The building fabric elements of a dwelling are considered when calculating heat loss and energy use in DEAP.


Building fabric inputs in DEAP take account of elements including:

  • Fabric insulation
  • Thermal bridging
  • Building envelope air permeability

Guidance and tools

Elements adjacent to unheated spaces

The procedure for treatment of U-values of elements adjacent to unheated space (also called semi-exposed elements) is described in:

  • IS EN ISO 6946
  • IS EN ISO 13789
  • BR443 Appendix A

The Ru for typical unheated structures is given in Building Regulations 2019 TGD L Appendix A. Ru can also be calculated using this calculator, which is based on BRE443.

Thermal bridging

The heat loss due to thermal bridging at junctions between building elements is accounted for by inputting a thermal bridging factor in DEAP.

You'll find the options for deriving the thermal bridging factor for DEAP in:

Thermal bridging factor calculator

BER assessors can use this thermal bridging calculator to calculate a non-default thermal bridging factor for use in DEAP.

The thermal bridging factor calculator contains the psi-values associated with the Acceptable Construction Details, published by the Department of Housing, Local Government and Heritage. You can also input certified psi-values when using this calculator to calculate the thermal bridging factor of a dwelling.

Acceptable construction details

The Department of Housing, Local Government and Heritage has published guidance on acceptable construction details.

  • Part 1 of the guidance covers the general theory of insulation continuity and airtightness in construction.
  • Part 2 provides indicative detail drawings of thermal insulation and airtightness provisions for specific construction interfaces.

To learn more visit the website of the Department of Housing, Local Government and Heritage.

Further information

For further information read:

Thermal bridging

8th December 2021

This webinar explains thermal bridging, the information required for a default thermal bridging factor of 0.08, a non-default thermal bridging factor with default psi values from Part L and certified psi values as an acceptable form of evidence to use in a DEAP assessment.

Thermal bridging webinar

Further support

Use these databases on the NSAI website if you need further support for building fabric inputs in DEAP.

BER Helpdesk

Call: 01 808 2029