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ESTIMATING ROOFING MATERIALS By Ian Elle Samonte

Roof Estimates

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ESTIMATING ROOFING MATERIALS

ESTIMATING ROOFING MATERIALS

By Ian Elle Samonte

GALVANIZED IRON SHEET

Most common roofing material.

Also known as GI sheet.

It is either plain or corrugated.

Plain sheets are used for gutters, flashing, down spout, ridge, hip, and valley roll.

Plain sheet standard commercial size is 90 X 240 centimeters long.

GI SHEET

Corrugated GI sheet is widely used for roofing and sidings

having standard width of 80 centimeters with varying length from 150 to 360 centimeters at consecutive intervals of 30 centimeters.

Long span corrugated sheets are also available on special order.

GAUGE NUMBER

The thickness of galvanized iron sheet is measured in terms of Gauge Number from 14 to 30.

The sheet becomes thinner as gauge number becomes larger.

Gauge 26 is the most extensively used for roofing and various tin works

Gauge 24 is specified for gutters and valley rolls.

Before estimating the required number of corrugated roofing sheets, the following information should be considered first:

1. Verify the plan if the side lapping is 1- or 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 long. This is important in determining the length of the sheet to be used.

4. Spacing of the purlins should be proportionally adjusted to the length of the G.I.

sheets to avoid unnecessary cutting or excessive overlapping. In short, the length of the roof sheet governs the spacing distance of the purlins.

5. A good roofing design minimizes end lapping joint. Longer length of roofing sheet is preferred for economical reasons.

EFFECTIVE COVERING OF G.I. ROOFING SHEETS

LengthFt - MeterEffective CoveringSide LappingPurlinsSpacingIn MeterNumber of Nails or Rivets per sheet1 2 5 1.506 1.807 2.108 2.409 2.7010 3.0012 3.60.70.70.70.70.70.70.70.60.60.60.60.60.60.60.60.75.60.70.60.67.6614141818222226

QUANTITY OF ROOF ACCESSORIES IN KILOGRAMS

Materials Number per KilogramGI Roof Nails120GI Rivets180GI Washers126Lead Washers75Umbrella Nails120
Size of Purlins (inches)Size of GI Strap in InchesNumber of Strap in One Plain GI Sheet 2 x 31 x 93842 x 41 x 103422 x 51 x 113122 x 61 x 12288

ESTIMATING G.I. ROOF AND ITS ACCESSORIES

Determine the length of the purlins along the gutter line. This distance is perpendicular with the roof direction.

Divide this length by the effective width covering of one G.I. sheet using either 0.70 for 1 corrugations or 0.60 m. for 2 corrugations. The result is the number of sheets for one row.

Determine the length of the rafter or top chord. Choose the right combination of roofing sheets that will satisfy this length considering the 25 to 30 centimeters standard end lapping.

END LAPPING

SIDE LAPPING

Example.esTIMATE THE GI SHEETS, RIVETS, GI WASHERS & LEAD WASHERS

6.00 M

14.00 M

Assume side lapping of 1 corr. And end lapping of 0.30m.

solution

Corrugated GI Sheet

Divide the length of the gutter by the effective width covering of one sheet.

14.00/0.70 = 20 sheets in one row

The length of the rafter is 6.00meters, referring to the table of effective covering, the combination of 3.60m(12 ft) and 2.7 m (9 ft) long GI sheet is appropriate.

ORDER:

20 32 x 12 corr. GI Sheet

20 32 x 9 corr. GI Sheet

Rivets

Refer to table

For 12 ft long: 20 x 26 = 520 pieces

For 9 ft long: 20 x 22 = 440 pieces

______________

Total rivets 960 pieces

Covert to kilograms

= 960/180 = 5.3 say 5.5 kilograms

GI Washers

Double the number of rivets

= 960 x 2 = 1920

Convert to kilograms:

= 1920/128 = 15.24 KILOGRAMS

Lead Washers

Number of rivets is the same as the lead washers+ 960

Covert to kilograms:

= 960/75 = 12.8 say 13 kilograms

SUMMARY OF MATERIALS

20 pcs 32 x 12 corr. GI Sheet

20 pcs 32 x 9 corr. GI Sheet

5.5 kg GI Rivets

15.5 kg GI washers

13 kg Lead Washers

Find the number of corr. GI sheets, rivets, GI washers, lead washers, and anchor strap required if the plan specify 2-1/2 corrugation for side lapping and 0.30 end lapping on a 2 x 4 purlins.

