Roof framing systems Flashcards
How is the span measured for rafters on a shed or lean to roof?
Is measured horizontally from the inner face of the tall wall to the outer face of the short wall
A roof slope is always expressed as a ratio of ____ to ____?
Rise to Run
Name the three sides of a roof slope triangle
Unit run
Unit rise
Unit line length
How could the run of a rafter be defined?
As the horizontal distance from the centre of the ridge to the plumb cut at the birdsmouth
How is the projection of a rafter measured?
Is measured horizontally from the face of the wall to the outer edge of the fascia
Gable roof framing calculation are based on two mathematical concepts, which are called the _____ and _______?
Pythagorean theorem
Ratio and proportion
What does the slope gain factor represent?
The length gain along the slope for each unit of run
What is the minimum length of bearing for a birdsmouth seat cut?
38mm (1 1/2”)
The calculated line length of the centre gable stud is equal to the ______?
Rafter Rise
What are the two common types of gable rafters?
Dropped
Notched
Identify three ways that the span of a rafter can be reduced?
Collar ties
Using struts
Using dwarf (Knee) walls
What must be added to the calculated length of a collar tie to find its actual length?
The horizontal distances beyond the birdsmouth, less 10mm (3/8”) at each end, must be added to the line length at each end of the collar tie
On a hip roof, what are the two extra common rafters called?
End common rafters
Pin rafters
The hip rafter and the common rafter have the same _____?
Rise
What is the shortening of a hip rafter at the upper end?
Half the diagonal thickness of the common rafter
What is the shortening of a hip rafter at the lower end?
Full diagonal thickness of the fascia
When first laying out the seat cut for a hip rafter birdsmouth, what determines the wood above plate measurement?
The wood above plate should be identical to the common rafter
What must happen to the hip rafter so that it does not interfere with the roof sheathing?
Dropped or backed
What type of cut is required for the upper end of a hip jack rafter?
Single cheek cut
How is the ridge line length determined for a hip roof?
Building length - Building width
What must be done to the line length of the ridge to find the actual length?
Add half the thickness of a common rafter to each end
Name the two basic types of intersecting roofs?
Equal span
Unequal span
Identify the types of valley rafters needed to frame an unequal span intersecting roof?
Supporting and supported Valley rafters
What types of cuts are made at the top of the supported valley rafter?
Square and Plumb cut
Valley jack rafters extend from the _____ to the ________?
Ridge to the valley rafters
What information is needed to calculate the common difference for valley jack rafters?
Slope gain factor of valley jacks and the on centre spacing of the rafters
Valley cripple jack rafters extend from the _______ to the ______?
Supporting valley rafter to the supported valley rafter
