CPD Specifier May 2015 issue September 2015 | Page 39

COMMON
OPENINGS?
DPC Height and
Shape Anomaly
According to Building Regulations, LABC Premier Guarantee and other
authoritative bodies, DPC’s and cavity trays over lintels should rise a
minimum of 150mm in the cavity. NHBC allows 140mm conditional on at
least 100mm of it rising through a defined clear cavity area. But several
anomalies can arise where openings are 1200mm wide or less and where
lintels are low profile with only 150mm bearings.
150mm bearings present the builder with a problem regarding to what
extent the accompanying DPC/tray overhangs the lintel ends. (NHBC
state not less than 25mm). This is because in face brickwork, the first perp
joint available to receive the obligatory stopend, can be 225mm away from
the opening edge (a whole brick) - unless the face brickwork breaks bond.
A greater projection of the DPC/tray beyond the lintel end is therefore
required.

Walls

The regulation-compliance protection missing on this
opening can be provided with a cavitray.
The absence of an inner skin bed joint in a convenient
place does not present a problem
when using self-supporting trays.

Type C self-supporting
cavitrays used with
metal L front support
lintel and rear concrete
lintel. Yellow insulation
profiled infill is also
offered by Cavity Trays.

Similarly, if the lintel is a low profile model it can mean any accompanying
DPC/tray rising above it and requiring support has no ideally located bed
course into which it can return?
(It needs support to hold it up and prevent distortion). Using a preformed
cavitray can overcome such shortfalls and provide benefits.
The Type C cavitray is preformed DPC for common openings. It is self
supporting and tensioned to accommodate the cavity width encountered,
so does not require support from the inside skin.
It harmonizes with the lintel and construction detail. Protection over
every opening is consistent and compliant with every cavitray extending
sufficiently beyond the lintel ends to always pick up a perp joint - so
locating the stopends correctly and maintaining bond is not a problem.
Where a drip line is required across the opening head (NHBC 6.1 D.6) the
preformed Type C is also able to positively provide it - difficult to achieve
using roll DPC?
Adding Type C cavitrays when scheduling your lintels can banish site
fabrication chance and waste. Type C cavitrays can be packaged per plot,
assisting site, stock and cost controls and offered in profiles to suit your
site requirement + bespoke service.

A preformed cavitray
protects the opening,
removes the chance of
DPC distortion / error and
always provides a perp
appropriate to receive
the stopends, regardless
of how the coursings fall
across the head course.
Also shown is caviweep to
evacuate arrested water.

Cavity Trays Ltd is the