Hemp in construction - The Hempcrete Topic: Designing and Building with Hemp-lime - page 45

sphere, releasing it again in response to a reduction in humidity. This characteristic ('hy-
groscopicity' - see Chapter 4, page 56 ) makes it especially suitable for buildings whose
fabric is designed to be permeable to moisture vapour, such as heritage properties and
hempcrete buildings.
Hemp-fibre insulation can absorb up to 20 per cent of its weight in moisture without any
reduction in thermal performance, in contrast to many synthetic quilt insulations, which
deteriorate significantly when they get wet. 7
To consolidate the hemp fibres into the quilt insulation, there is a need for an adhesive
binder, which is heat-sealed into the insulation during manufacture. This is typically re-
cycled polyester, which means that such hemp insulation cannot claim to be a completely
natural product. It is worth noting, for those wishing to minimize the presence of synthetic
materials in the fabric of their building, that different manufacturers of hemp-fibre insula-
tion use significantly different amounts of this substance in their products. 8
Those who are building with hempcrete, but don't wish to use it for the roof insulation,
may find that hemp-fibre quilt insulation is perfect as a complementary material. It can
also be used in a hempcrete building as a convenient insulating material between suspen-
ded timber floors and partition walls. At Hemp-LimeConstruct we also use the insulation
quilt to help provide airtightness at junctions between hempcrete walls and building ele-
ments made from other materials (see Chapter 21, page 297 ).