In relation to foundation design, because the foundations for a building and the structural members have to reflect the loads supported (including roofing materials, roof spans, floor spans, floor finishes, the spacing of piers etc.) all foundations and structural members have to be designed by an engineer.
A 200mm thick hemp masonry wall using the Australian Hemp Masonry Company’s mix guide is 146 kg/sqm; this is comparable to the weight of a single skin of brickwork.
The structural engineer for each project should design the foundations in accordance with Australian Standard “AS 2870 Residential Slabs and Footings” and sound engineering practice, appropriate to the soil conditions on which the house is to be built. As there are many variables involved in designing structures, the BCA and local government authorities require that for every building, a practicing structural engineer be responsible for the design of every aspect of the foundations and load bearing structures.
The engineer’s design may be for a strip footing, for a slab on ground or for piers and bearers which may be of timber, concrete or steel and the design will of necessity reflect the loads and the foundation materials which support the structure. The width of foundations is governed by the width of the walls.
A damp proof course should be used at the base of the walls to prevent damp from the ground rising in the masonry wall, as it would be with any other kind of masonry construction. It is important that applied finishes such as sheets or renders do not bridge this impermeable separating layer.
The installation of an impermeable barrier is always advised with the use of hemp construction to ensure the satisfactory long term performance of the walls. The ground should fall away from the walls of the building, to ensure walls are kept dry.