Design fundamentals - The Hempcrete Topic: Designing and Building with Hemp-lime - page 503

the face of the wall and the end of the rafter for single-storey pitched roofs, or 300mm for
double-storey, as an absolute minimum, unless exterior cladding or a hydrophobic render
is to be used. In each individual case the climate and topography of the site should be con-
sidered carefully along with the design to ensure that an appropriate detail is chosen.
While a good-sized roof overhang is probably the most reliable approach, many successful
hempcrete buildings have been built with a much smaller, or even non-existent, overhang.
Where this is desirable, for example for aesthetic reasons, the key to successful detailing
is to consider alongside the design of the eaves and rainwater goods the type of finish
that will be applied to the wall. The usual render finish for hempcrete is a lime-sand
render. This provides a good balance between breathability, flexural strength and resistance
to rainwater, but it remains relatively porous to moisture. If a design with no or very
little overhang is proposed, more protective forms of external finish should be considered.
These might include, for example, a timber rain screen or cladding, a more hydraulic lime
render, or a proprietary hydrophobic lime finish such as those made by Baumit and speci-
fied as part of the Tradical ® Hemcrete ® system.