Civil Engineering Reference
In-Depth Information
The double frame
Usually seen in new builds where external cladding is specified together with an internal
permanent shuttering board, the double frame is flush with both faces of the wall. It com-
prises an internal stud (usually the structural stud, taking the load of the roof and upper
floors), which also provides the fix for the permanent shuttering board, and an external
stud, usually of smaller-section timber, which takes the load of and provides the fix for the
cladding. These are joined by squares of timber board such as OSB or plywood, fixed to
each stud at vertical centres of around 1200mm. Although these extend through the wall,
they have little effect on airtightness, because both faces of the wall are covered: internally
they are covered by a plaster carrier board plus the plaster; externally there may be a pro-
tective basecoat render (see
Chapter 22
)
and/or a vapour-permeable membrane, which can
be joined to the airtight elements in other parts of the building. Again, hemp-fibre quilt in-
sulation can be used at junctions with other materials, or alternatively a synthetic expand-
able tape, although as highly processed petrochemical-based products these tapes have a
higher embodied energy and so increase the environmental impact of the build.
Junctions at the cross-over to another material
Where hempcrete meets another material, the junction needs to be carefully considered in
terms of possible hempcrete shrinkage. Examples of this include the junction between the
top of a hempcrete wall and quilt-type roof insulation material, or a hempcrete wall meet-
ing a masonry wall in an extension to an existing building.
There are many such situations and countless different materials that the hempcrete might
be adjoining, so we will consider a common situation: an offshoot extension to a solid-
walled brick property. Using Prompt in this situation could reduce shrinkage, but since
may not be an appropriate solution.
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