Cold vs. warm roof insulation

Posted on by Protech Roofing Team

Thermal design is important for any roof, as it guides the flow of heat and water vapor, both of which have an impact on the insulating properties of a roof and its performance in the home. The traditional cold roofing has been practiced in homes for many years, however, a few disadvantages have been identified recently, leading many people to choose warm roofing instead.

Whatever insulation you choose for your flat roof, your individual property and its needs and capabilities should always be considered first. Some factors that should be examined before you choose include;

  • The thermal performance needed for your roof, required by both the Building Regulations, government guidelines, and yourself. As the world becomes more concerned about rising CO2 levels, the UK government are attempting to meet emissions targets, meaning that building regulations request specific levels of insulation for existing flat roofs and ones built in the future.    
  • Type and amount of traffic that the flat roof is predicted to experience.  
  • The compatibility of the thermal design with current or planned roofing materials and structures.
  • Thickness of insulation that your roof can accommodate.

To help you choose, take a look at our guide to cold vs. warm roofing insulation.

Cold roofing

What is it?

In this traditional form of thermal roof design, the thermal insulation layer is place below the structural decking, insulating the voids in the roof between the deck and the ceiling. This type of thermal design is prone to “cold bridging” whereby water vapor, caused by the warm air, condenses on cold surfaces within the roof space, causing condensation and mould. To counteract this, cold roofing requires an incorporated ventilation system, ensuring that the roof void is constantly replenished with fresh air. These types of roofs are not recommended for new flat roof builds, because of the difficulties in providing a ventilation system and the obstacle of avoiding cold bridging.

Pros

  • Low initial cost.
  • Cold roofs are more suited to external outbuildings, as the possible heat loss will not impact any livable spaces.
  • Can keep your home cooler during the summer months.

Cons

  • Susceptible to cold bridging.
  • Not cost effective in the long run.
  • With the urge from the government to make our homes more energy efficient, cold roofing is not usually recommended for new flat roof builds, as it can allow some heat to escape through the roof. It is also recommended that if a cold flat roof requires refurbishment, then turning it into a warm roof should be considered instead.
  • Dirt, dust and creatures can enter the voids brought by the ventilation system.  

Warm roofing

What is it?

In warm roofing, the thermal insulation layer is located above the structural decking; this creates a clear roof void between the ceiling and the deck. Because the insulation is located in a part of the roof where there are no interruptions from a structural support, there is less likelihood of warm air condensing on any cold structures within the roof e.g. cold bridging. The bottom of the insulation layer is lined with a vapor control layer, and on the top with a waterproofing membrane; these are to protect the insulation from moisture, and ensure it is totally enveloped.

Pros

  • Improves thermal efficiency of a roof. Since 2010, there have been  government regulations issued that lay out some thermal and insulation requirements that existing flat roofs have to meet, and it emerges that a warm roof system is the best way of achieving the required standards.
  • Eliminates condensation and the need for ventilation in a flat roof. Warm roofs are particularly useful for kitchens, bathrooms or any high humidity areas where a cold roof may have been more susceptible to mould growth from condensation.
  • Lowers energy costs for the future.
  • The roof structure is better protected from extremes of heat and cold.
  • Stops warm air from moving from the building interior and into the roof void.
  • Upgrading to a warm roof will qualify your roof as having certain thermal properties that will be noted in the Energy Performance Certificate, something that all properties now require.

Cons

  • Higher initial cost.
  • Because the roof structure is exposed to more heat, this could mean that the components will wear out at a quicker rate.

Protech Roofing are award winning roofing contractors, providing a variety of expert roofing solutions, including flat roofing. Serving the Leeds area for over 25 years, we are a dedicated team, striving to provide quality customer service and tailor the delivery and final product to our clients’ individual requirements. Contact our team today, who will be happy to discuss your upcoming project.

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