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This chapter is intended for the skilled workmen who will lay the tiles on the roof structure. A pro-condition for proper installation is to look into the means of ensuring watertightness, especially for the most exposed areas: the sides and wall-plates. The battens supporting the tiles should be fixed by a skilled roofer. This is a delicate job requiring great precision. Before laying the tiles, the roofer should make sure that he has the correct quantity of tiles for the area to be covered. The final section of this chapter deals with the various criteria to be observed when laying tiles and fixing them on the roof frame.
In regions exposed to violent winds, special attention should be given to the edges. Two assembly systems are available to fasten the edge tiles securely and prevent wind penetration and uplift on this exposed section of the roof (see chapter VII, section III). The first solution is extremely simple: a small scantling is nailed at the end of the purlin (driving the nails upwards). This small block of wood will support the edge of the end tile and keep it level with the other tiles (figure 89).
Figure 89. Laying the last tile
across a scantling
The second system ensures better watertightness. The principle is the same: the edge of the tile rests on a scantling. The side of the roof is closed with boards to prevent the wind from penetrating under the tiles (figure 90).
Figure 90. Watertight closing of
sides
If a board is laid at the bottom end of the slope, the top part of the board should be at least as high as the battens (figure 91). This presents the twofold advantage of closing the void between the covering and the frame and supporting the last row of tiles so as to keep the roof slope level. If no board is placed at the bottom end of the roof, the last batten should be placed at a distance of a few centimetres from the lower edge of the rafters.
Figure 91. End
border
In hurricane climates it is advisable to place a waterproof sheet under the tiles. It offers protection against dust and water infiltration when the roof is subjected to strong gusts of wind. A polythene sheet is inserted between the rafters and the purlin. The polythene strips are placed horizontally starting from the bottom of the slope and should be left slack. Minimum overlap of strips is 15 cm.
Placing the battens requires precision. They should be strictly parallel. Battens have small sections (0.03 m × 0.04 m or 0.025 m × 0.05 m). If the roof is likely to be subjected to exceptional loads and pressures, the batten section should be increased.
Spacing of the battens depends on tile length and overlap. Pantiles measuring 25 cm × 50 cm should be laid on battens placed at precise 40 cm intervals. For correct spacing, a template may be used (figure 92).
Figure 92. Carpenter's template
for correct spacing of purlins
When the length of the roof slope is a multiple of 40 cm, an exact number of tiles may be used ("n"): all the visible parts of the tiles are identical. If the roof slope is not a multiple of 40 cm, the last two battens (close to the ridge) should be placed closer: the second row of tiles will be narrower than the rest.
Before laying the tiles, the roof structure should be checked for alignment. A sighting should be taken from an angle of the building to check that the upper and lower extremities of trusses and rafters are correctly aligned. Along the roof slope, battens should be absolutely level. To check this, a perfectly straight control batten should be placed along the roof slope, perpendicular to the battens. All the battens should be in contact with the control rod (figure 93).
Figure 93. Structural checks
before laying the
tiles
The outside dimension of pantiles is 24 cm × 49 cm. The size of screeding frames is 26.5 cm × 49 cm (the 2.5 extra centimetres are taken up by the curve of the tile).
Pantiles are curved. They fit laterally under the rib and lengthwise by simple overlap. Overlap should be 9 cm down the slope and 4 cm across.
The effective coverage area of the tile (or "bare") is 40 cm × 20 cm (two-thirds of total tile coverage area). Theoretically, 12.5 pantiles are required to cover one square metre of roof surface. For Roman pantiles, an average of 11.5 tiles are required to cover one square metre of roof surface.
In practice, the quantity of tiles required to cover a given roof surface will depend on:
- the pitch of the roof;- the measurements of the slopes: the length and width of the slope should be multiples of the tile dimension;
- regular placing of tiles;
- loss through breakage.
Remark
Several parameters may affect the outside tile measurements, such as:
- measurements of screeding frame (24, 24.5 or 25 cm);
- shape of the tile (pantile, roman tile, other).
1. Laving the tiles horizontally (across)
Theoretically, 5 well-laid tiles cover an average width of 1 metre. Inaccuracies in tile laying will result in the same number of tiles ("n" tiles) covering varying widths of roof.
Figure 94. Accurate placing of
tiles: 5 tiles/metre
Table 26. Comparison of widths covered with accurate and inaccurate placing of tiles
|
Number of tiles |
Accurate placing |
Inaccurate placing |
|
20 |
4 m |
3.6 m |
|
30 |
6 m |
5.4 m |
|
40 |
8 m |
7.2 m |
|
50 |
10 m |
9.0 m |
|
60 |
12 m |
10.8 m |
2. Laying the tiles vertically (down)
Theoretically, five tiles cover 2 metres lengthwise. Overlap is 10 cm.
Figure 95. Accurate placing of
tiles: 5 tiles/2 metres
3. Variation of number of tiles with roof slope
A relationship may be established between the width of a construction (roof span), the pitch and length of roof slopes (table 27). These parameters have a bearing on materials consumption; the designer may define roof measurements which are even multiples of the tile dimensions.
The length of the slope may be calculated on three different assumptions:
- the length of the slope is pre-established ("n" number of tiles): if the span increases (width of building), the pitch is less steep;- the span is pre-established: if the pitch becomes steeper, the number of tiles increases (length of slopes);
- the pitch is pre-established (degrees): if the span increases, the number of tiles increases (length of slopes).
