4
8. The Gross Internal Area of a dwelling is defined as the total floor space
measured between the internal faces of perimeter walls
1
that enclose the
dwelling. This includes partitions, structural elements, cupboards, ducts, flights of
stairs and voids above stairs. The Gross Internal Area should be measured and
denoted in square metres (m
2
).
9. The Gross Internal Areas in this standard will not be adequate for wheelchair
housing (Category 3 homes in Part M of the Building Regulations) where
additional internal area is required to accommodate increased circulation and
functionality to meet the needs of wheelchair households.
Technical requirements
10. The standard requires that:
a. the dwelling provides at least the gross internal floor area and built-in
storage area set out in Table 1 below
b. a dwelling with two or more bedspaces has at least one double (or twin)
bedroom
c. in order to provide one bedspace, a single bedroom has a floor area of at
least 7.5m
2
and is at least 2.15m wide
d. in order to provide two bedspaces, a double (or twin bedroom) has a floor
area of at least 11.5m
2
e. one double (or twin bedroom) is at least 2.75m wide and every other
double (or twin) bedroom is at least 2.55m wide
f. any area with a headroom of less than 1.5m is not counted within the
Gross Internal Area unless used solely for storage (if the area under the
stairs is to be used for storage, assume a general floor area of 1m
2
within
the Gross Internal Area)
g. any other area that is used solely for storage and has a headroom of 900-
1500mm (such as under eaves) is counted at 50% of its floor area, and
any area lower than 900mm is not counted at all
h. a built-in wardrobe counts towards the Gross Internal Area and bedroom
floor area requirements, but should not reduce the effective width of the
room below the minimum widths set out above. The built-in area in excess
of 0.72m
2
in a double bedroom and 0.36m
2
in a single bedroom counts
towards the built-in storage requirement
i. the minimum floor to ceiling height is 2.3m for at least 75% of the Gross
Internal Area
1
The internal face of a perimeter wall is the finished surface of the wall. For a detached house, the perimeter walls are the
external walls that enclose the dwelling, and for other houses or apartments they are the external walls and party walls.