U-Value Calculator

Pitched Roof
Flat Roof

Whilst the information and/or specification contained here is to the best of our knowledge true and accurate, we specifically exclude any liability for errors, omissions or otherwise arising therefrom. Details, practices, principles, values and calculations should be verified as to accuracy and suitability for the required purpose for use.

Mannok Products U-Value Calculator
W/m 2·K

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Free, Online U-Value Calculator

Our U-Value calculator is a free, online tool which will help calculate the required thickness of insulation to achieve the desired U-Value.

The calculator can be used to calculate U-Values for floor, wall, pitched roof and flat roof insulation applications.

There is a wide range of calculations available in the U-Value calculator which can be emailed directly to your inbox.

The Information You Will Need

To complete your U-Value calculation, you will need to have the following information:

Wall Insulation Calculations

  • Full construction build-up of wall construction from outside to inside
  • Type of wall construction e.g. cavity wall, timber frame, steel frame
  • The desired U-Value you want to achieve, if known

Floor Insulation Calculations

  • Perimeter area ratio. This is calculated by dividing the total exposed perimeter in meters (m) by the intended insulated floor area
  • Floor construction type, e.g. suspended floor, solid ground floor
  • Full construction make-up of the floor, e.g. 75mm screed, vapour control layer, 150mm insulation, ground floor slab, etc.
  • The desired U-Value you want to achieve, if known

Roof Insulation Calculations

  • Type of roof construction e.g. pitched roof or flat roof
  • Construction make-up of the roof including joist/rafter info
  • The desired U-Value you want to achieve, if known
  • If the roof is a ventilated or unventilated system


A U-Value is a measure of the heat loss through a building element. Otherwise known as thermal transmittance, it’s the rate at which heat transfers through a building element and is expressed as W/m 2K.

U-Values are used in construction to measure the effectiveness of the building’s envelope in preventing heat loss. Elements with lower U-values lose less heat. Building Regulations set a maximum permitted U-value for each element which must be matched or improved upon.

Calculating U-Values can be a complex process, so as well as our U-Value calculator, we have provided a number of U-Value calculations for our insulation products, which can be found on our Insulation Applications pages. Using our U-Value calculator will also allow you to calculate the U-Values for your specific construction project quickly and easily.

What thickness of insulation should I use?

Use our U-Value calculator to work out the required thickness of insulation for the application. You can adjust the insulation thickness in the calculation to achieve the required U-Value. We have also created U-Value tables for different floor insulation, wall insulation and roof insulation applications, which can be found on each of the different applications pages. The tables provide the U-Values for a range of insulation thicknesses for each application.

View our U-Value Tables: