Wallnuts U Value Calculator

Thermal insulation is one of the most important factors in creating energy efficient and comfortable buildings. Calculating U values to measure the thermal transmittance through a wall, roof or floor is fundamental to building design, but not all insulations are equal. Some cause significant pollution during manufacture and disposal, whilst others are renewable and relatively benign.

Wallnuts has been developed by Conker Conservation Ltd, Chartered Building Surveyors, in collaboration with programmer Kingsley Bickle, to provide a quick but comprehensive U value calculation for use on site or during preliminary design, and offer broad guidance on the environmental impact of the insulation materials.

The app contains over 60 common materials and air spaces, plus a wide selection of eco materials such as wool, hemp, cork, earth and chalk, for green designer. Each material is listed with its associated k values and an eco rating from A to E, which has been assessed by Conker*. The user has the ability to create any new materials or inhomogeneous layers and add them to their personal database. Navigation tools are provided to search the database.

The user is prompted to choose from 3 levels of workmanship to account for the gaps that unavoidably occur when using rigid insulation boards. There is a tendency in the industry towards over-optimistic calculation of U values, which results in under-performing buildings, we urge users to be realistic and factor in gaps at level 2 or 3. This can be compensated by using thicker insulation or more layers, or in some cases flexible insulation which is easier to lay without gaps.

The user has the ability to change any of the surface resistance (Rse or Rsi) values, although default values in accordance with BRE report BR443 are provided.

New inhomogeneous layers (or compound layers) can be created, such as rafters or wall studs with insulation between, and saved for use in the database. The app guides the user through the creating of these layers, where the percentage of each is input. There can be multiple materials in each layer.

Projects can be saved, edited and emailed via PDF attachment. The printed PDF lists the project name, project type, date and time of creation, each of the material layers, thickness, k value, R value and final U value.