@Yodhrim
Who would be the best person or company to speak to with regard to getting a near-passive retrofit done?
I've heard that MVHR units are problematic - requiring frequent maintenance and cleaning, otherwise getting blocked, etc. Is this true?
We live in a traditional, stone built, listed tenement - would it still be possible to fit a MVHR?
I don't think I'll be putting any sprayfoam in the wall cavities, that sounds like a slow motion (and difficult to reverse) disaster waiting to happen. It might be possible to further insulate the internal side of the walls (at the expense of partly covering the cornicing / skirting and making that look ugly)
Do you see how problematic everything is? Nowhere to turn... :-(