What is a gable?
The exposed triangular wall section of a double pitched roof (coupe or closed)
What is a verge?
The end section or edge of a roof structure which generally forms an overhang
What is an eave?
The lowest point of a roof structre which is normally horizontal
What is a ridge board?
This spans horizontall and enables the connection of two inclining symetrical rafters
What is a purlin?
Horizontal timber member used to support rafters across spans which are usually greater than 3.5m
What is a wall plate?
Provides fixing to rafters i.e bird mouth, fixing plate or nails
What is a ridge collar
Horizontal timber connecting 2 inclining rafters
What is a strut?
Supports purlin
What is a binder and hanger?
Binders are horizontal supports which support ceiling joists whilst hangers are vertical
What is diagnoal bracing?
Used to increase rigidity amongst trusses
What is a jack rafter?
The shorter rafter used in hip roof construction which fixed to the hip rafter
Evolution of roof coverings?
Used to protect occupants of weather
Evolution influenced by social, economic and enviormental factors and technology
Linkage between health and home so Building Act 1984 sets out minimum requirements regarding fire, insulation and moisture
Need to be durable, stable and light
Factors to consider include:
Roof void use, height, wind, budget, coverings
What are the key considerations to roof design regarding pitch?
Pitch is determined by structual needs and aethsetics generally
Higher pitch = more materials needed including timber and coverings
Greater depth = more stability
Greater spans = more sagging
When were timber standard sizes introduced?
1960s
Explain the mono pitch roof?
Common in extentions to victorian properties
Pitch is 40 degrees
Span between 2 solid walls around 3.5m with one wall taller than other
A wall plate will be fixed onto the shorter wall and will extend diagnoally to the taller wall and would be fixed into this, a second timber will extend hortizontall and be fixed to a timber which is fixed to the wall, at multiple centres
What is a gabel roof / double ptiched roof?
Two types include couple and closed
Both have a ridge board with 2 inclining rafters which extend down and site on wall plates either side
Usually covers spans of 3-4m and is 40 degrees
Concept of trangulation but still tendency for roof spread, therefore the closed type includes horizontal binders between the 2 lower ends of the rafters
Vunrabel to wind and roof spread but good for drainage
What is a Collar Roof?
Same as above but the horizontal binder is placed about 1/3 higher
What are the general eave details?
Rafters can extend past the supporting wall forming an overhang eave, this protects the building and has a soffit normally installed
Rafters can stop at wall line, a fascia can be installed directly over
Cavity is normally close off for fire safety and moisture control, but can be open with correct insulation
What are the purpose of purlins?
They are horizontal timber members which provide support to rafters which typically span greater than 3.5m
They extend from gable to gable
To further support purlins instead of using binders or hangers, struts can be used which sit on internal load bearing walls
What are trusses?
Can support purlins
Triangulation of timber memers to form a uniform structure which is capable of directing load transfer down the external load bearing wall and minimising bulging
pre-fab trusses were developed in 1960s
2 Key types include king and queens
King = 2 inclining rafters extend from top of king post down, form centre of either side of king post, 2 struts extend diagnonally connecting to the rafters
Queen = 2 vertial timbers extending up, and across this is a straining beam, to the triangle ends, there are two tie beams
What is a hipped roof?
No gable, all siding slops
Use of purlins and hip rafters
Jack rafters fixed to hip rafters
What is a mansard roof?
Roof with 2 different pitches, at meeting point there is a purlin, otherwise similar rafter arrangment as hipped roof
What are modern truses and how are they selected?
W shaped and fixed with nail plate
Come in many arrangement which are determine by shape, span and roof pitch
Load bearing of covering
Location of load bearing walls
Building height
Equipment
How are modern trusses fixed?
Strapped to wall plate or use of trus nail clips
Binders can be used to help space the trusses
Diagonal bracing used for increase in sturdidity
