Archive for Mike Henry

Biophilic design

At the first stop on a ferry trip down the Alaskan coast, I scrambled up a steep slope through a hemlock forest and my nose came close to the mossy carpet. the smell that greeted me was rich, earthy, it reminded me of a stout beer. I sat down, my back to a tree; a varied thrush sang its long human-sounding whistled notes in the distance. My eyes ran over the green carpet that covered every surface, following the contours of logs and roots, and climbing the lower trunks of trees. Feather moss, fern moss, lanky moss, cat-tail moss, electrified cat tail moss; the names are descriptive of the unique forms. I didn’t know why the varied branching shapes, quilting an irregular pattern across the forest floor, broken here or there by a fallen hemlock twig or cone, brought such a sense of contentment – now I understand more.

As the ferry sailed from Haines the sun was sinking low in the sky, and the snowy peaks of the coast mountains changed from fiery orange to cold blue.
I was on my way to O.U.R. Ecovillage, a community on Vancouver Island, British Columbia, where I wanted to see buildings built out of earth, and meet the people who made them.

At O.U.R. Ecovillage I stayed in a building named the Sanctuary, on the edge of a cedar swamp. I sat for a while on a living cedar log, surrounded by showy yellow blooms of skunk cabbage, listening to the long complex song of the winter wren, like tiny raindrops on a still lake. Rain chains hanging from the corners of the living roof of the Sanctuary building echoed the wren’s song. As my ear was drawn to the patterns in the song, so my eye was drawn to the pattern in this chain of tiny bowls linking roof to earth, and the perpetual motion machine of the water trickling down it. Inside the building, my hand reached for rough earth plastered walls and the uneven smoothness of roundwood posts. My feet pressed against the cool softness of an oiled earthen floor. My eye traced the linear path of beams to their meeting with curved walls, and subconsciously I found pattern in thousands of details of this building, each of which represented a choice made by a builder, and a statement about beauty.

Traditionally beauty is in the realm of art, not science. Lately, however, the two may be intersecting. Biophilia is a word used by evolutionary biologist E.O. Wilson to describe an evolved human affinity for nature. In 1961, as a young naturalist, Wilson first visited the rainforests of Surinam. As he became lost in the richness of the natural world here, he realized there was some larger idea that was eluding him. More than two decades later he would write “the image of the land I kept for many years symbolized the tangle of dreams and boyhood adventures from which I had originally departed, the home country of all naturalists, and the quiet refuge from which personal beliefs might be redeemed in a permanent and more nearly perfect form.” A poetic description of the naturalist’s experience, but Wilson came to believe that his own intense connections to nature are merely expressions of a broader human connection to the natural world, which has a genetic basis.

According to Wilson’s theory, being in contact with nature makes humans happier and healthier; and since it’s in our genes it is cross-cultural – everyone, rich or poor, rural or urban, will find solace in nature. One of the implications of this is that we may find something beautiful, or comfortable, because it emulates patterns found in nature. From there it’s only a short leap to design buildings that emulate natural patterns and processes. Termed biophilic design, it’s a leap that a number of architects and psychologists have already begun to make.

I’m reminded of a scene from the movie Black Robe, in which a Jesuit priest, lost in the Canadian forest, looks up into the trees and sees for a moment the columns in a cathedral. It’s a cinematic moment that has stuck with me when most other details of the movie have dropped away. Mathematician Nikos Salingaros suggests that some of the greatest religious architecture relies on natural patterns and symmetries to connect humans to the divine. According to Salingaros, “we engage emotionally with the built environment through architectural forms and surfaces. We experience our surroundings no differently than we experience natural environments, other living creatures, and other human beings.”

Biophilic design is not new; arguably it is best exemplified in traditional, or vernacular, architecture and often finds itself in opposition to modern, minimalist architecture. Consider some of the shared aspects of the forest and the sanctuary building. My senses were engaged. The earthy smell of moss in the forest, the faint odours of earth plasters and natural oils; songs of varied thrush and winter wren, the bell-like sound of the rain chains; the bark of a cedar tree and the feel of earth plaster that my hand instinctively reaches out to touch. We tend to think of what we see, but we engage the world with all of our senses.

