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Reprinted with permission from Back Home Spring 1995

Two Walls Are Better Than One

 

 


Stackwood x two + sun = warm home in a cold climate
By Richard Freudenberger

BACKHOME has always made a place in its pages for alternative and low-cost construction. For some readers, the process of buying and financing a home comes with a crushing debt and responsibility that they'd rather not buy into. For others, the process of planning and building their own house offers the rewards of experience and personal satisfaction. Still others see an opportunity to experiment and improve on conventional techniques.

For Cliff Shockey, all of the above could have played a role in his decision to build not one, but four structures using a resourceful variation on a building technique we've covered before in these pages: the stackwood, or cordwood, method.

Traditionally, cordwood building involves stacking 8" to 24" lengths of split or round logs crosswise on a foundation (like stacking firewood), with mortar between the pieces as in a block wall. In such construction, the "mortar" is actually a combination of three parts sand, one part masonry cement, and one part sawdust, often with a measure of hydrated lime added to make the mix more workable.

But Cliff and his wife, Jackie, live in the Province of Saskatchewan, not far from the city of Saskatoon yet still on the Canadian prairie where harsh winters are something to be reckoned with. Appealing as the cordwood technique is, Cliff felt he needed something extra to keep the elements at bay.

There were reasons for his concern. In 1972, after some 17 years of working a city job, Cliff Shockey chucked it to settle on a quarter section of land adjoining his brother's farm near to where he'd grown up. The property included an old farm house that, despite his investments in remodeling time and money, still managed to bum over 300 gallons of fuel oil in the worst winter months.

"By 1976, I was ready to explore the possibility of building a different—and energy—efficient-house. I joined a chapter of the Solar Energy Society of Saskatchewan and enrolled in a conventional log-building course at the community college. What I learned raised some questions about the practicality of a log home in our windy, 11,000-degree-day climate. Then I saw an article in an old issue of The Mother Earth News with a picture of Jack Henstridge and his $4-per-square-foot stackwood house. I thought, I can do that! ...and it set me thinking about what's come to be my double-stackwall passive-solar design."

Four-Up
Cliff's time spent in research paid off. He was convinced that in order for the walls to keep out the wind and weather, they'd need a sealed vapor barrier and a substantial layer of insulation. And the only way to do that, in his mind, was to build both an inner and an outer wall.

In 1976, he built his (and probably Canada's) first double-wall cordwood home: a 600-square-foot cottage made from materials recycled in just about every way imaginable. A string of abandoned telephone poles became the source of cedar rounds for the walls. Large rafter and framing beams were taken from dismantled barns and grain elevators. Old cedar fence lines got yanked up for the split wood they could provide. And with the help of a salvaged sawmill refurbished with tractor and truck parts, even the treated ends of power and phone poles were ripped, cut to length, and used as cedar roof shakes.

All told, that project took nine months to complete and cost about $8,200, measured in U.S. dollars. It also gave Cliff the confidence to start in on a second, larger home right next door— on the foundation of the original farmhouse, which had been moved to another site. Since the 9'-high basement had only 10" foundation walls, Cliff had to extend its outer perimeter by 14", using sunken pilings, to achieve the 24" wall width he needed.

The new house used a sturdy post-and-beam framework made largely from old hip-roofed barns he'd dismantled locally. The work was dusty and labor-intensive but provided a good deal of lumber and made a great family project.

That house, built between 1978 and 1980, is the one in which he and Jackie currently live. The basic structure— foundation, floors, walls and roof— came in at $13,500, and the finishing touches (including tile floors, cedar trim, spiral staircase, and whirlpool) added about $18,750 to that figure.

In 1985, a few years after they were married, Jackie and Cliff together built a 25' x 40' double-wall cordwood office in town to house the insurance agency Cliff had started several years before. It was built on a floating slab and used in-floor hydronic radiant heating supplied by a small gas-fired boiler. They were so pleased with the warm floors and low fuel consumption that they planned and completed a 392-square-foot cordwood addition on their house in 1990, using the radiant floor technique and as much recycled lumber as they could lay their hands on.

Beginning With an End in Mind
Cliff stresses the importance of planning well ahead of construction. He credits that insight to a book entitled The Seven Habits of Highly Effective People, in which the author views successful projects in terms of a "first" and a "second" creation; the former being the detailed mental planning and replanning, the latter the actual hands-on accomplishment.

"What you need most in stackwall building is time to sit down with some graph paper, turn your imagination loose, and draw up a few sketches to make sure everything will fit together. The more thought you put into the project, the better the house will turn
out."

For example, siting, especially in a solar design, is a primary factor. A home placed on the north side of a lot, facing south, allows access both to the sun and to ongoing activities. Since most solar homes have minimal north-facing windows, it makes sense to plan ahead so that the arrival of visitors, children playing in the yard, and so forth, are located where they can be seen from the house.

