Excerpts from “The Small House Book” on How to Build and Design a Small House

Posted March 1st, 2010 by Jay Shafer and filed in Issue 16: How To Design & Build a Home

How to Build a House on Wheels:

The Foundation and Framing

With little exception, my first portable house (also known as Tumbleweed) was built by using the most standard methods of construction. Like any other mobile home, my structure sit on a steel chassis – in this case, a 7’ x 14’ flatbed, utility trailer. I took most of the wooden deck off to save weight and put aluminum flashing over the gaps to safeguard against mice. The floor framing was laid on top of that. I used two-by-fours spaced about 24 inches apart on center.

Once that framing was assembled, I filled the cavities between the boards with foam board insulation and spray foam and capped the whole thing off with some ¾-inch plywood subflooring.

The walls were framed right over the wheel wells using headers just as you would over any other opening. I used two-by-four studs and rafters spaced twenty-four inches on center rather than the more typical sixteen inches. This is a fairly standard practice used to save both money and natural resources. At this point, I was using it primarily to save weight. My flatbed was rated to hold 7,000 pounds.


Tumbleweed would have to withstand not only the normal wear and tear of everyday living, but also the occasional jolts and gale-force winds generated by highway travel. To prepare for this, I used what has come to be called the “screw-and-glue” method of sheathing. This means that a bead of construction adhesive was squeezed onto the entire length of every framing member before 3/8” plywood sheathing was screwed (not nailed) to its surface. This makes for a structure far more resistant to lateral wind loads than sheathing secured with nails alone.

Preventing Condensation

The only other special building consideration, after the foundation and bracing, for a little house on wheels is condensation. Unless they are insulated, sealed, and vented properly, small spaces are prone to a lot of condensation. It simply takes less time to fill the air in a small enclosure with the moisture caused by bathing, breathing, laundry, and cooking than it does to fill a large one. If that warm, moist air comes into contact with a sufficiently cold surface, it will condense into water. That is the reason that cars come equipped with defrosters, and that small houses need to be equipped with the right insulation, vapor retarders, and ventilation.

I used expanded polystyrene foam board as insulation with expanding spray foam in the seams for two basic reasons: 1) It takes a thicker piece of fiberglass batting to get the same amount of insulating power as you get out of a piece of extruded polystyrene. As I didn’t have enough space for eight-inch-thick walls, this would have stood as reason enough for my choice. 2) Foam board is far more resistant to condensation.

With fiberglass batting and other porous insulations, you have to worry about moist air getting into it and condensing when the moisture gets to the cold part of the wall. At that point, the fluffy, pink stuff turns to mush, and mush doesn’t insulate. It rots. To prevent this, you have to use a vapor retarder. This is usually just a large sheet of six-millimeter plastic hung over the inside surface of the batting and sealed at its edges. If your seals hold and your plastic does not rip, your fiberglass should stay fairly dry.

Expanded polystyrene with an impermeable coating does not need a vapor retarder. Being virtually waterproof makes it its own retarder. I chose the white, expanded polystyrene over the pink, extruded poly because, while I love the pink stuff for its superior insulating qualities, bugs love it, too.

The threat of condensation is also what prompted me to use double-glazed, insulated windows. The glass panes on a little abode can fog up pretty quickly unless they are well protected against the cold. I’ve found that windows sold with gas between the interior and exterior panes work pretty well for this purpose.

The other primary way to eliminate condensation in a small enclosure is by venting it. I installed a fan at the peak of my loft. It sucks moisture-laden air out of my living quarters when I am cooking or bathing and helps keep the place cool during the summer. On cold days, the vent can be sealed with a plug I cut from some leftover scraps of foam board.

Subtractive Design:

A well-designed little house is like an oversized house with the unusable parts removed. Such refinement is achieved through subtractive design — the systematic elimination of all that does not contribute to the intended function of a composition. In the case of residential architecture, everything not enhancing the quality of life within a dwelling must go. Anything not working to this end works against it. Extra bathrooms, bedrooms, gables and extra space require extra money, time and energy from the occupant(s). Superfluous luxury items are a burden. A simple home, unfettered by extraneous gadgets, is the most effective labor-saving device there is.

Subtractive design is used in disciplines ranging from industrial design to civil engineering. In machine design, its primary purpose is demonstrated with particular clarity. The more parts there are in a piece of machinery, the more inefficient it will be. This is no less true of a home than it is of an engine.

Remembering Common Sense

Most of our new houses are really not designed at all, but assembled without much thought for their ultimate composition. Architects seldom have anything to do with the process. Instead, a team of marketing engineers comes up with a product that will bring in more money at less cost to the developer. The team’s job is to devise a cheap structure that people will actually pay good money for. Low-grade, vinyl siding, ornamental gables and asphalt shingles have become their preferred medium. Adding extra square footage is about the cheapest, easiest way there is to increase a property’s market value, so it is applied liberally without any apparent attempt to make the additional space particularly useful. The final product is almost always a bulky conglomeration of parts without cohesion — a success, by industry standards, where oversized invariably equals big profits.

Even when left to certified architects, the design of our homes can sometimes be less than sensible. Too frequently, a licensed architect’s self-perceived need for originality takes precedence over the real needs of his or her clients. Common sense is abandoned for frivolous displays of talent. Where a straight gable would make the most sense, a less savvy architect will throw in a few cantilevers and an extra dormer, just for show. Subtractive design is abandoned for hopes of personal recognition and for what is likely to be a very leaky house. Common sense is an inherent part of all great architecture. Sadly, this crucial resource has become anything but common in the creation of residential America.

Certainly the most famous example of those whose aspirations for a good name took precedence over good design was Frank Lloyd Wright. Wright was fond of innovative methods and extravagant forms. Those novel houses that once earned him recognition as a peerless innovator have since earned him another kind of reputation. Leaks are a part of many Wright houses. Wright has become infamous not only for his abundant drips but for his impudent dismissal of their significance. “If the roof doesn’t leak,” he professed, “the architect hasn’t been creative enough.” And to those clients who dared to complain about seepage, he would repeatedly quip, “That’s how you can tell it’s a roof.”

Subtractive design is integral to, and nearly synonymous with, vernacular design. Both entail planning a home that will satisfy its inhabitants’ domestic needs without far exceeding them. This is also what is known as common sense. When applied to buildings, the word “vernacular” in fact means “common”: that is to say “ordinary” and “of the people.” In contrast to housing that is made by professionals for profit or fame, vernacular housing is designed by ordinary folks simply striving to house themselves by the most proven and effective means available.

Webster’s defines vernacular as “architectural expression employing the commonest forms, materials, and decorations” (Webster’s Third New International Dictionary, G. and C. Merriam Co. 1966. p. 2544). If a particular type of roof works better than any other, then that is what is used. In short, vernacular architecture is not the product of invention, but of evolution—its parts plucked from the great global stew pot of common knowledge and common forms. Anything is fair game so long as it has been empirically proven to work well and withstand the test of time. By using only tried-and-true forms and building practices, such design successfully avoids the multitude of post-occupancy problems typical of more “innovative” architecture.

The vernacular home does not preclude modern conveniences. There are, after all, better ways to insulate these days than with buffalo skins. The vernacular designer appropriates the best means currently available to meet human needs, but, technology is, of course, employed only where it will enhance the quality of life within a dwelling and not cause undue burden.

Jay Shafer Tumbleweed Tiny House Company Internet: http://www.tumbleweedhouses.com - E-mail: email hidden; JavaScript is required – Postal: PO Box 941, Sebastopol, CA 95473