Chris Magwood

In terms of embodied energy, it's important to remember that although older buildings might be 1/20 or more in terms of EE to overall energy use, as we make more and more energy efficient buildings, EE's share of the energy inputs will rise dramatically. A net zero energy home could see the majority of it's energy impacts be at the EE level.

I think drywall overtook wet plasters because it takes less skill and it gives a more standardized appearance. Sheet goods delivered much better results when energy was cheap... as they took over the market, the costs were well below what it cost to pay people to do the same work. However, the price of sheet goods has been rising consistently ever since, and we're getting close to the point where human labour costs are getting closer to being on par. However, we've lost the skilled trades and the aesthetic that went with human-made building systems, so there's more than just cost factors holding them back. For somebody holding a conventional building mortgage, the bank will give them a certain percentage of their total budget for drywalling. But in most cases, they wouldn't give an owner a penny towards lath and plaster. So drywall wins...

Hi Conrad,

You are right, I didn't include log wall systems. The book definitely has a northern climate bias (where I do all my work), and it's just not possible to hit the kind of energy efficiency targets that I think it's important to reach with log wall systems. And in terms of impacts, a log home uses substantially much more wood than a similarly sized frame home or timber frame home. The energy expended to mill timbers is relatively small, and is more than offset by the reduced wood use.

As with all things, I think log homes can certainly fit certain needs and criteria for owners, so I don't think they are a bad idea. But they just don't come close to meeting the kinds of performance standards achieved by all the other materials featured in the book.

Perhaps if I do another edition, I'll run the figures for them for comparison's sake!

Hi again Matthew,

I definitely think that studs, lath and plaster are much faster than bales and plaster, especially since you're also framing a stud wall to go with your bales. In my course a few years back I had a team of three drywallers and with them we did the majority of the interior of a house in lath and clay plaster, and they were surprised to find that it was faster than they could drywall. There is no comparison between plastering over a flat, lathed surface compared to going over bales. Way less material and time!

I'm not very judgemental when it comes to how people decide to build. If somebody asks my opinion before they start building, I will make the case for the least intensive materials that meet their criteria, but if somebody chooses a concrete slab who am I to criticize that choice?!

I'll refer you to an article I just recently posted on the Endeavour web site http://endeavourcentre.org/2014/02/embodied-energy-is-it-important/ about why I think embodied energy is important. There's more to say than I want to re-type and post here, but check it out and see...

Hi Matthew,

You're definitely not the only person to use mini bales or half bales for interior walls!

As with all things in design and building, my first step is to assess the owner's criteria, and from there figure out what makes the most sense. You've listed your criteria, which is helpful. Definitely the mini bale walls will help reduce sound travel between rooms and keep the plastered aesthetic set by the exterior walls.

There are two main drawbacks to using bales in interior walls. The first is that it is more difficult to run plumbing and electrical services through a solid wall like a bale wall. It's do-able, but it can be a pain, and definitely takes longer. The second is the loss of interior floor space, as even the half bale walls are at least three times as wide as a stud frame wall.

One way that we go about matching the convenience of stud framing while keeping the hand-plastered aesthetic is to use old-style wood lath on the stud walls and then use the same kind of plaster we've used on the bale walls to cover the lath. To manage sound in certain rooms, we'll use cotton batt insulation between the studs. In this way, we end up with fairly typical sizes for the walls, use all natural materials and don't have to worry about the labour involved in cutting bales, stacking, pinning and routing services through it.

We have, on occasion, used bales for interior walls, particularly if the wall is curved. In that case, the bales can actually make it easier, especially if we've planned to keep plumbing services out of that wall. As you've noted, there is a lot more labour that goes into doing this! The studs with lath and plaster are every bit as fast as studs with drywall.

I would definitely seek out the clay pipe. The black plastic won't have as great a tendency to encourage condensation, but the clay will be much better.

I've used earth tubes made from black ABS plastic before, and I just made sure there was a way to clean them easily. I fed a rope through the pipes as I was assembling them, and now the owner can tie a sponge to the rope and pull it from one end of the pipe to the other a couple times a year. Apparently, there's only been wetness in the pipe at the height of summer heat/humidity.

Hi Jay C.,

You're right that there is a tendency to ignore historical systems of architecture in the natural building world (though people do like to ooh and aah over photos of old cliff dwellings). There's a tendency to want to throw out everything that has to do with "conventional" architecture without realizing that many of those conventions are a result of centuries of trial and error that have brought us to a point where we know how to make really good buildings. It's really the materials and design decisions that have gone off track with conventional building, but the traditional know-how that underlies much of conventional building is based on that hard-won concept of "common sense", which often takes generations to arrive at!

In terms of air tightness, we're probably not as far apart as it may seem. I'm not a Goretex fan, I'm more of a wool sweater person. That's the beauty of natural building systems... they work more like the sweater in that they are capable of absorbing/storing a lot of moisture and giving it up when the conditions are right. But if we're not building as air tight as possible (and this can be done with all natural materials... natural plasters are great air barriers when properly applied), we're not building as energy efficient a home as we can. Worse, those air leaks we leave in the building enclosure end up "ventilating" the home with less than ideal air quality. Air that's drawn through an insulated cavity is picking up dust, allergens and after a few decades probably mouse feces and other things that naturally accumulate in walls and attics. Air that leaves the building through those leaks introduces a huge amount of moisture to the building enclosure (in Ontario, studies show that a 2cmx2cm hole allows 30 litres of moisture into a wall/ceiling each heating season, whereas a wall surface with no leaks allows 1/3 litre).

All these reasons compel me to make buildings air tight. The comfort of living in an air tight home seals the deal. The straw bale house I'm currently in is extremely air tight, and we can set the thermostat at 19 C and be extremely comfortable. Most people are shocked when the see the thermostat setting, because they think the house is being kept really warm. That level of comfort and energy savings (we use over 80% less heat than a new code-built home) makes it worthwhile for me, and definitely worth the tradeoff of running an HRV for a few minutes a day. Our HRV "strategy" is that we turn it on each time we use the bathroom, and it's set to run for 5 minutes each time, so it typically runs 30-45 minutes a day). This level of ventilation is entirely adequate in a home that has lots of porous, absorbent materials, and could easily be achieved in a more passive way.

If codes would adapt to understand that natural materials offer huge advantages while being able to be air tight and require much less ventilation, we'd be on our way to much better buildings!

The only cautionary note I would add as you look into this system would be around the use of metal piping/ductwork buried under ground. You will be introducing hot and moist air into that tube/duct where it will cool rapidly. There is a good chance of condensation on the walls of the metal pipe/duct, and if it stays moist and warm enough, it could be a good spot for mould to grow. And if not dangerous mould, the potential is there for stale, musty air coming into the house.
If you were to use clay pipe (as many of the early civilizations who use this passive cooling would have done), the clay can absorb excess water and is less likely to grow mould.

Christopher,

A single 2x10 wouldn't be too narrow for this wall system, but it would create a lot of thermal bridging, as each stud would touch the outside and inside of the wall system. Better would be two 2x4 walls spaced to the same size as a 2x10... less wood, no thermal bridging.

Hi Mike,

Before anybody builds anything, I always like to start with the question "Why?", and then encourage people to set out their criteria for the building before attaching any technologies or materials to the project. Then, when a person knows what they want to achieve (and why), it's much easier to decide how to go about achieving it.

That said, I'll assume you've thought this through and your proposed building is what will best suit your needs/wants.

There is no good and accurate way to size an AGS system. There are only a handful that have ever been built, and of those, even fewer that have accurate test results that would help to create some guidelines. Either yourself or with a suitable engineer, you'd have to look at the heat capacity of the particular soil you're working with, and the Btus you can expect in a typical year from whatever sort of collector you'd be using. You'd have to guess at the system's inefficiencies and losses, and you'd arrive somewhere in some ballpark that might hopefully be reasonable.

Chief among the losses to consider is migration of your stored heat away from underneath your building. The ideal AGS system would be fully excavated, lined with a really good insulation, and then have the dirt returned to its insulated home. Without full insulation, losses downward and to the sides are substantial, as you are essentially trying to warm the planet in every direction under your home, and the planet has an almost infinite appetite for your heat. That's a lot to try and figure out accurately...

Arched, thin shell concrete has some great structural properties and can look great from the inside. Again, I always try to return to goals and criteria. Why this kind of ceiling? If there are compelling reasons, great. The thin shell concrete will not offer any amount of insulation value, so you'd have to not only figure out the roof design and green roof layers, but be sure to be including adequate insulation for your climate. You may have read that green roofs provide a reasonable R-value, but this isn't really the case. They definitely help keep a roof from overheating in the summer, but in the winter they offer little to no insulation value. An undulating roof like the one you are proposing would be difficult to insulate in any way other than spray foam. Nothing wrong with choosing spray foam unless concern for the environment is anywhere in your criteria...

The edges of such a roof assembly will be difficult to finish cleanly, and it will be hard to keep runoff from coming down the walls and staining them. Straight edges can be troughed, but round roof edges make it hard to collect/direct water.

There are many companies with mortar sprayers that you can hire. You can even buy a decent mortar sprayer (we own a Tirolessa http://www.tirolessausa.com/), but you'll still have to hand trowel the sprayed plaster unless you like the random, fuzzy, bumpy look of sprayed plaster.

Your project sounds interesting, could be feasible, and also seems like a lot of work! I would suggest making sure that you are getting what you want out of this design before committing to it.

Certainly there is some precedent that shows these enzymes work for roads. And I wouldn't say that they don't work for earth floors or plasters, I just don't know anybody who has tried it. I know my friend had his CEBs tested at Queen's University with and without the enzymes and found no measurable difference in strength or water characteristics. But new ideas can take a while to show up and be proven, so I wouldn't write them off...