What is a Ballasted Roof System?Basic Benefits

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A ballasted roof system is a warm flat roof system in which water proofing membrane is covered and secured against wind uplift pressure, protected from exposure and mechanical damage by placing a layer of gravel or paving known as ballast. Roofing Balast system started first time in early 1970s.

It looks similar to built up roofing (BUR) but there are some differences between these two-roofing system. Each roofing system uses a layer of crushed rock stones, but BUR uses a thin layer of crushed stones and size of stone is limited to quarter inch diameter and embedded into asphalt layer.

Also Read: Aluminum Pan Roofing Panels – Pros & Cons

This technique helps to protect it from sun’s UV rays. While in ballasted roof system the layer of stone is placed above water proofing system and minimum size of stone is inch in diameter. The stones in Roofing ballast system are placed heavily.

Ballasted roof is loose laid in which all the components including roof membrane and insulation which can be assembled without fastening them to each other or with a deck.

 In this system because the assemblies do not require any adhesives or fasteners so its costs less and it is quicker to install than other roofing system.

The ballast is placed on top of roof which act as an insulating material. This helps in reducing the solar gain during summer and prevent loss of heat during winter.it also provides a natural looking surface with wide range of architectural styles.

This ballasted design can be used for roof of plaza, patio and other outdoor space for recreation, relaxation or walking.

A roofing ballast system can be used for following types of roofs

  1. Low slope metal
  2. Green roofing
  3. Curved metal
  4. Membrane metal
  5. Valley metal
What is ballasted roof system?
What is ballasted roof system?

Consideration for roof ballast

The given below points should be considered before installing ballasted roof system.

  • The ballasted roof system consists of heavy layer of crushed stone which increases the weight of a building dead load. So, the structural design of building should be such that it must be able to support the load of stone layer.
  • There is very less maintenance requirement but in case of any leakage visual inspection will be difficult due to heavy layer of ballast and repair will require expertise.
  • A ballast roofing system is not a good option for taller buildings because as we move up velocity of wind increases, and it make stone ballast in to flying debris due to high energy of wind.

Pros of ballasted roof system


This roofing system use economical roofing material as compared to other roofs and it is among the fastest to install. This roofing system has one of the lowest lifecycle costs than other roofing in the market today.

Also Read: Overlapping metal roof lengthwise

Suitable for wide conditions

A ballasted roof is suitable for different weather and temperature conditions. This type of roof provides a suitable resistance against wind uplift pressure and protect the water proofing layer from sun UV rays. In summer it reduces the solar gain and similarly in winters it prevents the loss of heat and helps in maintaining the temperature of building for long time.


This type of roofing helps in increasing the beauty of top and attract building owners and architects. In ballasted roof there is a wide variety of different stones. It ranges from large round cobblestones to small stone of gravel size. The different size rocks combine with stones and provide a variety of textures which increases the aesthetics of roof.

Amenity space

The ballasted system is preferred for plaza roof, walking places, recreational areas and some other uses. This system helps in improving and enhancing the appearance of local environment. This system along with plants or greenery add more beauty to a place.

Energy efficiency

Ballasted roof system helps in saving energy of building and reduces the heating and cooling loads. A large layer of stone reduces heat gain of building which saves energy and in result cost of electricity is reduced in summers. Similarly in winters it helps in preventing the loss of heat and maintain the temperature of a building for long time.


Stones and concrete are good fireproof materials, and they resist high temperature. Ballasted roofs provide highest fire rating. Class-A fire resistance can be achieved by ballast material without using gypsum board and expensive fire-retardant chemicals.


A stone is obtained from high strength rocks and is highly durable. The stones usually do not wear or deteriorate with weather condition as fast as other materials do. Good quality stone provides better resistance to extreme sunrays and acidic type rain.

Easy repair of roof

The ballasted roof can be repaired more easily as compared to other roofs. There are no fasteners or adhesives used so it is easy to remove the damaged part and then replacing it with new part. In case if there is a need of replacing the waterproofing layer or any other insulating layer then same ballast stone can be reused after placing of waterproofing layer.


A ballasted roof is made of different sizes of crushed stone which can be removed without any damage and can be used again whenever we want. Similarly, water proofing membranes can also be removed and reuse again.

Cons of ballast roof

Increases Roof weight

As we know that the specific gravity of most stones ranges from 2.5 to 3.0. Due to its large weight, it increases the weight of roofing system.

Difficulty in finding leaks

A roofing ballast system is covered by heavy layer of stone. In case of any leakage from waterproofing membrane it will be difficult to find a damaged place due to covering membrane with stones.

David Noah

Howdy, I’m Noah Although I don't like all this internet thing but I love sharing my stories on the roof here. With my years of experience in number of roofing contractors across various boroughs of Florida, I'm here to answer all your roofing questions. I'm really honored to have you on my website browsing through our articles and hope you'll enjoy your visit and find my content helpful in every situation. You can contact me right away to discuss any of your roofing problem.

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