Our Passive Solar Straw-bale Home - Not a fairy-tale, but based on one
Remember the "Three Little Pigs" story, the part about the straw house, the stick house and the brick house? Well, our home is a hybrid of locally grown barley straw, wooden "2-by" framing (often known as "stick-built"), with masonry walls and floor. It's an example of how all three of the little pig's houses can work together - porcine co-operation!
A house is a live-in machine. It works to moderate temperature extremes, store your food, get you clean, keep you dry, deal with your bodily "wastes", extend your working/waking hours, and provide clean, fresh air and water. It allows you to sleep peacefully, eat comfortably, relax with friends or other diversions, and it is easy to get in and out of. We expect it to provide cheerful outdoor views, impress our friends and neighbors, and if it doesn't outlast us we at least want it to outlast our interest in it. That's a lot to ask from one machine, so most folks delegate the planning to architects and contractors.
How well the machine functions is a matter of design, construction materials, "work-person-ship", location, and its "fit" for the occupants or needed use within a specific climate. Neglecting any of these five will cause the machine to malfunction, at least in terms of satisfying our goals.
Our previous home was built off-grid, super-insulated, and solar/wood heated, using many recycled materials. Due to a changing political climate at the land co-operative we lived in previously (for 12 years, from 1988 to 2000), we wanted to quickly build a new home with little if any financing, utilizing very little hired labor, using mostly off-the-shelf materials purchased locally. So we charged ahead with nearly the same design concept on a very different site.
Buying materials primarily from a "lumber yard", all brand new, was a bit foreign to us. After all, about 48% of all energy consumed is used in building construction and operation. And about 8% of a building's total energy use is the energy used in construction and the "embedded energy" of its materials, from mining to manufacturing and shipping. But one of the primary foundations of Sustainability is Durability, and that's where our choice of materials begins to make sense.
A passive solar building uses the Sun's energy to directly heat a massive quantity of solids or liquids, usually in the form of a masonry wall, a concrete or packed earth floor, or transparent tanks of water. The south-facing window area, the amount of mass you're heating, and the insulation used to hold the heat within the structure must be carefully tailored to match the size and shape of the building and the climate it's in. Some good books to read on this subject are: "Passive Solar Architecture: Logic and Beauty" by David Wright (right-brained), and "The Passive Solar Energy Book" by Edward Mazria (left-brained).
After living for a number of years in our previous passive solar & masonry stove heated, super-insulated home, we discussed what we would change if we ever had to build again. The one thing that came up repeatedly was the insulating system. Our house at the time had a plastic vapor barrier with a 10.5 inch thick layer of Fiberglas insulation. Although it works well as an insulator per inch of thickness, Fiberglas is a poor insulator at really low temperatures, it is energy-intensive to produce, horrible to work with, and both the insulation and plastic vapor barrier out-gas chemical fumes.
Our new house (built in 1999, seen here in 2012) uses our preferred choice of insulation, locally grown barley straw. There were 1500 bales listed for sale in a local paper at $1.00 per bale from a nearby farm. We purchased 400 bales but only needed 200 to fill our walls. The roof cavity was blown full of cellulose instead, to save weight and ease installation. Our particular straw-bale house design uses the bales only as insulation, not as part of the weight-bearing structure. Typically the house stays above 60F at night, even when it's -25F outside, as long as we get sunshine during the day or do a quick, hot, single-load fire in the masonry wood-stove at night. For more information on our wood heating, Click Here.
What About Combustibility?
I have received some feedback from a reader on Stumbleupon.com asking, "What happens when it catches on fire"? Well, the roof is steel, the chimney is interlocked, triple-wall, ceramic-insulated steel, the exterior walls are cement-board, the interior walls are joint-compound-coated gypsum over an aluminum foil vapor barrier, the floor is concrete, and the ground surrounding the house is washed gravel. How do you propose that the house will ignite? And from what?
Construction started in October of 1999. The weight of up to 5 feet of wet snow on the roof is transferred through the roof steel, into flat 2x4's at 20-inch intervals, down into 14-inch, engineered I-joists, into doubled 2x12's, and finally into 5x6-inch treated wood posts resting on hand-poured concrete footings, buried 4 feet in "pea gravel". The posts are strapped into the concrete, the 2x12-inch headers are steel-strapped to the posts, and the I-joists are strapped to the headers. We added another row of doubled 2x10 joists and some locally-cut spruce posts in the middle of the house just to reduce roof joist deflection under really huge snow loads.
We started building the actual house framework in November of 1999 and moved in during May of 2000. This is photographed in November. The 14" engineered I-joists can be lifted into place easily by one person. The 4-foot deep, 2-foot wide holes for the post were done by hand with a "clam-shell" digger and back-filled with "pea gravel". I had some help lifting the doubled 2x12's into position between the 6-by-6-inch, ACQ-treated posts.
Moving from the exterior toward the interior, the walls are composed of:
5/16-inch thick, textured, painted, fiber cement siding, screwed into
- flat-faced 2x4's at a 24-inch spacing, directly touching
- side-stacked straw bales, with a thickness of 14 inches, directly against
- 1/2" sheets of foil-faced foam insulation (with the inner face foil-taped to make a vapor barrier), touching
- flat-faced 2x4's at a 24-inch spacing, directly touching
- 1/2-inch gypsum wallboard, covered with a 1/16-inch layer of joint compound, textured with a rubber roller, and painted with a zero V.O.C. latex paint.
The completed exterior wall resembles vertical, painted boards, but it is composed of 4x8-foot sheets of 5/16-inch cement board siding. The average wall insulation R-value is 50. The bales are tied onto the outer layer of 2x4's to prevent shifting during construction. The inner wall is textured using thick, troweled-on "joint compound" and a patterned rubber roller to look like a very coarse fabric, giving us the look of stucco, but without nearly as much work. And all of the plumbing and electrical runs are in the stud space between the foil vapor barrier and the interior walls.
This shows a wall being built from the outside in. The straw bales are stacked on edge against the outer wall studs. The foil-foam is pushed against the bales and held in place with the interior stud wall, built as the foam sheets are placed. All of the foam seams are foil-taped as the wall proceeds. Where the ceiling meets the walls, 6-inch wide, PVC foam "sill-sealing" material is duct taped to the ceiling foam on one edge and the wall foam on the other. The sill sealer pads the sharp edge where these two major planes intersect, preventing a break in the vapor barrier.
Moving from the roof's exterior to the ceiling, the overall roof is composed of:
- 3-foot wide sheets of galvanized steel roofing, screwed through:
- sheets of Tyvek semipermeable plastic, to prevent condensation from dripping into the insulation, covering:
- flat 2x4-inch "purlins" at 2-foot centers, screwed into:
- 14-inch deep, engineered I-joists with tightly-blown cellulose between them, covering:
- 1/2" sheets of foil-faced polyisocyanurate foam insulation (again with foil-taped interior seams), resting on:
- 2x2-inch wood strips screwed up into the I-joists, caulked at all the screw holes, covered by:
- 1x8 pine "tongue & grooved" boxcar-siding, nailed up onto the 2x2's.
This roof structure has a finished R-value of around 60. We started with the I-joists and moved upward to the steel in order to create a dry work zone below. The foam insulation, 2x2's, and finished ceiling were done next to make the inside liveable (in conjunction with closing in the exterior walls, of course!). Later, the cellulose was blown in to quiet the noise of hard rains on the roof, and to finish insulating. The pink foam on the ground was later covered with thick, aluminum-coated tarps and poured, fiber-reinforced concrete.
The cost of our home, with some materials purchased initially and some as we finished, added, or remodeled, can be broken down as follows:
Building Structure - exterior shell and finished interior: $23,050
- Utilities - PV solar electric system, batteries, wiring & fixtures, LP gas & cook-top: $18,480
- Heating System - masonry stove and solar air preheater: $3,024
- Water - rainwater cistern, pump, plumbing & fixtures: $2636
- Septic System - grey-water tank & drain-field: $596
Most of our window area faces South, with about 120 square feet of glass. This lets the Sun shine down on a 32-ton, 5-inch thick, fiber-reinforced, concrete slab floor. The slab measures 40x27 feet in total, with 37x24 feet showing inside (due to the 18-inch thick walls). The deep "window wells" were made less tunnel-like by widening each window's interior walls about 6 inches on each side, as you move inward. They're kind of like bay windows without the side views. Most of the South facing glass is ordinary double-pane, but the East and West windows, as well as the uppermost South windows, are Low-E, Argon filled. We use R-4, exterior, double-wall, extruded polycarbonate shutters in the Winter, only on the double-pane windows. This maximizes both daytime solar gain and window R-values.
These are the West windows framed in and strawed. The foil-foam insulation is partly up on the wall but finished on the ceiling. All foil joints are foil taped for a perfect vapor barrier. Even the plastic-headed nails used to put the foil-faced-foam up under the I-joists got foil taped.
This shows a detail of the side of a South-facing window. All foam seams are taped and the posts are wrapped in sill sealing foam. The window sides were later covered with vertical pine T&G, and the sills were covered with dark brown ceramic tile.
This shows the finished interior wall ready for "sheet-rock", texturing (using 1/8th inch thick joint compound and a rubber texturing roller), and painting with a zero V.O.C. paint.
The central South wall window, looking South, before adding the pine side-walls and 6-inch square, quarry-tile base. At first the quarry tiles were installed over untreated 1/2-inch plywood, then sealed with tung oil. After some time with potted plants over them, and many spills of water and dirt, I stripped the messed-up oil finish. Big Mistake!