Visually, I am drawn to ordered, but complex patterns. The parallel rafters as they meet the rounded wall, the rain chains. Or moss, like snowflakes never twice the same. This repetition of similar patterns has been called visual rhyming. Rhyming patterns occur on different scales, in the building or in the forest. Sometimes the pattern is only a texture when perceived from afar, but greater and greater detail is revealed as one moves closer. Michael N. Corbett describes this as an attraction to neither rigid uniformity nor wide variation, but rather small variations and imperfections in a general pattern. We are attracted to that which is made by hand, rather than by machine. At some very base level, it seems, we are all luddites.

This doesn’t imply that we all need to live in a cob house. Natural materials and design aspects can be incorporated into any building, and always have been. Many conventions in architecture and interior design probably derive from the natural world. I live in a 100-year-old building with wood floors and beautiful mouldings, and (recently added) earth plasters. I would say that many of the deliberate, and unconscious details of this building do reflect biophilic design. My addition of earth plaster only enhances this. The trouble with biophilic design is that so far we don’t really understand what it is, or what rules it follows. Even so, it’s a valuable concept to keep in mind while designing or choosing materials.

A good book of articles about biophilic design is edited by Stephen Kellert.

I haven’t seen this film yet, but I will when I have the chance.

Biophilic Design: The Architecture of Life (Trailer) from Tamarack Media on Vimeo.

Harold Orr’s Superinsulated Retrofits

Recently I had the privilege of interviewing Harold Orr, who was the project leader on the Saskatchewan Conservation House in the late 1970’s. He was involved in the invention of the residential HRV, and blower door tests, and his work influenced the Passive House and Net Zero movements. Now in his eighties, his brain contains a library of information on energy efficient building, and he talked to me for two hours straight. Orr’s main passion for the past several decades has been superinsulated retrofits of existing buildings, and he says the need for deep energy retrofits was obvious to him from early on.

The Saskatchewan Conservation House, now seen as a milestone in energy efficient building, was finished in 1977. “We recognized that as a first step,” Orr tells me, “the next step was to see if we can do this on a larger scale.” The province of Saskatchewan organized a competition, in which builders submitted proposals for a showcase of energy efficient homes – the challenge was to design and build homes that use only 25% of the heating of a conventional house. Orr was involved, along with Rob Dumont, in evaluating the proposals, “but we realized even as we did this that the number of houses that we build every year in a city is a small percentage of the houses that are already in a city.” Only in cities with a major building boom can you achieve a significant energy reduction, Orr explains, “so we were concerned about how we might do this on a conventional house.”

Orr and Dumont started looking for a house to retrofit and study the results, and by the end of 1981 they had found one in Saskatoon. This was the same year that the Superinsulated Retrofit Book, by Marshall and Argue, was published, describing double wall retrofits. The house Orr and Dumont had found was a 1968 bungalow with 2×4 stud walls and 2.95 air changes per hour (slightly better than the average house of that era).

“We decided to do a major energy retrofit on the house, and we wanted to bring it up very close to the level of the Saskatchewan Conservation House,” Orr says. The whole process of this renovation is described in a report that Orr wrote with Robert Dumont. They performed blower door tests at each stage of the renovation to see how air-tightness of the house was affected. They took off the stucco and wrapped the walls with polyethylene, which was sealed down to the foundation and up to the top plate of the house, and not surprisingly the house was considerably more air-tight. Next they hung a second 2×4 wall off the exterior of the house, with an eight inch gap between the old and new wall. By the time they had insulated the cavity and the new wall, the combined insulation (including the existing insulation in the old wall) was about R50.