Roof overhangs are another important consideration. At the Shockeys' 52° latitude, the angle of the sun ranges from a low 15° in the winter to 61° in the summer. South overhangs of 3' to 4' are part of the building's design to allow the use of large south-facing windows for winter heat gain. Through the summer months, this extra glazing would admit far too much heat if it weren't for the calculated shading provided by the overhangs. Moreover, the roof extensions give the cordwood walls additional protection from rain exposure.

Arectangular structure, of course, permits more window surface than a square one because it has two elongated sides. So to avoid a "squatty" appearance on a grade foundation, especially when using outsize over-hangs, a cordwood wall can easily be built a little higher—9' or more—without concerns over the limitations of standard plywood or drywall dimensions.

Since the prevailing winds are from the north, the Shockeys have no windows at all on that side of the house. Supplemental natural light is brought into the back rooms through a pair of insulated skylights. The bathroom, located at the rear of the house, was built with cedar-framed translucent door and wall panels to let ambient light through.

Occasionally, wind shifts bring frigid gusts against the home's south face, drawing heat from the double-glazed windows. Cliff installed homemade bifold shutters over those panes, operated by an electric garage-door opener. The newer home addition takes advantage of Heat Mirror 88 windows, which reportedly achieve a 4.5 R-value with a special heat-reflective coating between the two layers of glazing.

Within the structure itself, even distribution of heat is greatly aided by an open floor plan. With interior partitions kept to a minimum, a natural convective airflow exists. There is a wall separating the house and the addition, and a heavy insulated curtain across the upstairs bedroom loft prevents a buildup of warm air at that high point. The only other break in the flow is a suspended ceiling above the kitchen area, which offers some separation and a place to put lighting fixtures.

Double-Wall Details
After setting up the post-and-beam framework, positioning the rough window and door openings and lintels, and completing the roof—this so he could work in even poor weather conditions—Cliff laid the walls specifically to achieve protection from winter wind and retain the high insulation value he was after.

The exterior cordwood layer, made from logs cut to 8" lengths, rests on treated 2 x 8 planks bolted to the foundation, as in most structures. He was careful to leave from 3/4" to 1" of mortar material between each of the log "blocks" as he laid the courses, guided by a mason's line to keep the surface consistent.

Next, a layer of 5/16" particleboard sheathing was nailed to the inside surface, both to help stabilize the 9' wall and to serve as a barrier to mice and insects that might be looking for access to a home through cracks in the wooden blocks.

Following that, a thick layer of insulation—either stiff 8" batts or a multiple layer of 4" and 6" batting, depending on the width of the internal air space—was placed against the sheathing, hung on partially driven nails to prevent its sagging.

The next step was the application of a 6-mil air-vapor barrier, simply polyethylene sheeting sealed at the seams with acoustical sealant over a solid backing. In cold climates, this barrier is especially important to prevent drafts, especially around the borders and the window and door frames.

Finally, the inner wall, made from 6"-long logs, is laid on a separate 2 x 8 bolted sill to complete the inside surface. The resulting wall, a total of 24" thick, was so sized to match the 24" door and window frames Cliff salvaged from the barn wood. With sawdust in the mortar and 10" of insulation, he figures that the R-value of a typical wall approaches R-40.

Some might question the inconvenience of laying up two separate cordwood surfaces, but Shockey addresses that with two observations. First, he saved time by not having to cut each log to a precise length to keep the interior and exterior surfaces straight, since inconsistencies are hidden on the inside. Second, he solved a nagging problem of cordwood and log construction, how to run electrical service without exposing the cables to view. The wiring is run between the air-vapor barrier and the interior wall, and the outlets are mounted in notches cut into the inside block.

As for plumbing, Cliff brought it through the floor in the center of the house rather than running it along an outside wall—a technique that could apply in any climate, but again one that requires prior planning.

With so much recycled lumber available, the roof was made quite thick, as seen by its wide fascia. A layer of 2 x 12s on 48" centers provides support for a second cross-layer of edgewise 2x6s on 16" centers. This 18"-thick structure is covered with Cliff's hand-sawn cedar shingles and is insulated to an R-40 level.

For the Shockeys, there's no question that their home is a haven of comfort and relaxation. Jackie, who is a nurse and practices holistic healing techniques, emphasizes how natural their living space feels. The house won a Canadian publication's national energy-efficiency award a couple of years ago and continues to attract attention, most recently at the Continental Cordwood Conference held in upstate New York last summer.

Cliff Shockey's technique was intended for northern climates to be sure ...but it could be well suited to cordwood builders anywhere.

 


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