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| Map of Ireland showing wind-zones |
One of the most important environmental factors which affects the satisfactory performance of roofs is wind gusting. It is during these wind gusts that pressures are set up between the roof space and the outside of the roof tiles. The result is a wind force which can cause the total or temporary removal of roof tiles, allowing further damage by natural elements. This wind force results in a suction on both the windward and leeward sides of the roof. This suction or uplifting force, particularly on a low pitched roof is often the most severe wind load experienced by any part of a building. Under strong wind gusts, the uplift of the roof tiles may be in excess of the dead mass of the tiles, hence requiring them to be securely fixed, to prevent them being lifted from the building.
Recommended Nailing/Clipping as per requirements given in Irish Code of Practice for pitched roofs I.C.P.2: 2000
In the hatched area of the map every tile should be nailed or mechanically fixed. In the unhatched area every alternative tile should be nailed or mechanically fixed. The nailed tiles should be staggered between rows. Every edge or perimeter tile should be nailed. In the case of valleys, the first full tile should be nailed or mechanically fixed. On exposed sites and in built up areas subject to adverse wind effects such as funnelling, every tile should be nailed or mechanically fixed within the unhatched area. On all roofs at pitches 45° and over, each tile should be nailed or mechanically fixed. On all roofs at pitches of 55° and over, in addition to nailing each tile, the tail of the tile should be mechanically fixed.
Map shows the country divided into two zones on the basis of windspeeds.
Note: This map should not be interpreted literally. The location of major towns, which happen to be near the boundary between the zones, is only approximate, and their inclusion in either zone should be based on reasoned judgement or on advice from the Meteorological Services.
Clips
Function:
The function of these clips is to bring much greater resistance to tile dislodgement than can be obtained by the traditional method of head-nailing at site locations and on roof pitches where the forces tending to dislodge tiles are at their most severe. Where roofs are subjected to high wind lifting forces, the use of these specially designed tile clips is advisable as recommended and illustrated in this publication. It is also recommended that at pitches below 25°, high performance roofing felts should be used.
Wind Loadings/Tile Fixing
The principal factors to be considered in deciding on the necessity for additional mechanical fixings are:
1. The exposure and location of the site.
2. The height of the roof.
3. The roof pitch.
4. The higher wind loadings encountered at eaves and verges.
All factors are tabulated and discussed in detail in the Redland Wind Loadings Guide, to which reference should be made. Where a building is complex in shape, located on steep sloping ground or near to the edge of a cliff, further advice should be obtained.
Spanish Roll
When using Spanish Roll Roof Tiles eave filler units (Bird Stoppers) must be fixed along the topside of the facia board.
Redland Tile Clips
Tile clips are used:
1. Below 25° pitch, and
2. As additional fixings for nailed tiles where determined by wind loading calculations.
General Description
Redland tile clips have been designed to give the maximum security for the various patterns of roof tiles for which they are intended. The clips are:
1. Spanish Roll, Double Roman and Stonewold tile clips manufactured from corrosion resistant aluminium alloy specially for use with Spanish Roll, Double Roman and Stonewold tiles. Each clip is secured with a 50mm x 10g aluminium alloy nail.
2. Eave clips manufactured from acetal polymer to secure eave courses of Spanish Roll and Double Roman. Each clip is secured with a 65 mm x 12g aluminium alloy nail (enclosed with clip).
3. Verge Clips, manufactured from stainless spring steel are available in two versions:
I. for use with Stonewold slates or Double Roman tiles.
II. for use with Spanish Roll tiles.
Verge clips should be used as illustrated at both left and right hand verges. The clips should be double-nailed to the batten so as to grip the head of one tile/slate and the foot of the tile/slate overlapping. Verge clips are not necessary when Redland Dry Verge system is used.
Introduction
This section is a practical guide to general good practice on site, applicable to all tiled pitched roofs. It is based on 1.C.P.2: 1982 and Roadstone's long experience in roof tiling. For fixing details and specification clauses, please consult the Roadstone Redland Roofing Manual The performance of the finished roof is dependent on quality of workmanship, and Roadstone recommend the use of experienced roof tiling Contractors.
Underlays
Materials
Underlays which are not fully supported, that is draped over rafters, should be reinforced felt type IF to IS:36.
Laps Vertical laps should be not less than 100mm and each end of the underlay should be securely fixed over the rafters. The fixings should be not less than 50mm from the edge of the underlay. Horizontal laps should be-
| Rafter pitch | Minimum horizontal lap |
| 17.5° and under 55° | 150mm |
| 55° and above | 100mm |
The horizontal laps should preferably be under a batten with at least 25mm of underlay projecting beyond each end of the batten. Where a lap occurs between battens, it should be held down by an extra batten to restrain the lap from opening under wind uplift.
