External and Internal solid wall insulation


Solid Wall and cavity walls

Insulating your solid walls could cut your heating costs considerably, because solid walls let through twice as much heat as cavity walls do. The good news is that they can be insulated.

If your home was built before 1950, its external walls are probably solid rather than cavity walls. Cavity walls are made of two layers with a small gap or ‘cavity’ between them. Solid walls have no gap, so they let more heat through.

England, Scotland and Wales

Fuel bill savings (£/year) Detached


Semi Detached




Carbon dioxide savings (kgCO2/year) 1,900 kg 1,100kg 720kg 740kg 610kg
Typical installation costs* External wall insulation: £8,000 to £22,000
Internal wall insulation: £3,500 to £14,000

*Estimates based on insulating a gas-heated home. Costs may vary significantly depending on level of work required. Above estimates are based on a typical install, ranging between a small flat and a large detached home.

External wall insulation:

  • can be applied without disruption to the household
  • does not reduce the floor area of your home
  • renews the appearance of outer walls
  • improves weather and sound proofing
  • fills cracks and gaps in the brickwork, which will reduce draughts
  • increases the life of your walls by protecting the brickwork
  • reduces condensation on internal walls and can help prevent damp (but will not solve rising or penetration damp)
  • is best installed at the same time as external refurbishment work to reduce the cost
  • may need planning permission – check with your local council
  • requires good access to the outer walls
  • is not recommended if the outer walls are structurally unsound and cannot be repaired

Internal insulation?

Internal wall insulation is done by fitting rigid insulation boards to the wall.

Internal wall insulation:

  • is generally cheaper to install than external wall insulation
  • will slightly reduce the floor area of any rooms in which it is applied (the thickness of the insulation is around 50mm- 100mm)
  • is disruptive, but can be done room by room
  • requires skirting boards, door frames and external fittings to be removed and reattached
  • can make it hard to fix heavy items to inside walls – although special fixings are available

Contact Us

Contact us for a free quote or to book our services on 01223 755919.