Types of Wood to use for Cordwood
Rob Roy is Director of the Earthwood Building School, which has specialized in cordwood masonry instruction since 1980. Rob and his wife, Jaki, have built four innovative cordwood homes for themselves since 1975, including the Earthwood home where they have lived for over three decades. Earthwood is a 2400 SF two-story round, load-bearing cordwood home, earth-bermed and earth-roofed. Details of construction are in Rob's Earth-Sheltered Houses (New Society, 2006) and Cordwood Building: The State of the Art (New Society, 2003) two of fourteen books he is written in the alternative building field. Rob and Jaki have taught cordwood masonry in Earthwood Building School all over North America, as well as in Chile, New Zealand, Australia and Hawaii. They have helped scores of owner-builders with their cordwood projects, including homes, saunas and outbuildings. Earthwood has produced a 3.25-hour DVD on cordwood construction, which, with his books, can be accessed through the Earthwood website, or on the Cordwood page here. Rob is considered to be one of the leaders in the field of cordwood construction and earth sheltering. He does individual consultations at a flat rate of $75/hour, but answers questions here without charge. See also Earthwood Facebook. In July of 2015, Rob and Jaki, will be host the 5th Contintental Cordwood Conference at Earthwood CoCoCo/15, returning the conference to where the first one was held in 1994. Go to Earthwood Building School for information.
Q: I need to build a dwelling on a budget. I am a part time professional arborist\forester\nurseryman. Much of my work involves killing quantities of ailanthus (tree of heaven) which is an invasive here in south east Ohio. So far I find it even too useless to burn. Is it worthwhile for cordwood?
A: I'm afraid I am unfamiliar with the ailanthus (tree of heaven) wood. In fact, I have been getting a lot of questions lately about obscure woods with which I am not familiar. Therefore, I am going to repeat, in new form, the characteristics that you should be looking for in a good log-end, and let you evaluate a sample of the wood yourself.
1. Stability. Shrinkage and expansion are two sides of the same coin. Wood that shrinks a lot can expand a lot, and vice-versa. In general, dense, hard, heavy woods (usually characterized by small annual growth rings), will shrink more than light, softer, airy species. This may seem counter-intuitive, but, with few exceptions (such as hemlock), this is the case. Shrinkage is a cosmetic problem that can be addressed a year or two after construction, by a variety of methods described in the literature (and some of my other replies in this column.)
2. Insulation (R-value). Once again, the lighter airier softwoods perform better as insulation. Dense heavy woods are more like stone: they are good heat storage capacitors (thermal mass), but also transfer heat rapidly (poor R-value.)
3. Consistent dimension. By this, I refer to a log-end maintaining a consistency of size and shape from one end of it to the other. If there is a severe twist or taper to a majority of your log-ends, this will be a very difficult wall to build. Further, because there is no chemical bond (and very little "paste bond") between wood and mortar, a wall built of irregular log-ends will be inherently unstable. Cordwood is strong on compression, but not on tension, even worse than other masonry units such as brick, block, or stone. So, log-ends cut from "bushy" or severely twisted or tapered species are a pain to work with and will not yield as stable a wall.
4. Rot resistance . Oddly, wood rot is hardly ever a species-related problem, if you pay attention to basic building principles: (A) Do not use punky or insect-infested log-ends, (B) Get the bark off, (C) Don't have log-ends resting against each other, which traps moisture, (D) Keep the first course of cordwood masonry well clear of the ground, and (E) Use a good overhang on the building, at least 16 inches. With regard to "D", I like to keep the wood two to four inches off the ground in dry or "normal" areas like where I live in northern New York, 8" to 12" in wet areas. In Mountain View, Big Island Hawaii (with 190 inches of rain per year), we kept the wood a full eight-inches off the footings (on a course of blocks) and there has been no ill effects to the cordwood.
5. Aroma. This one rarely comes into play, but some woods do stink, like the so-called "piss elm." I'd avoid 'em. Some aromatic cedars may seem like a nice smell in small doses, but I know of one lady who had a sauna built for her of strong incense cedar and she could not go into the stove room at temperature. There is a reason that moths do not attack woolens in a cedar closet!
So, readers with rare woods please cut a log-end sample of the wood you have in mind and evaluate it yourself, keeping the five criteria above in mind.
Q: My wife and I live in north central Missouri. We are wanting to add on to the house and the shop with cordwood construction. The only thing is that we have only oak and walnut, some cottonwood trees also, mostly all hardwood. I guess we could import some softwood but I don't know. What is your advise on this matter? Would cottonwood work?
A: Of the woods you list, cottonwood is the best choice. The hardwoods are much more prone to both expansion and shrinkage, I know, cottonwood is technically a "hardwood," as it is deciduous, but it is a "soft" hardwood by comparison with walnut and oak. It has the light airy characteristics we are looking for. It is more stable and has a better insulating value.