Details
Eaves: the underlay should drain any water into the eaves gutter and should extend over the tilting piece and fascia board and well into the gutter. Water traps behind the fascia board must be avoided. Where the RedVent eaves ventilator is used this acts as a tilting fillet and extends into the gutter; in this case lay underlay to butt to the fascia grille of the eaves ventilator.
Hips: a strip not less than 1m wide should be laid over hips, overlapping the underlay of the main roof.
Valleys: One layer of underlay 1m wide should be lapped under the underlay of the main Roof when using Valley troughs.
Verges: underlay should be carried across the wall cavity.
Nail Holes
Holes in underlay should be kept to minimum. Where it is necessary to Nail underlay, use galvanised clout (large head) nails. It is also recommended that at pitches below 25°, high performance roofing felts should be used.
Setting Out
Careful setting out makes the actual tiling faster and will contribute to the finished appearance of the roof. It helps to avoid problems such as unequal over-hangs at verges and often makes it possible to avoid a lot of tile cutting at abutments, chimneys and similar obstructions. All Roadstone interlocking tiles have a tolerance of approximately 3mm in the sidelocks, giving considerable adjustment over the full width of a roof. With the use of half tiles where applicable, it is usually possible to avoid cutting. Joints between plain tiles should be slightly open. This also allows flexibility in setting out.
Method
Lay a course of tiles over the full length of the eaves, starting with the correct tile overhang at the right hand verge. When the left-hand verge is reached it will be apparent that by opening or closing all the tile joints, and if necessary substituting a half tile for a whole tile, equal verges can be achieved without cutting.
Perpendiculars
Strike perpendicular chalk lines from eaves to edge at three-tile intervals. Lay tiles with their edges along these lines and all will be truly perpendicular.
Horizontals
Alternative methods are:
1. Use a chalk line to ensure that each horizontal course is true, straight and square with the perpendiculars.
2. Use two timber distance pieces, each the length of the batten gauge minus the width of one batten. This method is particularly suitable for vertical tiling.
3. Mark the batten gauge on a rod by saw cuts, and use the rod as a guide to mark the underlay.
Positioning battens
For single-lap tiles the batten which is to carry the first or eaves course must be positioned so that the bottom edge of the tiles will be over the centre of the gutter. This normally requires an overhang of 50 to 65mm for a 100mm gutter. Positioning of top and bottom battens must take into account the location of the nibs in relation to the top of the tile. For plain tiles the battens for the eaves undercourse must be positioned so that the tails of the undercourse and the first tile course line up.
Batten Gauges
The distance from the top of the eaves batten to the top of the top batten must be divided into equal amounts, (the batten gauge), which must not exceed the gauge recommended for the tile to be fixed.
Eaves Fascia
The eaves course of tiles must follow the same plane as the rest of the roof. To achieve this the fascia board must project above the top edge of the rafter by the depth of batten section plus the overall thickness of tile at the bottom edge (plus the thickness of the counter batten on a boarded roof). The design of a bell cast or sprocket at the eaves is not recommended particularly when the pitch of the main roof is less than 30°.
Battening
Sizing
Minimum batten sizes (in mm) are shown in Table 1. Table 1: Minimum Batten Sizes
| Rafter Centres | 450mm | 600mm | ||
| width | depth | width | depth | |
| Single | 35 | 35 | 44 | 35 |
| Lap Tiles | 50 | 25 | - | - |
| Plain tiles | ||||
| Pitched Roof | 32 | 19 | 32 | 25 |
| Vertical Tiling | 38 | 19 | 38 | 25 |
Batten Fixing
Battens should be in not less than 1200mm lengths, and should be long enough to be supported at each end and intermediately by at least three rafters, trusses or walls. Battens must not be cantilevered or spliced between supports. Batten ends should be cut square and nails skew driven on each side of joints. Not more than one batten in four should be joined over any one truss or rafter. Battens on boarded roofs must be supported on counter battens to increase ventilation under the tiles and allow free drainage of any water that may reach the underlay. Counter battens must be fixed through to the rafters and not to the boarding alone.
Batten Nails
For duo pitch roofs of not less than 17.5° pitch with ridge height not exceeding 7.2m and where the basic wind speed does not exceed 48m/s, battens should be nailed with a 3.35mm diameter nails.
