Waterproof Flat Roofs
Flat roofs using concrete, FC and plywood, have
become very popular for houses with a view as it enables them to go higher
than a pitched tile or metal roof. They also provide an excellent surface for
air conditioning, solar panels and possibly recreational areas if permitted
by the local council.
From the waterproofing point of view, the key
question is whether the roof is insulated on top or below the concrete as FC
and plywood are normally membrane roofs. If insulating on top, called IRMA
(Inverted Roof Membrane Assembly), then Wrimco SBS plain is used, but if
exposed, then torch apply Wrimco SBS Granules.
New Flat Roof Construction
For roofs with stepped sections and parapets, it
is normal to run the membrane up and over, but if the height exceeds say 1 m,
then best to terminate with a Z section pressure seal and continue with an
external acrylic. Metal
not recommended as screws through the membrane should be avoided where
possible, even though they can be effectively sealed with brush applied
Wrimco Flashing and Polyroof SBS caulking mastic.
Where toppings or reinforced screeds are applied
over the membrane to create good falls, the membrane should be protected with
For large commercial buildings, pavers are often
supported on adjustable Polypads and laser levelled while the concrete is
laid to falls. To guard against fire from accumulated flammable debris that
may fall through the openings between the pavers, self protected Wrimco SBS
Granules should be used instead of protection boards.
Repair leaking roofs
Roofs are fairly easy to repair provided the
substrate can be viewed from below and high risk loose laid Plasticised
(Polyester) PVC or APP bitumen membrane have not been used, as the source of
the water penenetration can be fairly easy located with fully bonded system
having elastic properties.
If the old membrane has lost its properties due
to plasticiser migration, UV degradation, water ponding (latter especially
with acrylics) or movement in the structure, then it is always preferable to
replace it with Wrimco SBS rather than go over it. For liquid applied
membranes then cannot be readily stripped like sheet membranes and still
adhere strongly, then simply torch over with Wrimco SBS as the molten SBS is
an excellent adhesive.
Gutters and sheet metal ducts often should be
replaced but may be very difficult to do so in practice. For metal gutters,
self adhesive tapes (SBS or butyl rubber) over the joints followed by a
liquid applied membrane such as Wrimco supplied BLF latex/bitumen provide an
It is difficult but not impossible to torch apply
SBS onto metal because of its high expansion or Rigid PVC because of its low
decomposition temperature. Applying a first layer of SBS self stick such as
Self-adhesive SBS Membrane will greatly facilitate subsequent torch
application, or a second layer of Self-adhesive Granules can be used.
Where torch on membrane has lost adhesion to a
wall, but is still sound, retorch and apply a pressure seal. If there is a
problem with vent pipes, clamp a SS jubilee clip to ensure water does not
penetrate at such points.