ROOFING SHEETS

Length of gutter/0.60 = 18/0.6 = 30 pieces

The length of rafters is 6.00 m , so the combination is 3.60m and 2.7m GI sheets

30 pieces of 32 x 12 GI sheet

30 pieces of 32 x 9 GI Sheet

Since that is only one side, double the quantity.

60 pieces of 32 x 12 GI sheet

60 pieces of 32 x 9 GI Sheet

Considering the roof is hipped type, wastage on cutting cannot be avoided, hence provide add 5% to 10% wastage. Get a longer sheet to avoid excessive cutting.

60 + 60 = 120 x 5% = 6 pieces of 12

ORDER:

66 pcs 32 x 12 GI Sheet

60 pcs 32 x 9 GI Sheet

GI RIVETS

For 12 ft sheet = 60 * 26 = 1560 pieces

For 9 ft sheet = 60*22 = 1320 pieces

Total: 2880 pieces

GI washers

Double the number of rivets

2880 x 2 = 5760 pieces

Convert to kilograms

5760/126 = 45.7 say 46 kilograms

LEAD WASHER

Same as the number of rivets

=2880 pieces

Convert to kilograms

= 2880/75 = 38.5 say 39 kilograms

PLAIN GI ANCHOR STRAP

The size of GI Strap on a 2 x 4 purlins is 1 x10

Number of strap is equal to number of rivets.

2880/342 = 8.42 say 9 pieces 90cm x 240cm plain GI Sheet

SUMMARY

66 pcs 32 x 12 GI Sheet

60 pcs 32 x 9 GI Sheet

2880 pieces GI Rivets

46 kilograms GI washers

39 kilograms Lead washers

9 pieces - 90cm x 240cm plain GI Sheet

GUTTER, FLASHING, RIDGE, HIPPED, and VALLEY ROLL

Categorized as roof accessories under tinsmith work. Estimating these type of accessories is simply determining the number of plain GI sheets needed to fabricate it.

EFFECTIVE LENGTHS

Gutter 2.35m

Flashing 2.30 m

Ridge Roll 2.20 m

Valley roll 2.30 m

Hipped roll 2.20m

GUTTER, FLASHING, RIDGE

RIDGE ROLL

GUTTER

FLASHING

EXAMPLE.

Find the number of Plain GI sheets required to fabricate the gutter, ridge roll, and flashing.

GUTTER, RIDGE, FLASHING DETAIL

gutter

Total length of gutter = 20m

Divide effective length = 20/2.35 = 8.5 say 9 pieces gutter

Total width of gutter = 45cm

Compute no. of gutter that can be made out of 1 plain GI sheet

=90cm/45cm = 2 pcs.

No of plain GI sheets = 9/2 = 4.5 say 5 pieces plain GI sheet

FLASHING

Total length = 18m

Divide it by the effective length = 18/2.30 = 7.8 say 8 pieces

Width of flashing = 45cm

90 cm / 45 cm = 2 pieces can be made of 1 plain GI sheet

8 pcs/2pcs = 4 GI Sheets

RIDGE ROLL

Total length = 10 m

Width = 45cm

Divide total length by effective length = 10/2.2 = 4.5 pieces ridge roll

2 pcs of ridge roll can be made out of 1 plain GI sheet

Therefore , 4.5/2 = 2.25 sheets say 3 sheets

SUMMARY

GUTTER = 5 pcs 90 x 240cm Plain GI Sheets

FLASHING= 4 pcs 90 x 240cm Plain GI Sheets

RIDGE ROLL = 3 pcs 90 x 240cm Plain GI Sheets

TOTAL = 12 pieces plain GI Sheets