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The Affordable Natural House: An interview with Lou Host-Jablonski, AIA
By Janet Chen
Janet: Why use straw-clay construction, as opposed to straw bale construction?
Lou: I have looked at strawbale, adobe, rammed earth, and "earth-ship" construction using recycled tires. I researched alternative construction for years and years, looking for a system that did it all. It had to be energy efficient, buildable, low-toxicity and [not be too incompatible with] modern codes. It had to be reasonable in terms of costs and in terms of availability of materials. It had to be ecological and have longevity. And it seemed each system had some issues that didn't recommend it for use in this climate.
My concern with straw bale in this [Wisconsin's] humid climate is the potential for real moisture problems and structural issues. At that time people were trying to do load-bearing straw bale. The trouble is the [untreated] straw can get wet and grow mold, and be a big problem as a structural material. To grow mold you need air, moisture, the right temperature, and the micro-organism. Straw bales [hold] lots of air. An earth-plastered straw-clay wall will have much better moisture performance that a straw bale wall can have. Clay is the key to doing that. It's hydroscopic. It wants to absorb the moisture that's around it. It has the effect of pulling the moisture away from the straw and aiding in wicking moisture to the surface of the wall and getting rid of it.
In the early '90's I attended a straw-clay workshop in Iowa with Robert Laporte of the Econest Building Company. I took the workshop, did timber framing, straw-clay, and then earth plastering. By the end of the week I understood this was an integrated family of techniques that worked well together. Robert has been doing this for years, is a very conscientious and expert builder, and has done his homework, in terms of study and in going to Germany where a lot of these techniques have been developed. Plus there are options for using it with light framing which are more wood-efficient. We still have research to do and progress to be made but I remain convinced that it is a family of techniques that really works together well.
Janet: In that workshop you used post and beam framing. Here you are using light framing to reduce the use of wood.
Lou: When I took the workshop we did a timber frame home with "blind framing". This house is different. It has 2 x 6 studs at 24" spacing on center (O.C.). Everything - studs, floor joists, trusses - lines up exactly 24" O.C. the whole length of the building, with the exception of a 3' door on the north side. And we designed the roof trusses so the trusses frame the upper walls as well as the roof.
In addition, what is normal, 2 x 6 framing has a double 2 x 6 top plate. We've used a single 2 x 4 instead, to give us more room to place and compress the straw-clay. Then we took the other plate and turned it on edge, so now the plate becomes a ledger which has load-bearing capability. All the windows fit between the 24" O.C. studs, except in a few places where I cheated a bit to get slightly wider windows [because the use of the structural ledger allows some latitude in this regard]. We're able to eliminating all the headers over the windows and avoid doubling or tripling of studs to pick up large header loads. By sticking to that rigorous system we save a lot of wood.
Janet: What other refinements are you exploring?
Lou: We are working on ways to better mix the clay slip [a mixture of clay and water]. In the past we've mixed slip with a mortar mixer, eessentially a paddle mixing in a barrel. Combining clay and water directly results in clumping, though you can still get decent, workable slip for building purposes. For plaster we have been mixing the clay and sand ahead of time before adding water because the sand helps keep the clay from clumping.
A more effective way to mix slip is with a rotor-stator mixer, which shears the clay into very fine particles suspended in water. These mixers are used for mixing paint, putty, and other products. A client of ours in Minnesota [Douglas Piltingsrud], a scientist, took his rotor-stator mixer and mixed some slip. It was immediately apparent by looking at it and feeling it that the slip was mixed much better.
Once we have the slip, we mix it with sand [and other ingredients] to make clay plaster or with straw to make the walls. If you can put a wall in place that has a very thin coating of clay evenly over the straw fibers, you are going to get a better R-value, and a more sound wall, with less settling, more tensile strength, and more stability.
Janet: Where does the clay come from?
Lou: The clay you want should be granular form, not in clumps. We get shredded clay delivered from a landscaper who digs it out with a bobcat from a clay deposit in the earth, runs it through a topsoil shredding machine, and delivers pea sized particles. If you have good clay on your site you can get it yourself.
Janet: When is the best time to form the walls?
Lou: Ideally you want to do it between May and September [in Wisconsin's climate].We did our walls in October, which is late. A straw-clay wall needs to dry and shrink before plastering. Earth plaster can be directly applied to the interior. Since the studs are to the exterior you can nail siding directly on the outside or apply a stucco finish. This house will have an stabilized earth/lime stucco exterior.
