How much heat do you lose through your party wall?

It may surprise you to hear that you could be losing up to 10% of the heat from your home through the party wall between your home and your neighbours’. If your home is part of a terrace or semi-detached then you have at least one party wall. If this wall has a cavity it could be an important route for heat loss, especially if the cavity is not very airtight. Would you like to know how much heat you are losing? So would the UK Government.

Jason Palmer is coordinating a large research project for BEIS, the Government’s Department of Business, Energy and Industrial Strategy. This will help to quantify the savings from insulating cavity party walls.

We already know that cavity party walls can be a considerable heat loss but we need more data – we need to measure the heat loss in more homes – to see how big a problem this is.

The purpose of the research is to:

  1. Determine how much heat is lost through cavity party walls (see below)
  2. Determine whether heat loss through the party wall varies between construction types, and
  3. Confirm that filling the cavity fixes the problem.

The results of this research could lead to government policies aimed at encouraging people to fill party walls – as well as external walls – to reduce heat loss.

Insulating the party wall can cut heat loss to the loft

Insulating the party wall can cut heat loss to the loft

Do I have a cavity party wall?

Cavity party walls became fairly widespread after about 1945, motivated by reducing noise from neighbours. However, building regulations do not actually require a cavity, so many houses of all ages have solid party walls with no cavity. Homes built since 2010 had to have insulated party walls from the start.

We can tell you for sure whether your party wall has a cavity, but there are some rules of thumb.

Your party wall probably has a cavity if:

  • If your house was built since 1945 AND
  • Your chimney is drawn back from the boundary with the house next door, OR
  • Looking in the loft, the party wall is wider at the base and then becomes narrower just above the joists, OR
  • All blocks or bricks in the party wall visible from the loft are placed longways (with the ‘stretchers’ visible).

If you choose to take part

If you would like to take part, we need to fit sensors to your wall to log temperature and heat flow for up to three weeks. We will need to fit three sensors on each wall, in different rooms.

We can offer a cash payment of £100 as an incentive for taking part.


If you think you have a cavity party wall and you would like to take part, please contact Jason[at], including:

  • Your address
  • Your telephone number
  • When/how we can contact you