Insulation / heat transfer question

I calculated that a mediaeval castle made of two meters of stone wall could easily meet building regulations

As could a Neanderthal cave.

Cough. Have you informed your house insurer ?. If the house is unheated then the loft is getting colder then usual with all the risk of frozen pipework (assuming any pipes in the loft).

The party wall between me and my neighbour is a cavity wall with a one inch gap. The front wall (facing North) is a cavity wall up to 1st floor and then 9 inch hollow blocks above, V poorly laid. None of the perps are mortared including where a perp lines up with the party wall cavity !. Outside it is clad with plastic shiplap with plenty of gaps for air leakage. House and front small bedroom adjacent to party wall is noticibly cold during the sort of weather that we had recently.

If the thermal gradient across the party wall is greater than the thermal gradient across your houses external walls then I would expect your property to be a net gainer of heat (depending on the constructin of the party wall and your properties external walls).

In message <10g2g59$2jjao$ snipped-for-privacy@dont-email.me, at 20:45:29 on Mon, 24 Nov

I visit the house at least once a week, which more than complies with the insurer's requirements.

No pipes/tanks/etc in the loft. 98% of the pipes are in the gap between downstairs and upstairs, or in the floor of downstairs.

Indeed, and why discussions on such topics are typically couched in phrases like "all other things being equal" - which of course they rarely are.

However when trying to compare two situations in abstract - that is often the best you can do.

Thermal performance of a wall is significantly affected by exposure - so something (anything) screening it from wind alone can make a marked difference. Likewise, moisture content in the wall will also change the thermal performance.

In the case being discussed (adding insulation to a party wall), things like exposure, wind, rain etc are being (largely) screened by the house on the other side of the wall. So the rate of heat transfer through the party wall will be dominated by how well insulated it is, and the temperature differential. Assuming the adjacent empty property is not being heated, then the net flow will typically be into it and not from it - so more insulation would be better rather than worse.

Oops - my response assumed the other way around...

I suppose if you want to heat vampire, then you should leave a small fan running and pointing at the wall :-)