roof estimates
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roofing estimateTRANSCRIPT
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 3.60.70.70.70.70.70.70.70.60.60.60.60.60.60.60.60.75.60.70.60.67.6614141818222226QUANTITY OF ROOF ACCESSORIES IN KILOGRAMS
Materials Number per KilogramGI Roof Nails120GI Rivets180GI Washers126Lead Washers75Umbrella Nails120ESTIMATING 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