A: Oak has been used successfully. The danger is that unprotected dry hardwoods, such as oak, can take on water during construction (from rain, from water standing on the slab, etc.) and cause swelling of the wood, which, in turn, breaks up the wall. Even if you dry it quite a bit, the oak will probably still shrink anyway, but that is a problem that you can fix down the road. For all these reasons, I advise:
Q: I have recently purchased your book and am very excited to start and was wondering if poplar would be a very wise choice in building?
A: You don't say where you are from, so I am not sure which "poplar" you are referring to. In New York, "poplar" - often called "popple" - is similar to aspen, such as quaking aspen. As cordwood, it is a good choice: decent R-value and fairly stable with regard to shrinkage and expansion. In the south, Virginia and North Carolina, for example, there is a common wood called "tulip poplar," which is quite different. It is much harder and shrinks more. It can be used, but with more caution.
Q: Can you give me more detail on what precautions we should consider when using tulip poplar?
A: Treat the tulip poplar as you would any hardwood. It will shrink a lot, but, therefore, it is also prone to expansion. Do not over dry it, as wood expansion problems could occur. Work within the protection of a timber frame (post and beam framework). Do not build on a slab where water can stand against the first course (which will assuredly cause wood swelling and other nasty structural things.) If possible, use one of the more favorable species on the first course.
Q: Would you recommend Birch as a suitable wood for building a cordwood home? We live in Edmonton Alberta and this seems to be a common wood found in this area. There also is Poplar in abundance here as well. Recommendations?
A: Of two species or wood you have available - birch and poplar (which I assume from your Alberta location is quaking aspen and not tulip poplar) - I would consider the poplar to be the much better choice, because it is more stable (less shrinkage and expansion) and has a much higher R-value per inch of thickness. Poplar was used commonly in Manitoba as log-ends in "stackwall" houses in the 20s and 30s and many of these buildings are still in use today. Birch will not rot, providing the bark is removed, but it is subject to expansion and severe shrinkage problems. And it is a poor insulation. Of course, you should debark the poplar as well (easiest to do when the sap is rising in the spring). If your building schedule will allow it, it is good to dry the poplar at log-end length for a year. If you absolutely must use birch, bark it and don't over dry it, as nasty expansion (a structural problem) can occur. It'll probably shrink a lot, but at least that problem can be attended to a year or two after the house is completed. Oh, and one last thing: Dry the poplar in single ranks with the top of the cordwood covered but not the sides. Let the pile breathe, otherwise fungi are inclined to begin digesting your wood. Ventilation is the best preservative we have.
Q: I am preparing to purchase 3 acres in a burn zone in southern colorado. The pines are gone and there is a huge grove of aspens that died from the heat but are solid and still standing. Many still have the bark on them. My question is, after reading that the characteristics of cotton wood are favorable to cord wood construction would the Aspen render the same results. If so, what is the best natural preservative to reduce decay and waterproof?
A: The aspen is a good choice for cordwood masonry. Get the bark off, and cut it into your log-end length. Reject any pieces which might already be showing signs of deterioration. As with our northern poplar - very similar if not the same as quaking aspen - it is important to dry the wood in single ranks, the top of the rank covered, but not the sides. Finally, ventilation is the best wood preservative we have. I do not advise any other. And it meets your criterion of being natural. Cordwood gets wet and dry with rain and sun, but, thanks to cordwood masonry's unique ability to breathe along end-grain, the fungi - the little critters that cause wood rot - do not have a constant damp climate in which to propagate.
Q: Which of the following woods is best suited for cordwood construction, oak, pine or cedar?
A: There are a great variety of all three woods which you list in your question, so my answer must be very general in nature, and should not be taken as complete as I am leaving out many of the sub-species. In general, you want to use light and airy woods, as opposed to dense hard woods. The lighter weight woods will be better as insulation, and they will be more stable with regard to expansion and contraction (shrinkage). Here is a limited list in order of preference: white cedar, white pine, red pine, loblolly pine, red cedar, yellow pine, red oak, post oak, white oak, I would not use oak unless I had no other choice, and I would only use it (and the dense yellow pine) under the protection of a post and beam frame, with the roof already in place, and a good overhang. There are other good woods to use, such as spruce and quaking aspen, but I have limited my reply to the three large categories which you cited in your question.
Q: I live in northern Alberta, Canada. I would like to build a cordwood home and I am wondering what wood would be the best. We have a spot where there was a forest fire about 16 months ago. I have been cutting my fire wood there and I was wondering if I could use that wood to build with. There is an abundance of spruce and poplar. What would be the better wood to use if I could use it?
A: Spruce and poplar (quaking aspen) are both good choices for cordwood masonry. Fire-killed wood is also a good choice, particularly when the bark has burned off leaving nice clean wood, as we saw recently at Mesa Verde National Park in Colorado. A little charring can be removed quite easily and most of the log-end can be saved. Do not use deteriorated wood.
