Flat roofing installation is very different from pitched roofing. Shingles and tiles are not appropriate for flat roofing because water can seek below the tiles easily as there is no pitch to force it off the roof. It may seem that flat roofing is less expensive than pitched roofing as there is less challenge to flat surfaces but many roofers report that flat roofing installation is harder than it seems.

Flat Roofing Materials

Flat roofing is more prone to water damage because there is no pitch to drive water away from the surface. So if there’s a potential leak threat, why is flat roofing even used? Flat roofing is beneficial for two reasons; aesthetics and convenience. Flat roofing looks better when you have to add on extensions to a building so there are no uneven pitches and it is a convenient place to store heavy HVAC equipment.

Flat roofing needs to be waterproof in the same way as pitched roofing and this requires special application of adhesives or modified bitumen that can be installed to form a seal. The extra labor and materials can add up with flat roof installation making it just as expensive as pitched roofing. The labor for flat roof installation will depend on the area but you can use average material costs to make a fair estimate.

  • PVC membrane: The membrane and insulation board needs to be installed first to reduce energy costs and these are installed in rows that are mechanically fastened to prevent uplift.
  • EPDM rubber: EPDM membrane is available in large sheets that make it perfect for avoiding leaks at the seams, but the wide rolls are challenging to install. These sheets are like giant stickers that need to be carefully applied to avoid air bubbles.
  • Built-up roof: Multiple layers of ply sheets are bonded over each other to form this roofing. A top layer of reflective coating can be added or gravel for additional durability.
  • Modified bitumen: This is installed in layer with each being torched to the surface below it every quarter-turn of the roll. Installing modified bitumen is a lengthy and labor-intensive process and can only be done by a professional.
  • Spray-on roof: This may sound easy but it needs to be applied evenly and precisely to avoid problems. You can apply spray-on roofing over existing materials making it convenient to use.

Average Lifespan of Flat Roofing Materials

When considering what materials to use for roofing, you need to take into account how often the roof is accessed and the local weather. Frequent weather changes and frequent traffic can wear a roof down quickly, shortening its average lifespan. Before you spend money on installation make sure you get a material that lasts as long as you need it. The average lifespan for flat roofing materials is:

  • PVC: 15 to 30 years
  • EPDM: 10 to 15 years
  • Modified bitumen: 10 to 20 years
  • Built up roofing: 15 to 20 years
  • Spray-On: Up to 20 years

Choosing the Right Flat Roof Material

Flat roofing installation varies by material and labor costs. Before choosing a material you need to consider the costs and the benefits and disadvantages of each material.

  • PVC membrane: This is the most popular flat roofing material as it is strong and durable with a minimum breaking point of 300 pounds per inch. These are heat welded to create a waterproof seam and are usually white to increase energy efficiency. The major drawback to PVC roofing is that they are pricey.
  • EPDM rubber: The main reason EPDM is chosen over PVC is that it is cheaper to install. The seams of EPDM rubber are glued together and are not as strong as the heat-welded seams used on PVC roofing. EPDM also is darker in color which makes it less energy efficient.
  • Modified bitumen: This multi-ply roofing is one of the bigger advantages. The base layer is attached mechanically to the roof deck creating a strong and durable seal. The ply overlap is applied with a permanent adhesive and granules are placed on top to provide aesthetic and energy-efficient properties. Modified bitumen is challenging to install which can lead to costly labor bills.
  • Built-up roofing: These are essentially tar and gravel roofs, consisting of alternating layers of bitumen which are asphalt, coal tar, or other adhesive and a top layer of gravel. Built-up roofing can withstand heavy traffic and severe weather but they are heavy which will require additional support structures.
  • Silicon spray: You get the benefit of seamless installation with spray-on roofing. Despite seeming like it would be easy to spray on the roofing material, this is one of the most expensive materials to install for flat roofing.


The right material for your flat roof will depend on your budget, roofing needs, and issues that your roof will face such as weather and traffic. Each type of flat roofing comes with carrying benefits and disadvantages as well as different installation costs. Call us today to discuss your flat roofing options and we can help you find the best fit for your budget and needs.


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