Kumar IronUpdated
In this guide
Sheet width is not cover width
Every sheet has an overall width, and a smaller effective cover width. The difference is the side lap, the part that overlaps the next sheet. The overlap is hidden, so it does not count toward the roof.
The gap between the two numbers depends on the profile, not just the brand. Published data sheets show this clearly. Lysaght lists a maximum effective cover width of 762 mm for its CUSTOM ORB sheet. Apex Steel's Covermax data sheet gives 780 mm. Mabati lists 1015 mm for its MaxCover product. These are examples of how much the figure varies, not stock you will find in every shop. Use the cover width printed for the exact profile you are buying.
| Sheet | Effective cover width | Source type |
|---|---|---|
| Lysaght CUSTOM ORB | 762 mm (maximum) | Manufacturer page |
| Apex Covermax | 780 mm | Manufacturer data sheet |
| Mabati MaxCover | 1015 mm | Manufacturer product page |
How many sheets for a roof
Try it: Roofing sheet calculator
Overall width 1060 mm minus side overlap gives an effective cover of 1000 mm. Widths are typical; confirm with the sheet you buy.
- Roof area: 63.9 m² (687 sq ft), slope length 3.19 m
- Sheets: 40 of 10 ft (10 across × 2 down × 2 slopes)
- Ridge caps: 6 (2 m pieces, 150 mm overlap)
- J-hooks or screws (with washers): 378
- Least waste for this roof: 11 ft sheets
Take the roof width, measured across the slope from eave to eave for one side, and divide it by the effective cover width. Round the answer up. That is the number of sheets across. Then multiply by the number of sheet rows, which is the eave to ridge length divided by the sheet length (after allowing for overhang and end laps).
Do this for both slopes of the roof, and do not forget the ridge and gable ends. A roof with two slopes is not one big rectangle, so calculate each slope separately and add them.
- Count across: roof width divided by effective cover width, rounded up.
- Count along: eave to ridge length, plus overhang at the eave, plus end lap, divided by the sheet length.
- Multiply the two, then do the same for the other slope.
- Add a few extra sheets for cutouts around vents, skylights and corners.
Our roofing sheet calculator does this arithmetic. Enter the cover width for your exact profile, not the printed sheet width.
Choosing the length to avoid end laps
An end lap is the place where one sheet sits over the next along the slope. Every end lap is a joint that can leak, and it needs a purlin under it so it can be fixed down. Fewer end laps means fewer weak points.
Everest's installation guide gives an end lap of 150 mm to 300 mm, depending on roof pitch. It does not say which pitch takes which value, but flatter roofs generally need the longer lap. Side laps are usually one corrugation, or whatever the manufacturer specifies.
The best approach is to order full-length sheets that run from eave to ridge in one piece, where the dealer can deliver that length to your site. The practical limit is the transport and the lift to the roof, not the sheet itself. Ask the dealer what lengths can be delivered and carried up, and then plan the end laps only where the length is not enough.
- Measure eave to ridge on both slopes before choosing the length.
- Add the overhang and the end lap to that figure, then round up to a length that is available.
- Avoid very long sheets that cannot be lifted safely by the crew you have.
- Ask whether the lap is sealed or taped for your roof pitch and rainfall.
Side laps and overhang
The side lap is normally one corrugation to keep the roof leak safe, as Palram's installation guide says for its profiled sheets. On a flat roof, or in heavy rain, the maker may ask for more or for sealant. Lay each sheet so that its lap faces away from the prevailing wind.
At the eaves, let the sheet project past the last purlin so water falls clear of the wall or gutter. The purlin spacing and roof slope guide covers the detail.
Accessories to buy with the sheets
Sheets alone do not finish a roof. Order these at the same time so the crew does not have to stop halfway.
| Item | What it does | Buy how many |
|---|---|---|
| Ridge cap | Covers the top joint of the two slopes | Length of ridge, plus overlap at each joint |
| Eave and gable flashing | Closes the edge and keeps wind-blown rain out | Edge length on each side |
| Fixing: J hooks or self-drilling screws | Holds sheets to purlins | Per purlin, per crest, plus extra at the edges |
| EPDM washers | Seals each fixing | One per fixing, plus spares |
| End lap sealant or tape | Seals end laps where the maker recommends | Per end lap |
| Gutter and downpipe | Carries roof water away | Eave length plus bends and outlets |
| Valley or wall flashing | Seals where roof meets a wall or another roof | As per the junction |
Wastage and a practical check
Some sheets are damaged, cut badly or lost in handling. Our sheet count assumes a clean job. Add a few spare sheets for cutting around vents, skylights and corners, and keep the offcuts if they are long enough to reuse.
Before the order goes in, check the count against the roof width, sheet cover, length and the number of fixings. A quick second calculation on paper catches most mistakes.
- Confirm the profile name and the effective cover width in writing.
- Confirm the thickness (mm) and coating, since sheets with the same look can differ.
- Ask for the delivered length and whether the dealer can cut to order.
Share the length, width and slope of your roof and we will help you work out the sheet count and accessories. Rates change, so please call or WhatsApp the store for the day's price.
Frequently asked questions
- How many sheets do I need for a 10 by 6 metre shed?
- Divide the roof width by the effective cover width of your chosen profile and round up, then multiply by the number of rows. Use the calculator with the cover width printed for your sheet, not the overall width.
- Why is the sheet count different from the sheet width?
- Because each sheet overlaps the next. Only the effective cover width is exposed, so the count is higher than a simple width division would suggest.
- What length of roofing sheet should I order?
- Choose a length that runs from eave to ridge with the overhang and end lap included, so you have as few end laps as possible. Confirm with the dealer what can be delivered and carried to your site.
- How much overlap do roofing sheets need?
- End laps are commonly 150 mm to 300 mm, more on flatter roofs. Side laps are usually one corrugation unless the maker says otherwise.