FAQ Group: Questions about Hempcrete
Should I use boards, such as anti-racking (‘racking’) boards, as part of a hempcrete wall?
You should not use boards that are not vapour-permeable (or not sufficiently vapour-permeable) such as OSB or ply except as temporary shuttering boards – used to shutter wet-cast hempcrete. There are specialist vapour-permeable racking boards, such as Econic. If possible, it is better to add boards after wet-cast hempcrete has fully dried, as even vapour-permeable boards will significantly […]
Can I build a passive house with hempcrete?
Yes. You may wish to combine the hempcrete with other types of natural insulation such as wood fibre board to reduce the wall thickness somewhat. However, the hempcrete element, making up the bulk of the wall thickness, will provide greater thermal mass than most other natural insulations, and will increase the thermal performance of the […]
How much will it cost to build my hempcrete house?
Our team can give a broad per-square-metre of usable floor space* figure for building a brand-new hempcrete house. However, the actual cost will depend on how the building is designed, including design of the structural frame, the other materials involved and types of finishes, as well as factors such as ease of access to the site. If […]
What mixing ratio should I use for hempcrete?
Ratios for mixing hempcrete in a large forced action pan-mixer, or spray machine (bags of binder to bales of hemp shiv to water volume) are given in the individual product pages. If you are mixing on a smaller scale, for example in a cement mixer (Belle mixer), you can use “this rule of thumb” ratio […]
Can I use hempcrete to insulate a solid masonry wall in an old building?
Yes. Hempcrete, either in wet-cast or precast block form, can be used to insulate existing stone or brick walls internally – internal solid wall insulation (ISWI) – or externally (ESWI). It needs to be used with other vapour-permeable materials – for example lime or clay plaster, lime render and lime mortar. Generally it should not […]
Can I use hempcrete instead of concrete?
In comparison with concrete, hempcrete: is much less dense than concrete (at around 300 kg/m3 compared to over 2,000 kg/m3) is not a load-bearing material has a plant aggregate rather than stone has high vapour permeability, as opposed to very low vapour permeability is an insulation and mass material, rather than a mass material.
Where should hempcrete NOT be used?
Hempcrete is a non-structural medium density walling and insulation n material with a plant aggregate. It is not suitable for use as a load-bearing material, and should not be installed at or below external ground level, or anywhere else where it may be exposed to standing or running water. In some specific circumstances, hempcrete can be […]
How much will I need?
For hempcrete (wet-cast or blocks), or for lime plaster or render materials, we usually recommend allowing 5% for wastage/cutting on top of the volume you think you need. However this is obviously at the customer’s discretion. If you are calculating the area of plaster or render needed, don’t bother subtracting the area of any window […]