Best Roofing Systems for Flat Roofs

Though it may surprise you, replacing a flat roof actually requires different types of roofing materials than sloped (or pitched) roofs.

When considering your choices for flat roof material, there are four main options to choose:

• Built-up Roofing (BUR)
• Modified Bitumen
• Single-Ply membrane
• Spray Polyurethane Foam

Let’s take a look at each one individually!

Built-up Roofing (BUR)

Built-up roofing is made up of hot tar and gravel built up from waterproof material alternated with hot tar and supporting fabrics, which is then topped off with a layer of stone or gravel. It’s a great option for flat roofs as it creates a continuously sealed surface. In recent years self-adhered systems have been developed, which are rapidly replacing the older hot tar systems.

Generally speaking, BUR has the lowest initial cost of the flat-roof options. Built-up roofing can act as a fire retardant, which is always a welcome addition to any building. However, if leaks do occur, it’s much harder to find their source, which can lead to higher costs down the line. Further, washed-off gravel may clog gutters, which can cause headaches, extra maintenance, and more money down the road.

Modified Bitumen Systems

Modified Bitumen Systems use an asphalt membrane as the base of the roof, and are one of the fastest growing and most popular options out there for flat roofs. Depending on application techniques used, the system may be prone to buckling, which can reduce the lifespan of the roof.  Laps and seams are typically heat-welded using a torch, to create a monolithic system.

Because it’s less expensive, modified bitumens systems may be one of the best options for flat roof material. Light-colored gravel surfaces are available, which reflect heat from the sun, lowering energy bills, which is especially useful under the Arizona sun. MBS can also be given sealant treatment, giving it up to a 30-year lifespan.

Single-Ply Membrane

Single-Ply Membranes consist of sheets of rubber or synthetics that are then mechanically or adhesively applied to the roof deck (or insulation board) and/or ballasted.  Ballast refers to the process of applying weight on top of the system to hold it in place, typically gravel.  Although typically used for commercial roofing purposes, single-ply membranes may also be used for residential roofing. A variety of single-ply systems exist, including TPO, PVC, and EPDM.

Single-ply systems typically necessitate specialized tools to install, and are usually installed on commercial roofs. If leaks occur, repairs are generally straightforward. Single-ply roofs tend to have a lengthy service life, ranging from 20-30 years! TPO, the more recent addition to the single-ply family of products, is increasingly common in the Phoenix roofing market, since it holds up well in our climate and is available in a range of colors.

Spray Polyurethane Foam

Spray polyurethane foam is an excellent choice for flat roofs in our climate.  As the name suggests, it is spray-applied with heat and pressure.  As the product forms, it creates a monolithic system with no seams or laps to leak.  Foam provides insulation and a measure of sound-proofing.  A variety of coating options are available for application over foam, to protect the foam from the sun and also to provide additional heat-blocking benefits and aesthetic appeal.  Common coatings include elastomeric acrylic and silicone, both of which are available in a variety of colors.

Foam roof maintenance tends to be quite basic. An annual roof walk with a utility knife, a caulk gun and a tube of elastomeric or urethane caulk.  Any minor damages can be quickly remedied.  Periodic application of additional coating extends the life of a foam roof indefinitely.

Get Support for Your Commercial Roof from SUNVEK

When it comes to installing a flat roof system, there are many factors that can hang over your head. Luckily, SUNVEK is here to help you with the tough decisions so that the only thing hanging over you is your brand-new roof!