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Cordwood construction (also called cordwood masonry or cordwood building, alternatively stackwall or stovewood) is a term used for a natural building method in which short logs are piled crosswise to build a wall, using mortar or cob to permanently secure them. This technique can use local materials at minimal cost.
Walls are usually constructed so that the log ends protrude from the mortar by a small amount (an inch or less). Walls typically range between 8 and 24 inches thick, though in northern Canada, some walls are as much as 36 inches thick.
Cordwood homes are attractive for their visual appeal, economy of resources, and ease of construction. Wood usually accounts for about 40-60% of the wall system, the remaining portion consisting of a mortar mix and insulating fill. [1] Cordwood construction can be sustainable depending on design and process. There are two main types of cordwood construction, throughwall and M-I-M (mortar-insulation-mortar). In throughwall, the mortar mix itself contains an insulative material, usually sawdust, chopped newsprint, or paper sludge, in sometimes very high percentages by mass (80% paper sludge/20% mortar). In the more common M-I-M, and unlike brick or throughwall masonry, the mortar does not continue throughout the wall. 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. Cordwood walls can be load-bearing (using built-up corners, or curved wall designed) or laid within a post and beam framework which provides structural reinforcement and is suitable for earthquake-prone areas. As a load-bearing wall, the compressive strength of wood and mortar allows for roofing to be tied directly into the wall. 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.
Remains of cordwood structures still standing date back as far as one thousand years in eastern Germany. [2] However, more contemporary versions could be found in Europe, Asia, and the Americas. [3] There is no detailed information about the origins of cordwood construction. However, it is plausible that forest dwellers eventually erected a basic shelter between a fire and a stacked wood pile. [4] In the work of William Tischler of University of Wisconsin, he states that "current" cordwood probably started in the late 1800s in Quebec, Wisconsin, and Sweden. [5] He believes that the technique started in these areas around the same time. [6]
Cordwood construction is an economical use of log ends or fallen trees in heavily timbered areas. Other common sources for wood include sawmills, split firewood, utility poles (without creosote), split rail fence posts, and logging slash. It is more sustainable and often economical to use recycled materials for the walls. Regardless of the source, all wood must be debarked before the construction begins. While many different types of wood can be used, the most desirable rot resistant woods are Pacific yew, bald cypress (new growth), cedars, and juniper. Acceptable woods also include Douglas fir, western larch, Eastern White Pine, and Spruce Pine.
Less dense and more airy woods are superior because they shrink and expand in lower proportions than dense hardwoods. [2] Most wood can be used in a wall if it is dried properly and stabilized to the external climate's relative humidity. [2] Furthermore, while log ends of different species can be mixed in a wall, log-ends of identical species and source limit expansion/contraction variables.
Various experts advise different recipes for mortar mix. 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. [3] [2] Portland cement chemically binds the mortar and should be either Type I or II. [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. [8] [9] [10]
Depending on a variety of factors (wall thickness, type of wood, particular mortar recipe), the insulative value of a cordwood wall, as expressed in R-value is generally less than that of a high-efficiency stud wall. Cordwood walls have greater thermal mass than stud frame but less than common brick and mortar. This is because the specific heat capacity of clay brick is higher (0.84 versus wood's 0.42), and is denser than airy woods like cedar, cypress, or pine. However, the insulated mortar matrix utilized in most cordwood walls places useful thermal mass on both sides of the insulated internal cavity, helping to store heat in winter and "coolth" in summer. [3] Thermal mass makes it easier for a building to maintain median interior temperatures while going through daily hot and cold phases. In climates like the desert with broad daily temperature swings thermal mass will absorb and then slowly release the midday heat and nighttime cool in sequence, moderating temperature fluctuations. Thermal mass does not replace the function of insulation material, but is used in conjunction with it.
