Insulating solid walls can significantly reduce heating costs and improve home comfort, but it is more expensive than insulating cavity walls. Homes built before the 1920s likely have solid walls that cannot be filled with cavity wall insulation. However, solid walls can still be insulated from the inside or outside for larger energy savings.
Determining the type of walls you have is the first step in identifying whether or not your solid walls are insulated. To identify your home’s wall type, check the brick pattern or measure the wall width near a door or window. Cavity walls have an even pattern with lengthwise bricks, and a width over 260mm, while solid walls have an alternating pattern with smaller ends visible and a narrower width. Stone walls are usually solid and thicker. For non-traditional wall structures like steel-frame, timber-frame, or pre-fabricated concrete, consult a specialist insulation installer.
Internal wall insulation (IWI)
Internal wall insulation involves attaching rigid insulation boards to the wall or building a stud wall filled with insulation material like mineral wool fiber. It’s cheaper than external wall insulation, but reduces room floor area by about 100mm. The installation can be done room by room but requires removal and reattachment of skirting boards, door frames, and external fittings. It can make it hard to fix heavy items to the inside walls and cannot be done before fixing any damp problems.
External wall insulation (EWI)
External wall insulation adds a layer of insulation material to your wall, which is then covered with render or cladding. The finish can vary, including smooth, textured, painted, tiled, panelled, pebble-dashed, or finished with brick slips. It can improve weatherproofing, sound resistance, and the appearance of outer walls. It also fills cracks and gaps in the brickwork, reducing draughts, and can increase the lifespan of your walls. It may require planning permission and good access to outer walls, and is not recommended if the walls are structurally unsound.
Ventilation
When insulating older buildings with solid walls, water vapour can move freely through the building due to ventilation and the building materials. Insulation can reduce draughts, but may also create a barrier to vapour movement and make walls colder, leading to potential condensation problems. To avoid future damp issues, a moisture control strategy specific to the building may be needed, using breathable insulation or creating a continuous vapour barrier. An experienced specialist installer should be consulted, and an appropriate 25-year guarantee should be in place, such as those approved by Ofgem.