U Value Calculations

VIP System U Value Calculations

Vacuum insulation panels cannot be cut or adjusted on site and therefore cannot cover the entire area of a roof or terrace.

Each VIP scheme we design is individually calculated to allow for factors such as;

  • % of VIP cover generally accepted 80/20
  • Available insulation depth
  • Minimum backstop u value
  • Shape of structure

A working example based on an area of 100m² to achieve a u value of 0.15W/m²K 45mm of VIP will achieve 0.15W/m²K. However, 45mm of non VIP will not meet building regulations minimum back stop u value and based on 80/20 will only achieve a weighted average u value of 0.25W/m²K .

At CTF we have multiple solutions for both warm and inverted roof application, to ensure the minimum backstop U Value is maintained at all times. 

U value calculations assuming 100% VIP is incorrect and may result in breach of regulations.



Tapered Layer U Value Calculations

Heat loss through a tapered layer is not uniform, varying between the thinnest and thickest parts of the various sections that make up a scheme.

Each tapered scheme we design is individually calculated to allow for factors such as:

  • Rate of fall
  • Length of fall
  • % of Hips and Valleys

These all influence the final ‘U’ value, the building regulations lay down a series of complex logarithms in order to calculate the heat loss for these different shapes. Every tapered scheme is different and therefore a calculation must be carried out for every new scheme as this cannot be accurately estimated. At CTF we use a specifically designed programme in order to ensure our roof designs are compliant to the specified ‘U’ value. CTF eliminate the risk of non-compliance for your tapered scheme and ensure you meet your client’s requirements.

Average thickness ‘U’ values are non-compliant.