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
Gable Roof

section of roof

Remember the pythagoras theorem

x2=32 +6.12


Hence the  area  of  roof  is (6.8  i.e  x)+6.8  i.e y) multiply  by  length  25.2m=342.72m2

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.

hip roof plan fig 3

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)=311.28m2

Add 10%=311.28+31.128=342m2

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.

section of roof

x2=32 +6.12


So area of roof as previous is ( 6.8m+6.8m) multiply by length 22.8m=310m2

Add areas A,B,C

+310m2  +9.84m2 +13.44m2 + 9.84m2


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.

An architect with decades of experience


  1. 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.
    I love this, ride on Omion

    1. 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.

  2. 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.

  3. 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

  4. 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 u’ve 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, I’m alwys blessed by ur articles.

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

  6. 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

  7. 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.

  8. 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

  9. 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).

  10. 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.

  11. Weldone sir I appreciate all your effort but I still don’t understand the measurement presently I have 4 bedroom flat around odokekere and I’m about to roof it.the expert told me after carpentary work that I ll need a total 565m of aluminium roofing sheet or 15 bundles of pan depending on available cash plz how many sheet of aluminium roof sheet will I require base on that meters above. Please help me out.

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

  13. I really appreciate the knowlege shared by the initiator of this topic, it has been helpful really. Buy some things are not clear to me. After getting the overall enght required, how do we know the lenght to cut each plate into from d factory, since each plate has different lenght on the roof, especially in complex pitched roof with d highest plate at the apex. Thanks

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