Warm Roofs vs. Cold Roofs. The Difference

Warm Roofs vs. Cold Roofs, Whats The Difference ?

Cold Roofs

Despite the name, the roof isn’t actually cold. This is just a technique in which the roof is laid, in particular, where and how much insulation is installed. When speaking about a cold roof, the insulation is laid in between the rafters or joists. As this still leave the less thermal wood and gap between the insulation and the wood this type of insulation installation is inefficient.

Warm Roofs

With warm roofs being a lot simpler to install and also saving money on heating bills each year, it is easy to see why these are now being done on regular basis. During installation, instead of placing the insulation between the rafters, like you do if you was aiming for a cold roof, you would put insulation sheeting boards on top of the rafters. Popular makes of insulation include Celotex and Kingspan. Once this is installed you can then watertight the roof.



Under Part L of the building regulations, improving thermal efficiency is now a legal requirement. Any work in England, Scotland or Wales which is either a new build or is having at least 50 percent of it’s roof replaced (called a roof renovation) must therefore follow new regulations which involves relaying roofs to fit the criteria of warm roofs. As you can see below, the guidelines which have been set out insist on increasing the thermal capacity of roofs. The caveat is that if a thermal installation does not pay for itself within 15 years by decreased energy prices, Part L of the Building Regulations can be ignored.

Recommended U-Values – England

Domestic Non-Domestic
New Build Existing Buildings New Build Existing Buildings
Best Starting Point (Fabric Only) Extension Refurbishment Best Starting Point (Fabric Only) Extension Refurbishment
Wall 0.16 0.28 0.30 / 0.55 * 0.22 0.28 0.30 / 0.55 *
Floor 0.11 0.22 0.25 0.18 0.22 0.25
Pitched Roof – Ceiling Level 0.11 0.16 0.16 0.14 0.16 0.16
Pitched Roof – Rafter Level 0.11 0.18 0.18 0.14 0.18 0.18
Flat Roof 0.11 0.18 0.18 0.14 0.18 0.18

* A U-value of 0.55 W/m2K is used for cavity insulation and 0.30 W/m2K for internal or external wall insulation.