Page 20 - Haddonstone

20 4.5 Cold bridging & Insulation

73 All external walls should be designed to meet the requirements of the relevant Building
Regulations, in particular Approved Document Part L, and the general thermal insulation
requirements of the building. The implication of cold bridging and risk of condensation,
for example at exposed internal mullions, and window head and cill positions, should be
considered and cold bridge paths should be avoided. Consult your UKCSA supplier for
design information specific to the cast stone detailing of the project.

4.6 Prevention of Staining

Where the sectional profile allows it, all Lead or copper flashing over cast stone
projecting components should be detailed can cause staining. As an alternative, GRP
with a drip groove in an attempt to shed or metal pre-formed flashings should be
water clear of the face of the structure and used. All flashing or weathering details
to reduce staining. However, as indicated should be bedded at least 25mm into
in Section 4.3.4 the inclusion of a drip may the works and be provided with sealed
still not shed rainwater clear of the wall joints and adequate overlaps. Attention to
surfaces beneath. detail can prevent water from the flashing
washing over the surface of the cast stone.

4.7 The Design of the Element

As many UKCSA members offer a creating the same effect using the
bespoke service to customers, cost jointed components.
savings can often be achieved by
discussing customised components at the • Avoid mitred joints. The use of quoins
design stage. The following comments are is traditional for wall construction and
of a general nature only. jointed returns are an alternative, much
more robust solution.
• Avoid slender projections from the unit.
These increase the likelihood of damage Consideration should also be given
on demoulding and do not enhance to slenderness ratios when designing
either the appearance or authenticity of cast stone units to minimise the risk of
the final units. cracking.

• Avoid negative rakes as these present Please refer to Section 8.4.5 for more
difficulties in mould design. information.

• Avoid ‘U’ sections. These are very
difficult to mould and less robust than