Roofs are one of a building’s primary elements and play a major part in
giving a building its character.
There are several different types of roof in this one building.
Roofs
Subtitle
A roof must have the
following qualities:
• A roof must be weather resistant to rain, snow, wind and
sun.
• The durability of a roof should be equal to or in excess of
those materials used in the remainder of the building.
• A roof should have good thermal insulation properties.
• A roof should require a minimum of maintenance.
• A roof should be constructed in such a way as to retain
structural stability when dead and imposed loads are
applied to it ( dead loads is the weight of materials used to
make the roof, imposed loads are loads created by wind,
snow, etc.
Roof Elements
When designing a roof the following points should be considered in
relation to its final appearance.
Pitch
The steeper the pitch the greater the roof area visible. This will result in a
larger roof space, you can also use smaller cladding units such as plain
tiles and slates. Pitched roofs are the most suitable in countries where
there is a high rain fall.
Coverings
Materials used for roof coverings should harmonise with the local
surroundings. These materials
should be fit for purpose in their
ability to keep out the elements,
thermal insulation, durability and
appearance.
Concrete interlocking
roof tiles
Roofs
Valley Rafter
Ridge
Hipped End
Verge
Jack Rafters
Common
Rafters
Hip
Eaves
Gable End
Lean-to
Roof
Flat Roof
Terminology
Wall plate
Usually 100 x 50 mm softwood timbers are fixed to the top of
load bearing walls to distribute loads and provide fixings for
roof timbers.
Ceiling joist
These are timbers which provide a support for fixing ceiling
finishes and act as a collar to prevent rafters spreading.
Common rafters
These are inclined timbers fixed between wall plate and ridge
which transmit live and dead loads to wall plate.
Ridge
The ridge is a horizontal board set on edge to which the
rafters are attached (not required on trussed rafters).
Terminology
Hip Rafter
A hip rafter is a rafter running from the wall plate to the ridge
which forms the external angle of the sloping side of a roof.
Purlin
This is a horizontal roof member supporting the rafters and
usually at right angles to these. This enables small section
timbers to be used for the rafters.
Hangers
These are timbers hanging from the purlins to the ceiling joist
to give additional support to binders.
Fascia
A board fixed vertically to rafter ends, which provide an additional fixing
for gutters.
Terminology
Soffit
A horizontal board fixed to the underside of the rafter outside
the building.
Bargeboard
Verge or gable board.
Eaves
The lower part of the roof, which usually includes the end of
the rafter, ceiling joist, soffit, fascia and gutter.
Dormer
A vertical window coming through a sloping roof.
Valley
This is the name for the intersection between two sloping surfaces,
forming an internal angle ( the opposite to a hip).
Pitched roof
If the roof space is or may
be intended to be used in
the future, the structure
should be designed
accordingly.
Roof with a gable end
Hipped Roof
Pitched roof with dormer
windows
A pitched roof with dormer
windows.
When a steep pitched roof is used in
domestic construction dormer windows
can be used to create additional head
room in the roof space. This allows the
roof space to be utilised for habitable
rooms.
Timber to support the dormer
window
Lay
board
Common
Rafter
Roof parts
Ridge
Dormer window
Barge board
Gutter
chimney
Eaves detail
Door
Down pipe
Traditional cut Roof
Eaves detail pitched roof
Traditional cut roof
structure
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A traditional cut roof was the first development to create
pitched roofs as we know them today.
This type of roof structure is still widely used for individual
dwellings or for roofs of a complicated shape.
The timbers rafters are cut individually and nailed into
position.
A purlin is often placed half way up the length of the rafter
to help support the roof and allow smaller sections of
timber to be used.
Common rafters
Steel purlin
Pad-stone built into the
wall to help distribute the
load of the roof over a
larger section of wall.
Trussed rafters
A high percentage of roofs designed now
are constructed using prefabricated
trussed rafters. They have been developed
since the mid 1960’s.
The principal disadvantage is that the roof
space is occupied by a large number of
timber sections.
The following are the main reasons for developing truss rafters:
1.Smaller and light sections of timber can be used.
2. Speed of erection.
3. Semi-skilled labour can be used.
4. Eliminates the need for purlins and ridge boards.
5. Loadbearing partitions are eliminated, allowing greater freedom of
internal room arrangements.
Standard trussed rafter
Roof coverings
A wide variety of different types of roof
coverings are available including:
natural slates
man made slates
concrete tiles
Profiled metal sheet
Roof tiles
Profiled galvanized
metal sheet