The longer the logs (and thicker the wall), the better the insulation qualities. A common 16” cordwood wall for moderate climates comprises 6 inches (150 mm) of perlite or vermiculite insulation between mortar joints. Another insulation option, used for over 40 years by Rob Roy and other cordwood builders is dry sawdust, passed through a half-inch screen, and treated with builder's (Type S) lime at the ratio of 12 parts sawdust to 1 part lime. With light airy sawdusts, this insulation is similar in its R-value to manufactured loose-fill insulations, at a fraction of the cost. [2]
However, wood is an anisotropic material with respect to heat flow. That means its thermal resistance depends on the direction of heat flow relative to the wood grain. While wood has a commonly quoted R-value of about 1.25 per inch (depending on the species and moisture content), that only applies if the heat flow is perpendicular to the grain, such as occurs in common wood-frame construction. [11] With cordwood/stackwall construction, the direction of heat flow is parallel to the grain. For this configuration, the R-value is only about 40% of that perpendicular to the grain. Thus, the actual R-value of wood, when used in cordwood/stackwall construction is closer to about 0.50 per inch.
But the R-value of a cordwood masonry wall must take into consideration both the wooden portion and the insulated mortar portion as a combined system. 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. A paper reporting on their findings appears in Cordwood and the Code: a building permit guide The authors' summary says, in part: "Based on approximately three months of mid-winter temperature data, the wall was determined to have an RSI Value of 6.23 (m²K/W), R-35 for a 24-inch wall system." [2]
A thermal performance analysis in 1998 using “HOT 2000” computer software showed the relationship of domestic wall types and their insulating values. The simulation revealed an R value of 20.5 for the sample cordwood wall. Compare this to the basic 2 x 4 wooden stud wall, and 2 x 6 foam insulated and sheathed wall with R values of 15.8 and 25.7, respectively. [12] Cordwood walls are not the best natural insulators but can be built to thermal efficient standards. The R value of a cordwood wall is directly related to its ratio of wood to mortar and insulation medium. However, R value in cordwood construction is not as significant as it is in stick-frame building due to the high thermal mass which increases a significantly higher "effective R-value.” [13] Builders tailor their design and ratios to the existing climate.
R-value testing was completed at the University of Manitoba in the winter of 2005. 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. Properly built cordwood walls tend to have fewer maintenance needs than standard stick-frame, because there are fewer manufactured components (e.g., fiberglass insulation, nailings, sidings, flashings, etc.). Some maintenance still will be required, as there is wood and concrete exposed to the elements on the exterior side of the wall. A cordwood house that is poorly built without sufficient insulation can result in higher heating costs than a traditional stud-frame house.
In a 1998 comparative economic analysis of stud frame, cordwood, straw bale, and cob, cordwood appeared to be an economically viable alternative. [ 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. [ citation needed ] With the owner providing 99% of the labor, the house cost him $20.70 per sq. ft. [ citation needed ] A comparably sized and furnished stick-frame house in 1998 would cost between $75,000-$120,000 with zero owner labor. [ citation needed ] The 1997 residential cost data shows an "average" trim level 1,000-2,000 sq ft (190 m2) house costing $64.48-$81.76 per sq. ft. [15] Both the acquisition of materials and source of labor play major roles in the initial cost of building a cordwood house.
In certain jurisdictions construction plans are subject to the building inspector's approval. Before building, soil conditions on the site must be verified to support heavy cordwood masonry walls.
With felled timber, bark should be removed in the spring with a shovel, chisel, or bark spud. The sap is still running in spring time and provides a lubricating layer of cambium between the bark and wood, making separation an easier task than if left until the fall when the two layers are well-bonded together. Once debarked, the logs should sit to dry for at least three summers to limit splitting and checking. It is important to cut the logs, once debarked to the chosen building length. Richard Flatau, Cordwood Construction: Best Practices (2012) suggest splitting 70% of the wood for better drying and seasoning. [18]
After drying, the logs must be cut to the desired length (usually 8, 12, 16, 18, or 24 in.). In this case a metal handsaw is preferable to a chainsaw because its finer cut helps to ward moisture and pest penetration. [ citation needed ] Actually a "cut off " saw or "buzz saw" will make quick work of cutting cordwood into chosen lengths. For especially furry ends like on cedar, rasps can be used for smoothing.
