Hip roof – Rafters of the roof surface at the edge rafters
Rafters of the roof surface at the edge rafters
The rafter length is the distance between the edge rafter and the cap beam.
This is clearly explained in the drawings.
The rafter spacing is the same as that of the main rafters: 40 cm or 60 cm. It means, that the course of the primary rafter will be either 40 cm, or 60 cm. The easiest way to find the length of the first rafter is to use the third line of the rafter table
, where there are differences in the rafter length for the spacing 40 cm. Take a look at the column, which is the height at each 30 cm of the length of the run. The number at the intersection will give the length of the first shortest rafter. The second rafter will be twice, and the third – three times longer than the first, etc..
Example:
Find the first, second and third rafter for the roof with the following data:
roof slope (i) – 1/4 (14° or 25% or 0,25),
roof run (a)= 160 cm,
roof span (2 x a) = 2 x 160 cm = 320 cm,
rafter spacing = 40 cm,
number 40 cm of sections of the length of the run = a / 40 cm = 160 cm / 40 cm = 4 episodes,
number 30 cm of sections of the length of the run = a / 30 cm = 160 cm / 30 cm = 5,33 episode
Solution
– the drawing should be considered;
– height at each 40 cm, the length of the main rafter's run is – roof pitch x roof span : number 40 cm of the length of the run = 1/4 x 320 : 4 = 320 cm : 4 = 80 cm : 4 = 20 cm;
– there is a column on the upper scale of the drawing, in which the height of the run is 20 cm and where will we find the other two values we are looking for:
– main rafter length for each 30 cm is 36,1 cm,
– in the series of the difference in rafter length at the spacing of co 40 cm – the required length of the first rafter = 48,1 cm;
– second rafter length = first rafter length x 2 = 48,1 cm x 2 = 96,2 cm;
– length of the third rafter = length of the first rafter x 3 = 48,1 cm x 3 = 144,3 cm;
– the length of the fourth rafter, which is also the length of the main rafter of the roof = length of the first rafter x 4 = 48,1 cm x 4 = 192,4 cm. The length of the fourth rafter can be calculated from the length of the main rafter each 30 cm of the length of the run multiplied by the number 30 cm of the length of the run = 36,1 cm x 5,33 episode = 192,4 cm.
