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How To Estimate The Roofing Sheet Requirement For a Building

How To Estimate The Roofing Sheet Requirement For a Building

Let us Calculate the Number Of Roofing Sheets required for the below-given building.

How To Estimate the roofing sheet requirement for a building. 1

Given data:

Length of the building = 20 ft.

Width of the building = 15 ft.

Overhang on all four sides = 1ft

Angle θ = 50°


First, we have to calculate the roofing length & width over the building.

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Roofing length 

= [building length + overhang on 2 sides]

= [ 20 ft. + (2nos.× 1 ft.)]

= 22 ft.


As you can observe in the above drawing, the sheet is sloped on the width side of the building.

Let us redraw the roofing triangle for a clear understanding.

Roof Slop

Sloping length of the roofing

= [AC + (2nos. × overhang)]

Now, let us calculate the length of AC as follows.

By trigonometry,

sinθ = opposite / hypotenuse

In the above triangle,

Side AC = hypotenuse

Side BC = opposite.


Sin50° = [ 15 ft. ÷ hypotenuse]

0.766 = [ 15 ft. ÷ hypotenuse]

By Cross Multiplying,

Hypotenuse = [15 ft. ÷ 0.766 ]

             AC = 19.58 ft.


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The length of the roofing sheet

= [AC + (2nos. × overhang)]

=  [19.58 ft. + (2nos. × 1 ft.)]

 = 21.58 ft.

Sheet Calculation:

We will consider buying Tata dershane roofing sheets for this building.

Now, the effective width of this sheet after overlapping is shown below.

overall weight

Given data:

Effective cover width We = 1015mm.

Total width Wt =  1072mm.

Roofing length Wr = 22 ft. ( calculated)

a. Sheet calculation on length side of the building

 The number of roofing sheets required for a single row

= [length side of the building for roofing ÷ effective width]

= [Wr ÷ We]

By converting the effective width unit into ft.

(1mm = 0.00328084ft.)

We = [1015mm × 0.00328084]

    3.33 ft. 


Number of roofing sheets for a single row

= [22 ft ÷ 3.33 ft.]

     6.6036 sheets

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By rounding off the sheets, we need 7 numbers roofing sheets for a single row.

b. Sheet calculation on width side of the building

Total required sloping length as calculated =21.58 ft.

Let us provide an overlapping of 250mm. ( 10″) between the two sheets.

So, the total length of sheets required

= [slopping length + overlapping ]

= [21.58 ft. + 0.833 ft.]

( as 10″ = 0.833 ft.)

22.413 ft.

The available size of roofing sheets is shown below.
Total Coated

We will go for the 12 ft. length sheets for this building.

over lapping

Total sloping length after overlapping

= [ (2nos. × sheet length) – overlapping]

= [ ( 2nos. × 12 ft.) – 0.833 ft.]

23.167 ft. > 22.413 ft ✔ OK

So, we have to buy 14 nos. of 12 ft. length sheet for the roofing work of the building.



1. We can buy 7 nos. of 12 ft. length sheet for one row & 7 nos. of 10 ft. length sheet for the second row. But, here we won’t get sufficient overlapping between the two rows.

Thank you for going through this article. 

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About Raja Junaid Iqbal

Hi My name is Raja Junaid Iqbal and i am Land Surveyor by Profession but I've specialized in the field of Q,S and land development. As Professional Surveyor I engaged my self in all over the Gulf since 14 years.

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