A Quick Guide to U-Values
U-Values are also known as thermal transmittance or heat transfer coefficients and are used to measure the effectiveness of insulation materials used in buildings. The lower the U-value of the material, the slower the heat will transmit through the material. In the UK, builders, engineers and architects refer to the U-Value of the material in specifying how good the material is at insulating.
There are some set standards by the Building regulation in Part L of the approved document which needs to be achieved while carrying out building work. The required U-Value is based on things like
- Location of the building (England, Wales or Scotland)
- Application of thermal insulation (loft, wall, floor or roof)
- Type of building (non-domestic or domestic)
Recommended U-VALUES for England
Recommended U-VALUES for Wales
Recommended U-VALUES for Scotland
How to calculate the U-Value?
The U-Value can be calculated by obtaining the reciprocal of the sum of all thermal resistance (R-Value).
U-Value = 1/ (Sum of all R-Values)
The higher the R-value the lower the U-value of the material.
How to calculate R-Value?
R-Value = I (Thickness of material)/ λ (Thermal conductivity of material)
Whereas the R-Value of the material is affected by the application but the actual difference in R-value depends on the material itself.
What does W/m2K mean?
W/m2K is a unit in which U-Value is measured. W/m2K stands for Watts-per- meter-square-kelvin. The lower this value of material the better is the product in insulating the house.
Simple U-value calculations can be made easily but considering the building elements layer by layer can be time-consuming and complex. Moreover, it is less important to understand how to calculate the U-Value then to understand how to compare materials by their U-Value to get the best insulating material for your house.
There are a lot of software (U-Value Calculators) available online to calculate the u-value used by a lot of architects and builders to get the best material according to the requirement of the house.
How to calculate the heat loss once you have the U-value?
Once you have the overall U-value of the material then it is quite easy to calculate an approximate heat loss at a given temperature (outside and inside) which will help you to decide the size of the material to use for insulation.
Approximate Heat loss = U-value (W/m2K) x Temperature difference (inside and outside) x Surface area (m2)
For Example, let’s say
- The U-value of the product is 0.25 W/m2K
- Temperature inside is 22 degrees and outside is -3 degrees so the temperature difference will be (22-(-3) = 25)
- The surface area is 100m2
Approximate Heat loss = 0.25 x 25 x 100 = 625 W to keep the temperature inside at 22 degrees.
You will need to calculate the approximate heat loss for roof, walls, floors, doors, and windows to find the total heat loss of the house.
If you want to know more about the U-values of every insulation product we sell on Build4less, go through our range of products.