Building Regulations for New Roofs: Understanding Thermal Insulation.

When installing a new roof, proper insulation is essential to meet building regulations and ensure energy efficiency. There are two main ways to insulate a roof, depending on the roof design: Warm Deck and Cold Deck. 

The minimum U-value for warm and cold roofs in the UK are:

• Warm roofs: 0.18 W/m2K for insulation between and above the rafters 
• Cold roofs: 0.13 W/m2K for insulation between and beneath the rafters

Here's a breakdown of each approach for both flat and pitched roofs.

Warm Deck Insulation.

In a warm deck roof, the insulation is installed above the rafters or joists, with the roof covering placed directly over the insulation. This method eliminates the need for ventilation, making it more straightforward in terms of construction. 

Cold Deck Insulation.

With cold deck insulation, the insulation is placed between the rafters or joists. For cold deck roofs, ventilation is crucial, allowing air to flow and preventing moisture buildup. This method requires a 50mm ventilation gap above the insulation, and vents must be installed to ensure airflow.

Insulating Flat Roofs.

Warm Deck Insulation:- Typically uses rigid insulation boards of varying thickness, depending on the manufacturer’s recommendations.  Insulation is laid on top of the roof joists, with a layer of external plywood placed over it. The roof covering is then applied on top of the plywood.

Cold Deck Insulation:- The thickness of insulation varies by material and manufacturer. A 50mm ventilation gap must be left between the insulation and the roof covering. Ventilation openings should be provided, typically at the eaves, to promote airflow. A vapor membrane is placed beneath the insulation and secured to the joists before finishing with plasterboard.

Insulating Pitched Roofs.

Warm Deck Insulation:- Insulation is installed on top of the rafters, with a layer of felt placed over it. Battens and tiles are then fixed over the felt, completing the roof structure. The thickness of the insulation will depend on the manufacturer’s specifications.

Cold Deck Insulation:- Insulation can be installed either between the rafters or between the ceiling joists. Like flat roofs, the insulation thickness varies by material and manufacturer. Ventilation is essential: vents should be installed along the eaves on both sides of the roof, and ridge vents may also be needed if insulation is placed between the rafters.

 Key Points to Remember:- Warm Deck roofs: No ventilation required, insulation placed above rafters or joists, Cold Deck roofs: Ventilation is necessary, with insulation placed between rafters or joists. Always refer to the manufacturer’s guidelines for insulation thickness and materials. Proper ventilation is crucial for cold deck roofs to prevent condensation and ensure longevity.
Understanding these insulation methods helps ensure compliance with building regulations and creates a more energy-efficient, durable roof.

If you require additional information or would like to book a free quotation please contact us @ www.kenthouseextensioncompany.co.uk