Corrugated and Polycarbonate Sheet Calculator
Last reviewed How we calculate
Corrugated metal, fibreglass and polycarbonate sheets are the usual choice for patios, carports, lean-tos and sheds. They overlap along their sides and, on longer roofs, at their ends. This counts the sheets from the size of the roof and the sheets you are buying.
Sheets for a patio, carport or shed roof
Sheets for a patio, carport or shed roof, from the roof size, sheet width, length and end lap.
This calculator needs JavaScript to work. The measurements below are the ones you would need to do the sum by hand.
Sheets
- Sheets across
- Rows up the slope
- Area covered
Polycarbonate and fibreglass sheets move a lot with heat, so they need oversized holes, the washers made for them, and the minimum pitch the manufacturer states. None of these sheets can be walked on: work from crawl boards laid across the supports, never from the sheet itself.
How the calculation works
Divide the length along the eave by the covered width of one sheet, the width it covers once the side lap is taken off, and round up for the sheets across. If the slope is longer than one sheet, extra rows are added, each covering its length less the end lap. Multiply the two for the total.
A worked example
A carport roof 20 ft along the eave with a 12 ft slope, using sheets that cover 24 in and are 12 ft long, takes 10 sheets in a single row. If the slope were 20 ft, it would need a second row lapped 6 in over the first, and 20 sheets.
Fixing and safety
Polycarbonate and fibreglass expand and contract far more than metal as the temperature changes. They need pre-drilled oversized holes, the sealing washers made for them, and the minimum pitch the manufacturer states so that water runs off. None of these sheets can take a person’s weight. Work from crawl boards laid across the supports, never from the sheet itself; falls through roof sheets are a well-known cause of serious injury.
Frequently asked questions
What is the minimum pitch for corrugated roof sheets?
The manufacturer sets it for each sheet, and shallower pitches need longer end laps. Laying below the stated minimum lets water run back under the laps.
Can you walk on polycarbonate or fibreglass roof sheets?
No. Work from crawl boards laid across the supports, never from the sheet. Falls through roof sheets are a well-known cause of serious injury.
Why do polycarbonate sheets need oversized holes?
Polycarbonate expands and contracts far more than metal as the temperature changes. Oversized holes and the washers made for them let the sheet move without cracking around the fixings.