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Topic 18 – Framing Intersecting Roofs in Metric

As with using metric in gable roofs and hip roofs, all processes are the same for using metric in intersecting roofs. Some key points to remember:

– The unit run of common rafters and all roof members which run perpendicular to the ridge or exterior walls is 1000 mm (one meter = 1 unit of run)
– The unit run of hip and valley jacks is equal to 1414 mm, which will affect how we calculate the ULL of these members

Review Questions

  1. The deduction to make at the tail of a valley rafter for a 38 mm fascia is _____.
a) ½ the diagonal of the fascia deducted at 90° the plumb cut
b) Total diagonal thickness of the valley rafter deducted at 90° to the plumb cut
c) Total 90° thickness of the fascia deducted at 90° to the plumb cut
d) ½ the 90° thickness of the fascia deducted at 90° to the plumb cut
  1. The deduction to make at the bottom of a valley jack rafter for a 38 mm valley rafter is _____.
a) ½ the diagonal of the valley rafter deducted at 90° the plumb cut
b) Total diagonal thickness of the valley rafter deducted at 90° to the plumb cut
c) Total 90° thickness of the valley rafter deducted at 90° to the plumb cut
d) ½ the 90° thickness of the valley rafter deducted at 90° to the plumb cut
  1. Using the following information and the roof shown in figure seven, find the following below:
  • Rafter spacing 600 mm O.C.
  • Overhang 600 mm
  • Roof slope 400/1000
  • All framing material 38 mm thick
  • Double cheek cut

image

a) Theory length of ridge “A”
b) Actual length of ridge “A”
c) Theory length of ridge “B”
d) Actual length of ridge “B”
e) Theory length of ridge “C”
f) Actual length of ridge “C”
  1. Using figure 7 on the previous page, fill in the following table.

Rafter #

Name of Rafter

Total Run

Units of Run

Unit Line Length

Line Length

Length of Rafter Tail

Deduction at Top (mm)

Deduction at Bottom (mm)

1

2

3

4

5

6

7

8

9

10

11

12

13

Answers:

  1. B
  2. A
    1. 6000 mm
    2. 6038 mm
    3. 1800 mm
    4. 1819 mm
    5. 1800 mm
    6. 1819 mm
Rafter # Name of Rafter Total Run Units of Run Unit Line Length Line Length Length of Rafter Tail Deduction at Top (mm) Deduction at Bottom (mm)
1 Hip Rafter 1800 1.8 1470 2646 882 27 54
2 Hip Jack Rafter 1200 1.2 1077 1292.4 646.2 27 38
3 Valley Cripple Jack 1200 1.2 1077 1292.4   27 27
4 Supported Valley 1200 1.2 1470 1764 882 19 54
5 Hip-Valley Cripple Jack 600 0.6 1077 646.2   27 27
6 Hip Rafter 1200 1.2 1470 1764 882 27 54
7 Valley Jack Rafter 1800 1.8 1077 1938.5   19 27
8 Valley Rafter 1800 1.8 1470 2646 882 27 54
9 Valley Jack Rafter 1200 1.2 1077 1292.4   19 27
10 Common Rafter 1800 1.8 1077 1938.6 646.2 19 38
11 Hip Jack Rafter 1200 1.2 1077 1292.4 646.2 27 38
12 Common Rafter 1800 1.8 1077 1938.6 646.2 19 38
13 Supporting Valley 1800 1.8 1470 2646 882 27 54

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Carpentry Refresher Program Manual Copyright © by Saskatchewan Indian Institute of Technologies-Trades and Industrial is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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