“That did the walls quite well, but we wondered what on earth to do about the roof,” Orr says. “Because one of the major problems in housing is the leakage between the house and the attic space.” Because of wood shrinkage there is nearly always a gap where the drywall meets the top plate, which Orr estimates is commonly 1/16 of an inch. Drywall is also not normally air tight at the floorline – so in most older houses air can travel behind the drywall, from the living space into the attic.

“So we thought why don’t we cut the tail end of the rafters off so it’s nice and smooth at the edge of the wall,” Orr recounts, “and we’ll put a piece of plywood over the raw edges that we’ve cut off, and then we can carry the vapour barrier that we’ve already put on the outside of the wall right over the roof and down the other side.” This is what is now known as the chainsaw retrofit – a time lapse of a later chainsaw retrofit was filmed by Orr’s son Robert.

“So anyway we’ve got the vapour barrier on the roof and we’ve got it tight,” says Orr. “Now we put 2×8’s, one at the edge of the roof, one at the peak of the roof and one half way in between. On top of this we put new rafters down the roof. In the 2×8 we put R28 and in the 2×4 rafters we put R12 which gives us R40 on the roof. Plus the insulation we already had in the attic which is likely around R20. Now the we’ve got R60 in the roof. We’ve got the outside walls of the house and the roof done, and we’ve got the house very very tight.” In fact Orr says that the 1981 retrofit was almost identical in its performance to the Saskatchewan Conservation House.

Orr has worked on a number of retrofits since, most recently a four-suite apartment in Regina. This renovation of basement, walls and roof had a cost of about 11$ per square foot for materials (including metal roofing), and about the same again for labour. Because the retrofit turned it from an undesirable to a desirable place to live, with commensurate increase in rent that could be charged, it has an eight year payback time – making it a phenomenal investment.

So the economics of the double wall, or superinsulated, retrofit are not bleak, though it’s a large investment, and finding the right contractor to do it is going to be important. But how does it compare to just tacking some foam to the outside of the house and re-siding it? According to Orr there is no comparison.

“I took four walls and assessed them,” Orr says. “One I put 2 inches of styrofoam on, at R5 per inch that would be R10. When you put 2 inches on you really have to strap it, because you cannot put siding on over 2 inches of styrofoam. And unfortunately 1×3 strapping is the same price as 2×4’s. So if you’re putting strapping on, why not use 2×4’s?” And why not center them away from the wall, for a double wall retrofit? Since foam insulation is so much more expensive than batt insulation, says Orr, “I can put in R60 for the same price as R10. Now you’ve got to persuade me that R10 is better than R60.” That’s just materials, labour will change that somewhat, but the point is made.

Orr has more to say, however, adding that “when you put styrofoam on the outside of a house you’re not making the house any tighter, all you’re doing is reducing the heat loss through the walls. If you take a look at a pie chart in terms of where the heat goes in a house, you’ll find that roughly 10% of your heat loss goes through the outside walls.”  About 30 to 40 % of your total heat loss is due to air leakage, another 10% for the ceiling, 10% for the windows and doors, and about 30% for the basement. “You have to tackle the big hunks,” says Orr, “and the big hunks are air leakage and uninsulated basement.”

Air leakage in a typical house, from Keeping the Heat In

“I think the problem is that people don’t properly analyze where the heat is going. Get the book called keeping the heat in, it’s a publication of Natural Resources Canada [available as a free download], and anybody doing any work of this type should get this book and study it. If you look at where the heat goes the big chunk is air leakage, and usually putting styrofoam on the outside isn’t going to affect anything.”

I close the interview by asking why, so many years after retirement, he’s still doing this kind of work.

“It’s a passion with me,” he says. “I enjoy it. And I’m enough of a scotsman that it bothers me to see people wasting their money. I go by houses every day and I see them putting on an inch and a half of styrofoam, and lord help me – why don’t you do something for the same price and do it better?”

