Galvanized Iron Sheet is either Plain or Corrugated.

Before making an estimate of corrugated G.I. roofing sheets, the following important data should be considered first:

1. Verify the specifications for side lapping if it is 1-1/2 or 2-1/2 corrugations.
2. If it is 1-1/2 corrugations, the effective width covering per sheet is .70 meters or .60 meters for 2-1/2 corrugations.
3. The standard end lapping joint is from 25 to 30 centimeters.
4. The spacing between purlins should be proportionally adjusted to the length of the G.I. sheets to avoid unnecessary cutting of the sheets. In short, the length of the roof sheet shall govern the spacing distance of the purlins.
5. A good roofing design are those that minimizes the end lapping. Always specify longer length of roofing sheet for economical reasons.

Procedures in estimating G.I. Roof Sheet and its Accessories

1. Determine the length of the purlins along the gutter line. This distance is perpendicular with the roof direction.
2. Divide the length by the effective width covering of one G.I. sheets which is 70 centimeters for 1-1/2 side lap corrugations or 60 centimeters for 2-1/2 lap corrugations. The results is the number of corrugated G.I. sheets for one row.
3. Determine the length of the rafters or top chord. Choose the right combination of roofing sheets that will satisfy this length considering the 30 centimeters standard end lapping.
4. Multiply the result found in stes-2 by each length of G.I. sheet combinations.
5. Determine the number of G.I. nails or rivets and washers in kilograms.
6. Take note that the number of Plain G.I. anchor strap and lead washer is the same as the quantity of the rivets. The G.I. washer is double the quantity of the rivets.
7. Solve for the number of plain G.I. sheets required for anchor strap.