Cold Roof Vs Warm Roof

As you consider repairing or installing a flat roof on your property, two effective insulation options to keep in mind are a cold flat roof or a warm flat roof design. In the past, most people used insulation on flat roofs to keep their homes cold. However, recent changes in how we live – such as spending more time inside and having internal washing and cooking areas – have led to an increased need for water vapour control. Warm flat roofs are typically seen as the better design because they eliminate many of the issues that traditional designs have.

In this post, D&D Roofing are going to discuss the different types of insulation for flat roofs, their benefits and their drawbacks, so that you can make an informed decision about which one is right for your needs.

Method for Cold Roofing

The insulation layer is placed between, or under the timber rafters – level with the ceiling joist in the alternative roofing insulation design. As a result, the roof and trunks are kept cool by an air-permeable barrier that separates the insulation from the roof structure. In cold roofing designs, because of the necessity for ventilation in roofs, it is generally not advised as a new build flat roof design.

  • When creating a flat roof, a cold roof offers an easy alternative: simply insulate between the rafters.
  • When existing flat roof sections are too tall, they must be reduced to meet building code requirements.
  • The startup costs are much lower
  • External outbuildings are more likely to benefit from a good roof, as the possible heat loss will not affect any living areas.
  • Minimal impact.
  • This type of design method requires a good ventilation system in order to stop vapour-causing damp damage in between the insulation and the actual structure.
  • Receptive to water bridging
  • Banned in Scotland due to the different climate. The difference between inside and outside temperatures increases the condensation levels which is bad for cold roofs as the ventilation needs to carry moisture away.
  • In the long run, they are not very cost-effective.
Warm Roof Method

In a warm roof design, the insulation layer is situated either above the timber rafters or between the structural supports. This way, the temperature in the loft area is similar to that of the rest of the building, resulting in less heat loss.

Warm roofs are constructed to keep the entire building warm in order to prevent cold bridging, which is a term for when heat or energy escapes from one area of the structure and enters another. Warm roofs come in two varieties. A sandwich system is one in which there is a build-up of VCL, insulation & membrane over the structural deck. This can be done with full adhesion or mechanical fixing. An inverted system is where the insulation boards are laid over the structural deck and waterproof covering instead. The insulation is secured by a layer of ballast or paving slabs to prevent wind uplift from occurring.

  • It is very popular due to its simple design structure, providing an effective way to insulate a building.
  • The structure is more protected from extreme heat and cold temperatures.
  • Warm roofs are designed to stop cold bridging – where heat escapes through one area and enters through another.
  • Heat can easily be kept inside, so no requirements for void insulation on the roof.
  • Moisture can easily escape meaning a much lower chance of damp and rotting damage to the structure.
  • Very efficiently thermally
  • Cost-effective
  • NHBC actually recommend people get this roof as a standard construction practice.
  • Cost more to start up.
  • There can be issues with heights when refurbishing existing flat roofs.
  • It is known to be slightly more difficult than a cold roof design.

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