GC SHEET APPLICATIONS

While one of the most important roles of roofing is to fight the weather, they also have significant effects on the aesthetic, cost and durability of a building. In Roof Cladding, factors such as rainfall, wind speed, height of building and walking weight on roofs (arising out of maintenance) have considerable effect on design of roof slope, supporting structures and spacing between Purlins (Figure-1).

Design parameters for Wall Cladding is simple and straightforward compared to Roof Cladding. The main consideration in the design is spacing between the supports, known as “Side Girt” (equivalent of Purlins used in Roof Cladding). Wind speed and thickness of sheets play major role in arriving at the spacing between Side Girt.

SLOPE

Slope is a major component of roof design. In absence of adequate roof slope, there is danger of water accumulation, which can lead to leakage and reduced sheet life. Most commonly used roof slopes in India are 1 in 4 (14º) and 1 in 3 (18º) (Figure 2 & 3). However, various other slopes can be used depending upon the intensity of rainfall and wind force. In case of sinusoidal profiles, it is recommended that one should not go below slope of 1 in 12 (5º). It is important to use sealants at the end lap of sheets in case roof slope is below 5º.

OVERHANG

Overhang in Roof Cladding is important from the angle of complete weather-proofing of the building. While “End Overhang” maintained at the “Eave End” (Gutter end) of the roof facilitates proper drainage of water without drenching the inside of building from its front, the “Side Overhang” makes sure the rain water does not enter the building from sides (Figure-4). Overhangs are recommended below as per good engineering practice.

END OVERHANG (x) SIDE OVERHANG (y)
300 mm 100 mm

JOINTS ON THE SHEETS

Joints on the roofing sheets, also known as 'Laps', are critical in fabrication of leakageproof roofs. Joints on the side of the roofing sheet (along sheet length) is known as “Side Lap” (Figure-5) while joint at the end of the sheet (along sheet width) is known as “End Lap” (Figure-6). Slope of the roof plays a major role in deciding the area of laps.

SIDE LAP OF SHEETS

FOR ROOF CLADDING FOR WALL CLADDING
1½ CORRUGATIONS 1 CORRUGATION

Note: In areas of heavy rainfall, the laps at sides should be suitably increased..

END LAP OF SHEETS

ROOF SLOPE FOR ROOF CLADDING FOR WALL CLADDING
1 in 3 (18º) 150 mm 100 mm
1 in 4 (14º) 200 mm 100 mm

Note: For roof slopes lesser than 14º recommended end lap is 200 mm

END LAP OF SHEETS

LENGTH OF ROOF NO.OF SHEETS REQUIRED FOR DIFFERENT WIDTHS OF SHEETS
(mm) (feet) 800 mm 840 mm 910 mm 1220 mm
915 3 2 2 2 1
1525 5 3 3 2 2
3050 10 5 5 4 3
4575 15 7 7 6 5
6100 20 9 9 8 6
7625 25 12 11 10 7
9150 30 14 13 12 9
10675 35 16 15 14 10
12200 40 18 17 16 11
13725 45 20 19 18 13
15250 50 23 21 20 14
18300 60 27 26 23 17
21350 70 31 30 27 20
24400 80 36 34 31 22
27450 90 40 38 35 25
30500 100 45 42 39 28

CALCULATION OF NUMBER OF SHEETS REQUIRED FOR VARIOUS LENGTH AND WIDTH OF ROOFS:

L : Length of roof (in metre)
W : Width of roof (in metre)
L : Length of GC sheet used (in metre) S
N : Number of sheets required for a given length and width of roof, (fig.7) will be = N XN L LW
N : Number of sheets required along the width of roof W
Total number of sheets required will be N x N (for a given length and width of roof, dimensions explained in Figure-7)

WIDTH OF SHEET NO. OF SHEETS
ALONG LENGTH OF ROOF
NO. OF SHEETS
ALONG WIDTH OF ROOF
1220 mm NL= (L + 0.0875) / 1.1075 NW = (W + 0.4) / LS - 0.2
910 mm NL = (L + 0.0875) / 0.7975
840 mm NL = (L + 0.0875) / 0.7275
800 mm NL = (L + 0.0875) / 0.6875

Note:
(1.) End lap of 200 mm and Side lap of 112.5 mm considered to arrive at number of sheets across length of roof.
(2.) Overhang of 300 mm at eave-end and 100 mm at ridge-end considered to arrive at number of sheets across width of roof.