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).
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:
In our experience random or coursed stone walls tend to be either:
As part of our survey we will look inside the cavity with a boroscope and advise you on the options available.
‘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.
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