Roofs

Subtitle

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.

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.PitchThe 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.CoveringsMaterials 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

Verge

Ridge Valley Rafter

Hipped End

Jack Rafters

Common Rafters

Gable EndLean-to

RoofFlat Roof

Hip

Eaves

Terminology

Wall plateUsually 100 x 50 mm softwood timbers are fixed to the top ofload bearing walls to distribute loads and provide fixings forroof timbers.Ceiling joistThese are timbers which provide a support for fixing ceilingfinishes and act as a collar to prevent rafters spreading.Common raftersThese are inclined timbers fixed between wall plate and ridgewhich transmit live and dead loads to wall plate.RidgeThe ridge is a horizontal board set on edge to which therafters 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

Roof with a gable end

If the roof space is or may be intended to be used in the future, the structure should be designed accordingly.

Hipped Roof

Pitched roof with dormer windowsA 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

Common Rafter

Lay board

Roof parts

Ridge Dormer window Barge board

Eaves detail DoorDown pipe

Gutter

chimney

Traditional cut Roof

Eaves detail pitched roof

Traditional cut roof structure• 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

Pad-stone built into the wall to help distribute the load of the roof over a larger section of wall.

Steel purlin

Trussed raftersA 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

Profiled galvanized metal sheet

Roof tiles

A wide variety of different types of roof coverings are available including:

natural slates

man made slates

concrete tiles

Profiled metal sheet