Hempcrete eco house

Dorset: 0.1ac (0.04ha)

Brief

Create a cost, construction and time efficient, low carbon, super-energy efficient new-build with broad market appeal.

Proposal

Occupying a modest 0.1ac infill plot, the design is to be an ultra low carbon hempcrete insulated timber frame four bedroom chalet bungalow with local stone foundations and plinth, finished with lime render, vertical timber louvre cladding and light weight recycled car tire roof tiles.

Other significant features

• Hygroscopic, hypo-allergenic environment

• Consistent internal ambient temperature [without heating].

• Decentralised mvhr / pvhr

Project status

On site: Expected completion: Spring 2023

Hempcrete

As a building material the woody centre of the hemp plant 'hemp-shiv' is mixed with lime and water to form 'hempcrete', which is cast, sprayed, or installed in pre-cast blocks typically around a structural timber frame. Inherently hygroscopic and damp free a typical build-up is finished with lime render, cladding, breathable paints, or even left raw with no requirement for a vapour barrier.

Properties

At 350mm thick, hempcrete achieves exceptional insulation and thermal mass properties, with a typical u-value of 0.17 W/m2K, as well as a thermal mass capable of maintaining an internal ambient temperature of 14ºc (56ºf) irrespective of external temperature, ultimately resulting in minimal heating requirements and ultra-low fuel bills. And, because the entire build up is breathable, unlike most passivhaus systems, mechanical-ventilation-heat-recovery (MVHR) is also not essential.