The wood then needs to be transported to the building site. It is convenient to have the source of cordwood and construction site nearby. 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. Temporary shelters can be used to cover the worksite and cordwood from rain. A post and beam frame supplies this shelter for subsequent cordwood mortaring.
Inexperienced homebuilders should experiment with a number of practice walls. This will ultimately expedite the building process and provide more satisfying results. 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. Then logs are laid on top with consistent mortar gaps, protruding no more than 1 inch on the inside and outside of the wall. Actual placement will depend on the size and shapes of the logs. Another layer of mortar is spread, then insulation poured in between, more logs follow and so on. When experimenting with Throughwall, a thin, even layer of insulative mortar is laid along the foundation, then the logs are seated firmly in the mortar bed, in an even fashion, leaving only enough space between them to "point" the mortar. The mortar gaps are filled to make a relatively flat top surface, then another thin layer of mortar is added and the process repeats. The shape and exterior orientation of logs is important only for appearance. 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. They used to use mostly split wood, but now use mostly white cedar (or equal) rounds. 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. Further, the rounds are easier to point, because of the ragged edge that results on the bottom side of a split log. Finally, the greater amount of mortar using rounds is actually a plus because the mortared portion of the wall performs better, thermally, than the wooden portion. [2]
If constructing a house with corners, each course of cordwood should be cross hatched for strength. Near the end, small filler slats of wood may be required to finish the joining or tops of walls. Windows and doors are framed with standard window boxes and wooden lintels. Glass bottles can be inserted for a creative stained glass effect. (Plumbing and electrical wiring are issues to consider but will not be elaborated on in this article).
A cordwood house should have deep overhanging eaves of at least 12- 16 inches to keep the log ends dry and prevent fungal growth. If the ends are maintained to be dry and well aerated, they will age without problem. Some owners have coated their ends with linseed oil, or set the outside log ends flush with the mortar for further weatherproofing. Over time, some checking is normal, and can be remedied with periodic mortar or caulking maintenance. [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. [1] In frigid areas it is appropriate to either build a thicker 24-36 inch wall, or two separate super insulated walls. In predominantly wet areas, the outside walls can be plastered, smothering the cordwood ends from air and moisture, but this hides cordwood's attractive log ends and the logs will rot. The quantity of labor relative to gaining a specific R value for cordwood is higher when compared to straw bale and stick frame construction. Funds saved in construction may need to be allocated for heating costs or longterm exterior maintenance. [1] An organic, mortar-like cob creates less of an environmental impact because of the use of readily available mud and straw, whereas toxins emitted during the production of Portland cement are very harmful, albeit less tangible in the final product. Like many alternative building styles, the sustainability of cordwood construction is dependent upon materials and construction variables.
Following the Cordwood Conference in 2005 at Merrill, Wisconsin, a document was published to address best practices in cordwood construction and building code compliance. The document entitled Cordwood and the Code: A Building Permit Guide assists cordwood builders get the necessary code permits. [20]
Adobe is a building material made from earth and organic materials. Adobe is Spanish for mudbrick. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of earthen construction, or various architectural styles like Pueblo Revival or Territorial Revival. Most adobe buildings are similar in appearance to cob and rammed earth buildings. Adobe is among the earliest building materials, and is used throughout the world.
In building design, thermal mass is a property of the matter of a building that requires a flow of heat in order for it to change temperature. In scientific writing the term "heat capacity" is preferred. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structural elements can be designed to work alongside a construction's lighter thermal resistance components to create energy efficient buildings.
An earth shelter, also called an earth house, earth bermed house, or underground house, is a structure with earth (soil) against the walls, on the roof, or that is entirely buried underground.
