Roofing Formulas

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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.

Term	Explained
`count`	total counts
`len`	total metres measured
`area`	total square metres measured
`count, len or area / x`	total count/length/area divided by an `amount`
*`count, len or area x`**	total count/length/area multiplied by an `amount`
`ceil(x)`	rounding up a decimal value to the next whole number

Roofing

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

Part	Explanation	Formula	UMO
Roof area (26° pitch)	The area measured multiplied by the `roof pitch`	*`area1.113`**	m2
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 box`	*`ceil(area1.1138/250)`*	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 coverage`	*`ceil(area1.113/18)`**	rolls

Example Parts for 125mm half round guttering Length Measurement:

Part	Explanation	Formula	UMO
125mm half round guttering (7m lengths)	How many `7 metre lengths` are required of 125mm half round guttering	`ceil(len/7)`	lengths
125mm gutter brackets	How many gutter brackets are required for the `length measured` divided by `1.5 metres` intervals	`ceil(len/1.5)`	brackets

Example Parts for a downpipe Count Measurement:

Part	Explanation	Formula	UMO
100mm DVW pipe (6m)	How many `6m lengths` are required to complete downpipes when 3 metres `1/2 length (3m)` is needed for each downpipe	*`count0.5`**	lengths
100mm PVC 90° bend	How many `90° bends` are required when `3` are needed for each downpipe	*`count3`**	each
100mm saddle clip	How many `saddle clips` are required when `3` are needed for each downpipe	*`count3`**	each
100mm classic expansion outlet	How many `expansion outles` are required for each downpipe	`count`	each
Downpipe nozzle	How many `nozzles` are required for each downpipe	`count`	each
(optional) 100mm junction (for 80%)	How many junctions required for `80% of the downpipes` needed	*`ceil(count0.80)`**	each