I'm renovating my house built in 1985 and I really need to improve the insulation. I'm torn between doing it on the inside (cheaper) or on the outside (more effective but more invasive). Does anyone have recent experience with this? What do you think is the best choice in 2026?
External insulation is clearly superior for a house from the 80s, even if it's heavier to implement. The thing is, your house probably has thermal bridges everywhere - corners, wall-to-roof junctions, window sills. When you insulate from the inside, you leave all that cold structure in place, so you lose a ton of energy through those areas. On the outside, you wrap the entire building, you eliminate these bridges, and you really gain in comfort. It's not just a few percent better, it's a major difference.
The "invasive" side you mention, honestly it's temporary. Yeah, you need scaffolding, it's work, but once it's done you benefit from it for decades. Interior insulation eats away at your floor space (which really sucks especially in small rooms), it leaves the thermal mass outside, and you have to really carefully handle moisture rising on the walls - otherwise you've got condensation problems. On the outside, your structure keeps its thermal mass, you keep all your interior space, and technically it's more robust long term.
If you're really tight on budget, a compromise solution would be interior for the upper floors (less visible if it's attic space for example) and exterior for the main facade walls. But if you can afford to do exterior completely, it's clearly the smartest investment for a house this age.
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