Table 27. Relationship between the three factors which determine tile consumption: span. pitch, length of slopes
|
Pitch |
22º |
25º |
30º |
35º |
|
|
Span (metres) | |||
|
Length of slopes |
|
|
|
|
|
10 |
3.7 |
3.6 |
3.5 |
3.3 |
|
11 |
4.1 |
4.0 |
3.8 |
3.6 |
|
12 |
4.4 |
4.4 |
4.2 |
3.9 |
|
13 |
4.8 |
4.7 |
4.5 |
4.3 |
|
14 |
5.2 |
5.1 |
4.8 |
4.6 |
|
15 |
5.6 |
5.5 |
5.2 |
4.9 |
|
17 |
6.3 |
6.2 |
5.9 |
5.6 |
|
18 |
6.7 |
6.5 |
6.2 |
5.9 |
|
19 |
7.0 |
6.9 |
6.6 |
6.2 |
|
20 |
7.4 |
7.3 |
6.9 |
6.6 |
Three different situations are possible:
- measurement is not predefined: the builder may select one or two criteria;- one criterion is predefined: the choice of the other two criteria should be made in view of the possibilities;
- two criteria are pre-established; only one third criterion is possible.
The measurements of a building are as follows:
|
- Span |
: 6.70 metres |
|
- Width of roof |
: 7.50 metres (including eaves) |
|
- Roof pitch |
: 22º |
A span of 6.70 metres with a 22º pitch means that 18 tiles should be used. Across the roof, the number of tiles used varies between 38 and 41 depending on the skill of the workmen. A safety margin of 5 per cent should be added to cover breakage during unloading and handling.
Table 28. Tile consumption
|
|
Net tile consumption |
Gross tile consumption |
|
Accurate worksmanship |
18 × 38 = 684 units |
684 + 5% = 718 units |
|
Inaccurate workmanship |
18 × 41 = 738 units |
738 + 5% = 774 units |
Tiles are laid according to a well-defined progression. The first tile should be laid in the lower left-hand corner of the slope. The following tiles are placed in an upwards and left to right progression. Frequent checks should be made as the work progresses.
Before laying the tiles marks are made at one metre intervals on the battens at the bottom and top of the slope. A rope is stretched between the first two marks. Five columns of tiles should fit within this area (figure 96).
Each tile is laid and adjusted carefully. All the tiles in a given column should be accurately aligned. A straight batten placed flush against the column may be used as a template (figure 97). Faulty alignment should be corrected immediately. The nib should adhere closely to the batten.
Figure 96. Marker for alignment
of 5 columns of tiles
Figure 97. Checking tile
alignment
When the first slope is completed, the second slope is covered in an identical manner. The ridge tiles should be installed gradually as soon as enough columns are completed on the second slope. This avoids the need of climbing on the finished part of the roof.
A simple V-shape is a good design for ridge tiles. The angle of the open "V" depends on the roof pitch (see chapter III, section V.2). Depending on local custom or design preference, ridge tiles may be placed:
- butt to butt with mortar joints (figure 98 a);
- with single overlap (figure 98 b);
- with double overlap (figure 98 c);
- with special fit (specially moulded tile) (see chapter IV, section III.2).
If the first row of tiles is not closed with a bar, openings will remain between the lower edge of the ridge tile and the channels of the first row of roof tiles. These openings may be closed with mortar. Another solution consists in laying special tiles for the first row under the ridge (see chapter IV, section IV).
When roof repairs are necessary, a ladder may be placed in the direction of the slope, with the two uprights resting in the tile channels. The workman's weight will thus be spread over the whole slope.
Pantiles may be placed without any special fixing device. For increased security in wind-prone areas, tiles should be fixed to the structure. Three methods are possible, although systems 2 and 3 are recommended.
1. Wailing or pegging through the nib (figure 99)
Although this is the simplest method, it is also the riskiest: the hammer may skid on the nailhead and break part of the nib, the whole nib or even the tile. Driving a peg through the nib is not advisable since the nib might break up under the pressure.
2. Galvanized wire loop (figure 100)
The galvanized wire loop is cast in the fresh mortar when the tile is moulded (see chapter IV, section 11.4, step 12). The tile may be fixed by nailing the wire loop to the purlins or by tying it down through the loop around the batten. The fixing wire should be taut. If there is too much play, wind suction might cause the tiles to clatter. This produces an unpleasant noise and, if the uplift is very severe, may result in the tiles cracking.
3. Plastic cord (figure 101)
A length of plastic cord is slipped through the nib hole. The cord is tied around the purlins.
Figure 99. Nailing the tile on
the batten
Figure 100. Nailing through
galvanized wire loop
Figure 101. Tying down with
cord
In hurricane areas, special tiles are required: they are thicker (8 mm to 10 nun) and fitted with two nibs (see chapter IV, section 11.4, step 8-b).
Both the upper and lower nib are tied down with galvanized wire or plastic cord. When laying the tiles, the second nib of the upper tile and the main nib of the lower tile should be fixed to the same batten (figure 102). The tiles are thus fixed at their upper and lower end and cannot be lifted by rough winds.
Figure 102. Upper and lower
fixing around
batten
Grouting is not sufficient to fix ridge tiles (with or without special fit) on the ridge. When moulding the tiles, galvanized wire loops should be cast in the inner angle of the tile (see chapter IV, section III).
The tile is placed on the ridge. It is fixed to the roof frame with G.I. wire or a plastic cord. The wire or cord are either slipped under the purlins (figure 103), or looped around the ridge purlin (figure 104).
Figure 103. Tying ridge tile
around purlins
Figure 104. Tying ridge tile
around ridge
purlin
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