Commercial and Strata Property Roofing: understanding flat roof systems & maintenance

by on October 11, 2011

Commercial and Strata Property Roofing: understanding flat roof systems & maintenance

Several important factors come into play in protecting a commercial or strata property investment against the elements. Strategically choosing the type of roofing system used and having a proactive maintenance plan is are two very important factors. The performance of a roof has a profound impact on property operations, tenant & resident satisfaction and property owner costs.

This article contains a summary of the information our property managers share with clients seeking to understand their roofing system and the importance of maintenance. Kazawest often shares this type of information with clients such as commercial building owners & lease holders through to strata councils & residents of condominiums. Read on to get the information you need to understand flat roof system types and the maintenance that goes with them.

Flat roofs are the most common type of roofing system in use for commercial properties and certain types of strata developments such as low-rise apartments and high-rise condominiums. The most prevalent 5 types of flat roofing systems are:


Built Up Roofing (also known as BUR)

Modified Bitumen Roofing

Ballasted Roofing

Single Ply Roofing

Green Roofing Systems


Built Up Roofing (BUR) is also referred to as a tar and gravel roof. It involves a tar infused felt being rolled onto the roof with overlap between layers. Liquid tar is applied to the surface and in between the overlapping layers. Depending on conditions, generally this type of roof lasts 10 to 15 years and then will need additional layers added. A topping material, such as small rock, can be used to protect the roofing system and prolong the useful life of the roof.

Modified Bitumen Roofing is a hybrid of the BUR system where the material is manufactured in a factory and comes in rolls to be applied to the roof deck. The material itself is modified tar or asphalt with rubber typically added for improved performance. Normally a BUR roof underlay is used before the application of the modified bitumen which is applied with adhesive, torch, or hot mopping. A topping material is normally required to protect the roofing system. The lifespan of this type of roof typically exceeds 20 years.


Ballasted Roofing is a membrane roofing system that is usually loose laid on the roof deck and held in place by the weight of a topping such as small rocks or precast concrete pavers. A common material used as such a membrane is EPDM (Ethylene Propylene Diene Monomer). Seams and the membrane are joined with an adhesive. When well maintained, a ballasted roof will normally last over 30 years.

Single Ply Roofing systems simply a single ply sheets of a roofing membrane made from several types of synthetic polymers. During the installation, they are sealed at joints to create waterproofing. While they typically come with a higher price tag, you get what you pay for. Single ply membrane roofs can outlast just about any other roof type, however, it is critical to choose a single ply membrane with a heavy base layer and strong knit design. These membranes are generally excellent in UV and tear resistance; two factors that drive their longevity. In theory, with proper care and maintenance, a single ply membrane roof can last over 50 years. In practice, the better engineered ones were invented about 25 years ago and today the failure & replacement rate can be as low as 1%.

Green Roofing Systems have been used for centuries in Europe to reduce power consumption and manage the heat of city buildings. This trend has been catching in North America in recent years. Green roofs slow roof water drainage down, allowing vegetation to store the water and have water evaporate to the atmosphere directly from the roof. This reduces the burden on both building and city drainage systems tremendously. The basis for a green roofing system is typically the same, mechanically speaking, as a ballasted roof. Instead of the use of loose rock, soil and vegetation are applied. However, the key difference is that the material for the roof also must serve a dual function as a root barrier stopping penetration of roots into the roofing. It is advisable to consider the use of a roofing membrane specially designed for green roofing. A well designed and installed green roof can last over 20 years.



As can be expected from Kazawest, no article on building materials and technology should end without a mention of maintenance.  All roofing needs to have a solid preventative maintenance program in place including the removal of debris and dirt, inspection for damage, as well as the cleaning of downspouts and gutters

Pages: 1 2

{ 0 comments… add one now }

Leave a Comment

Previous post:

Next post: