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One of the advantages of building your own home is that you can declare your freedom from conventional construction techniques. In this section, we will describe some techniques that may be unusual in your neighborhood but that you may want to consider. They can enable you to create a home that is both unique and well adapted to your personal needs.
ill. 4-20: Adobe construction.
ill. 4-21 : (Right and left): This passive solar adobe home was built using the poured adobe method.
Earth is very likely the oldest building material known to humanity, and it's still widely used today. The strength, durability, and availability of earth makes it particularly attractive when other building material resources are in short supply. The “adobe style” has been energetically revived in the Southwest, for example. Some of the modem adobe homes in New Mexico, Arizona, and Colorado are among the most luxurious homes to be found anywhere.
Traditional “puddled” adobe bricks are produced from soil, ideally taken from a location as close to the building site as possible. The soil is mixed with water, shaped in a mold, dried in the sun, and then used to build walls. The earth mix is fairly sloppy, about the consistency of very heavy cream, hence the term “puddled.” The mortar used has the same composition as the bricks, except that the larger stones are screened out of it. The bricks must be cured before they are laid onto the wall; curing time will vary with humidity and temperature, but takes a minimum of a couple of weeks.
A variation of the traditional technique involves the use of a hydraulic ramming device to press the mud into bricks. Rammed adobe bricks can be produced at the astonishing rate of one every 12 seconds. The earth used to make these bricks has a relatively low moisture content, around 10 or 11 %, so they require a minimum of curing and can often be taken off the machine and built into a wall. They are more costly than traditional adobe bricks, but often the time and labor saved justifies the extra expense.
A major disadvantage to building with adobe bricks is that the technique is extremely labor-intensive. “Poured adobe” is a building technique that helps solve this problem. The best-known proponent of poured adobe is Mike Kinshaw, who built two houses using the technique on a ranch he owned near Phoenix, Arizona. His first house (1,500 square feet), built in 1975, cost $20 per square foot; the second house (4,000 square feet) was completed for around $30 per square foot.
Specially designed portable forms are the heart of the system. The first type of form is a collapsible box made with two 1” x 12” x 36” boards and two 1” x 12” x 24” boards (see figure 4-22). The box is hinged on one end and held together at the other with 3 all- thread rods. The plate at the unhinged end can be canted to create bricks that are thicker on the bottom than at the top, thus permitting the construction of tapering walls in the style of old adobe buildings. Several of these forms are built and placed on the wall or footing about 24 inches apart.
Dry adobe soil is loaded into a cement mixer or mixing truck through a 4-inch mesh, and water is added in the correct proportion. The adobe mud is then placed into the forms and tamped down. Depending on the temperature and humidity, the forms can be removed in 4 to 24 hours. The forms are then moved to a new section of wall where the process is repeated. The spaces between the resulting adobe bricks are filled by attaching two plates made of 1” x 12” x 36” boards wired together (see figure 4.22). Adobe mud is placed between these boards.
ill. 4-22: Belshaw collapsible-box form (a) and wood-plate form (b).
Poured adobe is a fast way to build an earthen house. Belshaw says that a three- person crew, working hard on a simple structure, can get a wall to roof height in about 16 working days. The greatest obstacle to the method is that it's not covered by model building codes, so you may need to work hard to win approval from building officials and lenders.
Rammed earth, also known as pise de terre or pise, is a method of constructing earthen walls by building up layers of compacted earth. Wooden forms are placed on a footing, and earth is placed in the form and tamped down (or “rammed”) in 4- to 6-inch layers until the forms are full. The forms are then moved up, new soil is put in and rammed—then the forms are moved upward again. The process is repeated until the wall reaches the desired height.
A rammed earth wall is self-supporting as soon as the ramming is complete, although it can take several years to reach full strength. After about two days, the wall is cured enough to install doors and windows. If you wait more than a couple of weeks to do this work, the wall may be so hard that you will no longer be able to nail into it and will have to drill with a masonry bit before fastening framing to it.
Owner-builders can build their own rammed earth walls by hand or hire a contractor (if such a person exists in your area) to build only the walls then do the rest of the work on the house themselves at a considerable cost savings. A 16-inch-thick wall may cost as little as $4 per square foot, while a 36-inch-thick wall may cost about $8 per square foot. These costs include the “bond beam,” a code-required reinforced concrete beam that runs along the top of an 8-foot-high wall, or at the top of each story in a two-story structure. Footing costs are not included.
Soil suitable for earth construction is found nearly everywhere in the world. Ideally, the soil should contain 70 % sand and aggregate and 30 % clay mix. Variations from these proportions may still result in strong walls, as long as the clay %age is kept low. If the proportion of sand and aggregate is increased, the resulting wall will be less resistant to erosion but will have greater compressive strength. The “bottom line” test for any soil is to make a few test blocks and see how strong and water resistant they are.
It is a common myth that earth construction is best used in hot, arid climates such as New Mexico. While it's clear that hot, arid climate zones are the primary locations for earthen buildings, it's also clear that earth works as a building material in wetter northern and eastern climates. Rammed earth walls don't require the curing time of adobe bricks, so they are especially well suited to wet, humid climates, where curing bricks would be difficult.
ill. 4-23: A forming system for rammed-earth walls.
Some builders “stabilize” their earthen walls to increase the weather resistance of the material. Traditional earth builders used straw, animal manure, and blood as stabilizing agents, but Portland cement or asphalt emulsion are more common today. Stabilizing eliminates the need for extra-long overhanging eaves, which might block the sun in a solar building.
Energy codes, where applicable, will require that an earth wall be insulated, since earth doesn’t have a high R-value. It makes the most sense to insulate on the exterior with one of the foam-and-stucco systems such as Dryvit. This keeps the walls on the inside of the insulation where they can function as thermal mass to moderate indoor temperatures. If you use such a system, there is little point in going to the expense of stabilizing the earth, since it will never be exposed to weather.
The Owner-Built Earth House
The main technical advantage of earth construction for owner-builders is that there are few “exact” rules that must be followed. There are rules, to be sure, but they are not as rigid as those for frame construction or even log building. If you’re willing to put in the time to gather the information, earth construction is easy to learn.
Earth construction has low materials costs and high labor costs (if you hire workers), so there is a real advantage to owner-builders who have the time and skill to do most of the labor themselves. A crew of two can produce 300 to 800 bricks per day, depending on the equipment they use. After the bricks have cured, a team of three can lay up as many as 800 bricks per day while standing on the ground and about half that number while working on a scaffold. Some owner-builders say they spent $10,000 to $30,000 on adobe homes that have market values of $80,000 to $150,000.
If your local code does not recognize earth construction, see Construction Industries. Make sure you get the current amendment. The New Mexico code should be a valuable aid in convincing your building department that earth structures are safe and structurally sound.
Earth-sheltered houses, sometimes referred to as “underground” houses, can be defined as homes that are built into or surrounded by earth. Energy conservation and protection from storms are major incentives for most owners of earth-sheltered houses. The decision to build such a house will profoundly affect your choice of a building site, the materials you use, and the design and layout of the living space.
George Golan, an authority on earth-sheltered homes, lists the following climates as being suitable for subterranean construction: (1) very warm and dry, such as the south western United States; (2) very cold and dry, such as central Canada; (3) temperate (cold and snowy in winter, rainy and relatively warm in summer), such as the upper mid-western United States.
Although other houses, such as super-insulated and passive solar homes, achieve similar levels of energy efficiency, the earth-sheltered house has several unique advantages:
• Temperatures below the surface of the ground are much more stable than air temperatures. In Minnesota, for example, the air temperature fluctuates yearly as much as 130 degree F (from -30T to 100 while the temperature of the earth 10½ feet below the surface fluctuates only about 18 degrees F (from 40F to 58°F) — a mild underground environment compared to the extreme aboveground environment.
• The earth gives up its summer heat slowly in the autumn and warms up slowly in the spring. This “thermal lag” means that the heating and cooling seasons are postponed for an underground house. lithe soil outside your walls remains warm in the autumn, you won’t need as much heat as you would if your house stood aboveground, exposed to chilling winds. Similarly, you won’t need to cool your house in the spring or early summer if the soil outside your walls stays cool.
• An earth-sheltered house is more likely to withstand the effects of severe storms such as tornadoes. The house hunkers down, where the winds can’t hurt it.
• If concrete and concrete masonry are the primary building materials, the house will be more rot-proof, vermin-proof, and fire-resistant than an above-grade house built with conventional materials.
• The sound-dampening effects of earth make earth-sheltered buildings much quieter than above-grade structures.
• Melvin Wall, the well-known architect and proponent of underground architecture, says that his main reason for going underground is “because it's so beautiful.”
ill. 4-24: Underground homes can be beautiful as well as practical.
Site and Structure
Sites with expansive soils or with bedrock or water close to the surface are not suitable for homes built under the surface. Nearly any site problem can be solved, but the solutions can be very costly and /or disruptive to the local environment. For instance, bedrock can be blasted away, but this is not a do-it-yourself job. A better solution would be to build aboveground and berm (pile earth against) the walls. If there isn’t enough soil on the site for this, you’ll have to haul it in, which can be expensive. it's always better to design your house for the site, rather than forcing an inappropriate structure onto a site.
If you know you want to build an earth-sheltered home and don’t own the land yet, look for property with soil that drains well, that can be excavated easily, and that can easily carry the load of your home. Obtaining a soils report before you buy is good insurance against expensive or disappointing surprises.
Earth-sheltered buildings are subjected to heavier loads than above-grade structures, since earth presses against the walls and (usually) the roof. (Some earth-sheltered homes have conventional roofs that protrude above ground level.) Considerable attention must be paid to adequate structural engineering. it's advisable to consult a professional structural engineer familiar with earth-sheltered design at the outset of the design process. Fortunately, there are a variety of materials to choose from to carry the loads borne by an earth- sheltered home.
Poured concrete or concrete block are logical choices for earth-sheltered construction, since concrete and masonry products are rot- and vermin-proof and have high compressive strengths. If you plan to do most of the work yourself, concrete block is a better choice than poured concrete, since laying up block is far easier than orchestrating massive concrete pours. We would suggest either a surface-bonded block or interlocking block wall rather than conventional mortar-jointed block. These systems are easier to build, easier to waterproof, and stronger than the more conventional mortared wall.
Another possibility for the dedicated do-it-yourselfer is all-weather wood (i.e., wood impregnated with wood preservative chemicals). We have reservations about the toxicity of the preservatives used in the wood, but the fact that you could build your underground house using basic framing techniques make all-weather wood an attractive option for an owner-builder.
Rob Roy has done some interesting work with low-cost “cordwood masonry” houses in the severe climate of upstate New York. We will describe this technique near the end of this section. Roy’s Earthwood Building School offers instruction in the technique.
Other materials such as thin-shell concrete domes and pre-cast concrete planks are not accessible to the owner-builder, but it's possible to hire professionals to erect the basic structure, and then you do all the finishing work yourself. Precast concrete is a commercial building material—you can probably find suppliers in your area by checking the yellow pages or calling commercial contractors. Thin-shell concrete domes must be built by contractors with the proper equipment and experience.
Despite the energy advantages of earth-sheltered construction, these houses must be insulated. There are currently many design theories about the amount and placement of insulation around an earth-sheltered house, but most experts agree on the following points: (1) insulating below the floor slab is not cost-effective; (2) where walls are not covered by earth or earth berms, insulating the perimeter of the foundation walls and insulating around the edge of the slab are good investments; (3) if the house is built of masonry, insulation should always be placed outside of the walls, which allows the thermal mass of the walls to moderate temperatures in the living space. Exterior insulation will also protect the waterproofing from abrasion during backfilling and from seasonal movement caused by freeze/thaw cycles.
In a study reported by the National Concrete Masonry Association, Energy Savings through Earth Sheltering (TEK 119), four cases for insulation placement were evaluated:
Case 1: If there is less than 5 feet of soil on the roof, the ceiling should be insulated. This is more cost-effective than to increase the structural strength of the house in order to carry a deeper earth covering.
Case 2: Insulating the ceiling and walls down to 6 inches below the frost line results in medium heat loss during both winter and summer and is well suited for temperate climates requiring both heating and cooling.
Case 3: Insulating the ceiling and the walls down to the footing yields low heat loss. This case is best suited to northern and high-altitude climates where heating requirements dominate the year.
Case 4: A good strategy in most climates is to place insulation on the roof, partially backfill the walls, place rigid closed-cell insulation outside this earth, and then continue backfilling over the insulation. The amount of earth in contact with the walls is thereby increased while the frost line is lowered. The earth between the walls and the insulation is shielded from the aboveground temperatures, resulting in excellent building performance in both winter and summer.
ill. 4-25: Four cases for insulation placement.
Drainage and Waterproofing
If water leaks from the soil into an earth-sheltered home, you won’t have just a wet basement you’ll have a wet living room, kitchen, and bedrooms. So preventing such leaks is critical. We recommend overdoing your waterproofing and drainage system to assure that you will never find yourself digging up your house to repair a leak.
A relatively inexpensive waterproofing system might include a layer of roofing felt, roofing cement troweled on over that, polyethylene sheeting (6 mil or greater) with generous overlaps over the cement, topped with more roofing cement, sand, and sod. Unfortunately, given the manufacturing defects and degradation that polyethylene is prone to, this system is probably a little risky.
A “built-up” roof may also be a relatively inexpensive answer, although there is some debate about how advisable such a roof is in a situation where it can’t be easily inspected and repaired. The roof incorporates multiple layers of roofing felt and asphalt or pitch. Glass-fiber membranes rather than organic felts are recommended, since the latter will rot if they are exposed to water over a period of time.
More sophisticated coatings are also available. Bentonite clay is very expansive when moistened, and as the molecules expand in a confined space, like on a bermed wall, they press closely enough against each other so that no water can pass through. There are several methods of applying this material, but it's generally not a do-it-yourself project. The warranty of at least one product, Bentonizing, is void unless the product is applied by a licensed applicator. Bentonite clay requires moisture to do its job, so it's not recommended for very arid climates unless precautions are taken to assure that it will never dry out.
A number of other products including butyl, EPDM, and neoprene membranes are also available. Although they are among the most expensive choices, remember that this is not a job you want to have to do again.
A successful system combines an effective waterproofing treatment with a drainage system that never allows water near the wall. Drain tile set in gravel must be set around the footing of the underground wall, and another drain tile at the top of a totally buried wall is also a good idea.
ill. 4-26: This is a standard waterproofing treatment for an underground home.
Earth on the Roof
The roof of an underground house can be covered with sod or several feet of earth. This can be an advantage in both summer and winter. Although earth is not a good insulator, it can be used to enhance the thermal effectiveness of a well-insulated roof. In very cold climates, sod can help to maintain the accumulation of snow on the roof — especially north-sloping or shaded roofs — which further reduces heat and infiltration losses. The cooling benefits in the summer are even clearer. Evaporation of rainwater and morning dew and the transpiration of moisture through grass blades can reduce the temperatures of the roof by 20 degrees F.
The sod roof often becomes a bed for wildflowers. Earth several feet thick covering the roof of an underground house makes the growth of root structures of larger shrubs possible, producing a lush hanging garden effect. Planting indigenous plant species on the roof and surrounding earth berms can result in the illusion that the house has always been there.
As you might imagine, an earth-covered roof can create severe waterproofing and structural problems if you don't do your homework or hire experts with earth-sheltering experience to help you with the design. Slightly sloping the roof is an inexpensive strategy that helps minimize leaks. Exposed flat roofs are notorious leakers—just ask any construction law attorney!
Codes and Financing
Like any other home that uses an unconventional building method, your earth- sheltered home is apt to run into trouble with your local building department and your lender. The building department will require a carefully engineered structural design before they issue the building permit, and building officials are likely to watch the construction process very carefully. Your best defense against problems is to develop a good working relationship with the officials early in the process. Find out what will be required of you before you apply for the building permit, to save costly and frustrating delays.
Your lender’s major concern is the marketability of the property. Lenders are hesitant to lend on unconventional houses because experience has taught them that the market for such houses is much narrower than for a more conventional house. If you should default on your loan, the lender is left with a property to sell that appeals to only a small minority of the home-buying public.
The burden is on you to educate the individuals and organizations that have the power to veto your project. Your architect (assuming you use one) and structural engineer will be powerful allies in this process. and you should educate yourself thoroughly about the type of house you plan to build. The time you spend doing so will not be wasted—having to satisfy the building department and lender will sharpen your own thinking about the project.
The cost of an earth-sheltered home depends on a myriad of variables. it's possible to build an underground home for less than you would spend on a comparable aboveground home, if you use inexpensive materials and do much of the work yourself. But the cost of excavation, a job that typically gets hired out by all but the most fanatical owner-builders, is apt to be higher than for a similar conventional home, and the extra structural strength required to retain earth and support earth roofs can result in construction costs 30 % higher than for aboveground construction.
The real savings in an earth shelter will be “life cycle” savings—what it costs to live in the home over the life of the structure. Heating and cooling costs should be low, and almost no exterior maintenance will be required. For those of us who don’t relish the prospect of painting or staining wood siding every few years, this is a major attraction.
For years, concrete masonry has been used as a moderate-cost alternative construction technique, with components constantly being improved. While in the past concrete masonry was used primarily for foundation walls, the benefits of using masonry for the entire home have become widely appreciated in recent years. As we mentioned earlier, increasing the amount of thermal mass in a home can have distinct benefits during the heating season, especially in passive solar applications: The mass stores heat during the day and releases it slowly during the night. Concrete masonry, like adobe and poured concrete, is an excellent thermal mass.
ill. 4-27, taken from the Passive Solar Design Handbook, shows the “diurnal heat capacity” (the daily heat stored and returned by various building materials in a direct-gain passive solar building). As you can see, concrete block has the best heat-storage capacity, followed by brick. The graph assumes that the storage materials are backed by insulation or by an equal thickness of the same storage material that is also used to store solar heat.
ill. 4-27: Daily heat stored and returned for different materials.
Besides its benefits during the heating season, concrete masonry can result in significant savings during the cooling season. it's now generally recognized that a well-insulated masonry home may not require expensive mechanical air-conditioning in climates where a conventional frame house would be uncomfortable without it. This can mean a considerable savings to the owner-builder in that the money for air-conditioning equipment can be put to other uses. The house will also be cheaper to live in, since cooling costs will be minimal or nonexistent.
In very warm climates, the thermal mass of solid-grouted masonry walls reduces the transfer of unwanted heat from the outside to the inside of the building and also absorbs unwanted heat that may have accumulated on the interior of the building. Best results are obtained by shading or earth-sheltering these walls, especially on the west side of the house. Placing the garage on the west is an effective strategy for reducing afternoon solar heat gain.
The wall itself can reduce heat transfer if it's constructed in the following manner, as recommended by the National Concrete Masonry Association (NCMA): First, fix foil-faced insulation or double-sided builders’ paper over the outside of the block; next, apply wood battens vertically and cover with the exterior siding, making sure to vent the enclosed air spaces. The outside of the concrete block is kept much cooler this way, allowing the whole concrete wall to absorb unwanted interior heat more effectively.
ill. 4-28: Recommended technique for insulating masonry walls: radiant wall barrier system.
ill. 4-29: Recommended exterior insulation thickness based on R-5 per inch nominal rigid insulation.
ill. 4-30: Typical air-core block cooling wall.
Another technique recommended by NCMA involves the use of hollow-core masonry walls inside the house as thermal mass. These walls can be cooled by nighttime outside air driven by fans through the cores, thus cooling the house’s interior. This “air-core” wall concept is also effective in controlling winter indoor temperatures by recycling warm air through the cores.
ill. 4-31: Log construction techniques: Traditional sod-covered roof (a); hand-peeled logs with saddle notch corners and gasketed tongue- and -groove connections (b); squared hewn beams with dovetail corners, rigid insulation, and inner wall of rough-sawn planks and plaster bands (C); squared hewn beams with dovetailed corners and 2 X 6 insulated inner wall (d).
Building homes with logs is a time-honored tradition. If a rustic aesthetic appeals to you, there are few building methods that offer the sense of comfort and security that a log home does. Typically, the skills needed to erect a log home are within reach of a motivated novice.
For the owner-builder who wants to build a log home, there are essentially two choices: purchase a kit or cut your own logs and do your own joinery. Over 150 companies make log home kits in the United States. Some of the kits fit together as readily as a child’s Lincoln Log set.
Air leakage is an especially vital concern in a log home, since every seam between the logs is a potential leak, and there are lots of seams. Also, logs are almost certain to shrink over time, and they will tend to expand and contract with changes of humidity and temperature. The intersections between the logs should be sealed with a material that can handle these changes, or you’ll find yourself having to renew the seal on a regular basis.
Log home manufacturers have made great strides over the years in developing effective sealing techniques. Comparing the techniques offered by various manufacturers should be high on your list of priorities as you shop for a kit. There are foam gaskets, flexible chinking, and caulks that do the job if installed properly. Pay special attention to the sealing at intersections between the log walls and the foundation, the log walls and the roof structure, and around any openings in the walls.
ill. 4-32: The structure of the end of an old log.
There is some controversy surrounding the relative energy efficiency of log structures. Much of the debate revolves around the R-value of a solid wood wall. Uninsulated log walls don’t satisfy the minimum R-value requirements of most energy codes. Different species of wood have different R-values, ranging from about .71 per inch for shagbark hickory to 1.41 for northern white cedar.
R-values, however, tell only part of the overall energy-efficiency story. The type and placement of windows, orientation of the building, air-tightness of the structure, amount of thermal mass, levels of insulation in other parts of the house, and the climate where the house will be built must all be considered to get a picture of how the house will function in the real world.
Log home manufacturers have long insisted that the low R-value of wood is offset by the massiveness of the logs themselves. They claim that the thermal mass effect is significant enough that log homes show overall energy performance equal to or exceeding that of conventionally insulated frame walls. and indeed a study conducted in Maryland showed that a log home may well outperform a conventional home in all but the harshest months of the winter. But bear in mind that Maryland has a mild climate; in general, we believe there are easier and more cost-effective ways to build an energy-efficient home in a severe northerly climate than with logs.
If you have a strong preference for log homes and live in a severe climate, we would strongly suggest that you have the design computer modeled for energy efficiency to assure that the structure will be as efficient as possible. Your log home dealer, local energy extension office, local owner-builder organization, or architect should be able to put you in touch with someone in your area who offers this service. If not, there are organizations around the country that can use data from your area to help you refine the energy efficiency of your log home. One good source is the Log Home.
The strength and durability of dome structures is well documented. While domes have been built of a variety of materials, including brick, concrete, and foam, the technique most accessible to today’s owner-builder is the wood geodesic dome.
A geodesic dome is a system of triangles that, when fitted together, approximate a half sphere. Since the triangle is the only self-bracing construction form, the resulting structure is extremely strong. As the number of triangles used increases, a closer approximation of the spherical form is achieved, and strength increases because the surface stress is more efficiently distributed.
ill. 4-33: This log cottage near Hjeltar Norway (1760 AD), combines vertical and horizontal logs.
In addition to being exceptionally strong, the dome encloses the maximum amount of space with the minimum amount of materials. It exposes the least possible amount of surface area to the elements and thus is economical to heat and cool. Like conventional frame structures, geodesics can be developed as passive solar homes, with direct-gain windows, sunspaces, and thermal walls and floors.
In traditional barn-raising fashion, many owner-builders have erected the shells of large dome homes in one or two days with a crew of family and friends—without any professional help. The money saved through the inherent economies of the building method can make a geodesic dome one of the more cost-effective building systems. An estimated 5 to 15 % savings over other types of frame housing is possible because a geodesic dome uses about 30 % less material to enclose the same square footage. Because of the amount of angular cutting involved, domes take longer to finish than a conventional home does; however, because a finite set of angles are symmetrically repeated, careful measuring and cutting will minimize waste of time and materials. Dome kits can greatly save labor time, but you will be paying a premium.
ill. 4-34: The geodesic dome is a geometrical idea that has been developed in many directions, a few of which are shown here.
Geodesics do have a few drawbacks. Because they consist of triangles, cutting and fitting of insulation materials can be time-consuming. Spray foam and cellulose insulation are more adaptable to this building style, but they are more expensive and require special equipment and professional skills. A related problem results from the entire wood structural frame acting as a “thermal bridge,” conducting heat from the inside to the outside of the building skin—a problem which in conventional construction can be solved by applying exterior insulation over the sheathing.
Whether you design your own dome, purchase a set of plans, or buy a kit, always make sure that a professional engineer approves of the stuctural design for the struts and the connector hubs before you begin.
If you’re drawn to the idea and aesthetic of living in a dome home, but are discouraged by the drawbacks of geodesics, consider a thin-shell concrete dome (also called “monolithic domes”). Because the process requires specialized equipment and skill, building a concrete dome is not a do-it-yourself project; however, it's possible to do your own finish work.
Building the concrete shell involves five basic steps:
1. After the foundation is poured, an air bag the size and shape of the desired structure is attached to the foundation and inflated. Urethane foam insulation is sprayed on the inside of the balloon to a predetermined depth, usually about 4 inches.
2. Openings for doors, windows, and other openings are prepared.
3. In some cases, the next step is to place pre-engineered steel reinforcement next to the foam. Some builders use an engineered concrete mix reinforced with needle-sized bits of steel instead.
4. Reinforced either way, the interior of the foam dome is then sprayed with 1½ to 4 inches of concrete. When the concrete cures, you have a concrete dome with exterior insulation. Among other advantages is the fact that the concrete serves as fireproofing for the foam.
5. The final step in completing the shell is to coat the outside surface of the foam. Urethane foam decomposes in sunlight. Several types of coatings are available to protect the foam. Your choice should be based upon color, texture, thickness, cost, and durability (the coating’s ability to filter out ultraviolet radiation, to expand and contract in response to temperature changes, and to breathe). Outgassing from the foam will cause bubbles to form in the coating unless the gases can escape.
Some areas specifically forbid dome buildings. Before you buy property, check the covenants of the subdivision and the zoning regulations of the local government that has jurisdiction over the lot you plan to buy. Even if there isn’t any official opposition, you may want to run your plans by your future neighbors to make sure you’re not making enemies before you even move in. Domes have an aesthetic that people either love or hate, so you may want to preserve any mature trees on the property to help blend the dome into its surroundings.
It seems likely to us that domes will become increasingly popular, particularly as labor, materials, and energy costs continue to rise. As more domes are built, more people will become more comfortable with the form. Although we realize the sample is self- selecting, it seems worth noting that virtually every person we spoke to who lives in a dome was passionately enthusiastic about his home. This enthusiasm is sure to be contagious.
Timber framing is a technique that goes back at least 2,000 years, and there are many timber frame structures still in use after 800 years. Before the development of nails and joinery hardware, timber framing was about the only way to build with wood—the frames were held together with wooden pegs. As nails came into more common use, timber framing went into a decline, largely because of the skill and care required to successfully use the technique. But timber framing is now enjoying a revival, and the combination of time-tested joinery techniques and modern tools is bringing these homes within financial reach of the average homeowner. Timber framing is a particular favorite among owner- builders because of the exceptional energy efficiency, beauty, and structural integrity of these buildings.
In contrast to conventional wood framing, timber framing uses large beams resting on large posts rather than 2-inch dimensional lumber to support the building. The posts and beams can be spaced far apart, which allows for larger openings in the exterior walls and increases your design flexibility on the interior of the home, since interior walls can be placed without concern about structural considerations.
The posts and beams can be left exposed on the interior, which adds warmth and drama to the home. The timbers are often planed and finished with oil, and the massiveness of these large wood members creates a sense of integrity and security that is impossible to duplicate in a conventionally framed home. Some talented carpenters carve the timbers, truly customizing the home.
Most framers consider oak to be the wood of choice for a timber frame. The timbers are connected by cutting precise joints, carefully fitting these joints, and fastening them together with hardwood pegs. Timber framers prefer pegs over metal fasteners for a couple of reasons. First, as the frame dries and settles, a metal connector will cause the joint to loosen. Wood and metal expand and contract at different rates in response to changes in temperature, which can loosen the joint. Secondly, the metal can draw moisture condensation into the joint, perhaps causing decay in the wood or corrosion in the metal itself.
ill. 4-35. The timber framed New Inn, Herefordshire, England.
There are many ways to enclose a timber frame, but the most attractive from the standpoint of speed of construction and energy efficiency is provided by foam-core stress-skin panels. These panels are typically composed of urethane or polystyrene foam sandwiched between ½-inch gypsum drywall on the interior and waferboard or plywood on the exterior. They are designed to resist the strains of tension and compression and can be used to span the 4- to 8-foot distances between timbers. A 4-inch-thick panel with a urethane foam core can have an aged R-value as high as 30. Always find out what the “aged” R value is, since the R-values of some foams degrade over time.
Since these panels are spiked to the outside of the timbers, they provide an uninterrupted foam blanket around the frame. Nowhere does a framing member pass through the shell to create a thermal bridge to the outdoors. The connections between the panels are made with wood splines or tongue-and-groove edges in the foam, and openings for doors and windows are reinforced with 2 X 4s that are recessed into the panels. If urethane foam panels are used, no additional vapor barrier is needed. If you anticipate a high-moisture problem or if your panels have polystyrene cores (polystyrene does not act as a vapor barrier), use a good-quality vapor barrier paint. Timber framed homes built with foam-core panels are extremely energy efficient, and they are fully compatible with passive solar heating.
Unless you are an accomplished woodworker, we suggest you hire an expert to cut the frame (you may be able to serve as helper) or buy a precut kit. Timber framers can be found all over the country, and most are highly skilled. Although the joinery is very exacting work and takes some time to do, many timber framers do the cutting in their shops and fit and raise the frame on your foundation, often with a crane, so the frame can be erected and wrapped with panels in just a few weeks. For the name of a timber framer near you, see Timber Framers Guild of North America.
Codes and Financing
It’s unlikely that you’ll run into as much resistance from building officials and lenders over timber frames as you might over domes or earth-sheltered houses. Some officials may hesitate before approving foam-core panels, if they are unacquainted with these items, but the panel manufacturer can supply you with any information you need to satisfy the officials. The frame will probably have to be engineered, but the framer you work with undoubtedly has experience with engineering timber frames.
Timber frame homes are so stunningly beautiful that any concerns your lender might have about marketability should easily be put to rest. These homes, by most estimates, cost about 10 to 15 % more than comparably finished conventional homes, but to many people the fine craftsmanship makes them worth the cost. The energy efficiency of a timber frame wrapped in insulating panels will also assure good marketability.
The unconventional construction methods we have already listed are generally the most promising for owner-builders. However, a few additional methods are also applicable in some circumstances. We will discuss these methods next.
If you grew up on or around a farm, you are probably at least passingly familiar with pole barns. Pole houses are built in much the same way. Pressure-treated poles are sunk in the ground (usually they rest on gravel or concrete pads), or they are bolted to concrete piers that rise above the ground. The supports for the floor framing are bolted to the poles. Walls are designed to connect the poles, thus providing bracing, or they can be allowed to “wander” independently, providing no structural reinforcement for the poles.
ill. 4-36: Timber frame construction with thermal shell of stress-skin panels.
The advantages of pole houses include relatively low construction costs, adaptability to difficult sites, design flexibility, readily available materials, and superior resilience in earthquake-prone areas. Since the poles form the foundation as well as the structure, the cost of building a complete perimeter foundation is eliminated. An added benefit is that extensive excavation is unnecessary, which means there is minimal disruption to the site. Pole homes are particularly well suited to very steep sites and ocean or lakefront properties in mild climates. They are also appropriate for hot, humid climates where the home can be cooled by outside air introduced from below the living spaces.
You can expect the same resistance from lenders and building officials as with any other unconventional building technique, so do your homework to avoid delays and other frustrations. If you plan to build in a rural area where barns and other utility buildings are built with poles, local officials may already be familiar with the method, even if they’re not used to seeing homes built with it.
Also known as log-end, stackwood, cordwood, or stackwall construction, cordwood masonry is one of the least-known building alternatives. The method is just what the name implies—pieces of seasoned firewood are laid up in mortar to form the walls of a building. In effect, you create a carefully structured woodpile, filling the spaces between the logs with sawdust and mortar on both sides of the pile.
Since in many areas wood is a plentiful and renewable resource, and cutting and splitting firewood are skills within reach of any able-bodied person, a cordwood home may be the ideal answer for those with more time than money. The prospect of building a home of indigenous materials that is energy efficient, attractive (assuming a rustic aesthetic appeals to you), and low-cost is very appealing. Schools offering instruction in cordwood construction are listed in a later section.
Cordwood construction is likely to raise more eyebrows at the building department and lending institution than the other alternatives we’ve mentioned. Since these homes can be very inexpensive to build, you may be able to eliminate the potential hassles with the lender by paying as you go. The building department will want proof that the building will satisfy local building and energy codes.
The proliferation of kit-home manufacturers is certainly a positive indication of the popularity of the owner-builder concept. Housing consumers can now choose from a staggering array of kits for everything from log homes to timber frame or pole homes. The attraction for the novice builder is obvious. Most kit-home manufacturers offer plans, many will customize the plans to meet the needs of the customer, and some will even assemble a materials list from the client’s design. The kit-home dealer then figures the materials for the house, gives the client a price on those materials, and delivers the home as a package of materials that the buyer assembles or hires someone to assemble.
Kit homes certainly offer advantages. Materials are generally high quality, and if your dream house includes materials that aren’t readily available in your area, a kit may be the answer. No running back and forth to the local building material yard, no chasing down bids from different suppliers, and no need to make up your own materials lists. If the kit is well designed and planned, you may be able to put it together rapidly with minimal building skills, and some manufacturers even include tools in the package.
Financing is a major marketing tool for some kit-home manufacturers. As we’ll discuss in a future section, construction financing is one of the most difficult obstacles for owner- builders, so a kit-home builder with construction financing for customers at competitive rates is sure to be popular. Some companies offer plans that require no down payment or only a minimal down payment. For some people, this may be one of the few ways they can afford a home of their own.
Unfortunately, some kit-home companies treat their customers less well than others do. Clearly, in buying something as important — and complex — as an unassembled house, you will want to take every precaution to make sure you’re treated well. Here are some things you’ll want to check out before you commit to the purchase of a house kit.
1. Make sure you know exactly what you’re getting for your money. Is it just the shell or are finish materials also included? How about mechanical systems? Does the manufacturer offer the options you want in your home? Is there any flexibility in what you can buy from other sources if the manufacturer doesn’t have what you want? Sit down and list everything you will need that is not included in the kit and figure the cost. It might also be instructive to take the final materials list to suppliers and get competitive bids to see how much of a premium you’re paying for the kit.
2. If you are uncomfortable with any part of the standard agreement the manufacturer uses, or if you have additional concerns you feel should be addressed, write an addendum designed to become part of the contract. Many contracts are not healthy agreements for consumers, and too many consumers don’t notice until they run into trouble. Your expectations of the performance of the manufacturer and the limits of that performance should be clear to both you and the dealer. If you can’t get the kind of information you need from the salesperson or dealer, or if you feel you are getting vague or evasive answers to your questions, find another kit dealer. Get a guarantee in writing that the manufacturer will replace any defective parts of the kit.
3. If the kit-home manufacturer advertises itself as supplying high-quality materials, make sure the quality is specified in your agreement and that the kit the company delivers to you contains materials of the specified quality.
4. Don’t forget the non-house costs. Roads, water supply, septic or sewer, site preparation, survey costs, permit fees, sidewalks, driveways, etc., are probably not included in the cost of your kit, and therefore are not included in the amount of the construction loan the kit-home dealer is making to you. The money for these extras — and it can add up to many thousands of dollars — is going to have to come out of your pocket, so plan for it. The responsibility for making sure all these details are taken care of is yours, although an experienced dealer can offer valuable assistance.
5. Get a list of local owner-builders that have worked with this dealer. Talk to these individuals to get a feel for what the company is like to work with. Ask whether they feel their expectations were met, whether they received competent technical support during the building process, and ask them how problems were handled. If there is an owner-builder organization in your area, call them to see if they or any of their graduates have had any experience with this company. If a dealer doesn’t want to give you the names of former customers, find another dealer.
6. Pin the dealer down regarding how much support you’ll get during the building process. Can you call with questions that come up on a day-to-day basis? If the company provides a building manual, read it carefully to get a feel for how complete it's .
7. Don’t use the fact that you’re purchasing a kit as an excuse for skimping on planning the project. Take the time to be certain that this is really the house you want. Take classes, attend lectures and trade shows, and read everything you can find on the house-building process. Some kit-home manufacturers give classes and workshops on assembling their product, but the quality varies widely. Take a trip to the local building department with your plans and specifications to assure that the house meets local codes. If you plan to hire out any of the work, check with the tradespeople to make sure they’re comfortable with the materials offered in the kit.