Indicative detailing - The Hempcrete Topic: Designing and Building with Hemp-lime - page 571

through the hydrophobic render. Again, this carries the risk of a build-up of moisture in the
hempcrete.
This idea, then, requires more investigation, and trials in practice. It may be that where the
wall is in a very sheltered position, the detail of hempcrete cast against masonry cladding
without a hydrophobic render could work. This would be based on an assumption of lim-
ited weather exposure, and plenty of time between heavy soakings for the wall to expel all
the water from the last rain. But if the wall was subject to even average exposure to rain,
except perhaps in very dry climates, such a detail would certainly be inadvisable. In ex-
posed locations, frequently subject to rain and high winds, this detail would not work, and
indeed a more appropriate material in such a case might be a hung slate cladding.
Openings
The main considerations at openings in the hempcrete wall, apart from the familiar ques-
tion of airtightness, are the need to provide a secure fixing for the window or door frame
and to ensure that the hempcrete is well supported above the opening.
Fixing windows and doors
Window and door frames need to be fixed to the structural frame or to something that is
strong enough to take the window or door frame fixings back to the structural frame.
Where the structural frame sits in line with the desired position of the window or door, the
fixing can be achieved with little difficulty. In situations where the two are not in line, the
detailing must provide a secure fix for the window or door frame. This can be done by box-
ing out with plywood or studwork and covering this with wood wool board to reduce cold
bridging and provide a substrate for renders and/or plasters if required. However, where
the windows sit towards the outside of the wall and the structural frame is positioned on
the internal face of the wall, a straight boxing-out would create a deep 'tunnel' window re-
veal that cuts out light due to the depth of the wall. A more tapered or even a curved reveal
can disguise the depth of the wall and increase the amount of light that can enter. This is
achieved by stepping the frame and tapering the shuttering: the reveals can be left tapered,
or brought to a curve with a nail float once the hempcrete has been placed (see Figure 36
opposite). It is more difficult to taper the reveals if a permanent internal shuttering board