Tuesday, October 17, 2017

Roof Shapes and Terminology

Roof Shapes and Terminology

Fig: 1.1 Duo pitched roof. This is the most common roof shape with equal pitches on either
side, i.e. angle A equals angle B.

Fig: 1.2 Asymmetric roof; angle C is not equal to angle D.
Fig: 1.3 Mono pitched roof; angle E equals 90°.

Fig: 1.4 Truncated duo pitched roof; angle F equals angle G. This truss form is often introduced into domestic housing in conjunction with the conventional duo pitched roof to form
an interesting roof line.
Fig: 1.5 Fink truss shape. This is the most common trussed rafter form used on spans of
up to 8 to 9 m.
Fig: 1.6 Fan truss shape. This is used on larger spans and is a common trussed rafter
Fig: 1.7 Double ‘W’ shape. This is used on spans above 14 m and is not often used on
Fig: 1.8 Howe four bay truss. This is often used in trussed rafters in girder form. This could
also be used in six bay confi guration.
Fig: 1.9 Pratt four bay truss. This is occasionally used in trussed rafters in girder form.

Fig: 1.10 Mono pitch truss two bay. This is a common trussed rafter form often used in
conjunction with trusses in Figs: 1.5 to 1.7.
Fig: 1.11 Attic or ‘room-in-roof’ truss shape. This is a popular shape in trussed rafters: there
are no minimum heights set for h and w, but for h a 2.3m minimum is recommended, with
1.2–1.5 m being the practical minimum height for w.

Fig: 1.12 Mono pitch truss three bay. This is similar to the mono pitch truss two bay (Fig: 1.10), but is suitable for larger spans.
Fig: 1.13 Scissor truss. This is a possible trussed rafter shape occasionally used to create
a feature ceiling in the lounge of a house.
Fig: 1.14 Raised tie truss also used to create feature ceilings. Often Fink-based with rafters
extended down to the wall plate.


Roofing terminology-roofconstruction-terminology.blogspot.com
Fig: 2.0 Roofing terminology

The reader is referred to Fig: 2.0

A – Wall plate – sawn timber, usually 50 × 100 or 50 × 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.

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

B1 – Jack rafters – sawn timber rafter cut between either a hip or valley rafter.

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.

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.

H – Dormer – the structure used to form a vertical window within a roof slope. 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.

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

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.

Roof Shapes and Terminology

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