Appalachia--Science in the Public Interest

A CORDWOOD BUILDING

No one knows who built the first stackwood or cordwood log
building (CWB), but some of these structures have withstood the
elements in northern Greece for at least a thousand years.
Northern Europe has many such buildings and the construction zone
extends into Siberia and the frigid climates of Canada. The CWB
is an appropriate technology for Canada because it requires very
little fuel wood to heat the building, even when outside
temperatures drop as low as 40ø below zero (Fahrenheit).

Why so few CWBs in non-frigid parts of the world? Maybe it
is due to the lack of accessible, long-lasting supplies of wood.
Granted, there is a loss of insulating ability in the end
direction of wood as opposed to laying materials lengthwise, but
this is compensated for by using thicker logs and cradling
insulation within the interior of CWB walls. Curiously, the
insulating ability of a cordwood wall is actually far superior to
that of a conventional log building. A 16-inch thick cordwood
wall has an insulating value of R-16, or a factor of resistance
to heat loss of R-1 per inch of wood.

1. Advantages

Some parts of the world build for hot summers and others,
for cold winters. But in a temperate zone builders must design
for hot and cold temperatures. Few structures serve both
extremes better than CWBs. Furthermore, CWBs are "solar"
buildings which capture the sun's rays in the form of wood (a
renewable resource) and do not require as much maintenance and
care as do more conventional solar houses. Unfortunately, many
people resist novel building ideas and balk at this approach to
low-cost building even though CWBs have several advantages:
CWBs are comfortable. They are easy to heat in winter and
easy to cool in summer.
CWBs can easily be constructed by people with average
building skills. People of moderate strength can participate in
CWB construction. This is contrasted with construction of
conventional log buildings which requires a great deal of heavy
lifting.
Discarded (recycled) timber and timber waste can be
incorporated into CWB construction.
CWBs are user-friendly and attractive.
CWBs pose a low fire hazard. This is important for people
who live in forested areas where fire insurance can be hard to
get. The walls of CWBs are almost impervious to fire.
CWBs are inexpensive for those with access to logs.
CWBs are easy to maintain.

One of the difficulties with CWBs is that they require wood
as a building material and so cannot be easily built anywhere.
However, wherever wood is used as fuel for heat, the amount saved
due to the high insulation value of a CWB could easily equal
amount of wood used for construction over the course of a decade.

2. Construction

In the books of Robert L. Roy (references 2 and 3) the
construction of CWBs is described in great detail. Site
selection is important for the total comfort, lifetime, and
economy of the building. Having a southern exposure is most
important for incorporating passive solar designs. Building on a
shaded hillside, away from the prevailing wind but with winter
exposure to the sun is ideal. CWBs come in a variety of building
designs, (e.g., post-and-beam, stack wall, curved--round or
oblong). As Roy points out, a 120-running foot wall building
could have a variety of internal areas, so the selection of shape
depends more on building material economy. In deciding upon a
shape, it should be remembered that curved wall buildings can
make arranging interior spaces difficult because of the
customary shape of furniture and appliances.

The type of wood one selects for the CWB is very important.
The type of wood most commonly used in northern climates is
Eastern red cedar (Juniperus virginiana), which is known for its
durability and resistance to rotting. Where plentiful, this is
an ideal CWB construction material because many of the trees are
of small girth and make good logs. For its CWB, ASPI used White
oak (Quercus alba), which is the most common tree of the central
Appalachian climax forest and a downed supply was available for
the taking. Another common tree, the Yellow poplar or Tulip tree
(Liriodendron tulipfera), has been known to remain solid and
sturdy in two-hundred year-old log cabins.

Selected trees are cut into double lengths for drying.
(Walls may be 12 or 16 inches thick; so double lengths are 24 or
32 inches). The cordwood is placed on stovewood type ricks and
allowed to dry. Cutting in autumn and winter before the sap
rises reduces drying time. At a minimum, wood should be cut,
split, stacked and dried out of the weather for at least one year
prior to construction. Pieces of old metal roofing over the rick
will keep rain off the wood during the drying period. Debark at
the appropriate time. Split larger logs (above 10 inches
diameter) for faster drying, and to prevent checking, starring,
or cracking after the wall is laid.

3. Wood Protection

A masonry or slab concrete floor will retard the action of
termites and other wood-eating insects. Precautions taken for
preserving and preventing such damage in other houses apply here.
The cordwood should begin to be stacked at least 12 - 18 inches
above the grade, with rocks, block, or other masonry forming the
foundation. Aluminum flashing should be applied between the
masonry foundation and the cordwood with ample caulking and
sealing to prevent air infiltration. The first course of stacked
wood should be treated with Thompson's Waterseal brand Water
Proofing Formula or other non-toxic wood preservative to deter
insects and prevent rot from the splash of rainfall and runoff
from the roof. Linseed oil and rape seed oil are good CWB
preservatives.

4. Cement Mixture Composition

The composition of the mortar used varies based on the
amount of shrinkage anticipated, the type of wood used, weather
conditions during the construction period, time allowed for the
cement to dry, and weather conditions of the first year curing
time. Because a slow drying time is necessary to prevent severe
shrinkage and break-away from the wood, some sawdust is included
in the masonry mixture. In the ASPI building, a composition of
almost equal parts sand and sawdust was used. The resulting
cement wall is soft and will crumble easily for a year or so.
During this time, hammering nails in the wall and similar
disturbances should be avoided. It may be wise to build a small
out building to try out various methods or mortar compositions
before beginning the larger undertaking.

ASPI used scrap insulation interwoven among the logs in a
sandwich fashion with cement on inner and outer sides.

[Diagram]

The roof should overhang the building about 30 inches to
protect the wood in the walls. Even though the CWB is built to
last for centuries, some maintenance is necessary. The masonry
portion of the walls will normally require repainting with
cementing mix. We strongly suggest a mix of yellow sand and
masonry cement (we used BRIXMENT brand type-N Coplary Cement,
ESSROC Materials, Inc. Speed, IN 47172). It sticks very well
to the wood and will not develop cracks provided hammering and
violent vibrations do not occur. The wood wall surface should be
re-coated with linseed oil, depending on the amount of
weathering. The inside surface of the log ends can last for four
or five years between applications, but parts of the outside
should be done every other year.

TYPICAL COST (Labor not included.)

Small CWB Cabin (20 by 20 feet) Total 400 square feet

Cement, sand $120
Chain saw fuel   $ 30
Four windows    $240
Two doors (galvanized steel) $200
Roof -- 500 square feet (including shingles,
plywood, tar paper, nails) $300
Guttering, downspout   $100
Floor (concrete, rebar) plus foundation $440
Paint, caulking    $ 50
Insulation        $120
Rafters (locally milled)   $150
Sheet rock (ceiling)   $160
Electric outlet, box, wiring $200
Plumbing and pipes $120
Vents       $ 20
Stove pipe      $ 50
Flashing           $ 40
Miscellaneous hardware    $ 60
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Total:           $2400

Analysis: 400 ft. building, $2400 = $6.00 / square ft.

REFERENCES

Square, David. "Poor Man's Architecture." Harrowsmith. #15
(1978): 84-91.

Roy, Robert L. How to Build Log-End Houses. New York: Drake
Publishers, 1977.

Roy, Robert L. Cordwood Masonry Houses: A Practical Guide for
the Owner-Builder. New York: Sterling Publishing Company, 1982.