Cordwood construction
Wood usually accounts for about 40-60% of the wall system, the remaining portion consisting of a mortar mix and insulating fill.
Instead, three- or four-inch (sometimes more) beads of mortar on each side of the wall provide stability and support, with a separate insulation between them.
Different mortar mixtures and insulation fill material both affect the wall's overall R value, or resistance to heat flow; and conversely, to its inherent thermal mass, or heat/cool storage capacity.
However, it is plausible that forest dwellers eventually erected a basic shelter between a fire and a stacked wood pile.
One recipe which has proven to be successful since 1981 is 9 parts sand, 3 sawdust, 3 builder's lime (non-agricultural), 2 Portland cement by volume.
[2] Builder's lime makes the wall more flexible, breathable, and self-healing because it takes longer to completely set than cement.
[7] Another recipe uses 3 parts sand, 2 soaked sawdust, 1 Portland Cement and 1 Hydrated Lime; intended to have the advantage of curing slower and displaying less cracking.
[3] Thermal mass makes it easier for a building to maintain median interior temperatures while going through daily hot and cold phases.
A common 16” cordwood wall for moderate climates comprises 6 inches (150 mm) of perlite or vermiculite insulation between mortar joints.
The only authoritative testing on the R-value of cordwood masonry was conducted by Dr. Kris J. Dick (PE) and Luke Chaput during the winter of 2004–2005, based on thermal sensors placed within a 24-inch thick wall at the University of Manitoba.
"[2] A thermal performance analysis in 1998 using “HOT 2000” computer software showed the relationship of domestic wall types and their insulating values.
The findings compiled by the Engineering Department, found that each inch of cordwood wall (mortar, log end and sawdust/lime insulation yielded an r-value of 1.47).
[14] A cordwood home can be constructed for significantly less initial out-of-pocket cost than a standard stick-frame house of comparable size, since sometimes labor is done primarily by the owner, or volunteers.
[citation needed] A two-story 2,512 sq ft (233.4 m2) cordwood house in Cherokee, North Carolina outfitted with "high quality tile, tongue and groove pine, Russian Woodstove, live earth roof, hand shaped cedar trim, raised panel cabinets, and a handmade pine door," cost the owner an estimated $52,000.
ft.[15] Both the acquisition of materials and source of labor play major roles in the initial cost of building a cordwood house.
In this case a metal handsaw is preferable to a chainsaw because its finer cut helps to ward moisture and pest penetration.
Once a proper foundation has been poured which rises 12-24 inches above ground level with a splash guard, construction of the walls can begin.
When experimenting with M-I-M, (the more common form), two parallel 3 to 4 inch beads of mortar are laid down along the foundation, followed by a middle filling of insulation material.
Pre-split “firewood style” logs check less when in the wall and are easier to point or smooth and press evenly around than round pieces because the mortar gaps are generally smaller.
[citation needed] Rob and Jaki Roy, co-directors of Earthwood Building School in West Chazy, NY for 36 years, take a different point of view.
The shrinkage is exactly the same in splits and rounds, and the Roys have found the wood easier to lay up because it more readily holds its shape from one side of the wall to the other.
A cordwood house should have deep overhanging eaves of at least 12- 16 inches to keep the log ends dry and prevent fungal growth.
[19] Although cordwood homes have been tested in -40F locations like Alberta, their thermal efficiency in any climate is below that of a purely cob house of comparable dimensions.
The quantity of labor relative to gaining a specific R value for cordwood is higher when compared to straw bale and stick frame construction.
