In the realm of natural building, you have many different options. From rammed earth to straw bale to adobe, there is a building method suitable for almost any situation within the United States.
In this article, we will be taking a look at a method that is perfect for the many forested areas of North America, cordwood construction. Low cost and fairly easy to learn, let’s take a look at constructing residences using cordwood.
What is Cordwood?
In case you are unfamiliar with the term “cordwood,” it is the name given to wood that has been cut to length (often 16” or thereabouts) and then split for use in a fire.
This split wood is put into stacks. If this stack of wood measures 4’ x 4’ x 8’, then you have what is called a cord of wood. This is the measurement most often used when selling firewood used as fuel to heat houses in a wood stove. People will often express the amount of wood required to heat their homes for a year in cords; in some areas you can get by on 2 cords while other areas with particularly cold and long winters might require 8 to 10.
In any case, cordwood is a short length of log that has been split into sections to be used in a heating appliance.
The Basics of Construction using Cordwood
When you have a bunch of firewood nicely split and stacked ready for the winter, it actually forms quite a wall in and of itself. It serves as both a visual barrier and a nice wind break. I am sure that everyone who has ever stacked their own wood has recognized this fact. Most homesteads have a wood shed to store the cordwood where the walls are made of this cordwood while it seasons. As such, it does not take a genius to realize that this wood could also easily be assembled into a wall of a more permanent structure. However, even a 4-foot-high stack of unsupported cordwood, let alone a full-height wall, is fairly unstable and easily pushed over if one so desired. So, in order to build from this material, this inherent weakness needs to be overcome.
Use Mortar for Stability
To remedy the inherent instability of a stack of wood, natural builders have turned to mortar to lock the individual pieces of cordwood into a single monolithic unit. The idea is to surround each piece of wood with mortar – you should never have two pieces of wood touching each other in the wall. The mortar forms a continuous structural web from side to side and top to bottom of the wall. It is this network that makes the wall a single strong entity.
There is significant debate as to which type of mortar to use. Most people use a lime-enhanced cement mortar. Some will add things like sawdust to the mortar to enhance its R-value. And others will say that a good cob is sufficient (especially in non-load-bearing walls). In any case, it is always a good idea to make several mixes and put a couple pieces of wood in it to see how much shrinkage occurs and how strong it feels. Choose the best one after conducting such tests using your own mixes.
Use Seasoned Cordwood
Green wood will shrink as it dries. Some wood will shrink just a bit, and other wood can shrink by quite a bit. For example, the volume of western red cedar shrinks by about 7%, while the volume of some hickories can decrease by about 17%. If you try to build a structure using green wood, it will pull away from the mortar as the wood dries out. This causes gaps to appear around the cordwood, and gaps are a no-no in any structure as they serve as ways for water to enter the wall.
Build with Generous Roof Overhangs
Make sure to build your structure with generous roof overhangs. The eaves of your roof should come out quite a bit from the wall to protect the exposed wood from the elements as much as possible. You must remember that while water does not travel across grain in wood very well, it does travel with the grain quite easily. In cordwood construction, the ends of the logs are sticking out, and so if the wood is constantly exposed to rain during a season, that will have detrimental effects on its long-term durability.
Choose the Right Type of Wood
Not all woods are created equal. They all have different traits that are useful in different sorts of situations. In the realm of cordwood construction, there are a couple traits that are important. Since you are building a wall to a home, insulative value is important.
Softwoods, being less dense, typically have a higher R-value than hardwoods. Another important trait is how much a wood expands and contracts with changes in water content. Once again, softwoods generally shrink less than hardwoods. Finally, there is rot resistance. In this category, hardwoods are often the better choice. However, if you build with wide roof overhangs, rot should not be an issue. So, putting all this together, a softwood is generally accepted to be the better choice in cordwood construction. Of course, this is all true if you have a choice of woods to use; however, if you live in an area where you only have a single sort of wood, just use that.
Make Sure to have an Adequate Foundation
A cordwood wall is much heavier than your average stick-framed wall. As such, it requires a stronger foundation. In addition to the strength of the foundation, you also want to make sure that the foundation raises the first layer of cordwood to be up off of the ground. The lower down the wall it is, the wetter it will be during rainstorms, and if the first layer of wood is in contact with the ground, it will rot far faster than wood that has been raised.
Pros of Building with Cordwood
Let’s look at some of the benefits that cordwood offers when it comes to building with it.
It is Fairly Simple
Building with cordwood is not all that difficult. As far as the different methods of building are concerned, this one ranks among the easiest. Even a DIYer of modest ability should be able to construct a small dwelling from cordwood.
Wood is Locally Available
Although it takes quite a bit of wood to construct a home from cordwood, most of the time, builders of these homes utilize wood cut from their own properties. Many times, the trees are felled from the exact spot where the house will be built or from the woodlot on the same property as the house.
The trees are then cut to length right in place and then can be split either by hand or machine on site. The material doesn’t need to be shipped in from some faraway locale.
Wood is Renewable
As is well-known, wood is a completely renewable resource. Many builders of cordwood homes will go on to replant the trees where they fell. It should also be mentioned that wood is a resource that needs to be managed for optimal growth. Any woodlot needs to have some trees removed to help the remaining trees grow better.
These “waste” trees can easily be used in cordwood construction even if they are not suitable for the production of lumber. In this way, you are both helping in the growth of a forest and building a house.
Cons of Building with Cordwood
Even though there are benefits to building with cordwood, there are also some cons to using corwood for your next building plan.
It Takes a Lot of Wood
A cordwood wall is mostly wood. As such, it will use up a LOT more wood than your average stick-framed or timber-framed house. All of this wood needs to be felled, bucked, and split. That is no small task.
It Takes a Lot of Mortar
Estimates put the amount of mortar to be between 30-40% of the surface of the wall. This is a whole lot more mortar than something like a concrete block wall that uses thin mortar joints.
I am not really referring to the time it takes to do the actual building of a wall with cordwood. In that regard, it is certainly faster than things like rammed earth or tires, but it is slower than stick framing. What I mean is that you need to plan quite a bit in advance and get everything ready. You need to cut down the trees, cut up the trees, and then split the wood.
All of this needs to be done a good year before you plan on building with the cordwood so that it has time to season. However, if you buy your wood pre-seasoned from a supplier in the area, this becomes a moot point.
So, is cordwood construction right for you? Maybe, maybe not. If you live in an arid area or the high plains with few trees, probably not. However, there are vast portions of the United States and Canada where cordwood construction is certainly a viable option. It can be very cheap to build with, and it can build very sturdy structures.
Cordwood Construction Resources
- Earthwood Building School’s full length how-to videos. cordwoodmasonry.com
- Best Practices with Cordwood Construction By Richard Flatau
- Table of Insulation R Values – inspectapedia.com
- Cordwood Building: The State of the Art, Rob Roy
- Complete Book Of Cordwood Masonry Housebuilding: The Earthwood Method by Rob Roy