” or “Low slope” roof, we use a membrane system to cover it. A membrane system is a sheet of roofing material which we install to keep even standing water from leaking into the building. The most common types of flat roof membrane systems are torch-down, single-ply, and built-up. The reason we use a membrane system is that shingles leak too badly on a low sloped roof – even on a 3 and 12 sloped roof you may encounter leaking with shingles under extreme conditions.

So, how do we prevent roof failure on a flat roof?

Simple. It’s in the installation, inspection, and maintenance. If you are familiar with commercial roofing, you know flat roofs have a bad reputation. They don’t shed water as well and are more likely to leak, plus leaks are harder to find.

However, there are ways to extend the life of your flat roof. Roofs tend to be the most neglected thing about any building and then we get called to fix something that needs to be replaced. You can help prevent this by getting regular maintenance on your commercial building roof: inspections every year. We do a short inspection that would be ideal for this type of upkeep.

A good roofing company needs to be able to apply the best product for the demands of the weather and the building. Depending on the building we may use:

  • EPDM single ply systems (stands for Ethylene Propylene Diene Monomore). This is basically, like all flat roofing, a big unbroken sheet of water-resistant material – in this case, it’s essentially rubber made from oil and natural gas and it’s black. This type has 15-20 year factory warranties. EPDM roofing – if it’s properly installed and sealed – is very good at handling rain, snow, UV rays, abrasions, ozone, and temperature fluctuations.
  • Heat weld TPO (which stands for Thermoplastic Polyolefin) is in the rubber family. This kind can be less expensive, used widely, and it is white, which makes it more ideal for some uses.
  • Hybrid single ply systems – this is two or more products proven to work together used for different applications on one roof.
  • Duro-Last pre-fabricated and field fabricated systems. This material is PVC – most known for the pipes it is used to make. It’s a hard, durable material with plasticizers so it’s relatively pliable. Prefabricated systems are factory measured, so installation is faster and easier. All PVC products are heat welded at the seams.

Take Away

While flat roofing is not the same in price or in longevity as a pitched roof, you may have one and it will need inspection and repairs over time. The best thing you can do for your pocketbook with a flat roof is to have Renovations Roofing and Remodeling, Inc. inspect it and help you maintain it. Contact us today!

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4 comments on “Flat Roof vs. Pitched Roof: What’s the Difference?
  1. David Clawson says:

    We just bought a house with a white membrane roof. No evidence of leaks but the roof is not new. We would like inspection, recommendations and quotes.

  2. Pete Tiller says:

    What does longevity mean

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