I live in a block of flats with neighbours on 5 sides and only one side open to the outside.

I understand that conduction is likely to be the main way I lose or gain heat to or from the neighbours on my floor (and this will be based on the temperature differential between our flats), but are there other factors to take into account with my neighbours above and below me?

I would guess that I have to take into account not only the average temperature differential between our flats, but also the temperature differential within our rooms, as the real differential between my flat and my neighbour above me is the difference between the temperature at the ceiling of my flat and the floor of my neighbour above.

Similarly, I would expect that I would be much less likely to lose heat into the flat below as it would be dependent on the difference between the temperature at the ceiling of my neighbour below and the floor of my flat.

As such, how would I work out whether it was worthwhile adding wall, ceiling insulation and possibly even under carper insulation, to minimise the heat losses to my neighnours.

  • 3
    Note that this depends entirely on whether you keep your spaces warmer or colder than your neighbors. If you are conservation minded it is likely that you keep it colder than your neighbors, so you would have a net gain of heat. To first order, if you have neighbors both above and below, you will gain from below an equal amount to what you lose to the above, if all thermostats are set the same. Commented Feb 8, 2013 at 13:23

1 Answer 1


Here's the basis of the calculation you need for losses through conduction:

heat loss rate = surface area x U-value of separater material x temperature difference.

There will also be losses from convection.

So, to compare the conduction losses through your external walls, to losses through your internal walls, do the calculation for each.

I expect that the temperature difference on external walls is so much greater than the temperature difference on internal walls, and that the U-value of windows in particular is so high, that external losses swamp internal losses.

There is one notable exception: cavity party walls. It used to be believed that they were reasonably good insulators. But that turned out to be false: there are big losses from convection bypasses within the partition and via lofts / basements.

  • That's a fascinating paper, thanks. I believe that there may be significant party cavities, so this could be worth investigating.
    – Mark Booth
    Commented Feb 6, 2013 at 14:12
  • Anecdotal; but one year when the people living in the apartment above mine kept their living areas ~10F hotter than I prefer mine was generally several degrees hotter than what I normally expected during the periods of the year when I was able to regulate it by how far I had the windows open/how fast I had fans running. Given the general cheapness of the buildings construction I doubt there's any insulation in my ceiling/their floor. Commented Feb 6, 2013 at 15:01

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