A ""THERMAL ENVELOPE"" TRAILER

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by Caroline Wareham

While constructing their house, this ingenious couple found a way to expand the living space in their camper and recruited the sun to help heat it . . . all for less than $1, 000!

Like a lot of folks who set out to build their own homes, my partner and I decided to park a mobile trailer on our property (a remote site in northern New Mexico) and use it for shelter until our permanent abode was completed. The advantages of using such a ready-made dwelling are many ("instant" plumbing, a built-in kitchen, a watertight roof, and the like) . . . but so, unfortunately, are the disadvantages. Not the least of these is a form of domestic claustrophobia with the main symptom best characterized as "If I'm stuck in this box another week, I'll go crazy!"

Some people, in fact, succumb to "trailer twitch" by prematurely moving into their still-under-construction homes or (what's even worse) by taking shortcuts to finish their houses quickly. I'm happy to report, though, that there's a much better solution to the problem . . . one that has allowed us to live in relatively roomy (and inexpensive) comfort while building our home exactly as we want it at a sensible pace. The secret? An insulated, sun-catching, heat-retaining "solar envelope" built around our trailer!

Actually, the structure is little more than a frame shed that has its south-facing wall glazed with plastic film to admit sunlight. It can't really compare with the much more costly and complex double-envelope solar homes that are designed for permanent residency. This design (the brainchild of architect John P. Friedman of Los Lunas, New Mexico) is intended specifically for low-cost, temporary quarters. Consequently, it's ideal for owner-builders in our situation . . . or for hunters or vacationers who simply want a bit more elbowroom (and warmth) while living in their trailers. One of the design's strongest assets, in fact, is that an end can be built to be removable—or even to swing open like a giant double door—so that you can drive or tow your camper out with ease. In our case, however, we knew that the only occasion we'd have to open the wall would be when it came time to return our rented unit to its owners, so we erected a more or less "standard" end panel. Once the camper's gone, we'll simply reattach the partition and use the envelope as a garage, a studio, or a woodworking shop.

CONSTRUCTION

With our 8' X 24' trailer parked on level ground and situated so that the long side—the one with a door—faced due south, we dug a rectangular 16' X 26' trench, about 9" deep, around the camper . . . and filled the moat with 3" of pea gravel. If you live in a cold region where frost heaving is a problem, you might want to dig a deeper trench and use more gravel (or, for a permanent foundation, you could pour a cement footing). On top of the fill we put up four stud walls, with the south-facing partition measuring 8' high and the northerly one 10'. We framed in areas for windows, too, on the east and west panels . . . and built a small access hatch on the east side near the trailer's hitch, so that we could easily use that otherwise wasted space for storage.

Next, we put up the roof, installing 2 X 6 rafters with a south-to-north pitch of 1 foot for every 8 feet. Then we stapled fiberglass insulation to the east, west, and north walls . . . and nailed tar paper to the outside of the three walls, using furring strips wherever necessary to cover seams and to help anchor the material. Because we didn't intend to install true siding, we also put a board diagonally across each tar-papered wall to serve as a brace.

When we'd done all that, we proceeded to nail corrugated metal roofing to the ceiling beams, insulate the roof, and cover the south wall (minus a full-sized doorway space) with a seamless layer of 6-mil plastic glazing. After that, all we had to do was to tack up glazing over the two windows and install a door. The trailer was then completely enclosed and "in the dry".

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