Corrugated Sheet Roofing, Corrugations
Corrugated sheet roofing material is widely available and easy to
Corrugations should run in a straight line between the highest and
lowest points, and at a right angle to the purlins (the
The overlaps (ends and sides) depends upon the sloop of the roof.
Purlin spacing should suit the end laps required for the size of
sheet to be used.
Sheets should be laid so that the side overlaps are directed away
from the prevailing wind.
All purlins should be in one plane and parallel to each other. They
should be properly anchored to the supporting superstructure.
Ends of all sheets should be supported by purlins. The free
overhang at the eaves should not exceed 300 mm.
8 mm diameter (min) hook bolts, crank bolts or coach screws, should
be inserted through 10 mm diameter drilled holes.- NEVER PUNCHED -
in the crown of the corrugations.
Nuts or screws should be tightened lightly at first, and then
tightened again when a dozen or more sheets have been laid. At
intermediate purlins, they should not be tightened in an attempt to
make the sheet rest on the purlins.
A cat-ladder or roof board should always be used when working on a
roof for safety of the person and to avoid damage to the roofing
Installation of corrugated roof sheeting
These notes are intended to cover the use and installation of
corrugated roof sheets such as PVC, other plastics and bitumen
fibre sheets. Although very different as materials and where they
are used, they do have similar properties regarding flexibility and
weight. One advantage of these corrugated materials is that it is
far more rigid than a flat sheet of a similar type and thickness.
This enables considerable savings in both weight and cost, it also
makes the sheet relatively easy to handle. Generally all these
types of material can be used either as roofing or vertical
Most of these sheeting tends to be susceptible to condensation when
used as cladding for outhouses etc. - being relatively thin they
tend to have low thermal insulation properties. Condensation will
be reduced if the interior of the structure is well ventilated.
Being thin sheeting, most types will act as a 'drum skin' when it
rains. The sheets can also become heated by direct sunlight and
this heating can be radiated into the building making it very
uncomfortable in hot weather. A false ceiling suspended under the
roof can reduce both of these problems, the void between the
roofing and ceiling must be adequately ventilated to avoid
excessive temperatures (especially important where plastic roof
sheeting is used) and to minimise condensation. Choosing light
colour sheets (or, where the material allows this, painting them
white/silver) will reduce the internal heating effect.
PVC has a service temperature range of -20°C - +70°C. Care must be
taken to ensure that it is not used in situations where the maximum
service temperature could be exceeded. As such it is not
recommended for use in situations where a false ceiling is to be
erected below the rooflight, as this will cause heat build up in
the sheet, exceeding the maximum temperature of +70°C which may
lead to discoloration or distortion of the sheet.
Storing before use
Plastic and bitumen sheets must not be stored in a stack in direct
sunlight, as solar heating will cause the sheets in the centre of
the stack to distort. If sheets have to be left outside prior to
installation, they should be covered completely by an opaque,
Avoid working with sheet materials in windy conditions, even in
light breezes it may be necessary to temporarily weight the sheets
while working with them - this is especially relevant to light
weight plastic sheets.
The underlying roof structure
The roof structure will comprise rafters and purlins. The rafters
take the full weight of the roof material plus any 'environmental
build-up' (such as snow) and anyone working on the roof.
The pitch of the roof will determine the amount of end overlap
necessary. In order to ensure that this can be achieved and to
leave a neat appearance, the sheets should first be arranged loose
on the roof. The end and side overlaps are a 'minimum', to avoid
unnecessary cutting of sheets, the overlaps can be increased to
hide any excess. At the same time, the positions of fixing screws
and any saw cuts which may be needed can be marked on the sheets.
The spacing of the purlins needs to be arranged to suit the roofing
while the rafters can be spaced as appropriate to take into account
the overall weight. The spacing of the purlins, the end and side
overlaps of the sheets depends on the angle of the roof - for most
types of sheet, the following are good guidelines but check with
the manufacturers of any particular type of sheet:
|Roof pitch||Support||End overlap||Side overlap|
|1 in 12 to 1 in 6|
(5 to 10 degrees)
|Decking or close boarding||300mm||2|
|1 in 6 to 1 in 4|
(10 to 15 degrees)
|Purlins at 450mm spacing||200mm||1|
|1 in 4 or less|
(over 15 degrees)
|Purlins at 600mm spacing||170mm||1|
note: Side overlap is number of corrugations
Purlins must be at the correct centres and size for the material
and slope of the roof. The position of purlins at the upper and
lower ends of the roof and at the sheet overlaps are the critical
points, there must be purlin where you need to nail. Having
determined the upper, lower and overlap purlins, evenly space the
remaining purlins in between. As an aid to setting out the purlins,
use a timber spacer to keep the purlins square to the eaves. It is
important that the maximum support centres given for the type of
corrugated sheet being used are not exceeded between purlins.
