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Flat Roof Insulation

December 15, 2021
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A flat roof is one of the most important parts of your building because it shields you from direct exposure to weather conditions like sunlight, rainfall, hailstorm, etc.

Sometimes; however, the weather conditions outside your building could be so adverse that you will experience extreme cold or heat. When this happens in your building, you should install a roof insulation

What Is A Flat Roof Insulation?

Flat roof insulation in simple terms, is the opposite of weather conditions. During winter, it makes your home warmer, while during summer, it makes your home cooler. It's the best way to make your roof more energy-efficient and reduce heat.

A flat roof has a little slope with a pitch that's typically below 10⁰. Flat roof insulation is crucial because It is a cost-effective option for heating and cooling your home. This way you have full control over the temperature of your home. Also, installing flat roof insulation helps you to increase the lifespan of your HVAC appliances (Heat pumps, air conditioners, furnaces, packaged units, air handlers, etc,) as these are known to last longer when they are used in moderation.

It also helps you to save money. This is because when a flat roof is insulated, heat loss is reduced, less energy is consumed, and this ultimately translates to a reduction in the home's energy bills

Forms Of Flat Roof Insulations

There are two major forms of flat roof insulation namely:

◾Warm flat roof insulation

◾Cold flat roof insulation

It is important to note that the approaches listed above refer to where the insulation is installed, not necessarily the types of flat roof insulation or materials available. Each of the two has its peculiarities, benefits, and disadvantages. The option you decide to go with will depend on the type of your building, the environment, and regulations from your local authorities. Be sure to talk to consult with professional roofers and get a professional recommendation before making a decision.

Warm Flat Roof Insulation

With this approach, insulation is carried out by placing the selected insulation material right on top of the flat roof. It is best to make sure that the insulation layer is positioned above the timber rafts. You will most likely need to set up a scaffold to access that part of the roof.

This insulation approach is perfectly suited to bathrooms, kitchens, and other areas of the building that are more likely to produce high levels of humidity and aridity during summer or winter. This works well when you want to insulate one or a few rooms in the building.

The benefits of the warm flat roof insulation are:

  1. Zero possibility of condensation because the insulation is positioned above the vapor control layer.
  2. It is cost-effective because it has a simple design.
  3. It allows the conservation of heat without needing the creation of roof void ventilation. This is known as optimal thermal efficiency.
  4. This approach to insulation provides better protection of the roof structure against extreme weather conditions.

The major downside of warm flat roof insulation is that it requires the use of equipment that is best handled by experts in the field.

Cold Flat Roof Insulation

This is another option to be considered. This time, however, the insulation material is not placed on top of the roof, but rather under the surface of the roof. That is, in-between the ceiling and the decking. In some buildings, it is placed under timber rafters. This approach is best applied to external buildings. If you reside in a hot region, this is certainly one option you might want to explore.

The benefits of cold flat roof insulation are

  1. It is a cheaper option when the expenses involved are compared with the warm flat roof insulation. One major expense that doesn't exist here is setting up a scaffold to access the insulation site.
  2. The expected heat loss will not affect the quality of life within livable spaces.

One downside of this approach is that it requires the creation of roof void ventilation.

Research has proven that the insulation materials used for a warm flat roof are more likely to degrade faster than those used on a cold flat roof. This is because they are placed outside; thus, they are more exposed to the harsh elements of weather.

Flat Roof Insulation Thickness

To get the best from your flat roof insulation, you must follow this simple recommendation:

The insulation boards you choose to use should be a thickness of about 150mm. This can be achieved by fitting boards of 100mm above the deck, and insulation of 50mm below the deck just between the roof joists.

Types Of Flat Roof Insulation Materials

The effectiveness of insulation is measured by the amount of thermal resistance it has. So, the higher the R-Value of insulation, the more effective it will be. Likewise, the longer its lifespan.

There are various types of insulation that can be used on a flat roof. They include:

◾Wood Fiber

◾Glass cells

◾Polyisocyanurate

◾Perlite

◾Polystyrene

Polystyrene is further subdivided into two types. They are:

  1. The extruded polystyrene insulation (XPS): This type of flat roof insulation is a better option for a flat roof that requires a higher compressive strength.
  2. The expanded polystyrene insulation (EPS): This type of flat roof insulation has a high rate of water absorption; therefore, it features lower thermal resistance.

All the flat roof insulation materials listed above have different thermal resistance values.

Be sure to consult with a professional roofer or roofing contractor to figure out what will work best in your building. Making the wrong choice could lead to a reduction in the lifespan of your roof.


Getting your flat roof insulation right will provide comfort for you and your family while helping you save money. You can contact us for a free quote and inspection on your roof. Likewise, for more information and help on how you can maintain your flat roof, install flat roof insulation, and other roof issues, reach out to us at 553 Prospect Avenue, Brooklyn NY 11215, [email protected], 6468380441.

Royal Renovators Inc is Fully Licensed and Insured, with Offices Throughout the NYC Area.
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