How should I insulate my pebbledash house?

We are renovating and extending our 1930s home in a conservation area. The house has stone quoins on all corners and pebbledash in between.

We have planning permission to fit an external wall finish comprising 40mm-thick insulation boards and 10mm-deep render between the quoins. However, this will not provide enough insulation to meet our goals.

I had previously thought of adding Kingspan insulation, sticking it to the plasterboard on the internal face of the structural wall. However, I have realised that this is not actually possible as it would involve moving a staircase and destroying wood panelling in two rooms. So, is it better to just externally insulate and fill the existing empty cavity, or should I scrap cavity fill and internally insulate all the easy-to-treat walls, leaving a couple of rooms cold?

Personally, I am a fan of adding cavity wall insulation, but only in areas of low exposure and obviously using reputable companies. If you have pebbledash on a 1930s building, then this is likely to be pretty hard and the external walls should be suitably rain and shower proof as a result.

ereafter I would probably be inclined to add any extra insulation where I could on the inside face of the external walls, (although this is of course often quite disruptive). is way the external proportions of the house should stay intact – although this doesn’t address whether you are keen to change the aesthetic appearance of the house exterior, of course.

One other thing to consider is adding heat recovery to your newly insulated home. is will help enormously in controlling condensation risks, including interstitial condensation, which is a potential issue with poorly-installed cavity wall insulation.