U-value & Interstitial Condensation Calculations


A U-Value is the unit for measuring the rate of heat energy lost through an element of a buildings structure (such as a wall, roof or floor).

U-values are used to assess the effectiveness of the buildings insulation, the more insulation in the structure the less heat is lost and the lower your U-value is.

In the UK there are minimum U-values that need to be achieved when undertaking building works and these are set out in the building regulation documents.

Interstitial Condensation

The elements of a building structure are usually made up of a number of layers (i.e. a wall can be made up of bricks, insulation, blocks and plaster) and each layer has a different resistance to water vapour.

If one of these layers has a high enough vapour resistance, and there is insufficient insulation or ventilation in the area, it is possible that condensation can form. This is known as interstitial condensation and it can lead to issues with damp, mould growth and even the deterioration of the fabric itself.

An interstitial condensation calculation will identify if there is a risk of condensation forming, and if so the point at which it would form.

Our Services

Thermal Economics provide a free U-value calculation and interstitial condensation calculation service for constructions using our products.

Our experienced advisors use the latest industry standard software and all calculations are carried out in accordance with BR443 and BS EN ISO13788.

If you would like to discuss any current calculations you have or would like us to work on some accurate U-Value & Interstitial Condensation Calculations for your development, please contact our Technical Department on 01582 544255 or email [email protected].