Trimming Small Openings

The openings dealt with here are those required for small flues and loft access hatches, as well as the smaller openings for roof windows. Large openings have been detailed in the relevant preceding chapters.

In designing the roof, careful consideration should be given to the location of any flue or chimney passing through the roof void, and its likely effect on the structure. Similarly the loft hatch should be considered, particularly in relation to the spacing of trussed rafters. Roof windows for fenestration reasons may have to take priority over the structure, but again with consideration, the readily available 550 mm wide roof windows should be used if possible to fit neatly between trussed rafters, thus achieving ultimate economy in the structure by avoiding trimmed openings.

Where brick flues pass through roofs, the Building Regulations stipulate that 40 mm minimum must be allowed between the structure and the brickwork face. Floor boards, skirtings, tile battens, etc., may of course touch the brickwork but not the actual structure itself. Please refer to the relevant Building Regulation clause for precise details with regard to different classes of appliance and flue sizes.

The Building Regulations do not stipulate minimum size for loft hatches, but the NHBC do in their Registered House Builder's Handbook, Vol. 2, Chapter 7.2, clause D14. This requires a minimum size of 520 mm clear in any direction. The clause also states that the opening should not be directly over stairs or in any other hazardous location, such as close to eaves where headroom in the roof space is limited.

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