What Is Cordwood Construction?
Cordwood masonry (also called stackwall, log-end, or stovewood construction) is a building technique where short lengths of debarked, seasoned wood are set in mortar to form a thick, monolithic wall. The end-grain of the logs faces out on both sides, giving cordwood homes their distinctive appearance. It's been used across Canada, the northern United States, Scandinavia, and Eastern Europe for centuries — and has seen a major revival among owner-builders and homesteaders.
The defining feature of a modern cordwood wall is the split mortar joint: instead of one continuous mortar bed (which would create a thermal bridge), two separate mortar bands — inner and outer — are applied with an insulated fill zone between them. This is the standard method promoted by Rob Roy of Earthwood Building School and Richard Flatau of Cordwood Construction, the two leading authorities on the technique.
How to Use This Calculator
- Enter your wall dimensions — total length and height of all cordwood walls combined. Adjust units (imperial or metric) at the top.
- Set your log length — this equals your wall thickness. 16 inches (≈ 40 cm) is the most common choice for residential builds in North America. Use the preset dropdown or enter a custom value.
- Add openings — deduct any doors, windows, structural posts, or corner beams that won't contain cordwood.
- Set mortar band widths — the standard is 3 inches inner and 3 inches outer (the remaining center space is insulated fill).
- Adjust the mortar face-area percentage — how much of the wall face is mortar vs. wood end-grain. 35% is typical.
- Enter prices (optional) for a material cost summary.
- The results update instantly. Use Print / Save PDF to save a clean summary.
The Formulas Explained
Face cords of wood = Net wall area ÷ 32 × (1 + waste%)
(Rob Roy method: 1 face cord of wood fills approx. 32 sq ft of wall face)
Mortar band area = Net wall area × mortar% × (inner band + outer band) / log length
This converts the 2-D mortar face fraction into the actual 3-D mortar zone volume.
Insulation fill volume = Net wall area × mortar% × (log length − inner band − outer band) / log length
The center zone between the two mortar bands.
R-value estimate = log length (inches) × 1.47
Source: University of Manitoba R-value testing of cordwood walls with sawdust-lime insulated mortar.
Mortar ingredient volumes are split proportionally by the mix ratio you enter (default: Rob Roy's 9:3:3:2 sand:sawdust:lime:cement by loose volume).
Frequently Asked Questions
- How many face cords of wood do I need for a cordwood wall?
- The Rob Roy / Earthwood method divides your net wall area in square feet by 32 to get the number of face cords, then adds a waste allowance (typically 10–15%). A face cord is a stack 4 ft high × 8 ft wide at the actual log length — not a full cord (which is 4×4×8 ft). For a 40 ft × 8 ft wall with no openings at 16-inch logs, that's roughly 10 face cords before waste.
- What percentage of a cordwood wall is mortar?
- Mortar typically covers 30–40% of the wall face area. With large, uniform round logs you'll be closer to 30%; with smaller or split pieces you can hit 40% or more. The calculator defaults to 35%, which fits most mixed-diameter walls. Keeping this number lower reduces mortar costs and improves R-value.
- What is the R-value of a 16-inch cordwood wall?
- Using the University of Manitoba figure of R-1.47 per inch, a 16-inch wall yields approximately R-23. This assumes proper sawdust-lime insulated fill between the mortar bands. A purely cement-mortar wall (no sawdust, no insulated center) would perform significantly worse. Compare to a 2×6 stud wall at R-21 — cordwood can match it if built correctly.
- What wood species should I use for cordwood construction?
- Light, low-density softwoods with stable moisture behavior are preferred: white cedar (the gold standard), eastern white pine, Douglas fir, poplar, and aspen. Dense hardwoods like oak and maple are less ideal because they have lower R-value per inch (parallel-to-grain heat flow) and a higher tendency to check and swell, which can crack mortar joints. Wood must be fully seasoned (less than 15% moisture content) before building.
- How long does it take cordwood to dry/season before building?
- Freshly cut wood needs to dry for one to three years depending on species, log diameter, and climate. White cedar dries faster (1–2 years); dense hardwoods can take 3+ years. Use a moisture meter and aim for under 15% MC. Building with wet wood causes shrinkage cracks at the wood–mortar interface.
- Can I use a different mortar mix?
- Yes — the calculator lets you enter any ratio. Some builders use a simpler mix (1 Portland : 2 sand) or add clay. However, Rob Roy's 9:3:3:2 (sand:sawdust:lime:Portland) is widely tested and recommended by Cordwood Construction org. The sawdust improves thermal performance and reduces cracking; omitting it is not advisable in cold climates.
⚠ Results are estimates for planning purposes only. Actual material quantities depend on log diameter distribution, building geometry, construction skill, mortar consistency, and local conditions. Always consult Rob Roy's Cordwood Construction Best Practices (cordwoodconstruction.org) and a qualified builder before finalizing orders. Not structural or engineering advice.