Roofs are generally one of three different classifications: pitched, low-pitch, or flat. Of the three different roof types, a flat roof does not make much sense architecturally because it inherently will not shed rain or snow. Isn't keeping the elements off the structure a roof's main job? Flat roofs can indeed keep a building dry, but in a different way than pitched roofs which have gravity on their side.
The first thing to understand when considering a flat roofing system is the different options out there for flat roofs. There are three main flat roofing systems: built up roofs, modified bitumen, and membrane roofs.
Built Up Roofs
This is the traditional tar and gravel roof that many think of when envisioning a commercial flat roof. Basically layers of waterproof material are built up with layers of hot tar in between. On top of the built up layers is layer a rock or stone. Traditionally these built up roofs were made of layers of tar paper but newer materials such as fiberglass membranes have become available increasing roof life.
Built Up Advantages
- Less expensive than bitumen or membrane roofs
- Attractive to look at
- The gravel or stone top layer is an excellent fire retardant
Built Up Disadvantages
- Very heavy
- May require structural reinforcement to carry the excessive weight
- High odor and can be very messy to install
- Finding leaks is difficult
- Gravel can run off roof system and clog drainage and gutters
Modified Bitumen Roofs
These roofs are system of a single ply rolled roof impregnated by a mineral-based topcoat as a wear surface. Originally a torch-down system installed by heating the adhesive, there are now also peel-and-stick torch less systems which are safer and easier to install.
Modified Bitumen Advantages
- Moderate in price, typically between built up and membrane systems
- Mineral wear coats can be light in color reducing energy costs by reflecting sunlight
- Peel-and-stick varieties offer a do-it-yourself option for homeowners
Modified Bitumen Disadvantages
- The torch-down installation process is a fire hazard
- Less wear resistant than membrane systems
Also referred to as rubber roofs, EPDM (short for ethylene propylene diene monomer) roofs are a true rubber roof. The membrane is very durable and resists both tearing and sunlight damage. Installation has many options including glue down, ballasted with stone, and anchoring with fasteners.
- Easily repaired or patched
- Scuff and tear resistant
- Easy to install, even for homeowners
- Vulnerable to punctures
- Standard EPDM is black and absorbs heat
- Energy efficient light coatings can cost extra
Understanding the three types of flat roof systems is the first step in choosing the right roof for your building. Consulting with a knowledgeable flat roofing contractor professional should be your next step. Using these tips to understand the different options for a flat roof will help you better understand the recommendations by your roofer.