For more severe conditions, annular ring-shank nails of the same diameter should be used, and nail resistance should be calculated.
In coastal areas, steel batten nails should be hot-dip galvanised.
Nailing
Aluminium alloy nails to I.S.105: Part 1 are suitable for normal use. Copper nails to I.S.105: Part 1 are also suitable for normal exposure. Silicon bronze nails are more durable and may be used in aggressive atmospheres. Stainless steel nails are suitable for all conditions. Galvanised iron and steel nails must not be used for tiling.
Mortar Bedding
All mortar used for bedding roof tiles and accessories must be 1:3 cement sharp sand. Plasticisers may be added in accordance with manufacturer's instructions. Units to be bedded (ridges, hips, verge tiles etc.) should first be soaked in water. Bedding mortar should be squeeze down and struck off to give a clean face: pointing should not be carried out subsequently or with different materials. Pigments complying with BS1014 may be added in a proportion of not more than 1:60. Too much pigment can impair the final setting of the mortar.
Flashings and Soakers Materials for flashings, soakers and saddles should preferably be lead to BS 1178 of the following minimum thicknesses: flashings, soakers, saddles BS Code No. 5, 2.24mm thick. Gutters BS Code No.6, 2.5mm thick.
Other materials complying with BS 5534: Part 1 clause 15 may also be used. To avoid the risk of bimetallic corrosion there should be no contact between different metals. Special attention should be given to detailing of flashing and underlay felt at abutments to chimneys and roof lights.
Roof Details
General good practice for traditional details is given below. Where Redland dry roofing systems are used, the manufacturer's instructions should be followed. Ridge Bedded Ridge Ridge tiles must be edge bedded only. No ridge tiles should be solid bedded except at butt joints or ridge end. Where solid bedding is required the mortar should be thinned out with pieces of broken tile, to reduce the mass of bedding and thus the risk of cracking due to drying shrinkage.
Four-point bedding (a dab of mortar at each corner of the ridge tile) is bad practice and should not be permitted.
Eaves
Single Lap Tiles
No mortar or undereaves course is to be used. The eaves course must be in the same plane as the other tiles. See Setting out. Sprocketed eaves are not recommended with single-lap tiles.
Sprocketed Eaves
Pitch should not be less than 35° concrete/40° clay. If the pitches of the main roof and the sprocket differ by more than 50 lead soakers should be used.
Verges
Single Lap Tiles
All single lap tiles have their side lock on the left; work must therefore start at the right hand verge and finish at the left.
Undercloaked Verge
Nail the undercloak to the end rafter, or bed it on to the brick wall ensuring the underlay is under the undercloak. Bed tiles in mortar on the undercloak, cutting back the mortar to form a sloping face; this will assist drainage and give a thinner appearance to the mortar. This is suitable for a 38 to 50mm over-hang. The undercloak course must not tilt inwards. A suitable undercloak material is fibre cement strips/slates 6mm thick and 1500mm wide, laid rough side up and nailed at not more than 300mm centres. For single-lap slates (Stonewold) the right hand verge is formed with half slates and full slates in alternate courses to maintain broken bond. The left hand verge is formed with half slates and purpose made left hand verge slates in alternate courses.
Abutments
Tile or cement fillets should not be used. Use tiles and half tiles etc. as for verges to minimise cutting and maintain broken bond where appropriate.
Valleys and Hips
Tile Cutting
For raking cuts at valleys and hips, mech-anical cutting is preferable to hand cutting since it gives a better appearance and avoids small body cracks.
Fixing
All cut tiles must be carefully bedded in mortar. If the nail holes are cut away the side of the piece must be notched and supported with a nail. Small cut tiles at hips can sometimes be supported by driving a long nail into a batten or hip tree to prevent them slumping when the hip tile is pressed home. Cutting bold-profile tiles often produces a deep mortar bed which may shrink on drying, resulting in cracking or loss of adhesion between mortar and tile. On hips, the use of the dentil slips set in the bedding should be considered to thin out the mortar and improve appearance. When forming a valley with interlocking tiles, great care must be taken not to leave any mortar in the sidelocks of the cut tiles, otherwise water will build up in the channels and spill back into the roof. For lead valleys, lengths of the lead sheet should not exceed 1.5m with laps of 150mm.
Provision should be made for a slip layer between the mortar bedding and the lead sheet. The use of secret valleys is not recommended because of the difficulty of keeping the drainage channel clear. Hip tiles should be edge bedded in mortar, with solid bedding at butt joints.
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