Q: I work in a pole yard and have access to stubs of treated lodge pole pine and western red cedar; will the treated sap wood cause any problems?
A: I would not use treated material for log-ends in a home, sauna or any place where people gather for a period of time. Maybe a garage or storage shed. Ventilation is the key to cordwood's preservation, but, it seems to me, that very ventilation will also promote the off-gassing of the various poisons used in treated wood. So you'll be ingesting a small amount of it with every breath. If you decide to use it despite my comments, you might want to look into a surface sealant, maybe two coats, that will keep the chemicals from off-gassing into the interior. But my disclaimer is that you are on your own, here. I wouldn't use it.
Q: I live in the Austin Texas area, and would like to build a cordwood home. The native trees on my property are live oak and scrub cedar. Can these be used in cordwood homes?
A: I am not familiar with these woods. I am familiar with some types of red cedar, and I have seen red cedar trees used successful as log-ends in Texas.
(Kelly) From my experience living in the West, and having read Rob's responses to other similar questions, I would say that the Live Oak is a very hard oak, and for this reason not as desirable as the Cedar, which tends to be a somewhat softer wood...although at the higher altitudes where the annual growth is so slow, even these woods can be quite hard. In any case, I would recommend the cedar over the oak any day, since it is also very rot resistant, whereas the oak is not.
Q: I have recently purchased 100 acres in Perham, Maine. There are plenty of natural resources on the property. I am wondering what is the best species to use in this type of climate?
A: I can say that in Maine you are, indeed, in the heart of favorable wood species. At the top of my list would be white cedar, followed not too far down the line by white pine and spruce.
Q: I plan to build a cordwood home in West Virginia and have tons of Virginia Pine that I'd like to clear out to allow the White Pine more room. I know pine in general is softwood, so I hope it is a reasonable choice for a cordwood home. Certainly must be better than all of the oak and hickory. If I cut the logs this May, how long do they need to dry or season before getting under way...or do I wait and cut during a better time of the year?
A: Virginia Pine has been used successfully for cordwood masonry. It would be best to season the wood (in log-end length) for a year before building with it. Cut it as soon as possible. Maybe the bark will come off easily in May, maybe not.
Q: Athena and I are building a sauna/utility room project here in the Gulf Islands of BC, Canada. We're staying fairly close to your sauna book plans (thanks, incidentally). We have found two excellent sources of wood. One is a local timberman who has 2 year old western red cedar about 12" minus in diameter. The other source is driftwood salvage - much red cedar but also spruce, yellow cedar and other fine woods. The wood from the lumberman is inexpensive but the driftwood is free and easy to collect. The lumberman's wood is very uniform in quality and appearance, the driftwood is variable but has loads of character. Here is my question: Does exposure to saltwater make driftwood unsuitable for cordwood masonry? I know that using saltwater to mix cement is a no-no, but does driftwood have enough salt in it to affect the mortar between the logs?
A: I have spent a lot of time looking through the driftwood on Vancouver Island, B.C. It always struck me that this would be a great source of cordwood. You could make a beautiful wall of it and I have to think that once it has been cut to log-end length and dried for a month, it must be very stable. No, I am not in the least worried about any salt that might be caught up in the wood. There won't be any salt on the part in contact with the mortar. I have heard of people building with driftwood before, successfully, but have lost the contact. I believe they used woods that washed ashore on the Mississippi.
Q: My wife's uncle has built a cordwood home and used telephone poles for his wood, before treated. Is this a good wood to use? I spoke with a place that has poles and their poles are Southern Yellow Pine, dried with approximately 30% moisture left in them. Is that to much moisture?
Q: My husband & I are preparing to build a post & beam frame home, with cordwood in-fill in Huntsville, Ontario. We have cedar, spruce & a variety of hardwoods, (oak, maple, etc.) on the property. Having read your book, we are aware that softwoods are the 1st choice. However, we wonder if we have the wood kiln-dried, can we use the hardwoods also? or do you recommend just sticking with the cedar & spruce?
A: Better to stick with the cedar and spruce. These woods are more stable and have a better R-value than the hardwoods. Kiln-drying will not help the hardwoods at all, would probably make matters worse.
A: We were down your way about 4 years ago. Did a cordwood workshop on South Island. I'm afraid I do not know the two species of pine which you reference, but pine is generally good. Choose the one which is lighter in weight. It will be airier and therefore have a better insulation value. And it will be more stable with respect to expansion and contraction.
A: I think that western red cedar is a good choice for log-ends.
Q: I am considering building a large work shop using cord wood. I live in the South Okanagan of British Columbia, Canada. The wood that I have available is Lodgepole Pine, Ponderosa Pine, Engelman Spruce, Western Larch, Sub-alpine fir and Douglas Fir. The lightest, airiest wood seems to be the Sub-alpine fir. What wood would you recommend that I use?
