The pitch of roofs shall, wherever possible, be preferably between 15- 18 degree, as recommended in I.S. should it however be inevitable to adopt roofs with lower pitch, ends laps shall be increased suitably
This spacing of purlins in roofs shall generally be restricted to 1400mm c/c for high tensile (550 MPa) steel. For slide cladding the maximum recommended purlin spacing is 1700mm, Ridge purlins shall be fixed at a maximum distance of 150mm from the apex of the roof. For our roofing, a maximum spacing of 1000mm is recommended
Thickness of sheets is a function of the strength of material used. Indian pre painted galvanized steel usually has yield strength varying from 180 MPa to 240 MPa depending on the manufacturer. Al-zn alloy coated steel comes in yield strength of 310 MPa(Grade 60 as per ASTM) or 550 MPa(Grade 80 as per ASTM). For thickness recommendation based on yield strength, reference may be made to table given in AZ brochure.
The crest of AZ sheet having return leg shall be covered by the half crest of the next sheet while laying.
From normal roof pitch that is, inclinations between 15 to 18 degrees, the end laps shall not be less than 150mm. For low roof pitches, that is, inclinations below 15 degree, the end laps shall be increased by at least 25mm for every 2 degree decrease in slope from 15 degree. Alternatively, a single sheet per slope may be used, eliminating end laps altogether. However, in use of such longer lengths, prevention of damage in sheets due to thermal movement need careful planning and detailing. Length of single sheet is best restricted to 12m, if used at all.
The free overhang at eaves, measured as the length of sheet from its edge to the centre of bolt holes, shall not exceed 150mm.
All metals expand and contract with changes in temperature. Although steel is by far the least affected of all the metals commonly used for roof and wall sheeting, the changes in length experienced in very long runs of roofing are significant. On a clear hot summer day, with no wind, the steel temperature in roof sheeting can reach approximately 50 degree C in Al-Zn substrate off white, 60 degree C in Al-Zn finish without color and more than 80 degree in darker colors.
The purlin section used and the type of coating guide the choice of fastners on the sheets. Self tapping, self drilling screws are not recommended for use with hollow sections as these invite the ingress of moisture into the closed internal surface of he section. For Al-Zn alloy coated sheets fastners must conform to class 3 of AS 3566(ITW Buildex or corroshield make) while for galvanised colour coated sheets any standard make of fasteners(Pooja, HP, Hilti etc) may be used.
Store sheets duly protected from damage at site, carefully stocked on firm level ground, resting on the wooden blocks as supplied. It is advisable to stack sheets of different sizes separately. Storing sheets as near as possible or within the building where they are to be fixed is recommended.
Rain or condensation is easily drawn between the surfaces of stacked sheets by capillary action, or they can be driven in by wind. This trapped moisture cannot be evaporated easily, so it can cause deterioration of the coating which may lead to reduced life expectancy or poor appearance.
If materials are not required for immediate use, stack them neatly and clear of the ground. If left in the open, protect them with waterproof covers. If stacked or bundled products become wet, separate it without delay, wipe it with a clean cloth and stack it to dry thoroughly.
Generally, keep your weight evenly distributed over the soles of both feet to avoid concentrating your weight on either heels or toes. Always wear smooth soft soled shoes; avoid ribbed soles that pick up and hold small stones and other objects. When you walk across the ribs, walk over or close to the roofing supports. Always take particular care when walking on wet or newly laid sheets particularly on steeply pitched roofs. If there will be heavy floor traffic on a roof, provide a temporary walk away or working platform to minimize damage.
On large building projects you can reduce handling time by lifting bundles with a crane direct from the delivery truck onto the roof frame. Use a spreader bar for long sheets. For small to medium size projects, without mechanical handling facilities, you may upload sheets by hand and pass them up to the roof one at a time. For personal safety, and to protect the surface finish, wear clean dry gloves. Dont slide sheets over rough surfaces or over each other. Always carry tools, dont drag them.
format of the number code is:
5.5 - 24
Screw size in mm Thread pitch
Fasteners WITH SEAING WASHERS SHOULD BE TIGHTENED ONLY UNTIL THE WASHER IS GRIPED FIRMLY ENOUGH TO PROVIDE A weather tight seal. The fasteners should not be over tightened because this may split the sealing washer or deform the sheet, wither of which could lead to water penetration. Special care is required in valley fixing because there is no flexibility with the sheet hard against the runners.
To reduce rain noise on metal roofing, an insulation blanket with aluminium foil laminate may be laid, before laying the roofing. It is important that the laminate is pulled tight enough to hold the blanket hard the underside of the roofing so as to dampen the rain induced vibration at the poing of impact. If the blanket is not hard against the noise reduction will not be as good. First lay wire mesh over the purlins, tighten and fix it, before laying the membrane.
For cutting AZ sheets on site, we recommend you use a power saw with a metal cutting blade because it produces fewer damaging hot metal particles and leaves less resultant blur than a carborundum disc. Cur materials over the ground and not over other materials where hot particles can fall and cause damage t finishes especially pre painted finishes. It is best to have the exterior colour finish of a pre painted sheet facing down; however you must then protect the paint finish from scratching by placing work supports. If you have to cut materials near sheets already installed, mask them or direct the stream of hot particles away.
starting work ensure that:
-The members of the building, on which the sheeting will rest, are truly in the same plane;
-The overhangs of sheets from the top and bottom supports don’t exceed 150mm, whilst also hanging at least 100 mm into gutters. Make any necessary adjustments before you start laying sheets, because they will be difficult or impossible to rectify later.
To ensure that side laps are protected, we recommend that you start laying sheets from the end of the building that will be in the lee of the worst anticipated or prevailing weather. It is much easier and safer to turn sheets on the ground than on the roof.