The R-value is a measure of how well a two-dimensional barrier, such as a layer of insulation, a window or a complete wall or ceiling, resists the conductive flow of heat, in the context of construction. R-value is the temperature difference per unit of heat flux needed to sustain one unit of heat flux between the warmer surface and colder surface of a barrier under steady-state conditions. The measure is therefore equally relevant for lowering energy bills for heating in the winter, for cooling in the summer, and for general comfort.
Straw-bale construction is a building method that uses bales of straw as structural elements, building insulation, or both. This construction method is commonly used in natural building or "brown" construction projects. Research has shown that straw-bale construction is a sustainable method for building, from the standpoint of both materials and energy needed for heating and cooling.
Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings and other structures, like bridges. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic. The manufacturing of building materials is an established industry in many countries and the use of these materials is typically segmented into specific specialty trades, such as carpentry, insulation, plumbing, and roofing work. They provide the make-up of habitats and structures including homes.
A structural insulated panel, or structural insulating panel, (SIP), is a form of sandwich panel used as a building material in the construction industry.
This page is a list of construction topics.
Natural building or ecological building is a discipline within the more comprehensive scope of green building, sustainable architecture as well as sustainable and ecological design that promotes the construction of buildings using sustainable processes and locally available natural materials.
Insulating concrete form or insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building. ICF construction has become commonplace for both low rise commercial and high performance residential construction as more stringent energy efficiency and natural disaster resistant building codes are adopted.
Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss by using much higher insulation levels and airtightness than average. Superinsulation is one of the ancestors of the passive house approach.
A masonry oven, colloquially known as a brick oven or stone oven, is an oven consisting of a baking chamber made of fireproof brick, concrete, stone, clay, or cob. Though traditionally wood-fired, coal-fired ovens were common in the 19th century, and modern masonry ovens are often fired with natural gas or even electricity. Modern masonry ovens are closely associated with artisan bread and pizza, but in the past they were used for any cooking task involving baking. Masonry ovens are built by masons.
Thermal transmittance is the rate of transfer of heat through matter. The thermal transmittance of a material or an assembly is expressed as a U-value. The thermal insulance of a structure is the reciprocal of its thermal transmittance.
Building insulation is material used in a building to reduce the flow of thermal energy. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation. Often an insulation material will be chosen for its ability to perform several of these functions at once.
Building insulation materials are the building materials that form the thermal envelope of a building or otherwise reduce heat transfer.
A thermal bridge, also called a cold bridge, heat bridge, or thermal bypass, is an area or component of an object which has higher thermal conductivity than the surrounding materials, creating a path of least resistance for heat transfer. Thermal bridges result in an overall reduction in thermal resistance of the object. The term is frequently discussed in the context of a building's thermal envelope where thermal bridges result in heat transfer into or out of conditioned space.
Masonry veneer walls consist of a single non-structural external layer of masonry, typically made of brick, stone or manufactured stone. Masonry veneer can have an air space behind it and is technically called "anchored veneer". A masonry veneer attached directly to the backing is called "adhered veneer". The innermost element is structural, and may consist of masonry, concrete, timber or metal frame.
Hempcrete or hemplime is biocomposite material, a mixture of hemp hurds (shives) and lime, sand, or pozzolans, which is used as a material for construction and insulation. It is marketed under names like Hempcrete, Canobiote, Canosmose, Isochanvre and IsoHemp. Hempcrete is easier to work with than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the brittleness of concrete and consequently does not need expansion joints.
Alternative natural materials are natural materials like rock or adobe that are not as commonly used as materials such as wood or iron. Alternative natural materials have many practical uses in areas such as sustainable architecture and engineering. The main purpose of using such materials is to minimize the negative effects that built environments can have on the planet, while increasing the efficiency and adaptability of the structures.
Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, triple glazing or a triple-paned window, or quadruple glazing or a quadruple-paned window, depending upon how many panes of glass are used in its construction.