A: There are three kinds of shrinkage that can be measured in wood: radial, tangential, and volumetric. Radial shrinkage causes a number of radial checks to form in a round log-end. Typically, one of these breaks through and becomes the primary check. Now, with the stresses released, the radial shrinking causes the primary check to get larger while the other little radial checks can actually close up. Tangential shrinkage is what causes the round log-end to loosen up in the wall, manifested by gaps between the edges of a round log-end and the mortar. Volumetric shrinkage is what the name implies: total volume loss, comparing green to fully seasoned wood.
Although most of my experience with cordwood is in the East, I have worked with a few southern and western woods. Lodgepole and ponderosa pine, two of the species you have available, have worked well. Douglas fir can shrink quite a bit, but the samples I saw (in BC) were quite dense, probably coast Douglas fir. Interior north Douglas fir shrinks less. Although I have had no personal experience with the Engelman Spruce and Sub-alpine fir, they seem to be good choices based upon shrinkage charts for woods. Here are the species you listed, with their percentage shrinkage values, listed in this order: radial, tangential, volumetric. Lodgepole Pine: 4.3, 6.7, 11.1; Ponderosa Pine: 3.9, 6.2, 9.7; Engelman Spruce: 3.8, 7.1, 11.0; Western Larch: 4.5, 9.1, 14.0; Sub-alpine fir: 2.6, 7.4, 9.4; Douglas Fir (coastal): 4.8, 7.6, 12.4; Douglas Fir (interior north): 3.8, 6.9, 10.7. Based on these numbers, your most stable woods are the Sub-alpine fir, Engelman spruce, and Ponderosa pine. You probably want to avoid the Western Larch and coastal Douglas fir.
Remember that expansion is the other side of the shrinkage issue, and expansion can actually break up your wall. To sum up: You have an excellent selection of available woods and it is okay to mix them. It should be safe to dry them as long as your schedule allows. Wood dries much faster in log-end lengths.
Q: I am from Iowa and have seen the suitable woods list. I am going to take down three large Chinese elms this winter and wonder if this wood has ever been used. Also, can different types of wood be used in the same house. Just found out about cordwood homes and am very excited about this building method.
A: Chinese Elm is a new one on me and is not listed in my chart of hardwoods. I can find American, Cedar Elm, Rock Elm, Slippery and Winged. We also have something up here in the Northeast known locally as "piss elm." It stinks. Most elms I am familiar with are stringy, hard to split and shrink a lot. They are fairly dense and, therefore, poor on insulative value. Perhaps your Chinese variety is different, but if it's a true elm, I'm not too optimistic about it. (If any readers of this column can shed any light on Chinese Elm, please ring in!)
Your second question is much easier to answer. Yes, there is nothing wrong with mixing different species of wood in a wall. My only advice on this is too try to maintain a consistency of style, pattern and texture, as you would want to do in any case.
Q: I began gathering loblolly pine for a cordwood house in the spring of 2001. I spent 2 years gathering & stacking and have been peeling it since. I plan to build a house in about another year. The wood is located about a mile south of the Ark/LA state line. Do you think the wood is too dry? What steps could I take to prevent possible expansion? I thought about maybe wetting the wood right before laying it up in a wall?
A: I don't think that wood expansion is a very great danger with the loblolly pine. In my somewhat limited experience and knowledge of loblolly, it seems that it does not have the density of Southern Yellow pine and the hardwoods, so expansion should be very much less. Still, it will be very dry when you use it (good to prevent shrinkage), so I would exercise these basic precautions against the danger of expansion:
Avoid the possibility of standing water against the first course. Either don't build on a slab immediately (footings only) or build under the cover of a post and beam frame (and roof), always a good idea in any case. If you want a slab, shoot it through doors and window openings after the cordwood work is completed and the roof is on.
Do not attempt to out-guess the rate of expansion by soaking (pre-swelling) the dry wood. You can't outsmart a log-end. Also, even if you were successful in avoiding expansion, pre-swelling would certainly cause shrinkage later on. With just a bit of care, here, you should wind up with a cordwood wall that will not require any treatment for shrinkage.
Q: I have access to a lot of basswood due to woods being cleared out. Can I use basswood in cordwood construction if I use the double wall technique described in your State of the Art book?
Q: We are looking into cordwood construction for a public bathroom in our quaint German town of Cole Camp Mo. The dept of conservation has a hedge or Osage Orange tree removal program. Is this wood suitable? I have seen the fence posts of this tree in perfect shape after 50 years in the ground. Heavy too, this stuff acts like concrete and is totally impervious to bugs. What do you think?
A: I think that the osage orange will work fine in your application. Deal with it as you would any dense hardwood: (1) Don't over dry it. (2) Keep it off the ground. (3) Build within a post and beam frame, under the protective cover of the roof.
