Cavity wall insulation for stone walls

Houses with random stone or coursed stone walls may have been built with a cavity which is suitable for cavity wall insulation. They do however need a more thorough examination than ‘standard’ brick built properties.

When a property has an outer wall made of stone, it is unlikely that the internal surface of the cavity will be smooth, in the way a brick wall is. Stone walls are therefore unlikely to be suitable for fibre insulation since blown fibre cannot be guaranteed to fill the cavity evenly (although it is perfectly suitable for brick cavity walls).

cavity insulation for stone walls
Homes built from stone are rarely suitable for the standard mineral fibre fill system, but for many properties bonded bead cavity wall insulation can provide the answer.

"Many stone properties, even dating back to the early twentieth century were built with cavities. Although these cavities may not be suitable for blown fibre insulation, other cavity wall insulation products are available to make these homes warmer and cheaper to heat.”

Calderdale Council.
November 2011
injecting EPS beads into a stone cavity
Injecting EPS beads into the cavity
of a stone house

For home-owners of houses with random stone walls we recommend either bonded Polystyrene beads or polyurethane foam since both offer excellent thermal properties and can be suitable for random or coursed stone walls. Polyurethane foam has the added advantage of increasing the structural stability of a wall, whereas bonded beads is the more cost effective option.

For properties with stone walls a more detailed examination is required. Specifically we check, that for each wall:

  • The cavity is of sufficient width to ensure it is fully filled with insulation, since by their nature stone walls may have an uneven cavity.
  • There are no obstructions in the cavity.
  • There is adequate sub-floor ventilation
  • There is no evidence of ‘bridging’ of the cavity, which would allow dampness to permeate from the outside to the inner wall.

In our experience random or coursed stone walls tend to be either:

  • Suitable for cavity wall insulation
  • Requiring some localised repair (e.g. resolving a dampness issue) before cavity insulation can be installed.
  • Not suitable for insulation (e.g. because of inconsistent cavity width, or obstructions).

As part of our survey we will look inside the cavity with a boroscope and advise you on the options available.

Thermal improvements with EPS bonded beads

How much difference does cavity wall insulation make?

‘U’ values are used to measure the thermal efficiency of different building elements and can be a useful way of comparing different materials. For example a wall with a U value of 2, loses twice as much heat as a wall with a U value of 1.

Typical U value (W/m2K)
 A solid brick wall  Around 1.7 to 2
 A brick cavity wall  Around 1.5
 A brick cavity wall insulated with  bonded beads or PU foam  Around 0.3 to 0.4

The table shows comparative U values for walls without insulation, and insulated with with bonded beads or polyurethane foam. These forms of cavity wall insulation can reduce heat loss by around 65-75%.

Unfortunately houses also lose heat through windows, doors, roofs, and floors, as well as from draughts. So just installing cavity wall insulation won’t reduce your heating costs by 65-75%. But since external walls make up the single biggest heat-loss surface in your home it makes sense to make them as efficient as possible.


Keeping Yorkshire warmer
cold walls, no ventilation cause damp, condensation and mould