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I'm having a bit of a debate with builder of our 12 mth old house. Issue is whether heating system is adequate. House design was registered in Dec 2006 (so ADL1A 2006 applies). Could someone please advise what is 'usable floor area'. I'm told it excludes stairwell and cupboards....is that right???
regards
steve

The 20006 AD calls it "useful" floor area and say it is defined in a EU directive. But it isn't!

However, I found this on the CIBSE website.

Total useful floor area
–
The Total useful floor area is the total area of all enclosed spaces measured to the internal face of the external walls, that is to say it is the gross floor area as measured in accordance with the guidance issued to surveyors by the RICS. In this convention:
–
a. the area of sloping surfaces such as staircases, galleries, raked auditoria, and tiered terraces should be taken as their area on the plan; and
–
b. areas that are not enclosed such as open floors, covered ways and balconies are excluded.

So stairwells and cupboards are included.

Excellent, thanks for that info.
There is one slight anomaly still though, the ADL1A does refer to 'useful' throughout wrt floor area, but the Domestic Heating Compliance Guide 2006 refers to 'usable' (Table 2). I agree that these words seem to be thrown in without proper definition in the docs....frustrating!!! I've not managed to find an authoratitive definition of 'usable' yet.....do you know of one ???!
Thanks for your help.
Steve

AD L1A 2006 (page 8) says:

b. the following terms have the same meaning as in European Parliament and Council Directive 2002/91/EC on the energy performance of buildings:
i.
ii.
...
vi. 'total useful floor area'

Unfortunately the EU Directive does not contain a definition of 'total useful floor area', neither does any other EU legislation! However, I found this on the Department for Communities and Local Government web site under "What Buildings will be affected?"

The Total useful floor area is defined as the total area of all enclosed spaces measured to the internal face of the external walls. Included are areas of sloping surfaces such as staircases, galleries, raked auditoria, and tiered terraces where the area taken is from the area on the plan. Excluded are areas that are not enclosed such as open floors, covered ways and balconies.

I believe that is exactly the same wording as I gave earlier.

As for "useful" and "usable", the OED defines "usable" as "able or fit to be used" and "useful" as "able to be used for a practical purpose". To my mind they are effectively the same.

Many thanks for your time and your advice....your comments have been invaluable...
regards
Steve