Q: Do you think that scrap 2x4 pieces would make a good material for cord style walls? I have a source of cutoffs, 1 foot lengths, for 10.00 a pickup load.
A: Many people have used scraps of dimensional lumber as cordwood: 2x4s, 4x8s, "beam-ends," etc. Finished 2x4s (actually 1.5" by 3.5") are fairly small in section, so it will take an awful lot of hem to build a wall. And the wall might tend to be a bit boring to look at, but, yes. it can be done.
Unfinished lumber, such as full-sized 2x4s, are very absorbent through the edges of the pieces. They will rob moisture from he mortar very rapidly, causing lots of mortar cracking. There is also the very real possibility that the moisture will cause a swelling of the pieces, leading to uplifting of the wall. For his reason, I always recommend the application of a water seal type product to all surfaces that will come into contact with mortar. Apply it at least a few hours ahead of time, so it has time to fully dry. This water seal will greatly reduce the transfer of moisture from mortar to wood, and will help reduce the probability of mortar shrinking and/or wood swelling. The advantage of full dimensional 2x4s is that you get 8 square inches of wall up each time instead of 5.25 square inches, more than 50% better coverage per piece.
Finished lumber is less absorbent than rough-cut, because it is planed. I am unsure if he water seal is necessary, but it certainly can't hurt. You could test a small section without it, if you like, say a 3' by 4' section. Let it set for a weekend then examine it for wood expansion and mortar shrinkage. To make sure you know the difference, take a very accurate measure of the height of the wall in three or four places, and compare that measurement a week later.
To give the wall interest, why not put a large piece every two or three feet, like a large beam end, or even round log-ends.
Q: I live in west Texas where just about the only tree we have in abundance is the mesquite. It is a very dense hardwood, but from what I have been able to find it is extremely stable. Is it an appropriate tree for use in cordwood construction?
A: I have heard (anecdotally) of mesquite being used successfully. Also, a student brought a sample to the building school, and it looked like it could work. If it is "stable," as you say, that is a plus. Nevertheless, take the same precautions you would use for any dense hardwood, as outlined in some of my other responses in this section. Finally, with any wood, try to choose sections which are straight and maintain a consistency of cross-section from one end to the other. Avoid gnarls, severe bends, crotches, and other irregularities. This just slows the work down. Exception: If you have a really beautiful irregular piece, it may be worth working around it with other odd shapes to make it work. I only mention this as I am wondering if mesquite is a wood which will give you regular cross-sections.
Q: I went through the "What type of wood to use" section of Q&A. I didn't see any questions from people in my area, the great north west. I would like to know if alder and cottonwood are good choices for a cordwood home. I live in the puget sound region where these two species are abundant. But I am looking to construct a home in the central part of the state; where it is much drier.
Q: I live in Hillsboro Oregon which is approx 18 miles due west of Portland. I have long contemplated securing some land in the nearby coastal mountain ranges. These areas abound in Doug Fir, Alder, some Spruce, and limited Western Red Cedar and assorted hardwoods- Maple, Vine Maple, White Oak, White Ash. I find cordwood construction very enticing. I do have a working knowledge of local construction and am adept at working with my hands and power/hand tools. Do you have any specific knowledge of using split or whole ALDER as mentioned above? It is considered a "soft" hardwood. It is very plentiful, grows very fast, splits easily when green, is relatively light weight when dry and has a light textured bark. Some of the mature trees are harvested for furniture but as this species grows so fast it is considered by some a "trash wood" and is often cut down and burned in large scale logging and used some as firewood. Doug Fir is King around here for logging purposes but it seems not that good for cordwood construction. Can/will you comment?
A: Douglas Fir varies a great deal in density depending on whether or not it is coastal or mountain. In general, the less dense varieties are best. Spruce is a good choice. I am not personally familiar with the alder, but your description of it sounds favorable. You say, "It is very plentiful, grows very fast, splits easily when green, is relatively light weight when dry." These are generally good qualities for cordwood. I would tend to avoid the hardwoods you list, as long as you seem to have other more favorable choices.
Q: How "wood" eastern Hemlock in Maine work in cordwood?
Q: I am delving into the world of cordwood construction. I live in the southeast. After going through the Q&A I did not see anything on the value (or lack of it) of sweetgum as cordwood for building. I have lots of it. It is a nuisance, but to be able to make use of it instead of killing it (I hate sweetgums) would sooth my conscience. So, how about sweetgum and elm?
A: We conducted a workshop a few years back in western North Carolina, and the only available wood was sweetgum. The walls of the post-and-beam framed barn were just 8 inches thick, because the building was framed by 8-inch square timbers. The workshop host had all his sweetgum barked and cut to nice neat and tidy 8-inch lengths, with diameters ranging from about 4.5" to 8". As there were no smaller pieces (which we like to fill in where there might otherwise be large mortar joints), my son and I decided that we would split some of the rounds into smaller pieces. How difficult could it be to split 8-inch long logs, right? The answer: next to impossible. This attractive hardwood is virtually impossible to split, and when you do succeed, the underside of the log (where the axe comes out) is a gnarled mess of fibres, a nightmare to point. In other words, it splits like elm, the other wood you mention. Fortunately, our host was a woodworker and had a large band saw, and we quarter-sawed a number of smaller pieces to fill large gaps. This worked very well, and the sawn log-ends maintained the clean and tidy appearance of the rest of the wood. The wall was beautiful.
