Terminology

Chapter 1 has given the history and derivation of some of the names given to roof structure members. The list below, although not exhaustive, describes the terms used on domestic roof structures.

The reader is referred to Fig. 2.15.

A - Wall plate - sawn timber, usually 50 x 100 or 50 x 75 mm bedded in mortar on top of the inner skin of a cavity wall. Straps must be used to secure the wall plate to the structure below (see Chapter 8, Figs 8.8 and 8.9).

B - Common rafter - sawn timber placed from wall plate to ridge to carry the loads from tiles, snow and wind. Long rafters may need intermediate supports from purlins.

B1 - Jack rafters - sawn timber rafter cut between either a hip or valley rafter (see Chapter 3, Fig. 3.6).

C - Ceiling joist - sawn timber connecting the feet of the common rafter at plate level. The ceiling joist can also be slightly raised above the level of the wall plate, but this would technically then be termed a collar. The ceiling joist supports the weight of the ceiling finish (normally plasterboard) and insulation. It may in addition have to carry loft walkways and water storage tanks, in which case it must be specifically designed to do so.

D - Ridge - a term used to describe the uppermost part of the roof. The term is also used to describe the sawn timber member which connects the upper parts of the common rafters.

E - Fascia - usually a planed timber member used to close off the ends of the rafters, to support the soffit M, to support the last row of tiles at the eaves N and to carry the rainwater gutter support brackets.

F - Hip end - whereas a gable end O is a vertical closing of the roof, the hip is inclined at an angle usually to match the main roof.

F1 - Hip rafter - sawn timber member at the external intersection of the roof slope (similar to a roof sloping ridge), used to support the jack rafters forming the hip (see Chapter 3, Fig. 3.6).

G - Valley - term used to describe the intersection of two roofs creating a 'valley' on either side. The illustration has only one main valley, the building being L-shaped on plan. A further small valley is illustrated on the dormer roof with its junction to the main roof. Valley jack rafters are fitted either side of a valley rafter, as illustrated in Chapter 3, Fig. 3.10.

H - Dormer - the structure used to form a vertical window within a roof slope (see Chapter 3, Fig. 3.17 for other shapes of dormer). This structure gives increased floor area of full ceiling height within an attic roof construction, and is usually fitted with a window, hence the term 'dormer window'.

I - Barge board - the piece of planed timber is in fact a sloping fascia. It is often fitted to gable ends, as illustrated.

J - Dormer cheek - the term used to describe the triangular infill wall area between dormer roof, main roof and the dormer front (see Chapter 3, Fig. 3.18 for the construction).

Fig. 2.15 Roofing terminology (see text for key).

Fig. 2.15 Roofing terminology (see text for key).

K - Roof window - sometimes termed roof light, the former being able to be opened for ventilation hence becoming a true window, the latter being fixed simply allowing additional light into the attic roof space.

L - Gablet - a small gable over a hip end. It is used as an architectural feature.

M - Soffit - the ply or other sheet material panel used to close off the space between the back of the fascia and the wall of the building.

N - Eaves - term used to describe the extreme lower end of the roof, i.e. the area around the fascia and soffit.

O - Gable - triangular area of wall used at the end of a roof to close off beneath the roof slopes. This is usually a continuation of the wall construction below.

P - Purlin - large section sawn solid structural timber, or fabricated beam, used to carry the common rafters on larger roof slopes where the commons are not strong enough or cannot be obtained in one single length, to span between the wall plate and the ridge (see Figs 3.1, 3.4 and 3.5).

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