Generally corrugated galvanized iron sheets are extensively adopted as a covering for roofs and sides of industrial sheds and buildings. These are commonly available in length of 2.5 meter having a width of 900 mm and 1000 mm. The sheets are available in thickness of 0.63 mm to 1.60 mm. These sheets are coated with zinc. The sheets are cleaned, bright, free from rust, breakage etc. These should be according to IS: 270 class 2. Hooks, bolts, bitumen and steel washer, nuts and other accessories should confirm Indian Standard No.730.
Iron Sheet Roofing - Solid and strong roofing
(This Picture is Contributed by "Sharmishtha Roy")
The holes are in the ridge of corrugation, not in the valley.
The slope of GI sheet roofing is not flatter than 1.5.
The slope 1.3 is adopted normally.
The sheets are laid at a minimum lap of 15 cm at the ends.
Wind tie must be provided on sheets to save it from disaster.
Proper ridge and valley gutter are fixed where required.
Layout of Iron Sheet Roofing
- The sheets are laid on Purlins with the line of corrugation truly parallel to the side of area to be covered.
- Each sheet is fixed by means of J or L hooks bolts and nuts are not less than 8 mm.
- The limpet washer fitted with bitumen washer and nuts are fitted tightly.
- Holes for hooks bolts etc. are drilled, not punched.
Raw Material for Iron Sheet Roofing
- Galvanized Iron Sheets
- Bolts and Nuts
- Bitumen and Steel Washers
- Frame / Purlins
- Ridge and Hip Cap
- Metal Valleys
Galvanized Iron Sheet: This material consists of sheets of hot-dip galvanized mild steel. The corrugations increase bending strength of the sheet in the direction parallel to corrugations but not across them.
Normally each sheet is manufactured longest in its strong direction. These sheets are nailed up to the top edges of trusses or rafters to tie the roof and to support roofing material together. The corrugated galvanized iron sheets are of the gauge specified. The sheet should be 22-swg and should conform to specification in all respects.
Hooks: These are galvanized J or L hooks bolts and nuts 8 mm diameter. Its length should be equal to Purlin + 76 mm for single sheet fixing and depth of Purlin +89 mm for two over lapping.
Bolts and Nuts: Bolts and nuts are zinc plated, cross head, complete with square nut. The spacing apart from hook bolts and GI bolt should not exceed 30 cm.
Steel Washers: Steel washers are also called cup washer that are made of metal. These are placed beneath the nut or joint to relieve friction and prevent leakage or distribute pressure.
Frames/ Purlins: Purlins of specified material or MS rolled section of required site are fixed over principal rafter. The top surface of Purlin should be uniform and plain.
Ridge and Hip Cap: Ridge and Hip cap of GI sheet roof are covered with Ridge and Hip sections of plain GI sheet, 0.6 to 0.8 mm thick and 60 cm overall width in a maximum lap of 20 cm.
Metal Valleys: Metal valley should be of plain GI sheet 1.6 mm thick and 90 cm wide. It is bent to desired shape and be fixed with main roof GI sheet. The lap with GI sheet should not be less than 25 cm on either side.
Glass and Iron -What a look of roofing
(This Picture is Contributed by "Sanjeev Thakur")
Advantages of Iron Sheet Roofing
- Iron sheet roofing is economical.
- It covers more space with less intermediate supports.
- It has a long life after proper painting.
- It takes less time for fixing as compared to RCC slab roofing.
Disadvantages of Iron Sheet Roofing
- Problem of leakage and rusting.
- It can not be used for second storey.
- It is more prone to weather effects.