More information


History of the Chainsaw Retrofit


Plaster Workshops 2014

2015 Workshops will be posted soon. Enter your email (on the right) to be notified.

Earth and lime plasters for natural buildings  June 21-22, 2014Earth plaster (spanish gold ochre)
Earth is an ideal material for plastering natural buildings. Its permeability prevents moisture issues, it is relatively easy and safe to apply, and beautiful. For exterior application earth can be used in combination with lime.Our next plaster workshop is scheduled for June 21 and 22 (2014), participants may choose to come for one or both days.This workshop will take place on a small hobby farm in southern Quebec. On the first day (June 21) participants will learn to mix and apply earth and lime-stabilized earth base coats, the following day (June 22) we will review the basics of earth and lime finish coats, with hands on application of lime plaster and test samples of earth. Emphasis throughout will be on learning, not covering wall area.

Participants will leave with the knowledge and recipes to get started in natural plastering, including a simple plaster recipe that can be used over drywall or painted walls. There will be the option to buy some tools and materials.

Instructor Michael Henry will share knowledge garnered from nearly a decade working with Camel’s Back Construction, a company that specializes in plastering straw bale buildings.

A detailed outline is available here

One day workshop fee 50$, Two day fee 100$, or Pay What You Can

Commute from Montreal is less than 1 hour, or rudimentary camping is free. A simple strawbale cabin, perfect for a couple, can be rented for the night. There’s a pub / restaurant within walking distance.

To register for this workshop, or receive updates about other workshops, contact


View Larger Map

Introduction to Tadelakt  July 5, 2014

 Natural Finish PlastersTadelakt is a highly polished, waterproof lime plaster that originates in Morocco. Its unique beauty comes partly from the final burnishing, which is done with a smooth stone.

This summer I will be offering another introductory tadelakt workshop through the Endeavour Centre, in Peterborough Ontario.

participants will learn to mix, apply and burnish a tadelakt-type plaster made with locally available materials. Students will practice on two small projects of their own. Mix materials and the necessary tools to continue with tadelakt will be available for sale at a reasonable cost.

About the Instructor

Michael Henry was trained as an ecologist, and began his career as a natural builder in 2004, working with Camel’s Back Construction. Since then he has brought his knowledge of ecology, and a science-based approach, to natural building – especially natural plastering. Michael is the lead plasterer at Camel’s Back Construction, where he has worked with a variety of earth and lime-based plasters, including tadelakt. He blogs about natural building at


Will straw bale buildings last?

After seeing problems in a few straw bale buildings, I’ve been thinking about this lately: is it a truly durable building system? By which I mean, will  a straw bale house measure its lifespan in centuries rather than decades? I’ve concluded that most will, some won’t. The ones that won’t are predictable, however, and for the most part they break the rules.

This wall is ready to be replastered after wet straw was removed. It had no overhang at all.

Architects occasionally design straw bale homes with no roof overhang, for instance. I’ve seen this twice, and in both cases an overhang was added before construction was completed. In one of them there were already some moisture issues a year or so after the wall was closed in. Water was sheeting down the wall in spring rain storms and working in through cracks. These were a few horizontal cracks which had reopened after crack filling. Straw at the base of the wall was saturated and had to be replaced – which was not as hard as I thought, and in a weird way I found that encouraging for the question of longevity. With the overhang in place I think this will be one that does last.

Other houses that I worry about don’t break the rules so blatantly, rather they push them a little, but they are on exposed sites. Driving rain is the enemy of straw bale houses, and gable ends are particularly susceptible. If you’re thinking of building a straw bale house on an exposed site – a hill or a lakeshore, or any site where you might consider using a wind turbine – your design must be impeccable. You might want to consider a bungalow with good overhangs all the way around, you should certainly avoid a large gable end on a windward side of the house. Gable ends in general should have some kind of skirt roof, and you may want to consider siding the upper part if it’s large or particularly exposed.

