Solid Wall Insulation

ROI
14.1-Years

If you have a very old house with solid walls then you are losing a lot of heat through the walls. Solid walls transmit heat at, at least twice the rate that uninsulated cavity walls do. Throughout the heating and insulation section of this site an average house is used and assumes that the walls have cavities, such that a three bed house with no insulation measures, is approximated to use 20,000kWh per year and the 5 bed house is approximated to use 30,000kWh. With a solid wall house the starting point is higher about 20% higher. So for this section we will use the numbers 24,000kWh for the smaller house and 36,000kWh for the larger house for the calculations.

There are two types of insulation for solid walls, external and internal. They are both expensive and both have their pros and cons, the energy savings trust has a good list of these on their site, they seem only to consider the savings if you are gas heated however (we assume). The main problem with internal insulation is the disruption to the house and the fact that your rooms will end up being a bit smaller, if however you are planning to redecorate it may be an idea. With the external wall insulation the whole house is likely to alter in appearance, this may be an advantage to some!

With external solid wall insulation you can reduce your energy bill for heating by about 45%, and for internal solid wall insulation by about 40%. The first table calculates the approximate pay back times for external solid wall insulation and assumes an installation cost of £ 11,000 for the smaller house about £ 15,000 for the larger house. The second table calculates the approximate pay back times for internal solid wall insulation and assumes an installation cost of £ 7000 for the smaller house about £ 11,000 for the larger house

External Solid Wall Insulation

 Approx % energy saving Approx energy saving per year Gas Electric  (Std) Economy 7 LPG Fuel   Oil 3 bed house 45% 10800 kWh £ 518.4 £ 1663.2 £ 810 £ 626.4 £ 464.4 Payback time with external wall insulation costing £ 11,000 (3 bed house) 21.2 years 6.6 years 13.6 years 17.6 years 23.7 years 5 bed house 45% 16200 kWh £ 777.6 £ 2494.8 £ 1215 £ 939.6 £ 696.6 Payback time with external wall insulation costing £ 15000 (5 bed house) 19.3 years 6 years 12.3 years 16 years 21.5 years Calculations assume the energy required to heat an un-insulated solid wall 3 bed house is 24000 kWh and a 5 bed house is 36000kWh.

Internal Solid Wall Insulation

 Approx % energy saving Approx energy saving per year Gas Electric  (Std) Economy 7 LPG Fuel   Oil 3 bed house 40% 9600 kWh £ 460.8 £ 1478.4 £ 720 £ 556.8 £ 412.8 Payback time with internal wall insulation costing £ 7,000 (3 bed house) 15.2 years 4.7 years 9.7 years 12.6 years 17 years 5 bed house 40% 14400 kWh £ 691.2 £ 2217.6 £ 1080 £ 835.2 £ 619.2 Payback time with internal wall insulation costing £ 11,000 (5 bed house) 14.1 years 4.4 years 9.1 years 11.7 years 15.8 years Calculations assume the energy required to heat an un-insulated solid wall 3 bed house is 24000 kWh and a 5 bed house is 36000kWh.

Is it worth doing?

Of the various insulation measures outlined on this site, this is probably the least cost effective simply because of the costs of installing it. The external insulation is more expensive and will require professionals to do it, so there are unlikely to be ways to reduce costs. With the internal insulation a competent DIY'er may be able to do the job and as such reduce the payback time. With expensive heating fuels the measure becomes more sensible for example if you use LPG or heating oil. The measure does however represent and enormous energy saving and corresponding reduction in C02, if this is a concern to you, and remember fuel prices are only going up!