Roofing Formulas
  • 03 Jan 2024
  • 2 Minutes to read
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Roofing Formulas

  • Dark
  • PDF

Article Summary

Before reading this article, ensure you have read Measurement - Parts & Labour and Using Formula within Groundplan articles to aid in understanding the following Formula examples.

Please note:
  • If there is more than one roof pitch required on the Project, each pitch must be a separate Measurement with the correct Formula, Parts and/or Labour applied.
  • The Roof Pitch Chart will assist with common roof pitches.
  • Find the secant of a slope using a scientific calculator.

📝 The Formula values provided in this article are for example purposes only.

counttotal counts
lentotal metres measured
areatotal square metres measured
count, len or area / xtotal count/length/area divided by an amount
count, len or area * xtotal count/length/area multiplied by an amount
ceil(x)rounding up a decimal value to the next whole number


Example Parts for Roof area (26° pitch) using an Area Measurement:


Roof area (26° pitch)The area measured multiplied by the roof pitcharea*1.113m2
Roofing screws (8 per m2)How many screws are required for the area measured multiplied by the roof pitch and allowing for 8 per m2 divided by 250 screws in a boxceil(area*1.113*8/250)boxes
Insulation / wool / sarking (18m2 coverage)How many rolls are required for the area measured multiplied by the roof pitch divided by based on 18m2 coverageceil(area*1.113/18)rolls


Example Parts for 125mm half round guttering Length Measurement:


125mm half round guttering (7m lengths)How many 7 metre lengths are required of 125mm half round gutteringceil(len/7)lengths
125mm gutter bracketsHow many gutter brackets are required for the length measured divided by 1.5 metres intervalsceil(len/1.5)brackets


Example Parts for a downpipe Count Measurement:


100mm DVW pipe (6m)How many 6m lengths are required to complete downpipes when 3 metres 1/2 length (3m) is needed for each downpipecount*0.5lengths
100mm PVC 90° bendHow many 90° bends are required when 3 are needed for each downpipecount*3each
100mm saddle clipHow many saddle clips are required when 3 are needed for each downpipecount*3each
100mm classic expansion outletHow many expansion outles are required for each downpipecounteach
Downpipe nozzleHow many nozzles are required for each downpipecounteach
(optional) 100mm junction (for 80%)How many junctions required for 80% of the downpipes neededceil(count*0.80)each

For Formula assistance, please reach out to Support. Go to: Help > Send us a Message.

Download a PDF copy of Using Formulas within Groundplan here.

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