Design fundamentals - The Hempcrete Topic: Designing and Building with Hemp-lime - page 507

side (see Figure 13(a), page 245 ) . Burnt sand mastic, as well as being free from the toxic
chemicals and high embodied energy associated with conventional sealants, will retain its
flexibility over time. In contrast, conventional mastics tend to go hard and brittle as they
dry out, making them unsuitable for use with lime renders. Another alternative is to design
out the bead altogether by extending the hempcrete over the window frame (see Figures
13(b) and 36(c), pages 245 and 337 ) .
Within the structural frame, timber studs to which window or door frames are fixed should
be protected with a 'breather' (vapour-permeable) membrane (see Figure 17 ). This is ne-
cessary because it is an area with a less-than-ideal covering of hempcrete, which is there-
fore susceptible to water ingress. An alternative would be to use hardwood or other rot-res-
istant timber in vulnerable locations such as these.
The plinth is designed to keep the hempcrete section of wall clear of any splashback from
rain hitting the ground, and should therefore be at least 250mm high. An increased plinth
height should be considered if the wall is in the drip zone of trees or exposed to the pre-
vailing weather.
Figure 17. Timbers around openings are vulnerable to moisture and need ad-
ditional protection.