Can a home with clay-straw walls replace the log cabin as the ultimate symbol of green living?
Our homes should be our sanctuaries. They should nurture our well-being. But they often do not. Sick-building syndrome and multiple chemical sensitivities are relatively new terms describing a growing phenomenon: people becoming chronically ill due to chemical and biological toxins found inside modern homes and workplaces.
After World War II, the booming building industry became the proving ground for new industrialized products which rapidly replaced building techniques that been perfected over centuries. Unfortunately, new has not necessarily proven to be better.
The impacts of industrial chemicals on human and ecological health has renewed interest in building methods such as rammed earth, cob, adobe and clay/straw. As an architect-and-builder team, we have looked to pre-industrial building materials and techniques, reevaluated them in terms of modern comfort and found them to be not only viable but, in many ways, superior to the mass-manufactured products used to build North American homes.
In our most recent book, Eco Nest: Creating Sustainable Sanctuaries of Clay, Straw and Timber, published by Gibbs Smith, we outline the advantages and techniques of combining timberframe and clay/straw construction and provide case studies based on our own projects.
Modern Mud Hut
Heavy clay construction, known as wattle and daub, has long been used in Europe and Asia as infill between timber framing. During the post-WW II reconstruction of Germany, builders began lightening this clay infill by adding much more straw, increasing the insulation value of the walls.
Robert first studied this technique in 1990 when he went to Germany in search of a natural wall system for his timberframe structures. Since that time he has continually refined the process for building environmentally sustainable and health-supportive “econests,” by wrapping his own timberframe structures with a light clay/straw mixture.
Our experience building and living in econests tells us that they are exceptionally comfortable: warm in the winter, cool in the summer and stable in temperature despite daily or seasonal extremes. However, until very recently, the only scientific information about the performance of light clay/straw as an insulating wall system was from Germany. And North American officials rarely recognize test results conducted outside the US and Canada.
In 2005, builder Joshua Thornton received a grant from the Canadian Mortgage and Housing Corporation to research the physical characteristics of clay/straw. And an architect in Wisconsin is pursuing similar research.
Both sets of tests provide hard data that the R-value of a 30-centimetre-thick clay/straw wall is equal to 15 centimetres of fibreglass batt insulation. In most areas of the country, this is a sufficient R-value for an insulating wall to pass energy code and pave the way for a building permit.
The Mass Wall Advantage
The job of the exterior wall is to slow down temperature and moisture transfer so that the home remains relatively comfortable. Until a century ago, all dwellings were made out of natural, locally available materials which provided breathable, or “flow-through,” wall systems.
Needless to say, without added insulation, a hollow stud wall of metal or wood does a very poor job moderating temperature and moisture. And standard insulations such as fibreglass batts perform poorly when moisture is allowed to travel through them. If enough water vapour condenses in the hollow cavity, it will cause mould, decay and eventually structural deterioration. To avoid this, insulated stud walls frequently have added moisture barriers.
But miscalculations in the application of this non-breathable approach often accelerate the process they were meant to avoid — moisture trapped within walls by plastic barriers has resulted in countless building failures, causing mouldy and unhealthy indoor air.
Massive breathable wall construction, such as clay/straw, eliminates this problem. Airborne moisture is intercepted by the clay in the first two or three centimetres of the wall, long before its reaches the condensation zone.
Clay/straw can withstand getting wet because clay is very effective at wicking water out of the wall and drying it. However, if impeded from drying, the material will eventually mould and decompose. As a result, the typical econest has a metre-and-a-half-wide roof overhang to serve as its ” rain hat.” The clay/straw begins half a metre above standing snow levels and, below the clay/straw, a masonry stem wall is protected by a stone wainscotting. This feature, like a good pair of boots, keeps the bottom of the clay/straw dry.
In addition, we provide a breathable overcoat. In wet climates with over 50 centimetres of rain annually, we use wood treatments such as shingles or siding over a ventilated space. Alternately, lime-based plasters are commonly used in damper regions of Europe and are also available in North America.
Avoiding Chemical Soup
Using solid-mass walls is a good starting point for a healthy home. The next step is avoiding toxic substances inside the house. Although the US Environmental Protection Agency (EPA) stated in its 1997 Budget Report that “indoor air pollution in residences, offices, schools and other buildings is widely recognized as one of the most serious potential environmental risks to human health,” it has not been as effective in protecting citizens as one might imagine.
After reading the warning labels on home finishing products or the material safety data sheets of common construction materials, it quickly becomes apparent that many of the products going into our homes can cause a myriad of adverse medical conditions, including respiratory damage, chronic dermatitis, central nervous system damage and multiple chemical sensitivities.
Suspected and known human carcinogens are in common use in the construction of standard homes. The cumulative and synergistic effects of these chemicals have never been adequately studied. That “new home smell” that we are familiar with is the aroma of chemical soup.
Designing for Health
Beyond creating a healthy wall system and choosing safe materials, there are several design features that help to promote health, and we incorporate them into econest design.
The attached garage is often a major source of pollution, especially when the separation walls and doors are not airtight, when the garage is not vented separately and when the occupants run the car in the garage.
Also, dirt, dust, pollen and pesticides tracked in on shoes are best left at the door. Home design can encourage the habit of shoe removal by simply placing the entry a step below the rest of the home, providing a space to sit and a place to store shoes.
Many reports and studies have pointed to the dangers of man-made electromagnetic fields. Simple precautions include using a metal cable or conduit to shield out electric fields; placing bedrooms away from appliances, like computers and refrigerators, that generate magnetic fields; and carefully directing wiring raceways away from living areas are.
Floor drains are often overlooked in standard construction when they’re not required by local building codes. Yet, including a drain where a water source might leak and flood, such as a laundry room, can prevent expensive damage as well as health-threatening mould conditions.
Serious illness and chronic ill health can result from exposure to by-products of combustion from home heating appliances. This damage can easily be avoided by isolating the mechanical room from the living space.
There is nothing complicated about building healthier homes. However, building for health is not the criterion for material choice or building practices in standard housing today.