CPD Specifier May 2015 issue September 2014 | Page 13

Walls

Damp and thermal
deterioration
following
winters
driving
rain?

Ordinary closer integrating with Type GBOT Balcony
Opening Tray. It can also accommodate the thermally
efficient Continuity Closer.

The Continuity Closer wraps around the cavity
insulation, blocking gaps and closing the heat
loss path.

Last winter’s weather highlighted weaknesses
in cavity wall construction. Dampness appeared
at junctions, openings and abutments previously
thought to be satisfactory. Wind-driven rain
resulted in masonry rapidly reaching saturation
point. This water then gravitated within the
masonry and also ran down the cavity face of it.
DPC protection that was inadequate, defective
or simply incorrectly installed failed to prevent
such water from reaching those parts of the
structure that should have been kept dry. So
what went wrong and how can one avoid a
reoccurrence?
Some masonry might not be as resilient to water
penetration as one might assume. Masonry
tested to BS4315 might be described as having
very low levels of rain penetration, but the test
can involve water spraying for one minute only
every half hour. Over a 48 hour test period that
amounts to just 1½ hours spraying. If the rain in
your district only ever falls for one minute and
is always followed by half an hours’ drying time,
then perhaps the test is meaningful, albeit not
realistic of the climate experienced in the UK?
Water migration through masonry requires
arrestment and evacuation. Once an average
brick becomes saturated, its conductivity can

CAVITY TRAYS OF YEOVIL

double. So the thermal behaviour of the outside
skin is less conducive to heat conservation and
thermal integrity of the structure when it’s wet.
It’s another reason why controlling water and
evacuating it out of the structures as swiftly as
possible makes good sense.
Cavity walls with partial fill insulation can suffer
coldness and dampness around openings
because the partial fill insulation is kept back
from the reveal face so the reveal closer
has sufficient space to fit. Unfortunately it
is commonly kept back too much, resulting
in a gap between the closer and the cavity
insulation. This gap creates a non-compliance
(L1A 5.9 states there shall be no unreasonably
avoidable thermal bridges caused by gaps). This
thermal Achilles heel is easily remedied using a
Continuity Closer that has a shaped insulating
core that wraps around the insulation, blocking
any gap and closing the heat loss path. Whether
first or second fixed, it provides a level of
integration not possible with an ordinary closer.
The general rule is for a closer to terminate
below sill level, but there are a couple of
applications where this rule is reversed to avoid
possible damp ingress: One such application is
where a balcony structurally links through the

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wall interrupting the open cavity, and another
is where the area below a balcony is not an
open space - ie: it is part of the building. In both
situations the closer should terminate into and
integrate with the balcony horizontal protection,
rather than continuing below sill level. Called
a Type G Balcony Opening Tray, the Type
GBOT consists of a self-contained specially
shaped tray that accommodates the lower end
of the reveal cavicloser. It links with adjoining
horizontal Type G trays and has upstands to
prevent discharge into the protected area under.
Type GBOT trays are handed to suit both sides
of the balcony doorway frame and are linked to
a connecting cavitray that runs underneath the
sill to