Estimating your roof area may seem complex due to the triangular shape. You may be tempted to use angle calculations and all that, but you don’t need to worry. It’s a quite straightforward process. Below are methods you can use to estimate your roofing sheet area.
Method 1. Area method
An experienced roofer once mentioned that he found out the roof area comes to 1.5 times the floor area.
That means if your floor area is 200 square meters for instance, the estimated roof area is 300 square meters. Consider adding some percentage due to the roof lapping over each other and off-cuts when installing roofing sheets.
We checked this on some of our projects and found out it’s fairly accurate. It however depends on the slope of the roof.
Simply multiply the floor area by a factor of 1.5 to get the estimated roof area.
Calculation.
Floor area= 200sq.m
Roof area= 200sq.m x 1.5 =300 square meters roofing sheet
We add 10 percent for roofing sheets lapping and off-cuts.
This comes to 330 square meters.
Method 2. Perimeter Method.
The perimeter of the floor multiplied by the height gives a good estimate of the roof area.
Since the roof area is a function of the perimeter and height, it makes perfect since that these two parameters can be combined into a formula to the roof estimate. This assumes the roof to be a sides of a box.
Then this box is collapsed into a triangular roof with the edges of the box making up for the slope of the roof.
Calculation:
Typical roof height is about 5 meters
If floor area is 200 sq.m, we assume length is 20m and width is 10m (The perimeter is best measured on site)
Perimeter =20+20+10+10= 60
Roof area =Perimeter x height
60×5= 300 square meters
We add 10 percent of roofing sheets lapping and off-cuts.
This comes to 330 square meters.
Method 3. Parametric method
This simply involves taking the information from a parametric software and deriving the roof area from there.
See image below:
The yellow highlighted information shows an estimate of 297 square meters for the same floor area used in methods 1 and 2. We approximate this to 300 square meters. Then add 10 percent for roofing sheets lapping and off-cuts.
This comes to 330 square meters.
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