When talking about flat roofing and in particular the repair or maintenance you will undoubtedly be asked “what type of roof is it, warm or cold?” by a roofing contractor. Most residential flat roof owners won’t have a clue, so this article is to help you understand the two types.

The construction of the roof deck and the ceiling has a crucial effect on the how well the waterproofing material works on top. Within the building industry the terms Warm Roof and Cold Roof are used to describe the two different types of flat roofs.

Warm Roof

This type of flat roof construction has the roof insulation above the roof deck or framework.  This tends to keep the deck ‘WARM’ and is usually the best construction for domestic properties, particularly in colder climates. Warm roofs are better insulated and can reduce heating costs as well as having the desirable green element. A typical warm roof is shown below.

Cold Roof

In contrast to this many older residential flat roofs will have the waterproofing laid directly onto the roof deck, with the insulation placed above the ceiling. This is why the deck is then terms ‘COLD’ and therefore a Cold Roof.

What’s the main difference?

The differences really come into play when in colder climates such as found in the winter months of the UK. In colder weather, cold roofs are at risk to condensation build up, which can cause the roof materials to corrode and distort. To combat this it is important that the roof has enough through-ventilation. This has to be provided to each space above the insulation. Often this is hard to achieve depending on the way the property is built such as when the roof abuts the wall of a house.  The warm roofs do need this ventilation and so have a better chance at a longer lifespan depending on how it was built and with what materials.

So while cold roofs are not regularly endorsed for the climatic conditions like in Scotland, according to the Building Standards (Scotland) Regulations, warm roofs are recommended instead by roofing contractors. On the whole in the UK, the Warm roof is strongly recommended.

Conclusion

Just because you have an existing cold roof it doesn’t mean you need to rush out and get a warm roof. As long as there is adequate insulation and more importantly, ventilation, the roof should be fine. What material is being used for the waterproofing and how it is fitted will have much more of an effect.

So now you know that there are two different types of roofs, warm and cold, what they are and what the differences are. To help you remember when you investigate your own:

Insulation ABOVE the deck = Warm Roof

Insulation BELOW the deck = Cold Roof