Cement-lime plaster tends to make things worse. There’s an unfortunate tendency to gravitate towards cement-lime on very exposed sites because it is the most durable plaster. Cement-lime won’t erode away under driving rain, but it will trap in moisture more effectively than any other plaster. High lime content helps a lot, but pure lime is better, or an earth-lime hybrid system; in rare cases exterior earth plasters may even work on their own (note that the right paint is important for earth and lime plasters). In any case, if you’re very worried about your plaster eroding under driving rain, you probably have a design problem and cement-lime plaster is likely to make it worse. You need to redesign, or possibly you just shouldn’t be building a straw bale house there. An oft-overlooked alternative that can eliminate most external moisture issues, even on exposed sites, is to use siding or rainscreen over bale walls. And keep in mind that whatever you build on an exposed site, bale or otherwise, you’ll need good design and attention to detail.

Cracks must be filled. I’ve seen a house that went maybe 8 years without crack filling and painting, and it was fine! But I’ve also seen disastrous results from unfilled cracks. Again, the site seems to make all the difference, but there’s no sense pushing your luck. Fill your cracks within a few months, or if you plaster in the fall, wait until the following spring or early summer – but not years.

This sounds like a whole lot of bad news, so why build straw bale at all? Is it worth the hassle, and is it really a sustainable wall system? To put this in perspective, when a 100-year-old hay-bale house was dismantled in Nebraska the hay was in such good shape that cows ate it. Or consider that straw bale building is not alone in having had its share of mistakes – modern building practices have created a “perfect storm” of stucco failures on conventionally built homes. In some ways, bale walls are better, they can be more resilient than some conventional wall systems. As soon as you add  insulation to a wall you’re inviting moisture problems – the more insulation you use, the harder it is for the wall to dry out if any moisture gets in, because the middle of the wall tends to stay cool. Superinsulated homes are built to have very low air leakage for energy efficiency, but also because air leakage can cause moisture problems if water condenses in the wall.

Straw bale walls can likely handle small to moderate moisture loads better than conventional wall systems because of the vapour permeable plaster skins on either side, and because the straw itself can act as a large reservoir for moisture without ill effects, so long as it does not exceed an upper limit, and the conditions occur for drying. It’s still very important to air seal a straw bale home properly, and many natural builders have been slow to realize how important air sealing is. In my experience those days are over and air sealing is a priority for most natural builders, which means some kind of air fin behind all plaster joints, and of course good detailing around electrical boxes etc.. This is not just a question of energy efficiency, but also is likely to extend the life of the home.

There are other benefits to straw bale, of course, that I should mention briefly: A relatively high R value (at least double that of a 2×6 stud wall with batt insulation, but still less than most superinsulated homes); low embodied energy and local sourcing of the building materials; and aesthetics. Straw bale is not for everyone, and is certainly not the only ecological way to build, but it has a role to play when done correctly.

A literature is beginning to develop around moisture control in straw bale walls. Here’s a short list of important resources

Design of Straw Bale Buildings

Moisture Movement and Mould Management in Straw Bale Walls for a Cold Climate

Moisture Properties of Plaster and Stucco for Straw bale Buildings

Building Science for Strawbale Buildings

Many of the best practices of design, air detailing, flashing, and other details of conventional homes also apply to straw bale homes, and for this one of the best resources is the Builder’s Guide to Cold Climates.

Video of leveling earth plaster with a darby

Trever Miller from Evolve Builders came out and helped us with some plastering. I asked him to bring his darby (a three foot long leveling trowel) to help us level the kitchen wall behind the cabinets. Trever has years of experience leveling walls with a darby, I filmed this video of him at work.

Window shaping in straw bale homes: a how-to and slideshow

Window curves are one of the most distinctive features in straw bale homes, and are often a big consideration in the choice to go with straw bale over other forms of construction. But information on how to shape curves is sparse, so I thought I’d share some of what we’ve learned over years of doing bale work.