After a few years water vapor passed through the unglazed tiles and condensed in the plywood, causing it to rot. In 2011 we ripped out the tiles and plywood and replaced it with dense, closed-cell, styrene foam and 3/8-inch granite tiles. Since the straw below the windows had settled and gapped a bit from the window frames, leaving an outdoor air pathway under the window sills, we also injected "spray foam" under the sills where they meet the straw. Better insulation and sealing solved the condensation problem on the sills, making the whole window area warmer in the winter.
And in latest news (October 2012) we have added some exterior insulating shutters. You can link to the full PDF showing the details here (requires a free Adobe Reader download).
Here I am cutting tongue-and-groove 1x8" boards to nail up onto the 2x2" "furring strips" that are caulked and screwed up into the I-joists above them. This is the only other spot in the house that nails were used. Everything else used screws, lag screws, or bolts.
This partly filled pantry is closed off from the otherwise open floor plan. It keeps our dried and canned foods cooler and in the dark. In its floor is a 3-foot by 6-foot cement pit, 2.5 feet deep, which is one of our root cellars and our water supply's "pump pit". Access is through 4 insulated trap doors made from plastic decking.
And this is a photo of the sauna we added under the porch roof, seen from its entry door. It is heated by a small, antique, wood cook-stove, and the two-layer "Reflectix" (mylar foil -"bubble-wrap"- mylar foil) insulation gets the temperature up quickly and keeps it high for a long time. The interior is 5/16" tongue and grooved red cedar. With 5/4-inch cedar decking on the bench. The sloped back can be removed for more bench depth or to make a shelf for food drying, when the weather doesn't cooperate with solar drying. The tiny window is coated with a heat-reflecting layer, and has a screen for summer use as a "summer kitchen".
clicking here, or by e-mailing us at our Secure GMail.com account listed as "bobdowser".
A Tiny House Built for a Friend
And what if you want a small, functional house for one, but don't have land to put it on just yet? A friend asked me to build a portable home that I call a "Mobile Homestead". This is a 24-foot by 8.5-foot trailer used normally to haul heavy machinery. In our State, if you keep a structure under 13.5 feet total height and within this width you can legally haul it down the road without special permits.
Here I am caulking some treated 2x4's onto the steel frame of the trailer with PL400 construction adhesive. They got screwed onto the steel with treated, hardened deck screws. The trailer alone cost over $5000, about a third of the entire cost of the building.
In this shot you can see the basic framing beginning. The corners are a combination of three 2x4's and a 2x6 ripped to 5 inches, to make a nearly circular, hollow corner post that holds insulation, making a "warm corner".
Here is the nearly complete exterior shell, except for window framing and the east and west sides. The rafters are 2x6's on 2-foot spacing, not all up at this point.
Here you see the south side of the house with semi-permeable plastic "house wrap" used to allow vapor out but to keep rainwater off under the final siding. The windows and doors are in and caulked. The galvanized steel roofing is screwed into flat 2x4-inch "purlins", and roof extentions on the east and west are made using upright 2x4's, "toenailed" into the outermost 2x6's at their ends and screwed to the sides of the flat 2x4 purlins.
Here you see the 5/8-inch bamboo flooring going down over 1x2 pine spacers that are screwed into the treated wood decking of the trailer through a solid layer of Reflectix bubble-wrap/mylar insulation. An additional layer of Reflectix is placed between the 1x2's. Some of the exterior siding is up, but you can still see daylight over it in spots. Still more Reflectix was planned for installation under the trailer framing, but bags full of leaves were used as perimeter insulation instead.
This is the interior with Reflectix bubble-wrap/mylar insulation being stapled over 6-inch Fiberglas on the ceiling and over 3.5-inch Fiberglas on the walls. The Reflectix gets foil-taped to make a complete vapor barrier.
This is the nearly complete exterior, almost ready for the road. I was just about to box in the eaves using 1x4 cedar nailed over some window screen, with gaps between the boards to ventilate the roof through the eaves. Detachable roof overhangs for the north and south sides were planned but not shown. They need to be off the structure to legally tow it down the road. Also purchased but not shown is a 6.5-foot by 16.5-foot, pre-fabricated, aluminum and polycarbonate greenhouse that covers most of the south side.
When the house was moved from the construction site in our yard I rode inside to check for creaking joints, etc. Nothing was heard, even when it was towed across some very rough field roads. This little house resided about a mile away from us for a couple of years, on rented land. The owner reported, even during our -22F nights, that the house was very comfortable, easy to heat, and cheerful.
Updates on the tiny house project:
Big News! Lea bought land adjoining ours and the tiny house is now down off its wheels and tied down to her new property. To see a free 7 MB PDF download of the additions (as of October, 2011) just Click Here.