Guide To Warm Roofs and Cold Roofs

Last updated: March 5, 2025

One of the most important questions asked during roof insulation is: what type of roof style insulation do you have? There are two options to choose from in this scenario. The warm roof option and the cold roof option. In this guide, we’ll look at what they mean and the benefits of each type of roof.

What is a warm roof?

Using a warm roof, the insulation is attached to the floor decking and rafters, which provides the best thermal protection. As a result, it is also a more budget-friendly option. In rooms with limited ceiling heights, the insulation may affect the height of the room, as well as the opening of doors and windows. Typically, warm roofs are found on pitched roofs with a higher profile, where this is less of an issue. Because of this type of insulation, the roof performs better, thereby earning the name “warm roof”.

What is a cold roof?

There is small to no loss of height with cold roof insulation because it is placed between the floor joists – however, ventilation space is required. The reason it is called “cold roof” is not because it is cold, but because it is less efficient than a warm roof. As a result, the rafters themselves remain uninsulated. As a result of thermal bridging, the rafters conduct some of the cold into rooms below (on a cold day). The effect can be reduced by insulating the ceiling at floor level. By doing this, you can lower the ceiling by 50mm while preventing thermal bridging. Insulating between floor decking retrospectively can be messy and time-consuming, while a cold roof is easier to install during the construction phase.

Which is better, cold or warm roof?

Insulating a cold flat roof requires removing old boards and replacing them, as well as replacing the roof surface. Warm roof insulation provides better thermal efficiency. Warm deck roofs are easier to install, offer superior thermal performance, but add height to flat roofs. Due to the height difference, warm roofs cannot be used on balconies and flat roof extensions. As an alternative to warm roof insulation, cold roofs are preferable in these situations.

How thick should the insulation on a warm roof be?

The thickness of insulation on a warm roof will depend on the brand of the insulation and the material used. We recommend talking to a professional roofer, or if you have questions about other roofing materials get in touch with our team.

ERoofing Ltd

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