Blog Archive How to Calculate or Estimate Longspan

Blog Archive How to Calculate or Estimate Longspan

How to Calculate or Estimate Longspan aluminium roofing sheets.

Refer to old articles of aluminium roofing sheets, they come in rolls of average of 600mm to 1300mm depends on the manufacture and specifications. As stated in previous articles, the aluminium sheets comes in rolls at the factory just like toilet rolls but with different widths and thickness based on specifications.

Calculating the roof required could be done by calculating the surface area in square meters of the area covered by the aluminium and for some companies it could be calculated in meter lengths ,knowing the width which is 600mm above as constant.

For a simple gable roof as shown in pic 1 with length of 25.2m. First you must know the height of roof from the section.

For this sample we  are taken the eight to be 3meters (10 feet)to know the length of leaf x or y

Gable Roof

Remember the pythagoras theorem

x 2 =3 2 + 6.1 2


Hence the  area  of  roof  is (6.8  i.e  x)+6.8  i.e y) multiply  by  length  25.2m=342.72m 2

If  the width of the roof comes  in 600mm or 0.6m, the  length of  the roof   require will be  342.72/0.6m

=571.2 meters length

So for some companies they could give their quotations in meter length so just ask for the width of the rols and follow steps above.

For a complex roof like pic 3 above, then you can  opt to do a fast estimate  based on the linear area covered as shown by roof plan as it may be a bit complex and difficult, so you can divide the roof plan to sections of rectangles or squares as it may applies –(four right angles). Then add  the areas together and add 10% of the same area, because the higher the  roof, the more the plates. and the  more complex the roof the higher the numbers of offcuts which will also increase the numbers of aluminium /plates required. So for pic 3 ,add areas of rectangles A,B,C and D which is the big center.

i.e (8.2m x 1.2m)+(1.2mx8.2m)+(1.2mx8.2m)+(22.8mx12.2m)=311.28m 2

Add 10%=311.28+31.128=342m 2

Now  for a more accurate and scientific calculation, you must know the height of the roof. have the basic knowledge of calculating area of a triangle  which is ½ base x height. And Pythagoras theorem to know the  side of any triangle. Also remember the area for a rectangle is simply length multiplied by breadth.

Assuming the height of roof is 3meters as as previous in fig. 2, and taken the   major part  D as a simple  gable roof  (check the different sections on plan fig 3) and ignoring the hipped or bevelled section.

x 2 =3 2 + 6.1 2


So area of roof as previous is ( 6.8m+6.8m) multiply by length 22.8m=310m 2

Add areas A,B,C

+310m 2  +9.84m 2 +13.44m 2 + 9.84m 2

=343.12m 2

With your estimate is also the RIDGE and GUTTERS.

Ridge is the roof material you use that will cover and seal up the points where two leaves of your aluminium sheets meet to protect the  interior from rain, it usually overlaps the two adjacent leaves of roofing sheets .

And gutter is usually underneath, it gathers rainfall and  help to channel it to wherever deem fits according to design. Is at the taper ends of two adjacent leaves of aluminium sheets to collect water.

The difference between gutter and ridge. While the ridge is up protecting rain water the gutter is down collecting rain water and channeling  to some drains.

This entry was posted on Sunday, March 3rd, 2013 at 11:12 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response. or trackback from your own site.

31 Responses to How to Calculate or Estimate Longspan aluminium roofing sheets.

This and other articles by Arc. Omion have been very helpful. Omion is one of the rare experts in his field who has single out himself to practice his profession not for the sake of money, but to be a solution to humanity.


Ur description is too technical always. Kindly find ways of simplifying wwhat youre saying. Im personally still in the dark.

Anifowose, M.O Says:

Nice job, this is a refresher course thanks.

emma Says:

All the articles on this site are written bearing in mind that they would be read by a layman, infact they are not meant for the professionals so the articles are extremely simplified already but I will try more.

Theo Osunsami Says:

Good reminder to our O level mathematics.Highly informative and educative. To a great extent, this will reduce some of the sharp practices by fraudsters.

Keep up the good job.

Olusola James Says:

Hello, thanks for all your efforts in making construction actually very interesting in one way or the other. Pls kindly email all the registered Building/Civil Engineering firm/company in Lagos state that you have their records including their email addresses, location, website if they have. Thanks, God bless you. I

dare Says:

Well Sir, dt was very easy and straight forward. I must admit dt most of ur articles I av read and are extremely helpful.

But calculation a long span is yet more complex and yet easy, but not as uve outlined. If u do, u will either be wasting material or end up not avin enuff.

Some factors are so necessary before the calculation. Like the thickness, the slope, the width and the numbers of gutters.

Well I knw ds cos av worked with an indigenous roof manufacturing and installation copoarte company, and a building technologist. Though jobless now.

But all the same Sir, Im alwys blessed by ur articles.

Ameen H. Says:

Thanks for droping this at our doorstep.


Thanks for educating the people in order to guide them in their project execution. God will enlarge your own coast

Infact i can build now

Glory Says:

Now please i still do not understand. I want u to help me to calculate how mush will it couses me to Roof 4bed room flat apartment, and 2flat apartment 3bedroom each in a flat bout roofing sheet and wood. thanks

Saint Dahks Says:

Good we are grateful with your post keep it up thanks. But sir i wish to know sizes of roofing sheets

Ahmed adebayo Says:

Infact this is aided and encouragious


This is an incredible roofing estimate diagram you have designed her regarding aluminum roofing shingles. you really go into detail her with your expertise. i just learned some new things by reading this entry. The calculation that you have put together here come from a true roofing expert in the industry. Very solid material.

Roofing sheets is a good technologythanks for posting in your blogkeep on posting about Roofing Sheets.

Abdul Adeniyu Says:

I will like to knw if it is wise t buy d aluminiom sheet frm Tower lagos, bcos I learnt dat its cheaper dan in ilorin. Thank u

simon Says:

Tnx alot 4 dis internet classroom,nd i wish 2 knw of wat length s a roofing sheet projecting beyond faecia board(concrete nd wooden).

Mercy Says:

You have really help alot of us here. Thank you very much.

samson tj Says:

tnks,kip it up,it realy help me

David Says:

I just want to say You are a great man. The information is worth more than a million my brother. Just know that only a flowing river is contantly refreshed. information sharing is key.

Adekola Taofeek Says:

my house measures 26mX11m, with 4m kingpost my engr quoted 790k for aluminium roof,including labour. is it a good deal. thanks

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