I have said that sweetgum is attractive, and I would add that it is nice to work with, outside of the splitting part. However, it is a dense hardwood, and is prone to great shrinkage. I brought a couple of samples home with me, and the larger 4.75" diameter
My advice is to use sweetgum as cylindrical log-ends, not splits, and be sure to keep branch pieces right down to 1.5" in diameter. Dry it a year in single ranks, if you can, and then treat it as a dense dry hardwood, to wit: Work in a protected application, such as under the roof of a completed timber frame. Don't build on a slab which can collect water and cause it to stand against the cordwood. (The danger here is wood swelling, which can break up the wall.) Either build on a course of concrete blocks, or pour the slab later, after the walls are done.
Elm doesn't perform any better than sweetgum, maybe worse. If anything, it is even stringier, and some of the elm stinks pretty bad, whereas sweetgum has much less odor and is not unattractive. Try to find some less dense woods, such as loblolly, to use for the first course or two, keeping the sweetgum (and elm) up a little higher for expansion protection. (Cordwood expansion problems always seem to originate "down low.") Elm and sweetgum make good firewood, as long as you have a powerful hydraulic splitter available.
A: Tamarack (or larch) is more than suitable, Robert. I saw a beautiful cordwood home made of it in western New York. You can mix woods, too. I'd use the tamarack before the balsam fir.
A: I have never built of locust. Most dense hardwoods tend to expand and contract quite a bit. You seem to think the locust you have is stable, but before embarking on a big project, I would do a test panel of - say - three feet by four feet. Then watch it for a couple of weeks. Expansion will manifest itself by mortar cracking between all the log-ends. Shrinkage isn't that big a deal. There are lots of ways to deal with that. In any case, I would build in a protected application, where water cannot stand next to the first course of cordwood.
A: As you are from Ontario, I presume that you are referring to balsam fir and not balsam poplar. Balsam fir is a pitchy wood, from which turpentine is made. The aroma can also be reminiscent of Christmas wreaths. We have it on our property in Northern New York, and I have had many occasions where I have had to cut up fallen trees. However, I have never used it in a cordwood wall, so I cannot give first-hand experience that way. My sense, though, from cutting it to 16" logs, both round and split, is that would be about as good as the other two woods you mentioned: poplar (quaking aspen) and basswood. I have the most experience with basswood, and slightly prefer it to poplar. It splits cleaner.
Hoping for some further insight, I called my good friend (and cordwood writer, builder and teacher) Richard Flatau in Wisconsin, to get his view, which, it turned out, was virtually identical to my own. He agrees that there isn't much difference between the three woods that you mention. They should all be seasoned in the same manner (and time) as the white cedar or white pine. The balsam fir is very pitchy. We would not recommend it in a sauna. You can do a lot about the pitch by getting the bark off early or by splitting the wood, although it tends to split erratically.
Why not try all three and give us a report? I don't think you can go too far wrong.
Q: I live in Astoria, Oregon in the great pacific northwest with a very wet climate. The most common trees we have available are red alder, douglas fir, sitka spruce, hemlock and some shore pine.
A: Sitka spruce may be the best of the woods you list, although the Douglas fir might be okay, too. I do not know what shore pine is, and have never seen it listed. Perhaps it goes by another name?
Q: I'm considering a cordwood building in New Zealand and have an available supply of the following three woods: Eucalyptus Globulus, Eucalyptus Niten, Acacia Delbata. My question is; do you have a preference, or can you give some advice on how I might determine if these breeds are suitable for cordwood?
A: I am afraid that I am not familiar with the woods you name. In general, you are looking for the airiest (least dense) wood for cordwood masonry.
Q: My wife and I have 38 acres of mountain property in the Blue Ridge (Roanoke, Va) and are relocating there from Wisconsin. The property is full of small red oak 6-16" in diameter. I know this isn't the best choice for cordwood homes, but will it work?
A: You know that red oak and other hardwoods are not the first choice for cordwood. But if that is what you've got, and you really want a cordwood home, you will have to make it work.
Don't dry the oak too long, as it will shrink anyway, even if you dry it a year or two. The danger with the dense hardwoods is swelling, which can break up the wall. Shrinkage is a cosmetic problem that can be attended to after the house has been heated for a year or two.
Build under cover, such as within a post-and-beam frame with the roof on.
If you really want a slab, consider pouring it after the cordwood is completed. Build the cordwood walls on the footings, so that rainwater cannot on the slab and stand against the bottom course, which will cause swelling.
