Roof framing systems

Question 1

How is the span measured for rafters on a shed or lean to roof?

Answer 1

Is measured horizontally from the inner face of the tall wall to the outer face of the short wall

Question 2

A roof slope is always expressed as a ratio of ____ to ____?

Answer 2

Rise to Run

Question 3

Name the three sides of a roof slope triangle

Answer 3

Unit run
Unit rise
Unit line length

Question 4

How could the run of a rafter be defined?

Answer 4

As the horizontal distance from the centre of the ridge to the plumb cut at the birdsmouth

Question 5

How is the projection of a rafter measured?

Answer 5

Is measured horizontally from the face of the wall to the outer edge of the fascia

Question 6

Gable roof framing calculation are based on two mathematical concepts, which are called the _____ and _______?

Answer 6

Pythagorean theorem

Ratio and proportion

Question 7

What does the slope gain factor represent?

Answer 7

The length gain along the slope for each unit of run

Question 8

What is the minimum length of bearing for a birdsmouth seat cut?

Answer 8

38mm (1 1/2”)

Question 9

The calculated line length of the centre gable stud is equal to the ______?

Answer 9

Rafter Rise

Question 10

What are the two common types of gable rafters?

Answer 10

Dropped

Notched

Question 11

Identify three ways that the span of a rafter can be reduced?

Answer 11

Collar ties
Using struts
Using dwarf (Knee) walls

Question 12

What must be added to the calculated length of a collar tie to find its actual length?

Answer 12

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

Question 13

On a hip roof, what are the two extra common rafters called?

Answer 13

End common rafters

Pin rafters

Question 14

The hip rafter and the common rafter have the same _____?

Answer 14

Rise

Question 15

What is the shortening of a hip rafter at the upper end?

Answer 15

Half the diagonal thickness of the common rafter

Question 16

What is the shortening of a hip rafter at the lower end?

Answer 16

Full diagonal thickness of the fascia

Question 17

When first laying out the seat cut for a hip rafter birdsmouth, what determines the wood above plate measurement?

Answer 17

The wood above plate should be identical to the common rafter

Question 18

What must happen to the hip rafter so that it does not interfere with the roof sheathing?

Answer 18

Dropped or backed

Question 19

What type of cut is required for the upper end of a hip jack rafter?

Answer 19

Single cheek cut

Question 20

How is the ridge line length determined for a hip roof?

Answer 20

Building length - Building width

Question 21

What must be done to the line length of the ridge to find the actual length?

Answer 21

Add half the thickness of a common rafter to each end

Question 22

Name the two basic types of intersecting roofs?

Answer 22

Equal span

Unequal span

Question 23

Identify the types of valley rafters needed to frame an unequal span intersecting roof?

Answer 23

Supporting and supported Valley rafters

Question 24

What types of cuts are made at the top of the supported valley rafter?

Answer 24

Square and Plumb cut

Question 25

Valley jack rafters extend from the _____ to the ________?

Answer 25

Ridge to the valley rafters

Question 26

What information is needed to calculate the common difference for valley jack rafters?

Answer 26

Slope gain factor of valley jacks and the on centre spacing of the rafters

Question 27

Valley cripple jack rafters extend from the _______ to the ______?

Answer 27

Supporting valley rafter to the supported valley rafter