A. Shingled Roofs Not Plastered.*

Total load, 48 pounds per square foot.

Size of Joists.

Dist. on Centre.

Hemlock.

White Pine.

Spruce or

Norway

Pine.

Oregon or Texas Pine.

Georgia Pine.

Ins.

Ft.

Ins.

Ft.

Ins.

Ft.

Ins.

Ft.

Ins

Ft.

Ins.

2

X

4

16

7

4

7

9

8

4

9

6

10

10

2

X

4

20

6

7

6

10

7

6

8

6

8

10

2

X

6

16

11

1

11

7

12

6

14

2

15

0

2

X

6

20

9

11

10

4

11

2

12

8

13

4

3

X

6

16

13

7

14

2

15

3

17

5

18

3

3

X

6

20

12

2

12

8

13

8

15

7

15

4

2

X

8

16

14

9

15

6

16

8

18

11

20

0

2

X

8

20

13

3

13

10

14

11

16

11

17

10

2

X

8

24

12

1

12

7

13

7

15

6

16

3

2

X

10

16

18

6

19

3

20

10

23

8

25

0

2

X

10

20

16

7

17

3

18

8

21

2

22

3

2

X

10

24

15

1

15

9

17

0

19

3

20

4

B. Slate Roofs Not Plastered, or Shingle Roofs Plastered.* Total load, 57 pounds per square foot.

Size of Joists.

Dist, on Centres.

Hemlock.

White Pine.

Spruce.

Oregon Pine.

Georgia Pine.

Ins.

Ft.

Ins.

Ft.

Ins.

Ft.

Ins.

Ft.

Ins.

Ft.

Ins.

2

X

4

16

6

9

7

I

7

7

8

8

9

2

2

X

4

20

6

0

6

4

6

9

7

9

8

2

2

X

6

16

10

2

10

7

11

6

13

0

13

8

2

X

6

20

9

1

9

6

10

2

11

7

12

3

3

X

6

16

12

6

13

0

14

1

15

11

16

9

3

X

6

20

11

1

11

8

12

7

14

3

15

0

2

X

8

16

13

7

14

2

15

3

17

4

18

3

2

X

8

20

12

2

12

8

13

8

15

6

16

4

2

X

8

24

11

1

11

7

12

6

14

2

14

11

3

X

8

16

16

7

17

4

18

9

21

3

22

5

3

X

8

20

14

10

15

6

16

9

19

0

20

1

3

X

8

24

13

7

14

2

15

3

17

4

18

4

2

X

10

16

17

0

17

8

19

2

21

7

22

10

2

X

10

20

15

2

15

10

17

1

19

4

20

6

2

X

10

24

13

10

14

6

15

7

17

8

18

8

* These tables allow for a snowfall of 2 feet. In the Southern States the spans in section A will be safe for slate or gravel roofs, if the joists are full to dimensions.

C. Slate Roofs Plastered, or Gravel Roofs Not Plastered.* Total load, 66 pounds per square foot.

Size of Joists

Dist. on Centres

Hemlock.

White Pine.

Spruce or

Norway

Pine.

Oregon or Texas Pine.

Georgia Pine.

Ins.

Ft.

Ins.

Ft.

Ins.

Ft.

Ins

Ft.

Ins.

Ft.

Ins.

2

X

6

l6

9

5

9

10

10

8

12

1

12

9

2

X

6

20

8

6

8

10

9

6

10

9

11

5

3

X

6

16

11

7

12

1

13

1

14

10

15

7

3

X

6

20

10

4

10

10

11

8

13

3

14

0

2

X

8

16

12

7

13

2

14

2

16

2

17

0

2

X

8

20

11

3

11

9

12

9

14

5

15

2

2

X

8

24

10

3

10

9

11

7

13

2

13

10

3

X

8

16

15

5

16

1

17

5

19

9

20

10

3

X

8

20

13

9

14

5

15

3

17

8

18

8

3

X

8

24

12

7

13

2

14

2

16

2

17

0

2

X

10

16

15

9

16

6

17

9

20

2

21

3

2

X

10

20

14

1

14

8

15

11

18

0

19

0

2

X

10

24

12

10

13

5

14

6

16

6

17

5

2

X

12

16

18

10

19

9

21

4

24

2

25

6

2

X

12

20

16

10

17

8

19

1

21

8

22

10

2

X

12

24

15

5

16

1

17

5

19

9

20

10

* These tables are intended for climates where a snowfall of 2 feet may be expected. In the Southern States, where there is no snow to speak of, the spans in Section A will be safe for slate or gravel roofs if the joists are sawn full to dimensions.

Table VI. - Weight Of Rafters Per Square Foot

Size of Rafters. Inches.

Spruce, Hemlock, White Pine, Spacing in Inches. Centre to Centre.

Hard Pine, Spacing in Inches, Centre to Centre.

16

20

24

16

20

24

lbs.

lbs.

lbs.

lbs.

lbs.

lbs.

2

X

4

1 1/2

1.2

1

2

1.6

1 1/3

2

X

6

2 1/4

1.8

1 1/2

3

2.4

2

2

X

7

2 5/8

2.1

1 3/4

3 1/2

2.8

2 1/3

2

X

8

3

2.4

2

4

3.2

2 2/3

2

X

10

3 3/4

3

2 1/2

5

4

3 1/3

Wooden purlins will weigh about 2 lbs. per square foot of roof surface when the span is between 12 and 16 ft.

For steel roofs the size and weight of the purlins and rafters should be computed for each particular case.

For a rough approximation the weight of steel trusses, purlins, and bracing in a roof covered with corrugated iron with no ceiling will run from 4 to 6 lbs. per square foot of horizontal surface covered. The steel work for slate roofs with suspended ceilings below will run about 7 1/2 lbs. per square foot when the span does not exceed 50 ft.

Steel roofs supported by arched trusses will weigh from 8 to 12 lbs. per square foot of roof surface. Examples of the actual weight of several steel roofs are given on pages 186 and 189.