Put a good protective overhang on the building.
If you manage to get a couple of courses up, and keep the work dry, apply a coat of water seal to the wood and the mortar. This clear treatment will prevent a tremendous amount of water absorption. I would just do it on the inside, if you are building on a slab.
The main consideration is to protect the first course from standing water.
Another trick in this regard (assuming that you want a slab) is to lay down a course of 4" solid concrete blocks on the footing, getting the cordwood work an additional four inches off the slab. Or even thicker, such as eight inches. Build the cordwood on this concrete block course. You may went to place extruded polystyrene insulation (such as Dow Styrofoam) on the exterior of these blocks to prevent "energy nosebleed." Protect the foam with a cementitious coating.
Q: I see that you've stated that trembling aspen is a suitable wood for cordwood building. Is it also a suitable material for the post and beam components of a home? If so, what advice do you have concerning drying time and procedures?
A: (Kelly) I have some limited experience with quaking aspen, which is probably what you are referring to, as post and beam elements. This wood is extremely heavy when green, as it holds a tremendous amount of water in the sap. Once it dries, which would take several months in an arid environment, it is a relatively light, soft wood. Debarking while still green will assist with the drying procedure. I used several beams of roughly 6 inch diameter in my earthbag house and they served the purpose fine, although there was some minimal checking that didn't affect their strength. Aspen would not be my first choice for this purpose, but if this is what is available, it can be pressed into service.
Q: I live in Texas and plan to build a cordwood house in central Texas. I have a lot of post oak and yaupon on the property. Hopefully someone could tell me their thoughts on cordwood construction with yaupon, The cordwood wall would consist of logs 2" to 3" in diameter. How strong would this wall be compared to larger diameter logs? Is yaupon too much a hardwood or too tight grained?
A: I have never heard of yaupon, so cannot comment on it. You seem to fear that it is "too much a hardwood" and "too tight-grained." This seems to be the case with most of the woods in central Texas. You can use them, but you need to take the precautions that I have outlined several times in this column. As for using 2" to 3" diameter log-ends, well, that shouldn't be a structural problem. But you are going to be doing a lot of picky work. You will probably use more mortar, too, but that is not really a problem, either. In point of fact, the mortared portion of the wall has the superior thermal characteristics.
Q: I live in Southwest Michigan and am currently deciding where to purchase land and create my own remote secluded private utopia. I just purchased your book on Earth Sheltered Housing. The Cordwood method looks pretty good to me. I have found 15 acres that is an old apple orchard with many acres of apple still standing. Would this be usable wood for construction?
A: No, I would not consider apple to be a suitable wood for cordwood masonry. It has a lot going against it. It is hard to bark, is often gnarled and twisted, and has a high sugar content. I am afraid of deterioration in the wall, fungal growth and a possibly sickly smell. We also have old apples on our property, which I occasionally clear for one reason or another. I would not dream of using it for cordwood masonry, but it does make excellent hot-burning firewood. Sorry I can't be more encouraging.
Q: We live in Southern Spain and were thinking of some cordwood elements in our new House. I am wondered if you could tell me if you think olive wood is a suitable material?
A: I'm afraid I have no personal experience with olive wood. The olive trees that I have seen seem to have been somewhat gnarled and twisted, but I suppose that is true of many orchard trees. It is good if the wood is somewhat straight, which saves on mortar and building time. I also have a fear that olive is a dense hard wood, but I could be wrong about that. (I recently saw an old olive grove on Santa Cruz island off Malibu and the trees were still quite small for their age, suggesting small tight annual growth rings. The National Park service had cleared some of them to a pile, but, alas, I did not examine them carefully. Now I wish I had.)
Q: I'm considering using cordwood masonry for a market-type building I'm designing for the Niagara (Southern Ontario) wine region. Could I use old weathered grape stakes that have been used in the vineyards? Also, should I be concerned about possible vapours given off by treated stakes? Grape stakes are available both treated and untreated, but farmers are much more likely to donate treated stakes as they cannot be used as fire wood - they give off toxic gases only when burned. I'd appreciate any advice you have to offer!
Q: I'm trying to find information on building a single, dry stack wall out of cordwood. This is for an art gallery, and is meant to be semi-permanent with the flexibility to take wood out or add it back through the seasons. I am looking for advice regarding species, moisture content, and what type of other materials are okay to be in contact with the wood - especially regarding corrosion issues (aluminum, etc.).
A: I presume that your intent is to build this wall without mortar. And I am guessing that you will be building it in a protected (covered) application. Assuming this is the case, my gut reaction is that you want clean, fairly dry wood. It should be barked of course, as this is part of keeping the wall clean. I don't think the species matters very much and it might suit your intent by mixing species, maybe rounds and splits. You don't mention the thickness of the wall, but, whatever thickness you decide on, it is probably a good idea to have your wood all the same length, give or take a quarter inch. Also, for stability, you will want log-ends that maintain a regular shape from one end through to the other. This eliminates severely tapered logs-ends and pieces with branches coming in. Have fun with it.