Laying the sheets
Commence fixing sheets at the lower edge of the roof at the
opposite end to the prevailing winds. Stagger the sheets using a
half sheet to start the second row.
Commence fixing ridges at the opposite end of the roof to the
prevailing winds. Overlaps should be about 125mm.
(the ends of the roof)
To prevent the ingress of water from driving rain, the sheets
should be arranged to overhang the verge (the ends of the roof) by
approximately one corrugation. Do not overhang the fascia by more
than 70mm. If larger verge or fascia overlaps are used, the wind
will tend to catch this area and wind damage to the roof may
Verges should be formed by either nailing the final corrugation
over a raised barge board or using a ridge piece to lay over the
Do not overhang the fascia by more than 70mm. Draughts may be
reduced by using foam filler pieces at the eves, but don't exclude
Always follow the manufacturers guidelines for cutting the sheets.
If cutting PVC is necessary, use a fine toothed hand saw or
circular power saw - practice on a scrap piece of material to
ensure that the material can be successfully cut. Lubricate with a
general purpose lubricating oil to prevent binding.
Corrugated material is supplied in various lengths, so cutting can
often be avoided by selecting the appropriate size (or a number of
sizes) at the planning stage - you will probably need to cut
alternative ends sheets lengthways so that the vertical joins are
staggered. Where cutting across a sheet is necessary, lay one sheet
on top of the sheet to be cut to mark the cutting line. If it has
to be cut, to fit around projections for example, use a fine
toothed hand saw at a shallow angle, supporting the sheet to
minimise vibration. The sheet may be cut by sandwiching it between
the others, leaving the part to be removed projecting from the
Some plastics may crack or split if sawn or drilled in cold
weather, so leave the sheets in a warm room for 2 or 3 hours prior
to sawing or drilling.
Try to arrange that cut edges are concealed by the overlap of
It is generally best (although more awkward) to drill sheets
in-stitu so that holes line up with the purlins and holes in
overlapping sheets line up. To accommodate thermal movement, the
fixing holes should be drilled about 5mm greater in diameter than
the fixing shank for sheet lengths up to 2m and an additional 2mm
per additional metre length of sheet. Fixings should only be
positioned on the crown of ridges when mounted and should always be
used with a sealing washer which will normally eliminate rainwater
seepage. Specially designed spacers which prevent profile
distortion are available to remove the chance of inadvertent
Drill over a firm support using light pressure with a hand drill or
slow speed power drill fitted with a suitable drill bit. Make sure
the drill bit does the cutting, this should avoid splitting of the
Nail through the crown of the corrugations into the purlins or
decking. Nail every corrugation at the sheet overlaps and at the
top and bottom of the slope. Nail centres may be reduced to
alternative corrugation at immediate purlins. So you don't 'lose'
the purlins on opaque sheeting, mark the position of them on the
top side of each sheet as you lay it, use a straight edge or taut
line to position the fixings across the sheet. Do not nail the top
row or underlapping side fixings until the overlapping sheets are
Lap sheets away from the prevailing wind and use Sealing Tape to
prevent ingress of dust and dirt. Use Wall Flashing at the top of
the slope in lean-to situations or a ridge piece as appropriate.
Use Foam Filler at the bottom of the slope to prevent draughts but
don't forget to ensure adequate ventilation. Eaves fillers used at
other purlin positions are useful in preventing 'roof-chatter', a
common problem with lightweight roof coverings. The cladding should
be supported at maximum centres as specified by the manufacturer -
and fixings should be a minimum of 50mm from sheet ends.
Corrugated bitumen sheets, one of the most affordable solutions for
roofing and wall paneling, have been in use all over the world for
decades. Cost-Effective, maintenance free, high laying performance,
long life, low- weight and durable under all conceivable climatic
The upper layers of the sheet are saturated during production with
color and resins, because of which the possibility of subsequent
peeling-off of the color is eliminated. The sheets reveal the true
intensity of their coloration only after a certain time on the
roof. Owing to the natural oxidation of the bitumen on the surface,
the sheets become lighter and thus brighter.
In order to guarantee a uniform quality, bitumen corrugated sheets
are continuously quality-monitored and tested by the MPA of the TH
High stability with low weight
KRS bitumen corrugated sheets, thanks to the patented multi-layer
structure, have a very high stability, and at the same time, a low
The fibers, the majority of which run parallel to the corrugation,
result in a high flexibility. The KRS bitumen corrugated sheets thus facilitate an optimum matching even
to uneven under-constructions. Thanks to this property, they are
ideal for sanitation. Arching radii above 8 m can be laid without
All corrugated bitumen sheets are CE certified and comply with the
European Standard EN 534: