When we first came up with the idea to buy acreage and build a new home, I wanted to use natural building methods. These include strawbale, cob, clay-slip (or chip-slip, made with wood chips instead of straw), cordwood, and rammed earth. The main appeal of these methods are: small environmental footprint, ability to use local materials, and low materials cost. Natural homes can be stunningly beautiful, with styles ranging from organic free-form “hobbit houses” to elegant luxury homes. The costs also vary dramatically.
Due to our climate and my own aesthetic tastes, we immediately ruled out strawbale, cordwood, and rammed earth. I also don’t like the “hobbit house” look, which ruled out load-bearing cob. That left a timber skeleton with either cob or clay-slip/chip-slip infill. I spent at least two years heavily researching the subject and talking to local experts (we happen to live in a community with a fairly high concentration of cob buildings), but in the end we decided against a “natural-built” house. Here’s why:
The low-cost appeal of natural building is immediately erased when, like us, you aren’t willing or able to do the work yourself. Most people around here rely on work parties where friends, family, and interested folks in the community come together to make cob and assemble walls. Like moving house, you can only rely so long on the good nature of people to provide hard labour in return for beer and pizza before you end up having to do the rest of it yourself, and this can wreak havoc with your timelines.
Natural building methods are labour intensive, and when you have to pay for that labour, any cost savings from the materials goes out the window. You need experts for the walls, for the natural plasters that coat them, and for the earthen flooring. There aren’t that many around, they aren’t cheap (for good reason), and chances are you’ll have to keep bringing them back for regular maintenance. To top it off we live in one of the few places, apparently, that doesn’t have much clay so it needs to be hauled in from elsewhere at added cost.
Aside from cost issues, the use of cob or slip as infill comes with certain practical and aesthetic limitations:
(1) It’s difficult to run plumbing and electrical through solid walls. The pipes or electrical conduits can provide a dew point surface onto which condensation will form in your wall (not good). Or you can build an extraneous structure, like a hollow internal wall, soffit, or other such system, which can be tricky and perhaps not aesthetically pleasing.
(2) The walls need to be finished with a natural plaster inside and out, which requires hiring an expert (or becoming one yourself). I personally wanted wood cladding on the exterior, but I couldn’t find anyone who knew how to do that and some experts recommended against it. You can’t paint natural plasters like you do a conventional drywall surface – instead they are tinted upon application and you are basically stuck with that colour forever (redo-ing a plaster wall is a far different project than repainting drywall). Admittedly, I find the colours of natural plaster very beautiful, but I wasn’t sure I wanted to limit myself in that way. Bathrooms are a particular problem as moisture can build up around tiles and other impermeable substances; the most recommended solution is a lime-based plaster called tadelakt, which also requires a good deal of expertise and doesn’t come cheap.
(3) The timber skeleton presents issues with thermal bridging across the wall, and a consistent interface between cob/slip and wood can be difficult to maintain (cracks are common). To do it right takes time between applications. And you need to time your construction right so that the infill can dry properly before the wet weather sets in. In addition, cob is not a very good insulator and walls are typically a foot thick or more. You’ll need either thick logs that require a proper timber framing crew ($$$) or extra-wide studs and planks. I was unable to find consensus on whether to leave the timber exposed on the inside and outside wall surfaces or to bury it beneath a layer of cob or plaster.
In the end, aside from the high cost of getting the natural home I wanted (we were quoted about $300/sq ft by one leading company), what finally drove us to abandon our natural building plans was that we simply weren’t convinced that all the kinks had been worked out of using cob or clay-slip in our unique climate over the long term. It’s not that I don’t believe such methods can be used successfully, we just couldn’t shake the feeling that the industry was still in its early stages here, and we weren’t ready to risk such a huge financial and emotional investment on something we just weren’t comfortable with. Instead we plan to use natural building methods for a shed, workshop, or small barn some time in the future and maybe, based on what we learn from that experience, we will feel confident enough to build a retirement cottage using natural materials.