Party Wall Cross-Scheme Guidance & Convention (2.24a).

In this context a ‘party wall’ (also known as ‘separating wall’) comprises any wall between the dwelling and another heated space which can be:

  • another dwelling;
  • commercial premises;
  • a heated corridor or stairwell in a block of flats;
  • a heated common area.


The primary method of identification is from viewing the party wall within the loft space, and it is only the construction in the loft space that is relevant.

When identifying, you should first identify the brick pattern. If laid in solid brick pattern (stretchers and headers), timber framed or system built then you should enter as such.

However, it has always been difficult to identify the construction of party wall when laid in stretcher bond only. 

So, in an attempt to simplify the process, the RdSAP Conventions group has written a new convention (Convention 2.24a), with a helpful flowchart.

It states:

Basis for determining party wall type to be entered when stretcher bond brickwork/blocks face on only and laid upright and are encountered and there is no other specific construction evidence.

Party wall types: 

In some situations, it will not be possible to conclusively identify the construction of a party wall in these cases select Unable to Determine and the software will assume a U-value of 0.25 W/m2K for houses and bungalows.

Situations where party wall construction is not visible could include:

  • Where a room in the roof is present;
  • Basement /Ground and mid-floor flats (especially Converted warehouses and factories);
  • No loft access hatch / inaccessible loft hatch / H&S hazard in loft space;
  • Too much clutter in the loft to see gable end/too far away;
  • Plastered / boarded loft (hobby rooms, etc.).


In all cases, the reason for being unable to identify the construction must be detailed in the Energy Assessor’s site notes.