Garage Insulation for a Flat Garage Roof

a flat roof
  • 4-8 hours
  • Intermediate
  • 400-1,200

Whatever your reason for installing garage insulation, it needs to be done correctly to ensure that you get the maximum benefit from your investment. There are a number of factors to take into consideration when installing insulation on a flat-roofed garage. This article will outline these unique features and offer advice to help you put theory into practice.

Pooling Water

Of the many types of roof available, flat roofs are the only design that can result in water pools forming on the surface if they are not properly designed. All other designs have some degree of the gradient, allowing the water to drain off. This provides a challenge not only for adding insulation but also for leak prevention. Before you begin with any improvement plans, make sure that your roof is in good condition. Otherwise, you will be wasting your money.

Choosing Insulation

The type of insulation you use will depend on your budget, needs and, to a certain extent, personal preference. There are three types of insulation: blanket, blown and rigid. A huge range of materials is used to manufacture insulation including styrofoam, fiberglass and mineral wool. It is recommended that you research the different types of insulation available and seek advice from experts before making your decision.


Providing adequate ventilation is an essential part of insulation and will allow hot air to escape from the garage in winter as well as preventing moisture build-up. A ventilation gap of 2 inches between the insulation and the underside of the roof is required as standard. Ventilation should be provided either from side vents or from elevated roof vents. The roof vents should be adequately sealed to prevent water ingress.

Sealing Gaps

Any areas where the insulation does not meet without a gap or space remains uncovered are known as bypasses. An example would be where you need to cut a hole for a light fixture. In order to keep the insulation in good condition and prevent moisture build-up, you need to seal all of the bypasses in your roof. One way to do so is by using expanding foam. It is easy to apply and forms a tight seal in all of the gaps. Take care when using the expanding foam as it can be quite messy if you do not keep control of the applicator.

Vapor Barrier

Although the ventilation will allow most of the moisture that enters the garage to escape, a small amount may remain. A vapor barrier will provide protection between the insulation and the drywall or ceiling panels and prevent mold or rot from forming. Vapor barriers are usually made from polyethylene film or paper-backed aluminum.

Additional Materials

Another material that can assist with the temperature regulation of your garage is light-colored pebbles or stones on top of the roofing material. These will help to reflect sunlight and heat from the building and prevent it from heating up excessively during summer months, thus reducing the amount of work that the other features have to do and making the garage more efficient.