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also victorian end of terrace here
Would the plan be to remove the existing render? Is the new external insulation breathable?
apc-
Is the new external insulation breathable?
Depends which material you pick as insulation. There's synthetic and natural stuff that both claim to be breathable. Picking an installer with half a brain so that they don't fuck it up somehow will be 80% of the battle on that I reckon.
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Would the plan be to remove the existing render?
Yes - the acrylic render is just about the worst possible thing for a solid wall building. It fails (without fail), prevents drying out, and allows damp to penetrate.
Is the new external insulation breathable?
It isn't. However, in theory at least, it moves the dew point further out of the building, and removes any cold bridging problems.
If the render on top of it fails, it is also easier to repair & less damaging to the substrate.
Again - in theory.
Ideally, I'd like to lime render properly, but that is just as expensive, harder to find trades with the actual experience. And we'd still have an insulation / cold bridging / condensation problem.
Howard
NotThamesWater
We're getting quotes in for external insulation at the moment (Victorian end of terrace, currently acrylic render, couldn't look much worse), and are being told that the roof will need extending. Which will mean a new roof entirely, as it's on it's last legs as it is.