Roof Terms Glossary
Birdsmouth - a small 90 Degree check out of the Rafters where the Rafter sits on top of the frame, the Birdsmouth allows the Rafter to have a sound "Bearing" on the Top-plate of the frame
Half Span - is half of the Span and for a standard pitched roof will be directly under the centre of the Ridge
Pitch - The term used to describe the angle of the roof, usually expressed in "Degree's" i.e. 30 Degree Pitch roof
Pitch Ratio - another way of expressing the angle of the roof, an example would be expressed as 1.000 : 1.500 and means for ever 1 metre the roof rises vertically the roof half span will be 1.5 metres
Rafter Foot or Feet - this is where the Rafter sits on top of the wall frame, it is the location of the "Birdsmouth" this is where the Rafter is fixed to the Top-plate of the frame, and to the Ceiling Joists if the roof is a "coupled roof"
Rafter "Left On" dimension - this is the distance measured vertically along the "Plumb" Line at the "Birdsmouth",and from the "Level" Line of the "Birdsmouth" to the point where the plumb line of the "Birdsmouth" intersects the top of the Rafter
Rise per metre Run - is another way of describing the angle of the roof, it is usually indicated as "Rise/m Run", an example would be expressed as 0.500m Rise/m Run meaning for every 1 metre of Run the roof Rises 0.500 metre's
Run - is the way of expressing horizontal distance in relation to roof members, it is always a measurement that is measured "Square" off the external frame no matter what roof member it relates too.
Span - is the overall width of the frame that the roof relates to, and is measured horizontally across the building from outside of frame to outside of frame
Note: the definitions for all roof members can be found in the appropriate Australian Standard, it is highly recommended that if you are considering constructing a Pitched Roof that you obtain a copy for reference.
Half Span - is half of the Span and for a standard pitched roof will be directly under the centre of the Ridge
Pitch - The term used to describe the angle of the roof, usually expressed in "Degree's" i.e. 30 Degree Pitch roof
Pitch Ratio - another way of expressing the angle of the roof, an example would be expressed as 1.000 : 1.500 and means for ever 1 metre the roof rises vertically the roof half span will be 1.5 metres
Rafter Foot or Feet - this is where the Rafter sits on top of the wall frame, it is the location of the "Birdsmouth" this is where the Rafter is fixed to the Top-plate of the frame, and to the Ceiling Joists if the roof is a "coupled roof"
Rafter "Left On" dimension - this is the distance measured vertically along the "Plumb" Line at the "Birdsmouth",and from the "Level" Line of the "Birdsmouth" to the point where the plumb line of the "Birdsmouth" intersects the top of the Rafter
Rise per metre Run - is another way of describing the angle of the roof, it is usually indicated as "Rise/m Run", an example would be expressed as 0.500m Rise/m Run meaning for every 1 metre of Run the roof Rises 0.500 metre's
Run - is the way of expressing horizontal distance in relation to roof members, it is always a measurement that is measured "Square" off the external frame no matter what roof member it relates too.
Span - is the overall width of the frame that the roof relates to, and is measured horizontally across the building from outside of frame to outside of frame
Note: the definitions for all roof members can be found in the appropriate Australian Standard, it is highly recommended that if you are considering constructing a Pitched Roof that you obtain a copy for reference.
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