Advanced Spray Foam Ltd.
The importance of a material's heat resistance
Also known as the coefficient of heat transfer, a measure of the rate of heat loss or gain across a material through the process of conduction. U-values gauge how well a material allows heat to pass through. U-value ratings generally fall between 0.16 and 1.20. The lower the U-value, the greater a product’s resistance to heat flow and the better it’s insulating value.
U-values are expressed in units of W/m2 °K. The R-value is the reciprocal of the conductivity of a material and is the measure of the capacity of a material to resist heat transfer. The higher the R-value of a material, the greater it’s insulating properties.
It is important to be aware that R-values depend not only on thickness but also on material type and installed weight per unit area. The effectiveness of an insulation’s resistance to heat flow also depends on how and where the insulation is installed. For example, compressed mineral wool will not provide its full rated R-value. The overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists.
In general all domestic buildings where work has commenced on or after December 1st 2011 are required to comply with the revised Technical Guidance Document Part L 2011. If you have applied for planning permission or received approval on or before 30th November 2011 you are required to comply with the TGD 2008 Part L.
Building Regulations 2008 – Part L Conservation of Fuel and Energy – Buildings other than Dwellings relates to residential buildings, places of assembly, offices, shops and industrial and storage buildings an includes both new build and change of use / material alteration works.
The chart below illustrates the U-Value requirements for relevant buildings based on the elemental method where work commenced or took place on or after July 1st 2008.