Insulation summary

When introducing fabric measures the potential saving in running costs is dependant on a number of variables. The main ones are:

• The type of heating system used;
• The thickness and type of any insulation material;
• The lifestyle of the occupants (e.g. whether or not they open windows regularly, the times that they have the heating and hot water system on and the settings on thermostats etc.).

Because of these factors, it is not possible to give a single value for the saving resulting from the measure. However, in order to gain some understanding of how different measures compare, the table below has been prepared. The values in this table have been calculated using the BREDEM-12 (BRE Domestic Energy Model), which is the basis for the SAP (Standard Assessment Procedure) energy rating method. A typical heating pattern was used, with the whole house heated to a good standard. Then for both the cash and the carbon saving, two figures have been calculated, representing the savings that would typically result if the house were heated by different heating systems.
Lower figure - gas condensing boiler A-rated (SEDBUK¹ 90%) with TRV's
Higher figure - electric storage heating

Savings for a typical semi detached house		Running cost saving (£/yr )		Carbon saving kgC/yr
		From	To	From	To
External and internal insulation to U-value 0.35	115	490	460	1110
Internal insulation to U-value 0.35	115	490	460	1110
Internal insulation to U-value 0.45	110	465	440	1060
External insulation to U-value 0.8 (e.g. insulated render)	85	370	345	835
Loft insulation 250mm in empty loft	70	270	270	690
Flat roof insulation (U-value 0.25)	65	260	265	640
Cavity wall insulation	65	285	265	640
Internal insulation to U-value 1.58 (e.g. 10mm latex foam)	35	145	140	335
Single to low-e double glazing	30	125	120	290
Solar water heating	25	110	90	175
Secondary glazing (U-value 3.0)	20	70	85	195
Hot water tank insulation	25	120	95	150
Floor insulation 100mm @ 0.04W/mK	15	75	60	135
Loft insulation 250mm top-up from 75mm	10	45	45	105
Draught-stripping windows and doors	5	30	25	65

Source BRE

Technical Guidance
» GK 31 'BRE Domestic Energy Model', BREDEM SAP 2001
» Click here for Best Practice publications on insulation.
» Guide to solid wall insulation for local authorities and housing associations

¹SEDBUK stands for Seasonal Efficiency Database for Boilers in the UK

Download documents

  Guide to solid wall insulation for LAs HAs