A Comparison of Several Flat Roofing Types

Depending on where you live, flat roofs may or may not be common in residential areas. Warm and dry climates tend to yield flat roofs since there’s little worry about snow and precipitation. But for commercial and industrial buildings, flat roofs have been a go-to design for decades. No matter where you’re from, it’s not uncommon to see businesses with a flat, industrial roof. But how are these types of roofs maintained?

Low-slope (or flat) roofs differ from a typical peaked residential design. A flat roof presents a variety of different maintenance questions. How will snow or precipitation drain from the roof? Will the flatness create a greater likelihood for leaks? What is their heat absorption or reflection like?

Built-up and single ply EPDM roof systems both use specific designs to help prevent such problems. With knowledge of flat roofing systems, you can choose the best type for your building. Read on to investigate these major flat roofing systems.

Single Ply Roofing Systems

Single ply refers to the amount of layers in the roofing type, and its specific installation process. It remains one of the most used systems for low-slope roofs.

Cost Comparison

Single ply systems have a higher initial cost than built-up systems. But, single ply can last longer with regular maintenance. If a single ply roof needs repairing, though, it will cost more than a typical built-up roof repair. Thus, both system types present pros and cons as far as value goes.

Materials and Installation

Single ply systems feature two main types of membranes: thermoset membranes and thermoplastic membranes. The former involves cured membranes that seal by way of an attached adhesive. Thermoplastic membranes require heat or solvent welding upon installation. Below are three ways to install a single ply membrane:

  • Mechanical: the installer uses mechanical fasteners to seal or affix the membrane to the roof deck.
  • Full adherence: Installers bond the membrane straight onto the substrate or roofing plane.
  • Point-affixed: also referred to as loose-laid or ballasted, this involves welding the roof membrane to metal plates placed at intervals.

Other Factors

Colour is an integral part of a single ply system. White materials like TPO (thermoplastic polyolefin) and PVC (poly vinyl chloride) reflect heat and light. These two materials are useful for reflecting heat and light and work well in hot climates.

The black colour of ethylene propylene diene monomer (EPDM) absorbs heat. This trait allows EPDM to work well in cold climates. EPDM is a lightweight synthetic rubber that can last up to 30 years. Easy manufacturing and installation also make EPDM is a common choice for commercial low-slope roofs.


Most single ply roofing systems work for both a full roof replacement as well as covering an old or damaged surface. If you choose a single-ply system, learn these physical variances to get the best possible material.

Built-Up Roofing Systems

The name itself describes the idea behind this system: several layers “build up” to keep damaging elements out of the roof plane.

Materials and Installation

Unlike the plastic-based materials of a single ply system, built-up roofing uses layers of roofing felt and waterproof materials. Such “waterproof” materials can include:

  • Coal tar pitch
  • Asphalt (hot or cold adhesive)
  • Bitumen or modified asphalt

This “sandwiching” effect of bitumen and fabrics work together to create a watertight membrane. After applying the layers, installers use a final layer of gravel, crushed rock, or similar aggregate.

Cost Comparison

Built-up roofing systems feature easy installation and maintenance. This is because of affordable materials and simple processes. They feature an aggregate or spreading of gravel to coat the top layer of asphalt. If maintained correctly, this layer offers UV ray protection and helps keep the integrity of the entire roof.

Other Factors

Much like an asphalt road, built-up systems can deteriorate with exposure to the elements. Sunlight breaks down asphalt bases, and moisture creates potholes and cracks in the asphalt.

Although built-up roof repairs are simple, it’s important to get regular roof inspections to keep the aggregate intact. As long as you are able to maintain your chosen roof system, the durability and lifespan should last without problems.


Built-up roofing works well for low-slope commercial roofs. However, this specific roof system may be less successful in long, wide open roof expanses. Built-up materials have only a 10% ability to stretch and relax with thermal and structural changes. As mentioned before, this causes cracks, potholes, and breakage in the asphalt.

But, built-up rooftops work well where the roof has mechanical applications and heavy traffic. The thicker built-up membrane style can support this kind of movement, and holds well against blunt forces


Choosing the Right System

Each roof is different and presents various needs specific to its situation. Now that you know a little more about flat roof types, you can make an informed decision that fits your needs. Consult your Calgary roofing company to find the best roof type for your home or business.