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How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required - Properties - Nairaland

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How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by saydfact(m): 1:44pm On Oct 09, 2018
Good Day; Its feels good typing 'see who's back' - with my last post over a year now - apologies to my followers and thanks to those who kept it touch.

I've been wanting to do this topic but couldn't come up with the easiest way to teach it; while it is possible to measure the quantities of roofing sheets needed for your project even before you set the first block using the Architectural drawings; it requires a lot of experience especially in trigonometry and site visualization. I have however found an easy way around it; as would be discussed below.

I have carefully designed and attached a roof plan for this purpose, (feel free to use should it fit your building design... lol)

Calculating the quantity of roofing sheet needed is done is meter square (m2), same parameters used for selling and purchasing roofing sheets hence we would expect to use the AREA FORMULAS (i.e Area formulas for Rectangle / Square, Triangle, Trapezium and Rhombus), sounds easy right? Yes it is!!!

The most difficult aspect of calculating Area of Roofing is FINDING THE TRUE LENGTH (Technical Drawing students should understand this) and that is infact why I opted for the practical way to calculate because I expect the roofing carcass to have been done on site before you can apply this teaching by asking your carpenter to measure key length as we would explain soon. (We would also discuss finding TRUE LENGTH in brief at the end of this tutorial)

LETS GET TO BUSINESS....

Diagram 1: shows the roof plan and the front elevation of a building while
Diagram 2: shows the division and label to guide us in our calculation.
Diagram 3: shows the dimensions of lengths that are ALREADY IN THEIR TRUE LENGTHS (those not labeled would have to be measured on site or calculated)

We would calculate the roof per section eg R1, R2, etc and add up later. (PRINT OUT THE ATTACHED DIAGRAMS)


Let's start by calculating R1.

The shape R1 is a triangle, so we would use the triangle formula (½BxH) where B = (A+B) in Diagram 2 = 9m and H is the true length of C. (ask your carpenter to measure (A+B) and C on site and write down the distance in meters). Measuring from my drawings C = 6.15m

Hence area of R1 = (9m x 6.15m) / 2
Area of R1 = 27.68m² (what this means is that minus waste, we need 27.68m² of roofing sheet to roof R1 alone) we would add waste after the entire exercise.

Now let's calculate R2:

The shape R2 is a trapezium hence the formula would be ½x(A+B)xH - (notice i divided R2' out) here the carpenter should measure the following distances and you can note them down; R, (F-K) and D in true length. R = 7m, F-K = 18.4-2.4 = 16m and D = 6.15m (measured from my drawings).

Hence area of R2 = ½ (7+16) x 6.15 = (23m x 6.15m) / 2
Area of R2 = 70.73m²

I separated R2' to make the calculation and formula application simplier. R2' wld now be calculated as a Rhombus using formula L x B.

Hence area of R2 = O x O' = 2.4m x 3.05m (measured from my drawings as I expect you to measure from site)
Area of R2' = 7.32m² also note that R2' = R7 hence R7 = 7.32m²

LETS FAST TRACK THE CALCULATIONS

Calculating R3:

R3 = R2 - (the small triangle in R4&R5) so I'll calculate the small triangle and subtract from R2.
hence; the area of the smaller triangle using same principle from R1 = (7m x 4.7m ) /2 = 16.45m²

R3 = 70.73 - 16.45 = 54.28m²

Now let's calculate R4 & R5: The trapezium formula applies here also; measure F, I and Q where F is the true length and F = H in the formula ½x(A+B)xH
= ½ (3.99+7.49) x 4.8 = (11.48m x 4.8m) / 2
Area of R4 = 27.55m²

Area of R5 = 27.55m² also


Now let's calculate R6 and R8: If you look at the roof plan critically, you would notice that R6 + R8 = A perfect Triangle; so instead of calculating them separately, draft it into a complete triangle and calculate using the triangle formula. Coincidentally also, R6 +R8 = R1 so lets just pick the figures from R1.

Hence R6+R8 = R1
Area of R6+R8 = 27.68m²

TOTAL AREA OF ROOFING SHEETS NEEDED THEREFORE = R1+R2+R3+R4+R5+R6+R7+R8
= 27.68 + 70.73 + 7.32 + 7.32 + 54.28 + 27.55 + 27.55 + 27.68
= 250.11m²

Now lets add waste of 10% - 20% depending on the roofing material e.g. Gerard roofing sheet would generate more waste than Long Span roofing sheet.


ADD 20% = 250.11 + 20% of 250.11 = 250.11m² + 50.02m²

TOTAL AREA OF ROOFING SHEETS = 300.13m²


Multiple 300.13 by the price of 1m² of roofing sheet eg N3200 (Gerard) = 300.13 x 3200 = N960,416:00k (Minus Accessories)


I'll briefly explain calculating TRUE LENGTH of C in R1 below.

