I see this question asked regularly through the years, so looking for some up to date ideas.

I've just purchased an 1890's 2 storey brick house in the UK. The rooms are quite large (3.6m height and most rooms 3-5m across) The brick walls are solid and have no cavity. I can't insulate from the outside (planning approval + aesthetic). Interior walls are plastered.some have lining paper/paint/some weird rough finish. I am happy to hack back to the brick internally. I have recently moved in and am beginning renovation work so open to any change. The Nest is reporting heavy heating usage already and it's only October....

I've looked at a combination of thin and effective insulating material that can be applied to the interior of the external walls. Some cursory research shows many new companies starting up in this space but I don't know what is currently effective. I.e. there is 10mm "spacetherm" board advertised but other companies suggest a minimum of 100mm for effective insulation.

Also open to alternative suggestions.

  • Is there currently exposed brick on the interior of the house or is there interior finishing? Are you in the process of moving in, renovating or have lived there and tired of bills? Oct 10, 2016 at 21:12
  • Have updated with some more info
    – beirtipol
    Oct 10, 2016 at 21:27

2 Answers 2


The awkward truth is that you don't have a lot of great options here. External insulation or cavity fill are by far the preferred options. If those are off the table, you can apply insulation board to the interior if you're prepared to lose some floor space, but it's not a perfect solution: there will be big thermal bridges where interior walls and floors meet exterior walls. 10mm of insulation won't do much. You really need to do at least 50mm of a decent insulator to make it worth it.

This approach will be very expensive or labor-intensive (or both) since you'll need to redo all the trim and cabinets, extend electrical boxes and plumbing lines, possibly replace toilets, and things like that. You'll also need to finish the new interior walls with plasterboard or skim coat plaster, if the insulation board you use is cementitious, like Ytong autoclaved aerated concrete insulation panels. The problem with those is that they aren't very good insulators for their thickness--not as good as the plastic foams. But foam boards will need substantially more finish work.


I've just renovated a 30's solid brick house - we insulated between the floors and under the suspended floors downstairs, however we've not done the loft. Currently, downstairs actually holds the heat extremely well to the point where there's a distinct wall of heat as you come down - to that end, my next focus is huge amounts of insulation in the loft as that must be where we're losing the vast vast majority of heat.

I can't imagine that 10mm of insulation would do anything worth writing about - that's tiny, even for boards. Putting 100+mm in, plus 12.5 mm plasterboard means you're losing a good amount of space. Personally, I'm not so sure it would be worth it - it'd be very interesting to the unbiased savings calculations because I can attest that insulation is expensive and presumably this method involves battening out every single external wall, too. If your stairs are on the external wall, that's going to be complicated too.

Realistically, you probably need a professional to come and calculate the U value requirements and to give you realistic analysis. I suspect that spending your money on more conventional upgrades (Double glazing windows, loft insulation, floor insulation, modern central heating) will give you a much better ROI

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.