Can I get a U-value calculated for my flat roofing project?
Absolutely! Please contact our freephone technical helpline on 01543 678777.
Does thicker insulation always provide better thermal performance?
Increasing insulation thickness will generally increase the thermal resistance of the insulation layer, but thickness alone does not determine the thermal performance of a complete roof.
The thermal conductivity of the insulation, the other components within the roof build-up and the construction details all contribute to the final U-value.
Different insulation materials can therefore achieve similar thermal performance at different thicknesses.
This is particularly relevant where roof build-up height is restricted, because high-performance insulation can help achieve a required thermal target without simply increasing the thickness of conventional insulation.
What if I cannot provide all of the information required for thermal calculations of a specific project?
It is possible for us to make certain assumptions when performing a calculation, but this can reduce the accuracy of the final result. Assumptions are routinely made about the types of fixings to be used, but we will always try to inform you if a general figure has been used where more accurate data could affect the calculation result.
What is the difference between a U-value and an R-value?
U-values take into account all elements of a construction, including thermal bridges. They can only be worked out by calculation. The R-value, or thermal resistance, is a measure of the insulation board on its own, dividing the thickness (in metres) by the thermal conductivity (lambda value, W/m.K). The R-value can be used to compare how different thicknesses of products with different lambda values perform comparatively.
What is the difference between U-value, R-value and thermal conductivity?
U-value measures how easily heat passes through a building element such as a roof, wall or floor. It is expressed in W/m²K. A lower U-value generally indicates better thermal performance.
R-value represents the thermal resistance of a material or construction. A higher R-value indicates greater resistance to heat flow.
Thermal conductivity, represented by the Greek letter λ (lambda), describes how readily heat passes through a material. It is expressed in W/mK. A lower lambda value generally indicates a material with better insulating properties.
Importantly, the U-value of a roof is determined by the performance of the complete construction, not simply the lambda value of the insulation product.