Roofs are generally one of three different classifications: sloped, low-pitched, or flat. Of the three different types of roofs, a flat roof doesn’t make much architectural sense because it inherently won’t shed rain or snow. Isn’t keeping the 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, 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 the 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 of layers of tar paper, but newer materials, such as fiberglass membranes, have become available, increasing the life of the roof.
Accumulated benefits
- Less expensive than bitumen or membrane roofing
- Attractive to the eye
- The top layer of gravel or stone is an excellent fire retardant.
Accumulated disadvantages
- Very heavy
- May require structural reinforcement to support excessive weight.
- High odor and can be very difficult to install.
- Finding leaks is difficult
- Gravel can run off the roof system and clog drains and gutters
Modified bitumen roofs
These roofs are a single layer rolled roof system impregnated with a mineral based top layer as a wear surface. Originally a down torch system installed by heating the adhesive, now there are also peel and stick torchless systems that are safer and easier to install.
Advantages of modified bitumen
- Moderate price, typically 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
- Downward torch installation process is a fire hazard
- Less wear resistant than membrane systems
Membrane
Also known as rubber roofs, EPDM roofs (short for Ethylene Propylene Diene Monomer) are a true rubber roof. The membrane is very durable and resists both tearing and damage from sunlight. Installation has many options, including gluing, stone ballasting, and anchoring with fasteners.
Advantages of the membrane
- Light
- Easily repaired or patched
- Scratch and tear resistant
- Easy to install, even for homeowners
Disadvantages of the membrane
- Vulnerable to punctures
- Standard EPDM is black and absorbs heat.
- Lightweight, energy-efficient coatings can cost more
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 roofing contractor should be your next step. Using these tips to understand the different options for a flat roof will help you better understand your roofer recommendations.