The first thing you really need to think about is radius of curve. To visualize this take a string nine inches in length, pin it at one end and attach a pencil to the far end. Now draw a quarter of a circle – this is roughly what a nine inch window curve looks like. Try the same thing with a 16″ length of string, and you’ll see how dramatically different this window curve would look. Generally we find large radius curves that open out quickly from the window are more popular because they let in more light and make the window seem larger. However many people really like windows that come out straight and then have a smaller curve at the end. The sides of windows usually have curves anywhere from 9″ to 16″ radius.

Window tops and ledges can be straight or curved. Flat tops generally need some extra wood framing.

There are three steps to shaping a window – carving, stuffing, and attaching mesh.

First you need to carve the bales to match the shape of the curve. We try to do the bale work fairly tight to the window, but typically the bales are set back 1.5″  because we push them up against the framing without notching. In preparation for shaping we cut one string, and carve the bale to the shape of the curve using a grinder with a lancelot blade. Cut a plywood template that you can hold up against all your curves as you grind them, to help keep them uniform over the curve and consistent from one to the next. Stand back and look at it from a few different angles. Try to get it perfect, but when in doubt err to the side of too low, you can always fill with plaster.

Next stuff loose straw in the voids. If the carving was done well, you hopefully won’t need too much stuffing. To finish the stuffing, you’ll need to attach the mesh to hold the loose straw in place.

We do a lot of our window shaping with tenax mesh instead of metal lath. If a curve is done well it is easily shaped with plastic mesh and a little stuffing, and is actually easier to plaster than curves shaped with metal. Curves that need a lot of stuffing are formed using metal lath, also called diamond lath (and sometimes ‘blood lath’ because it tends to draw blood from those working with it).  Keep a consistent staple line with your mesh or lath, make sure it is on straight and even, and you should end up with an good curve.

The common origins of Superinsulation, Passivhaus, and Net Zero homes

A lot of valuable lessons were learned as a result of the oil crises of the 1970’s. Unfortunately in the 1980’s many of the conservation initiatives from the 70’s were abandoned – but the skills, knowledge and awareness garnered at the time were not lost, and we’re benefiting from them today. In building science big strides were made in insulation and air sealing of houses, and a lot of this knowledge came out of two projects in Illinois and Saskatchewan.

In 1976 a group at the University of Illinois at Urbana-Champaign developed a design which they named the “Lo-Cal” house, which used two adjacent stud walls, with alternating studs, to achieve R30 insulation and eliminate thermal bridging through the framing. The term “superinsulation” was coined by Wayne Schick, project leader, to describe the high insulation levels used in the walls, attic, and basement. Several houses, duplexes  and condos based on the Lo-Cal design were built in Champaign-Urbana, Illinois between 1977-79.

The Saskatchewan Conservation House was built in Regina in 1977, using similar principles but went further with R40 walls. Again the walls were built out of two stud walls, and the extra 10 insulation points were gained by adding a cavity between them. The whole wall assembly was filled with blown-in cellulose insulation. Another thing that these two projects had in common was a science-based approach, with extensive modeling of the designs, and monitoring of real-world performance.

One of the most important things that both the Saskatchewan and Illinois teams learned was that in most houses the heat is simply slipping through the cracks, and they needed to develop techniques to dramatically increase the air-tightness of buildings. When they realized they were removing all the natural / accidental ventilation from the house, the Saskatchewan team created one of the world´s first air to air heat exchangers, or heat recovery ventilators (HRVs). There´s now a global market for HRVs, and in most cold climate areas some type of air sealing is now required by building codes. In Canada the creation of the R2000 system (a voluntary system for building efficient homes) was credited to lessons learned from the Saskatchewan Conservation House.

The lessons of sealing and air exchange have been widely adopted, but the idea of superinsulating a house to R40 or above, or emphasizing passive solar heating, have remained relatively on the fringe. One of the people who noticed the Lo-Cal and Saskatchewan Houses was Wolfgang Feist, the originator of the Passivhaus standard – a very rigorous system of building that is popular particularly in Europe where there are some 20,000 certified passive houses. Feist lists Harold Orr, an engineer who worked on the Saskatchewan House, as one of his influences. And it’s probably no coincidence that Urbana-Champaign, origin of the Lo-Cal house, is one of the centers for the passive house movement in the United States.

