For new build projects, follow the information contained in this leaflet
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 overleaf.
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
First measure the slope of your roof to do this simple 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.
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.
orrugation end lap: 30cm
Corrugation side lap: Two
Nails per sheet: 20
Nail every corrugation along the eaves, either side of the vertical laps and every other
corrugation on the intermediate purlins in an offset pattern.
The covering of roofs can be hazardous. Always work from a secure
ladder or platform and use the appropriate safety equipment
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
Complete the fixing by clipping
the integral cap onto washer body
to create a weather-tight seal to
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.
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
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
cut / 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
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 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.