Increasingly I have to meet lower U-values demanded by Building Regulation requirements, but what exactly is a U-value?
In a nut shell, a U-value is the measurement of the transmission of heat through a building element.
Essentially the U-value or thermal transmittance of a building element, such as a wall, roof or window, is a measure of its ability to conduct heat, from a warmer environment to a cooler one. It can be used to indicate potential for heat loss in the various parts of a building. The higher the U-value the worse the thermal performance of the building envelope.
The U-value for walls can be complex to calculate as it comprises multiple elements. For a wall, the U-value figure is generated by totalling the thermal resistances (R value) of each material within the total wall construction including; the plaster, internal block, insulation, cavity and clay bricks etc. and taking the reciprocal (a reciprocal is the number needed to multiply by a fraction to get an answer of one). Or, as a formula, the calculation can be expressed as: U = 1 divided by the sum of the R values.
It is important to be aware that the thermal resistance of a layer is the thickness divided by the product’s thermal conductivity. The thermal conductivity value is the intrinsic thermal property –independent of thickness – Forterra provides for our brick and block range. This should not be mistaken for the U-value.
Actual U-value calculations can be more complex than described above with the effect of wall ties, mortar joints, air gaps etc being taken into account as well. So, to help builders work out the U-value Forterra offers a U-value calculation service for all our masonry products.
The Building Regulations set standards for design to ensure buildings use less energy and are comfortable to live in with the consequence that lower U-value targets have to be met to ensure compliance. A low U-value usually indicates the need for high levels of insulation. Using Forterra’s Thermalite blocks with their inherent thermal properties reduces the need for excessive insulation. Click here for further information about Thermalite Products and U-values