GRP Dormer - IG Lintels

STEP 4
STEP 5
Batten installation
Final tiling & flashing
Now that dormer is secure,
normal tiling/slate batten
installation can take place.
75Min
m .
15 Max m
0m .
m
GRP dormers normally
have 2 different types of
fixing/flashing details, A)
secret gutter & B) Mortar bed.
Battens are secured in same
way on both.
To secure batten correctly
remove section marked X
as to ensure batten does
not ‘kick up’ causing open
void problems.
GRP Dormer
Transportation, Storage
& Fitting Instructions (Enc)
In order to avoid damage, dormer
should be stored with the back face to
the ground on a flat and even surface
as shown, preferably under cover. Care
should be taken when handling to avoid
compromising the finished surface.
x
Due to the lightweight nature of the
products, damage may occur in windy
conditions. On no account should weight
be put on them to hold them down.
GRP dormers can be supplied with either code 4 lead or a rapid flashing apron fixed to bottom
edge. In order to support this apron and avoid a water pooling effect, IG GRP recommends the
installation of a timber support filet. The support fillet can be a flat ply section which is secured to
extra support batten.
A
A - SECRET GUTTER
Secret gutter dormers come complete
with a foam compression strip to provide
secondary cloak to open verge. Particular
care must be taken when securing batten
through GRP as to not penetrate GRP
too close to secret gutter. Suitable verge
fixing clips to match your roof covering
are screwed into position leaving around
25-50mm distance from GRP side cheek
to clip.
B
B - MORTAR BED
All mortar bed dormers are manufactured
with 2No. weather bars spaced 50mm apart,
these have a keyed surface to aid with mortar
bonding. When dormer is secured a bed of
mortar is laid the full length of dormer. Suitable
verge fixing clips to match your roof covering
are screwed into position leaving around
25-50mm distance from GRP side cheek to
clip. Roof tiles are locked into position as per
normal verge construction ensuring the end tile
is suitably bonded onto mortar bed. When tiles
are secured, please finish verge by pointing full
length of dormer.
Ensure flashing is pushed back to clear working
area. Secure extra batten to act as support for
ply section. Note batten must extend further
than flashing.
Fix ply section to tiling batten to create
path for flashing to follow. When in situ, fold
flashing over tiles as shown.
IGGRP -Ballyreagh Ind. Est,
Sandholes Road,
Cookstown, BT80 9DG
T: 028 8676 2184
F: 028 8676 1011
E:[email protected]
Transportation
Storage
www.iggrp.co.uk
STEP 1
STEP 2
Roof preparation
IG dormers can be
installed on a pitched
roof in a number of
different ways.
STEP 3
Roof membrane
As per normal
roof construction,
membrane is now laid
onto roof before dormer
installation.
B
IG GRP’s preferred
method of installation
is illustrated below in
details A & B.
Dormer installation
At this stage the roof is prepared for
the installation of the GRP dormer.
Dormer should be craned into position
using suitable slings. Slings to pass
through window opening and under
sacrificial lifting beams. Lower dormer
into position ensuring the inside wall
of the dormer is vertically aligned
with the inside face of the dormer
support rafters. (Measurement noted
on technical drawings) dormer is now
ready to be secured.
Should dormer need
to be installed before
roof membrane, ensure a
secondary membrane is secured
under dormer position so main
roof membrane can lap under.
A
Variable
METHOD A
The ply seat method is installed between
dormer double support rafter and the
adjacent rafter.
To fix ply seat, secure 2 No. battens to the
inside face of both rafters so both battens
are facing each other. Ensure battens are
positioned lower than top of truss to allow
for thickness of ply (typically 18mm).
Cut ply to correct width and length (check
dormer GRP fixing flange), lower ply onto
battens and secure with wood screws at
450 centres into each batten. At this stage
a check should be made to ensure top of
ply and top of rafter are level.
METHOD B
Loose truss method is again installed to
support dormer fixing/flashing flange.
Measure the distance from the inside of the
dormer wall to the outside edge of the GRP
fixing/flashing flange (shown as variable).
Cut and install timber noggins between
dormer support rafter and adjacent rafter
and secure with screws. Ensure noggins are
secured at a distance apart greater than
dormer fixing/flashing flange.
Cut intermediate support rafter and position
between noggins at desired width as
determined by the variable measurement.
Trim away roof membrane to expose structural
opening. Excess can be discarded.
Directly above the highest point of the dormer,
Directly above the highest point of the dormer,
at the first membrane overlap, cut a secondary
membrane secton approx 600mm wider than
O/A dormer width. This section is to be slid in
between overlapping joints leaving enough to
lie onto dormer fixing/flashing flange.
In order to secure dormer to support rafters
use fixing plates (4 No), plates to be secured
to timber side cheek and secured to inside
face of support rafter. Ensure all fixing holes
are secured and a minimum of 2 No plates are
used on each side.
With dormer secure, lay out secondary
membrane on top of rear dormer flashing/
fixing flange (this membrane is required to
direct any moisture onto GRP gutter).

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