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require additional trays. The cavity tray walls, parapet walls and retaining walls Position of DPC in parapet wall
should over lap the vertical DPC at the jamb. exposed to the weather, should preferably
be provided with a coping.” Copings should
4.3.2 Jambs have a drip on the underside, positioned
a minimum of 40 mm from the face of the
To prevent the transmission of moisture, wall. Where for aesthetic or other reasons
a continuous vertical damp proof course a capping is used, consideration should be
should be included behind jamb sections given to the durability of the construction
and this should extend at least 25mm into beneath which may be exposed to wetting.
the cavity beyond the cavity closer. The DPC A coping with drips positioned as indicated
can be fixed to the window frame. Vertical may still not shed rainwater clear of the
DPC’s at openings should be located so as wall surfaces beneath. A continuous DPC,
to overlap the horizontal DPC at cill level, supported over the cavity, will be required
whilst being overlapped by the horizontal below a capping or coping detail to prevent
DPC at the head. the downward transfer of moisture into the
wall. This DPC should be bedded on both
4.3.3 Cills sides so that it is sandwiched in the joint and
projecting 5 mm beyond each face of the
A horizontal damp proof course with stop wall below.
ends should be provided in all jointed cills
or sub-cills, for the full length and width of In parapet walls, a stepped cavity tray will
the cill bed. If the damp proof course is in be required which should fall a minimum
contact with the inner leaf or cavity infill, the of 150mm across the cavity. Weepholes,
DPC should be turned up at the back and 75mm high are required at a maximum of
ends for the full depth of the cill. A cavity 1m centres.
barrier/thermal barrier will be required to
prevent cold bridging. Preformed cavity Further reference should be made to BSI
closers are available which provide both Standards Publication PD 6697: 2010 and
the damp proofing and thermal bridging BS 5642: Part 2:1983
requirements in one component.
Refer to BSI publication PD 6697 for full
details.
4.3.4 Cappings and Copings
BSI Standards Publication PD 6697: 2010
states that “Chimney terminals, freestanding
4.4 Position of Water Bars
In cases of high exposure and to prevent
water penetration through the joints in
the cast stone, stainless steel water bars,
bedded in polysulphide mastic, should be
specified.
