Flat Roof Materials

There are over 20 different types of flat roofing materials and hundreds of brands to choose from – but which flat roof is right for you? It is a difficult question, but will try to help you choose the best combination of the most economical, longest lasting flat roof, with as little maintenance as possible.

First lets look at three main categories or types of flat roofing:

  • Built Up flat roofs or BUR
  • Single-ply flat roofing
  • Spray-on / paint-on roofs

The list above shows the 3 main types of flat roof installation, and from the type of roof application you can choose different flat roof systems, that will work best for you. Now let’s take a quick look at each type of roof application.

BUR or built-up roofing:

The name says it all – the roof is built up using multiple layers, of either tar-saturated paper and liquid tar with gravel, or asphalt or multiple layers of other types of roof “membrane” such as rolled asphalt or Modified Bitumen roof. Layers of roofing materials are added on top of one another, usually in criss-cross position, until required number of layers or plies is achieved.

Often, a built up roof will have a layer of pea-size gravel on top, to protect the roof from sun’s devastating UV rays.

As a side note, I have to mention that rolled asphalt roofing can also be considered a single ply roof, depending on how it is installed (number of layers). However, it is such an outdated and inefficient low slope roofing material that we do not recommend using it at all.

Single Ply roofing:

Unlike built-up roofing, single ply roofs are just that – one layer of roofing material is a waterproofing membrane and a weathering surface in one “bottle”. Single ply roofing membranes are much thinner and lighter than built-up roofs. Average thickness of a single ply roof ranges from .o45″ to .090″ or 45-90 mil. Single ply roofing the most common flat roofing material on the market today – both residential and commercial.

Single ply roofs are typically installed either in fully adhered (glued to the insulation or fiber board below it) or mechanically attached to the roof deck with corrosion resistant fasteners and barbed plates.

Most common single ply roofing systems today are EPDM Rubber roofing, PVC roofing (poly-vinyl chloride – don’t be so scared by the name though) and TPO roofs (thermoplastic polyolefin).

Rubber roofing is usually black and unenforced, and uses adhesives to keep the seems together and watertight. EPDM rubber roof is the oldest single ply roofing material on the market today, and although it has many limitations, such as no ponding water warranty, and almost certain maintenance after 7-10 years on the roof, they are still the most popular roofing material for flat roof. Popularity of rubber roofs is mainly attributed to it’s very competitive pricing and the fact that there is no special installation equipment required to install them.

PVC and TPO roofs on the other hand are usually white, reinforced membranes, with hot-air welded seams. Read this excellent article to find out the big differences between TPO and PVC roofing. In just a couple of words, PVC roofs have been around much longer than TPO and have a prove track record. TPO is considerably less expensive than PVC, and was actually created to become a cheaper alternative. However there are many issues with TPO roofs, which still have not been resolved, and roof owners opting for a less expensive TPO roof are taking a gamble. Take a look at our comparison of TPO and EPDM rubber membrane roofs.

Both TPO and PVC roofing material requires special hot-air welding equipment to weld the seams and all flashing. Below is a video of an automated hot-air welder, welding the seams on a PVC roof:

Spray-on and paint-on roofing:

The are two main types of liquid-applied flat roof systems: Spray-foam insulation or SPF roofing and roof coatings.

Spray foam roofing is a two part insulation sprayed directly onto the roof, and then coated either with acrylic or urethane coating and a thin layer of tiny crushed stones or sand.

Coating is essential to long term performance of any SPF roof, as the the UV from the sun will quickly destroy the foam, unless it is protected by a layer of coating and send. Also, SPF roofs have to be recoated every ten years to extend the leaks free performance life of such roofs.

The benefits of SPF roofing is that you get a high R-value seamless insulation, and tight seal around all roof penetrations. One of the drawbacks of the SPF roofing is that the birds will often eat the insulation, creating potential leaks. However it is rather easy to repair such damages with premium, roofing grade caulking.

Roof coatings are made for existing roofs and can often extend the service life of your roof by 10-15 years. Roof coatings can also act as an additional waterproofing layer on your roof. However, not all coatings are waterproofing products, even despite some manufacturer’s claims.

Roof coatings are best used on smooth surface roofs such as old EPDM rubber roofs, low slope standing seam metal roofing systems (such as those on space metal buildings) and smooth surface modified bitumen roofs. Coatings are not the best solution for roofs with lots of dirt and debris, such as tar and gravel roofs, as it is nearly impossible to thoroughly clean them, which is a must, before applying the roof coating.

Flat Roof Examples:

PVC / TPO single-ply roofing installation:

EPDM Rubber Roofing

PVC / TPO Single=ply thermoplastic roofing

Tar & Gravel / Built-up Roofing

Roof Coatings:

One thought on “Flat Roof Materials

  1. I have 71,000 square feet of roof to be repair. It has an old tar and fiber type roof that is breaking apart and the monthly maintenance fee is getting out of control. I like the longevity of PVC so about how much should I be prepared for for this much roof area? The roofers around my area are pushing for me to go with TPO, but I am now having second thought about TPO after having read your review. Thank you for your guidance.

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