Roofs are generally one of three different classifications: sloped, low, or flat. Of the three different types of roof, a flat roof doesn’t make much architectural sense because it inherently won’t shed rain or snow. Isn’t keeping elements out of the structure the main job of a roof? In fact, flat roofs can keep a building dry, but in a different way than sloped roofs that have gravity on their side.

The first thing to understand when considering a flat roof system is the different options that exist for flat roofs. There are three main flat roof systems: constructed roofs, modified bitumen roofs, and membrane roofs.

constructed ceilings

This is the traditional tar and gravel roof that many think of when they envision a commercial flat roof. Basically, layers of waterproof material are built with layers of hot tar in between. On top of the built layers is a layer of rock or stone. Traditionally, these constructed roofs were made from layers of tar paper, but newer materials such as fiberglass membranes are available to increase the life of the roof.

Cumulative Advantages

• Less expensive than bitumen or membrane roofing
• eye appeal
• The top layer of gravel or stone is an excellent fire retardant.

Accumulated Disadvantages

• very heavy
• May require structural reinforcement to support excessive weight
• Lots of odor and can be very tricky to install.
• Finding leaks is hard
• Gravel can run off the roof system and clog drainage and gutters

Modified Bitumen Roofs

These roofs are a single-ply rolled roof system impregnated with a mineral-based topcoat as the wear surface. Originally a torch system installed by heating the adhesive, there are now also torchless peel and stick systems that are safer and easier to install.

Advantages of modified bitumen

• Moderate price, generally between built and membrane systems
• Mineral wear layers can be light in color, reducing energy costs by reflecting sunlight
• Peel and stick varieties offer a DIY option for homeowners
• Light

Disadvantages of modified bitumen

• The torch installation process is a fire hazard
• Less wear resistant than membrane systems

Membrane

Also known as rubber roofing, EPDM (short for ethylene propylene diene monomer) roofing is a true rubber roof. The membrane is highly durable and resists both tearing and damage from sunlight. Installation has many options including glue down, stone ballast, and anchoring with fasteners.

Membrane Advantages

• Light
• Easily repaired or patched
• Rip and tear resistant
• Easy to install, even for homeowners

Diaphragm Disadvantages

• Vulnerable to punctures
• Standard EPDM is black and absorbs heat.
• Energy efficient light coatings may cost extra

Understanding the three types of flat roof systems is the first step in choosing the right roof for your building. Consulting with an experienced flat roof professional should be your next step. Using these tips to understand the different options for a flat roof will help you better understand your roofer’s recommendations.