Calculating Permitted area of glazing TS 6 - Scotland


A wee Monday morning tip - by taking the insulation between rafters from ceiling ties or ridge down to the wall head (as you know I prefer to do this), the upper floor area is normally always the same as the ground floor area - not a lot of people know this (as that famous actor says) - under the elemental calculation method this allows a lot more glazing than you might normally calculate. Here's how - the key is reading regulation J2.5 (especially part (b) and (c)) as following extract shows:-

CALCULATION OF AREAS
J2.5 In calculating areas:

a. all areas are to be measured in m 2 unless otherwise stated; and
b. the area of a floor, wall or roof is to be measured between finished internal faces of the external building elements of the building, including any projecting bays and, in the case of a roof, in the plane of the insulation; and
c. floor areas are to include stair wells within the heated envelope and non-useable space such as service ducts; and
d. in calculating the maximum permitted area of glazing for an extension to a dwelling, the floor area of the whole dwellingmay be used; and
e. the area of an opening is to be measured internally from reveal to reveal and from head to sill.

In an attic, the wallhead and insulated roof normally meet at the attic floor level and under (c) above the non-useable attic perimeter spaces (storage or non-useable) can be included within the floor area as they are within the heated envelope created by the insulation between the rafters coming down to wallhead level. Under part (a) and (b) above, the ground and first floor areas include the partitions, stairwells and other non-useable areas as service ducts, alcove cupboards, etc - as long as they are within the heated envelope and within the internal face of the external building elements and in the case of a roof, in the plane of the insulation. B/Control accept this.

Posted: Mon - January 31, 2005 at 11:16 AM          

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