In covering iron roofs the slates may be laid on boarding or battens, or upon angle-iron laths filled in with wood and fixed at the proper gauge, in exactly the same way in which they are laid on wooden roofs (see p. 194).

When it is wished to make the roof fireproof the woodwork may be entirely dispensed with by laying the slates directly upon angle-iron laths (as in Fig. 388), to which they are secured by copper nails or wire bent round the laths, by copper or zinc clips, or by leaden pegs.

Shouldering

In exposed situations, especially when the slates are rough, their heads are imbedded for a width of about two inches in hair mortar, mixed with ashes (so as to resemble the slates in colour). This is termed "shouldering." It keeps the slates down tight at the tails, and effectually prevents the wind from penetrating.

Shouldering 100348

Fig.455

Rendering

Slates laid on battens are frequently rendered all over the under side with lime and hair. This may be done even when the roof is boarded, in order to give the slates a firm bed and to enable them to withstand traffic over them.

Torching

Sometimes the slates are laid dry, and the joints between the tails of one course and the heads of another are afterwards pointed from the inside with hair mortar; this, however, does not last long under changes of temperature.

Felt

The boarding is frequently covered with felt, which delays the passage of heat and cold, and keeps the roof dry in case of defects in the slating. It is a good plan to fix battens upon the felt, to which the slates may be better secured, so as to have a circulation of air just above the felt, which preserves it from decay.

Table showing the Sizes and Weights of Slates and the numbers required for Roofing.

Name of Slate,1

Size.

Gauge for 3-inch lap nailed in centre.

Gauge for

3-inch lap nailed 1 inch from head.

Number of squares covered by 1200.

Weight of 1200.

1st quality.3

Number required to cover one square.

Weight per square.

1st quality.3

Nails required per square.

Iron.

Copper.

Inches.

Inches.

Inches.

Cwts.

Cwts.

Number.

lbs.

Singles 2

12

by

8

4 1/2

4

2.8

17 1/2

430

6 1/4

860

5

Doubles

13

by

6

5

4 1/2

2.5

15

480

6

960

6

Ladies (small)4

14

by

12

5 1/2

5

5.0

31

240

6 1/4

480

3 1/4

Do. (large)

16

by

8

6 1/2

6

4.3/4

25

300

5 1/2

600

3 1/2

Viscountesses5

18

by

10

7 1/2

7

6.0

36

200

6

400

2 3/4

Countesses

20

by

10

8 1/2

8

7.0

40

171

5 2/3

342

4

Marchionesses6

22

by

12

9 1/2

9

9.4

55

130

6

260

31/4

Duchesses

24

by

12

10 1/2

10

10.0

60

125

6

250

3

Princesses

24

by

14

10 1/2

10

12.3/4

70

94

5 1/2

188

3

Empresses

26

by

16

11 1/2

12

15.1/2

95

79

6 1/3

158

3 1/2

Squares Covered by 1 ton.

Imperials

30

by

21

13 1/2

..

2.5

..

48

8

96

3

Rags

36

by

24

16 1/2

..

2.2

..

40

9

80

3 1/2

Queens .

36

by

24

16 1/2

..

2.5

..

40

8

80

2

1 Besides these there are intermediate sizes such as "broad ladies," "long ladies," "doubles." A fuller list is given in Part III.

2 Singles are sometimes 10" x 8". Slates 12" x 8" are sometimes called wide doubles, sometimes smalls.

3 Slates of inferior quality are thicker and heavier.

4 Sometimes called wide headers.

5 Sometimes 18" x 9".

6 Sometimes 22" x 11".

Slate Slabs are sometimes laid without boards from rafter to rafter, the lap being as usual, the side joints being covered with narrow slips of slate bedded in putty. They save the expense of boarding, but are very heavy, costly, and easily broken.

Large Slates- - A very economical system of slating with large slates is as follows: - The rafters are placed at a clear distance apart about 1 1/2 inch less than the width of the slates. Down the centre of each rafter is nailed a fillet, thus forming a rebate on each side, in which the edges of the slates rest, being secured by black putty, or - as this looks smeary and uneven - by a second fillet 2 inches wider than the first, nailed over it so as to cover the edges of the slates and hold them down. Each slate laps about 3 inches over the one below it; only half the number is required in this as compared with the ordinary method of slating, and no boarding or battens are necessary.

Ornamental Slating

Slating is sometimes laid in patterns, and also lozenge-wise - that is, with the angles up and down, but this latter arrangement forms a less durable covering than the ordinary method.

Open Slating1 is sometimes used for sheds or other inferior buildings.

The slates, instead of being laid with close side joints, are about 1 1/2 inch to 4 inches apart. This requires only about 2/3 the number of slates used for the ordinary method, and keeps out the wet sufficiently for very common purposes.

1 Sometimes called Half-Slating.