Insulating hard-to-treat cavity walls

Question: We have purchased a 1960s bungalow in an exposed site near the sea (500yds away) that has cavity wall but currently no insulation. There is a problem in some areas with condensation (black mould behind furniture placed on exterior walls ie wardrobe). Plans for an extension are currently awaiting planning approval and we have been advised by the architect that cavity wall insulation would not be appropriate for the original walls that remain after the extension is built due to the exposed site and the risk of cavity wall insulation bridging the cavity causing problems. Could you advise on what would be the best alternative ie exterior or internal wall insulation as I am slightly confused as both of these options seem to be remedies for solid walls only. I would be most grateful for any advise you are able to provide Please note that all the external walls are rendered with pebbledash and will have to remain so as this is something Snowdonia planning dept insist on.

Answer: It is difficult to comment on the suitability of your cavity wall for insulation without seeing it but a cavity wall insulation installer would be able to properly examine it – by putting a camera inside the cavity.

Cavities not suitable for insulation:

• Too narrow/ irregular shaped
• Filled with rubble
• No cavity trays
• With through tie-stones

Whether the cavity is suitable for insulation or not, I would suggest that the safest option would be to use external wall insulation because you alleviate the problem of water penetration into the cavity through driven rain. External insulation works really well as it covers up all the junctions (and thermal bridges) and the render acts as a good airtightness barrier. As you already have pebbledash rendered external walls this shouldn’t create problems with the planning department.

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