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What is a Ballasted Roof System

what is a ballasted roof system

A ballasted roof system is a type of roofing.

It consists of a framework, which creates the shape and size of the roof, as well as providing support for insulation materials. 

The framework must have sufficient strength to withstand the weight of snow or other loading conditions.

A ballast is required to provide this stability. 

This post will explore what a ballasted roof system entails and how it can be used on homes that need an alternative to conventional shingle style roofs.

Why are ballasted roof systems so popular?

If you are wondering why ballasted roof systems have become a popular choice for commercial building roofs, here’s a list of some reasons:      

  • They are easy to install
  • They require no special equipment      
  • Most types can be installed with little disruption to day to day business operations
  • Mini roof repairs can be done on ballasted roofs      
  • The system is cost competitive with other systems
  • Installations are faster than most systems      
  • Ballast rock can be recycled from a site, saving money on disposal 
  • The surface of a ballasted roof provides a non-slip surface for workers and pedestrians        
  • Ballast roofs are more comfortable to walk on during warm weather months  
  • Ballast roofs insulate better than many other systems           
  • They don’t require storage of heavy equipment                        

Roof types that use a ballasted system include:

  • Valley metal
  • Low slope metal
  • Green roofing
  • Steep slope metal
  • Curved metal
  • Membrane metal
house, large roof terrace

How does a ballasted roof system work?

Ballasted roof systems are usually implemented in two different ways. 

The first being that they are installed on top of an existing roof (usually built up roof system or single ply membrane). 

They can also be used on new construction to ballast the roof on a 5/8″ OSB deck. All roofs must first be properly waterproofed before installation.  

The second component of ballast is the product that actually holds the mat down. This consists of either stone (gravel) or plastic pellets (polymer or rubber). 

Both are designed to hold very heavy equipment without shifting; in addition, they both will improve the overall pendulum impact resistance of your roof by adding weight.

  • Stone is made of quarried rock and is designed to weather and blend in with the color of your roof.
    • Stone also comes in a variety of colors for those looking for an aesthetic upgrade.
    • The one disadvantage to stone as compared to polymer (plastic) pellets is that it cannot be moved once installed, whereas polymer can be easily added or removed as needed.
  • Polymer pellets: The other option is the use of polyethylene or plastic pellets.
    • These lightweight, durable and easily added or removed polymer pellets serve as ballast for the matting.
    • Polymer pellets are generally black but can be found in a variety of colors depending on quantity being purchased.
Refurbished half of a flat roof

What are the benefits of a ballasted roof system?

A ballasted roof system provides a lightweight, durable and easily maintained seamless membrane roofing system. 

It is cost efficient as compared to other options. There are no seams, so there is no worry about leaks at seam junctures.

In addition, because the weight of the matting and substrate weighs down on the membrane, it prevents the membrane from moving around and going over the edge. 

This occurs as a result of wind uplift, which is the number one cause for roof system failures.

What are ballast mats made of?

Ballast mats are most commonly made from PVC or Polypropylene. 

There are also some that incorporate both into their construction to provide strength and durability.

Polymer pellets are made from 100% post industrial recycle material; in addition, they can be easily removed and replaced if necessary. 

Most high-end ballast mats are a minimum of 1/4″ thick, and any seams utilized in their structure will be heat sealed to prevent failure.

Common misconceptions about ballasted roofs

  • Ballast is a requirement for a ballasted roof.
    • This is only partially true, as there are plenty of roofs that use ballast but do not have a “ballasted” system.
    • The misconception comes from the fact that the most common type of ballasted roof uses stone as its main element for weight distribution and adhesion.
    • Due to this misconception, many people assume that stone is the only viable choice for ballast.
    • This isn’t true since there are many possibilities to use different materials as ballast for your roofing system.
  • Downspouts are an optional feature.
    • Another common mistake about ballasted roofs is thinking that downspouts aren’t required.
    • The truth is they are an important part of the ballasted system since they help direct water away from the roof.
  • Stone weights are equal.
    • Another common misconception is that all types of stone are weighted equally, which isn’t always true because different stones have different densities.
    • The result of using different weights for materials is that some areas might be more vulnerable to uplift in the wind.
  • Stone is only used for ballast.
    • The biggest misconception about ballasted roofs is that stone is the only material used in this type of system, which isn’t true at all since there are many other possibilities to use materials as your weighting elements.
    • Some examples are slag, glassphalt, and mineral fiber (MMFX).
  • There is only one type of ballasted system.
    • Last but not least, many people think that there’s only one type of ballasted roofing system, which is also incorrect.
    • There are some variations to this type of roofing system such as the weight percentages and the materials used for adhesion and distribution.
    • In addition, there are different styles such as the shingle style and the traditional style.

Final Thoughts

The ballasted roof system has been widely known to be the least expensive and quickest solution for a pitched membrane; it is simply an easy system to install. 

It may not be the best aesthetically but it does get the job done and that’s what counts in some cases.

If you are looking to install a new roof on your home or business, it is important to research what type of roof will best suit you. 

The ballasted roof system may be right for some homes but not for others.

No matter which type of roof you choose, know that there are reliable contractors in your area that can install them correctly and safely on your property. 

Always remember to do your homework before hiring a contractor and check their references.

flat roof with gravel