U-Values

Wall U-Values

External wall types

External wall types use a lookup table of U-values based on the wall construction and age band of installation. This data is sourced from RdSAP (9.94) Tables S6 to S8 depending on the location of the property.

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Internal wall types

Internal wall U-values are used in room heat load calculations to size heat emitters, they have no effect on the total property heat loss.

The exact U-value will depend on the wall construction type. This data is simplified from CIBSE Domestic Heating Design Guide (2021) Table 3.18.

Internal Wall Construction	U-Value (W/m².K)
Aerated block	1.06
Breeze block	1.43
Solid brick	1.82
Stud partition	1.92

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.

Party wall types

Party wall types use a lookup table of U-values based on the party wall construction. This data is sourced from RdSAP (9.94) Tables S8B.

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Floor U-Values

Ground floor types

Ground floor types use a lookup table of U-values based on the floor construction, level of insulation and age band of installation. This data is sourced from RdSAP (9.94) Section S5.5 alongside Table S3 (where required).

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Exposed floor types

Exposed floor types use a lookup table of U-values based on the level of insulation and age band of the property. This data is sourced from RdSAP (9.94) Table S12.

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Internal floor types

Internal floor U-values are used in room heat load calculations to size heat emitters, they have no effect on the total property heat loss.

The exact U-value will depend on the level of insulation and direction of heat flow. This data is simplified from CIBSE Domestic Heating Design Guide (2021) Table 3.27.

Internal Floor Construction	Insulation	Heat Flow Direction	U-Value (W/m².K)
Intermediate floor	None	Upwards	1.73
Intermediate floor	None	Downwards	1.41
Intermediate floor	100mm	Upwards	0.32
Intermediate floor	100mm	Downwards	0.31

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.

Party floor types

Party floors apply to flats and maisonettes only.

The exact U-value will depend on the party floor construction and level of insulation. This data is derived from CIBSE Domestic Heating Design Guide (2021) Table 3.27.

Party Floor Construction	Insulation	U-Value (W/m².K)
Timber joists	None	1.75
Timber joists	100mm	0.33
Timber joists	150mm	0.23
Concrete slab	None	1.82
Concrete slab	100mm	0.57

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.

Ceiling U-Values

External ceiling types

External ceiling/roof types use a lookup table of U-values based on the roof construction, level of insulation or age band of installation. This data is sourced from RdSAP (9.94) Section S9 or S10.

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Internal ceiling types

Internal ceiling U-values are used in room heat load calculations to size heat emitters, they have no effect on the total property heat loss.

The exact U-value will depend on the level of insulation and direction of heat flow. This data is simplified from CIBSE Domestic Heating Design Guide (2021) Table 3.27.

Internal Ceiling Construction	Insulation	Heat Flow Direction	U-Value (W/m².K)
Intermediate ceiling	None	Upwards	1.73
Intermediate ceiling	None	Downwards	1.41
Intermediate ceiling	100mm	Upwards	0.32
Intermediate ceiling	100mm	Downwards	0.31

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.

Party ceiling types

Party ceilings apply to flats and maisonettes only.

The exact U-value will depend on the party ceiling construction and level of insulation. This data is derived from CIBSE Domestic Heating Design Guide (2021) Table 3.27.

Party Ceiling Construction	Insulation	U-Value (W/m².K)
Timber joists	None	1.75
Timber joists	100mm	0.33
Timber joists	150mm	0.23
Concrete slab	None	1.82
Concrete slab	100mm	0.57

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.

Door U-Values

External door types

External door types use a lookup table of U-values based on the door age band and what it opens to. This data is sourced from RdSAP (9.94) Section S15A.

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Internal door types

Internal door U-values are used in room heat load calculations to size heat emitters, they have no effect on the total property heat loss.

The exact U-value will depend on the door construction. This data is derived from CIBSE Domestic Heating Design Guide (2021) Table 3.20.

Internal Door Construction	U-Value (W/m².K)
Solid wood	3.0
Solid wood (25% single glazed)	3.7
Solid wood (50% single glazed)	4.4
Solid wood (25% double glazed)	2.9
Solid wood (25% double glazed)	2.8

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.

Window U-Values

External window types

External window types use a lookup table of U-values based on the window age band, glazing type and frame type. This data is sourced from RdSAP (9.94) Section S14.

NOTE

Refer to Appendix S - Reduced Data SAP (9.94) for more information.

Internal window types

Internal window U-values are used in room heat load calculations to size heat emitters, they have no effect on the total property heat loss.

The exact U-value will depend on the window glazing type. This data is simplified from CIBSE Domestic Heating Design Guide (2021) Table 3.20.

Glazing Type	U-Value (W/m².K)
Single glazed	4.8
Double glazed	2.8
Triple glazed	2.1

NOTE

Refer to CIBSE Domestic Heating Design Guide (2021) for more information.