Planning & preparation
- For new build projects, follow the information contained in this guide to create a long lasting trouble free corrugated sheet roof covering
- For an existing roof, survey your roof structure. This will allow you to decide if it requires maintenance, upgrading or strengthening prior to fixing the sheets. Make a note of the roof construction; you will require either a purlin on rafters, or decked roof e.g. roofing grade OSB or plywood supported on a trussed roof structure as detailed below
- Take care to fix the bitumen corrugated sheets the correct way up. The top of the sheet has a smooth grained surface, whilst the underside of the sheet is identified by its dimpled rough surface finish
- The sheets also finish with the corrugation edge facing down to the surface of the roof
Do it right
- The angle and slope of your roof will determine the level of support needed for the bitumen sheets
- Use our guide below to check that the supports are sufficient, and increase support if necessary
- The covering of roofs can be hazardous. Always work from a secure ladder or platform and use the appropriate safety equipment
- First measure the slope of your roof. To do this, simply measure the angle of your roof with a protractor. Then select one of the three options detailed below that best matches the slope of your roof
- The selected option details the minimum support required below the sheets, how to lay the sheets with appropriate corrugation end and side laps and finally the sheet fixings required
- Nail every corrugation along the eaves, either side of the vertical laps and every other corrugation on the intermediate purlins in an offset pattern
Roof slope 15° & over
Fix sheets on purlins at maximum centres of 61cm. Corrugation end lap: 17cm Corrugation side lap: One Nails per sheet: 20
Roof slope 10° to 15°
Fix sheets on purlins at maximum centres of 45cm. Corrugation end lap: 20cm Corrugation side lap: One Nails per sheet: 25
Roof slope 5° to 10°
Sheets must be laid on fully supporting roof deck. Corrugation end lap: 30cm Corrugation side lap: Two Nails per sheet: 20
Start alternate courses of sheets with a half width sheet; this forms a broken bond sheet pattern, thus avoiding a 4 ply sheet thickness build up at the corners of sheets.
Position and fix an additional purlin at the ridge to take ridge fixings. The sheets should be laid to ridge apex to ensure sufficient weathering cover is provided.
Check the deck is at least 20mm thick to accept nails. If thinner you can either apply battens, or boarding as detailed above, or substitute nails with screws.
Fix by nailing through washer assemble and top of the sheet corrugation into the purlin below. The nail will penetrate the purlin by nominally 20mm.
Complete the fixing by clipping the integral cap onto washer body to create a weather-tight seal to the roof.
Alternatively, substitute nail with 65mm exterior screw. Length of screw can be reduced (55mm min.) for fixing onto thin decks. Check cap will clip over screw head.
Cutting the sheets
Measure the size of the material required and mark out the line to be cut with chalk line or pencil onto the sheet surface prior to cutting. Always measure twice so you only cut once!
When cutting complex shapes use a pair of oiled tin snips. First mark the cut line onto the sheet and then cut to required shape.
Support the sheet and cut using a coarse bladed saw, taking time to clean and lubricate with a spray of oil on the saw as required.
Alternatively a circular power saw can be used; support the sheet either side of line to be cut, using saw in accordance with manufacturer’s instructions.
First mark out cut line in the base of the sheet corrugation. Then cut or score the sheet with a knife.
Next fold back the sheet along the scored line to separate the cut sections of the sheet.
Overhang the sheets at the fascia by 5cm to form a drip edge. Reduce the fixing centre to the first purlin up from the eaves by 5cm to compensate for overhang.
Ensure the sheets are positioned square to the line of the eaves and verge, first nailing the sheet edges (allowing for laps) to keep sheets square to the eaves line.
Position and fix the verge barge board within the last sheet corrugation then fold down over the board and nail using 10mm galvanised clout nails at 15cm centres.
Alternatively, align and fix the verge barge board level with top of purlins, then overlap the sheet by 5mm off the roof edge and secure by nailing the sheet at every purlin.
Fix the sheets to ridge line, overlay ridge piece and mark out fixing line then nail ridge to one roof slope. Then next carefully bend ridge and fix to reverse side of the roof.
The ridges feature pre-formed end alignment grooves which are embossed into them. Simply overlap and align them and you are assured a professional finish.
Fitting the ridge piece
The ridges are flexible enough to be formed to the required roof angle. Lay them square to the ridge line and fix one side first by nailing every other corrugation.
Fix timber ridge board level with corrugation height to rear of building; then fix ridge to the roof and fold ridge and nail to the ridge board to finish.
Terminate the ridge end by marking out and cutting a treated timber finial to match the ridge profile. The ridge piece is lapped onto the finial.
The finial is then simply fixed to the verge barge boards and finished to match the decorative finish applied.