Cordwood Construction: A Comprehensive Guide to Building with Log Masonry

Cordwood construction is a unique building method that combines the structural properties of masonry with the natural insulation of wood. By stacking short logs—known as cordwood—within a mortar matrix, builders can create durable, aesthetically pleasing walls. Whether you are an experienced builder or a sustainable architecture enthusiast, mastering the process of selecting, seasoning, and laying cordwood is essential for a long-lasting structure.

Key Facts

• Seasoning: Debarked logs should dry for at least three summers to minimize splitting.
• Cutting: Metal handsaws or buzz saws are preferred over chainsaws to reduce moisture and pest penetration.
• Foundation: Walls must sit on a foundation rising 12-24 inches above ground level with a splash guard.
• Protection: Deep overhanging eaves (12-16 inches) are critical to prevent fungal growth on log ends.
• Materials: White cedar rounds are often preferred for their shape and ease of pointing.

Preparing the Materials

The quality of a cordwood wall begins long before the first log is laid. In many jurisdictions, construction plans must first be approved by a building inspector, and soil conditions must be verified to ensure they can support the significant weight of cordwood masonry.

Debarking and Seasoning

Timber should be debarked in the spring. During this season, the sap flows, creating a lubricating layer of cambium (the cellular plant tissue between the inner bark and the wood), which makes separation much easier than in the fall. Once debarked, logs should be left to dry for at least three summers to limit checking and splitting. According to Richard Flatau in Cordwood Construction: Best Practices (2012), splitting approximately 70% of the wood can improve the drying and seasoning process.

Cutting and Transport

After seasoning, logs are cut to specific lengths, typically 8, 12, 16, 18, or 24 inches. While a "buzz saw" or cut-off saw is efficient for bulk cutting, a metal handsaw is often preferred for its finer cut, which helps ward off pests and moisture. For woods with "furry" ends, such as cedar, rasps can be used for smoothing. Ideally, the timber source should be located near the building site to simplify transport.

The Construction Process

Before wall construction begins, a proper foundation must be poured, extending 12 to 24 inches above the ground. To protect the materials from rain, builders often use temporary shelters or a post-and-beam frame.

Wall Construction Methods

There are two primary methods for laying cordwood walls. Inexperienced builders are encouraged to create practice walls to refine their technique.

• M-I-M (Mortar-Insulation-Mortar): This common method involves laying two parallel beads of mortar (3 to 4 inches wide) on the foundation. An insulation material is filled between these beads, and logs are laid on top. The logs should protrude no more than 1 inch from the interior and exterior surfaces. This layering of mortar, insulation, and logs is repeated until the wall reaches the desired height.
• Throughwall: In this method, a thin, even layer of insulative mortar is laid. Logs are seated firmly in the mortar bed with just enough space between them to "point" (fill the gaps) with mortar. This creates a relatively flat top surface before the next layer is added.

Rounds vs. Splits

While some builders prefer split wood, Rob and Jaki Roy of the Earthwood Building School suggest using white cedar rounds. They note that shrinkage is identical for both, but rounds are easier to lay because they hold their shape across the wall. Additionally, rounds are easier to point because they lack the ragged bottom edges found on split logs. From a thermal perspective, the increased amount of mortar required for rounds actually improves the wall's performance.

Finishing and Maintenance

For houses with corners, each course of cordwood must be cross-hatched to ensure structural strength. Small filler slats may be used to finish the tops of walls or joints. Standard window boxes and wooden lintels are used for framing, and glass bottles can be embedded in the walls for a decorative stained-glass effect.

To ensure longevity, the structure must have deep overhanging eaves of 12-16 inches. This keeps the log ends dry and prevents fungal growth. Some builders further weatherproof the walls by coating log ends with linseed oil or setting the exterior ends flush with the mortar. While some checking (small cracks) is normal over time, it can be managed with periodic caulking or mortar maintenance.

Feature	Requirement/Recommendation
Seasoning Period	Minimum 3 summers
Foundation Height	12-24 inches above ground
Common Log Lengths	8, 12, 16, 18, or 24 inches
Eave Overhang	12-16 inches
Preferred Wood Type	White Cedar (Rounds)

Frequently Asked Questions

When is the best time to debark logs?

Logs should be debarked in the spring because the running sap creates a lubricating layer of cambium, making it much easier to separate the bark from the wood.

Why are metal handsaws preferred over chainsaws for cutting cordwood?

Metal handsaws provide a finer cut, which helps protect the wood from moisture penetration and pest infestation.

What is the difference between M-I-M and Throughwall construction?

M-I-M uses two parallel mortar beads with a center filling of insulation, whereas Throughwall uses a single layer of insulative mortar with logs seated firmly and then pointed.

How do you prevent rot and fungal growth in cordwood walls?

The most effective prevention is installing deep overhanging eaves (12-16 inches) to keep log ends dry and well-aerated. Linseed oil or flush-setting the logs in mortar can also provide extra weatherproofing.

Are rounds or split logs better for building?

While both have similar shrinkage rates, rounds are often preferred because they are easier to lay, easier to point, and provide better thermal performance due to the increased mortar usage.