Timber, Lime & Hemp

Image - Hempcrete on site in Kilchoan
Words, Colin Baillie.

Hempcrete is made from fibrous hemp shiv, which is an excellent natural insulator, mixed with a lime-based binder. One of its attractions, for us, is that it’s a simple, low-tech material to work with. It’s malleable and can be used in different forms, or for different purposes. Depending on the how the constituent materials are produced and sourced, it can be carbon neutral or carbon negative, and contains no harmful chemicals or plastics. It can be cast in-situ, in thick monolithic walls of 400mm or more. What it can’t do, is anything structural.

Walls of cast hempcrete are often formed around a lightweight timber frame. This works well, but in the wet and humid conditions in the West of Scotland, drying time can become an issue.

Working instead with pre-cast hempcrete blocks, in one of our ongoing projects in Ardnamuchan, we designed a post and beam frame using locally sourced Douglas Fir. This allowed the structure of the building to be constructed right up to, and including, the roof finish. Hemp blocks were used to infill between the post and beam frame, under the shelter of the deep eaves, leaving the timber exposed. Two leaves of blocks were used, with in-situ hempcrete filling the void between, to create a single solid wall.

The blocks will be finished with a thin coat of lime plaster inside, between the posts, and a thick coat of lime harling outside.