17 Likes 10 Shares

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by saydfact(m): 1:45pm On Oct 09, 2018
HOW TO CALCULATE THE TRUE LENGTH OF C IN R1 (diagram 1,2,3 above) also see attached diagram below

From the Architectural Drawings you can get the HEIGTH AND BREATH OF THE ROOF, what the drawings won't tell you is C (I dimensioned it thou for learning purpose in the attached diagram)

USING TRIGONOMETRY A² + B² = C²
= 4.2² + 4.5² = C²
= 17.64 + 20.25 = C²
C² = 37.89

C = Root of 37.89
C = 6.15548

C = 6.155 (same with the dimension from AutoCAD)

Thanks

8 Likes 5 Shares

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by siralos135: 1:57pm On Oct 09, 2018
Weldone my brother! Great Job.I really wish this was done when I was doing my roofing.Quite sure a whole lot of people will find this very beneficial.

2 Likes

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by updatechange(m): 2:02pm On Oct 09, 2018
Nice one, reminds men of the days in T.D classes. Btw, i will rather have a company do all that while I get the best price and pay for the service but nonetheless good job�

2 Likes

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Sirheny007(m): 2:02pm On Oct 09, 2018
grin grin
Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Juicybreed(m): 2:03pm On Oct 09, 2018
Okay
Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Teewhy2: 2:04pm On Oct 09, 2018
Great Job OP , it is well detailed.

Alternative building material.
https://www.nairaland.com/3726763/alternative-building-material-expanded-polystyrene/9

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by clefstone(m): 2:05pm On Oct 09, 2018
all these stuff are just theory in a sense. You can know all the formular and all but you will never be able to get the estimation right.
1. How will u climb and measure the lengths
2. There is what they call cut and use. The experienced roofer uses this to save material.

Best bet is to get quotations from at least 3 roofing contractors and go for the cheapest but don't compromise on quality sha

NB I'm speaking from experience

5 Likes 1 Share

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by PqsMike: 2:05pm On Oct 09, 2018
I'm a Building Expect and I approve this analysis.


Meanwhile, I doubt if a layman will be able to handle such calculations having in mind that there are more complex roof designs.

Also,

Roof assesories like the hip cap, valleys e.t.c aren't taken into consideration.

3 Likes 2 Shares

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by dbtt: 2:06pm On Oct 09, 2018
The carpenters will not like this
Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Chisaedhor: 2:06pm On Oct 09, 2018
Buhari can no do this maths na

This was why he left school oo

2 Likes 1 Share

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by chukslawrence(m): 2:07pm On Oct 09, 2018
Good bro

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by hucienda: 2:07pm On Oct 09, 2018
Thanks very much Sir.

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by ba7man(m): 2:08pm On Oct 09, 2018
clefstone:
all these stuff are just theory
You obviously know nothing.

4 Likes

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Originalsly: 2:10pm On Oct 09, 2018
Hmmm......I'll need 2 calculators!.... don't have to do roofing..... but this is interesting ...knowledge put before me...free of charge. ...free space in my brain...I'll take it! Nice one OP!

2 Likes 1 Share

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by imrany20(m): 2:10pm On Oct 09, 2018
Good

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Pabloosas(m): 2:11pm On Oct 09, 2018
Nice. Thanks for this

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by holyidol(m): 2:12pm On Oct 09, 2018
You tried but you can't use the formula in all roof plan.
Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by zikter(m): 2:12pm On Oct 09, 2018
great insight. little comments. not a Bobby thread anyway

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Korofoh: 2:12pm On Oct 09, 2018
wink
Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Codo22(m): 2:13pm On Oct 09, 2018
too bad i cant relate

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by btrocky09(m): 2:13pm On Oct 09, 2018
Nice

2 Likes

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Rigel95(m): 2:14pm On Oct 09, 2018
Good, but it does not apply to all roof plans. Get a good Quantity Surveyor to avoid stories that touch.

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Edoziesmart(m): 2:17pm On Oct 09, 2018
very nice and educative article. keep it up OP.

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by Nobody: 2:17pm On Oct 09, 2018
Saving this for my building projects.

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by frowland(m): 2:18pm On Oct 09, 2018
siralos135:
Weldone my brother! Great Job.I really wish this was done when I was doing my roofing.Quite sure a whole lot of people will find this very beneficial.

Well said mate.

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by nwaobitex: 2:18pm On Oct 09, 2018
sad

1 Share

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by rhektor(m): 2:20pm On Oct 09, 2018
PqsMike:
I'm a Building Expect and I approve this analysis.


Meanwhile, I doubt if a layman will be able to handle such calculations having in mind that there are more complex roof designs.

Also,

Roof assesories like the hip cap, valleys e.t.c aren't taken into consideration.


Eave angles as well as other flashing will consume materials it must also be provided for
Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by GreenArrow2: 2:23pm On Oct 09, 2018
I remember loving this particular part of Estimating Quantites back in uni days as it gave us a break from the usual structural mechanics courses every once in a while. Nice one o.p.

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by AmazingELixir: 2:26pm On Oct 09, 2018
grin

Very kool stuff Op ..well done.

Please correct the nomenclature for Area R2..... should be ( P - K) and not ( F - K )

1 Like

Re: How To Practically Calculate The Quantity (m2) Of Roofing Sheet Required by karlswizzy(m): 2:30pm On Oct 09, 2018
op are you a quantity surveyor. nice job

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