The following are concrete and earth based wall systems that do not offgas toxins and are suitable for the chemically sensitive. Something a little different from the standard timber frame, spray insulation and gypsum boards:
A mix of pumice and concrete are poured into forms to create these non-toxic walls. They can be made load bearing with a concrete beam. Test pumice for radioactivity and for odours that it may have picked up prior to installation.
An interesting material making a comeback, Hemp Crete is blocks made of hemp and a lime based binder. The blocks are used to form the walls and act as insulation. They are not load bearing so are used with a timber frame.
Wood Insulated Concrete Forms
Forms are made of a mix of remineralised wood and concrete. Inside, rebar is used as reinforcement and then they are filled with concrete. Insulative fibers can be added or they can be filled with part concrete and part clay or a non toxic insulation. Brands include Durisol and Faswall.
Aerated Autoclaved Concrete
Concrete based blocks made from quartz, lime or cement, and aluminum powder. Test thinset mortor for sensitivity.
Magnesium Oxide Board is the cleanest option. I talk more about it in my post on Bathrooms.
A FAQ is whether there are non-toxic drywalls. Of the wall boards out there DensArmor Plus is recommended by some – it is low-toxin, but not non-toxic. I do not know of any zero VOC conventional drywalls.
Natural Building: Earth Based Walls
Cob, Adobe, Light Clay-Straw, and Straw Bale and Rammed Earth
|Adobe house from trails.com|
These are all different types of walls made of clay, straw, and sand. But instead of giving a comprehensive overview I will comment briefly on the suitability of these building materials for the chemically sensitive. Houses made of all natural materials feel great to be in and there is no need to worry about any offgassing. However there are precautions that should be taken to avoid mould. These types of builings might be best suited to dry climates so that there is no chance of mould forming. Some people seem to be doing very well in adobe houses in the south-western US.
If straw is used in the walls it should be carefully sourced to be free of mould and pesticides. When building with cob, adobe or light clay straw there needs to be a dependable dry season of three months for the walls to dry out properly. They are particularily suited to be heated with wood stoves as that dries out the walls well in the rainy and damp seasons (source: Econest). An above grade stem wall and proper drainage around the house is also very important to keep the walls from getting damp.
|Rammed Earth from sirewall.com|
Another natural wall system worth mentioning in a little more detail, Rammed Earth, uses sand, gravel and clay has had an interesting development recently. Foam has been added for insulation and steel for support, and 5-10% cement is added to the clay mixture. It’s called Stabilized Insulated Rammed Earth.
Water does not penetrate the walls.
Paula Baker-Laport has more tips for mould free construction of earth based walls in her book Prescriptions for a Healthy House: A Practical Guide for Architects, Builders & Homeowners