Janet: Are you planning on having an additional workshop?
Lou: Yes. There will be a workshop in the Spring. There is a little more straw-clay work to do. At that time the walls in the main house will be cured and we will do some earth plastering as well, We always try to show the whole family of techniques, even if only for a few hours of each process.
Janet: Are you also planning on insulating your roof with straw-clay?
Lou: No. This roof will be insulated with cellulose. Cellulose is recycled, ground-up newspapers with borax added as fire retardant. A straw-clay wall, because it's so dense, has excellent fire resistance. It's like trying to burn dirt. Straw roof insulation on the other hand would be installed loose and not packed in, so it could burn - not a good thing.
Janet: Your house has a double peak. Will you would be collecting hot water with solar panels?
Lou: Essentially the double peak on this roof is an oversized vent that is part of the passive cooling system. [There will be no mechanical air conditioning in the house]. In a conventional roof design you need to ventilate the insulation. In this climate moisture from the house goes into the insulation despite having vapor barriers. Condensation in your roof system can create soggy insulation [drastically reducing it's insulating value] and in the worst-case scenario you can get rotting roof sheathing.
What I'm experimenting with here is an oversized ventilation system which I'm hoping will also have some cooling effect in the summertime. When the sun is striking the shingles, it's heating up that roof cavity. If I can effectively vent away much of that heat, it should keep the house cooler.
There is a second thing going on there. Last year [in Wiscosnin] we had a lot of ice damming. Ice damming is caused when the roof surface is warm enough for the snow on the roof to melt a little bit. Water runs down the roof and then when it gets to the cold edge of the roof, it refreezes, creating an ice dam. Eventually there is a puddle of water at the top of the wall which creeps back up underneath the shingles and leaks into the house.
The solution is to keep the roof cold so the snow doesn't melt in the first place. [One way is to] build a double roof where you allow cold air to circulate under the primary roof sheathing. In my house I'm doing that in a lower cost, lower-tech way using a house-wrap type of material to layer underneath the roof sheathing as the secondary 'roof'.
As for water heating, on this house I'm experimenting with solar panels that are integrated into a passive solar skylight system. The closeness of the house and the tree next door blocks some of my solar access. I needed something up on the roof to get solar heat, so why not put the water collectors inside the skylight and collect heat for hot water as well as heat for the house and daylight for the plants through the same glass?
Janet: Why large roof overhangs?
Lou: Large roof overhangs are a good idea in rainy climates. We are going to have earth stucco on the lower part of the wall so overhangs are very important [to protect the stucco]. I had noticed this years ago when I lived in a conventional house that had no overhangs and walls with wood siding. [Besides the solar shading of windows in Summer], big overhangs allow use of siding material that is more natural than, say, vinyl. I can use it well, use it durably, and use it confidently. It's not a stylistic thing. It's not just an esthetic thing. It's a building longevity thing.
Janet: Are you going to have radiant floor heat?
Lou: The new section will have radiant in floor heat, hydronic and a little energy-efficient boiler in the basement. About 2/5ths of the radiant floor heating, at the bathroom and the bedroom. The other 3/5ths under the kitchen, living, and dining room will have an air core floor.
Janet: What is an air core floor?
Lou: An air core floor is a slab on grade type of floor which has air channels underneath. It's used to store heat. At the south edge of the floor there will be registers. At the north end there will be a plenum below the floor with a low-energy blower that will continually pull air through the cores below the floor from the south. Warm air will come into the south registers, travel underneath the floor, store heat in the floor, and then be recirculated by the fan. I expect the south side of the house will collect a lot of heat [because of the big windows and skylights] and this is a way for me to use the thermal mass of the floor to store that excess heat for use at night when it is needed.
Janet: One of the descriptions of this house is the natural affordable home. What is the cost of an affordable home?
Lou: The word means different things to different people. For example, the Madison Area Community Land Trust and area developers of affordable housing define it as homes that are affordable to a person or families who's income is at 80% of the median income level of Dane County [Wisconsin, USA]. Another developer might define it as 50%. How I use it, I'm referring to a house that is modest in size, do-able for the average family. That's a more loose definition. And with my house I'm referring to the main part of the house, not the [connector and original cottage] parts in back, which are the result of this particular property and the zoning.
Lou Host-Jablonski, AIA, is an architect with Design Coalition. The home project described here is his own home.
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