Rob Dumont, one of the engineers who worked on the Saskatchewan House, went on to build his own house in 1990, which at the time was the most highly insulated house in the world. Surprisingly, the extra insulation, upgraded windows, and a solar thermal heating system, only added about 7% to the building cost. “If I´d put brick on the outside of the house instead of siding,” says Dumont, “the brick would have cost more than all of the energy conservation features. I´d much rather have an energy-efficient house than a brick house.” In fact, the energy efficiency finished paying for itself in 2008, after 16 years – now it´s all gravy.

Conrad Nobert, owner of the Mill Creek House in Edmonton had the same experience with cost. “We got 80 to 85 % of the way to net zero, versus a conventional home, for about 20 to 25 thousand,” says Nobert. “So you would call that a net 0 ready house.” When Conrad talks about net zero, he means that the house will produce as much energy as it uses, by balancing energy use with energy production from solar panels on the roof. It sounds easy – just keep adding solar panels until you reach net zero – but in fact very few houses have enough room on the roof, or even on the property, to compensate for the energy they´re using for heat and electricity. The Mill Creek House uses similar systems to the Saskatchewan House, only better – it has double stud walls, spaced 16´´ apart to get R60 walls, an advanced HRV, and triple glazed windows that are R8.

Peter Amerongen, who built the Mill Creek House, credits his career as a builder of super-insulated houses to a talk he attended about the Saskatchewan House. “I heard Harold Orr in 1978 and it just stopped me in my tracks,” says Amerongen. Ever since then, Amerongen has been building R2000 or better homes. Before building his first net zero house, Amerongen went on a pilgrimage to Rob Dumont’s house to learn what he could from it. Then he took it even further.

Likewise the Passive House movement has gone far beyond its inspiration of a few superinsulated homes built during the late ’70’s. But the original superinsulated homes should not be forgotten, if nothing else for their simplicity and affordability, as evidenced by Rob Dumont’s 7% incremental cost to build the world’s (then) most highly insulated home. What that tells me is that we should be building all our homes to a much higher standard. And I’m sure that change will continue to happen, slowly. Meanwhile the Passive House and Net Zero homes are the pioneers that we can look to for examples of how far we can go.

More information about the Lo-Cal House can be found in a presentation by Michael McCulley.

Notes on toxicity

People who are new to natural plasters sometimes think they are non-toxic: earth plasters are made out of materials dug from the ground, right, how could they be dangerous? In fact, while the end result is non-toxic, these products can still be hazardous to work with. Take clay for instance, which often contains large amounts of crystalline, or ‘free’, silica (fine quartz), which when inhaled causes silicosis (a debilitating lung disease) and lung cancer. Silica is also found in cement and fine sand, but not in pure lime (which nevertheless isn’t great to breathe in). The long and the short of it is that plasterers work with materials in fine powder form and need to be very careful about what they breathe in.

  • Always wear a respirator when mixing, or anytime there is dust  – including cleanup!
  • Use a mop, or a vacuum with HEPA filter, instead of sweeping when fine plaster dust is present.
  •  Read the Material Safety Data Sheet (MSDS) for materials you are working with, including bagged clays and pigments

MSDS sheets can be found for most materials using an internet search. For example an internet search for “msds epk” finds that EPK bagged clay contains 0.1 – 4% crystalline silica, whereas the MSDS for Bell Dark Ball Clay shows it contains 10 – 30% silica. Kaolin clays often contain less than 1% silica, and are good for earth plaster finish coats. Ball clays and fire clays are more common in earth plaster base coats, and typically have large amounts of free silica. Site clays are typically processed wet, so they are hazardous only during cleanup.

Pigments vary greatly in their toxicity. Here’s a website that gives a summary of composition and toxicity of a few common pigments. The colour index can be helpful in trying to figure out what pigments are made up of.