Q: I recently reviewed an old article from "The Mother Earth News" from 1980 about growing hybrid poplar trees that are available from a nursery in Pennsylvania (the family still runs the nursery) for a steady supply of firewood. The trees are fast growing and would be harvestable for firewood in about four years. I had the thought that if someone were to purchase a section of land that was formerly farm field, planting these hybrid poplars would be a great way to come up with cordwood construction material at some point down the road. It would serve the dual purpose of providing much needed trees for habitat and shade. Although a monoculture stand like that is not necessarily the best for ecological diversity, over time the trees could be thinned and interplanted with other species or an understory of berry bushes. The trees can be cut and the stump will grow a new tree without any planting. From all that I've read from "Ask the Experts" column on your website, this seems like a good choice for cordwood construction since it is not too dense and should not shrink or expand too much.
A: The late great cordwood teacher and advocate Jack Henstridge had the same idea 25 years ago. He liked to say, "Grow your own house in 5 years with hybrid poplar." Another fast growing wood which has been used successfully in this way for cordwood houses is powlonia. I have friends in Alabama who used it very nicely. Be careful, though, it might be considered by some to be an "invasive species."
Q: Is locust post (untreated) suitable for building small structures, ie sheds, barns ranging 20 x 10 or smaller?
A: Yes, as long as you are not expecting to heat the building, as locust would have a very low R-value. To lower the risk of wood expansion, take the same precautions that you would use for any other hardwood.
Q: I am looking at building a cordwood house in West Tennessee and this is kinda a two-fold question. As for species of tree to use for the walls, I have the following options: loblolly pine, shortleaf pine, Virginia pine and eastern red cedar. Which would be a better choice for a mid 90s summer and humid, and lows in the 20s to mid teens for winter temperature? Second, what would be a good length of log to use? 16"? I would like to use 24" but those size timbers for post and beam will be hard to come by.
A: Being from the north, I am not familiar with the shortleaf pine, but a comparative list of woods shows that it has a similar shrinkage to the loblolly, which has been used successfully with cordwood masonry, so I think you will be okay with it. Virginia pine is another good choice, with slightly less shrinkage. The eastern red cedar has the least shrinkage of all the woods you mention. Frankly, I think you could build with cordwood masonry in Virginia with any of the wood species you list, and there is nothing wrong with mixing them. Try to maintain consistency of texture and style throughout the building.
Q: We have recently purchased land on Lake Marion, SC. We have been reading about cordwood construction for a couple of months and are very excited to learn we can build a home without a huge mortgage! Our place though is populated with ONLY OAK! We have read all of your suggestions and understand the alternatives when using hardwoods. We are also cutting down trees at our present home to give it more curb appeal. The tree type in question is Silver Maple. Medium to fast growing and the bark comes off easily by hand! But how is it on shrinkage? And what is the best way to judge the amount of shrinkage? It is a beautiful white wood with medium growth rings.
A: Being from the northeast, I am not familiar with silver maple. So I went to page 33 of my old book Cordwood Masonry Housebuilding, where I have a chart reprinted with permission from Sterling Publishing's The Encyclopedia of Wood (1989). I was encouraged to learn there that silver maple is one of the best of the hardwoods with respect to shrinkage: Radial shrinkage is 3.0%, tangential shrinkage is 7.2% and volumetric shrinkage is 12.0%. These are pretty good values, but you would have to compare them to other hardwoods and softwoods to make sense of them.
Q: You say the yellow pine is denser than what good cordwood should be, and not to use hard woods unless you must. So I want to know if yellow poplar or the yellow pine would be better. I have plenty of poplar and they are straight and only a few limbs. Pine is knotty and twisted around here. I know that the walls need to stay dry to keep moment to a minimum. I'm not worried about the wall getting wet since it will be under a 8ft porch.
A: Longleaf pine, also known as yellow pine or southern yellow pine (technically a softwood) has published shrinkage values as follows: Radial, 5.1%. Tangential, 7.5%. Volumetric, 12.2%. Yellow poplar, technically a hardwood, has very similar values: Radial, 4.6%. Tangential, 8.2%. Volumetric, 12.7%. Variations in samples, based upon growing conditions, really make these two woods virtually identical in their shrinkage (and expansion) characteristics. You could get very slightly larger primary checks in cylindrical log-ends and maybe a little more edge shrinking with the yellow poplar, but this really falls within the margin of error for different field samples taken.
Expansion is like the other side of the coin: What shrinks a lot will swell a lot when it takes on moisture. What goes up, generally comes down. With either wood, you will want to pay attention to the special care which should be used when using dense woods, described in some detail in several other of my answers in this column.
Q: I have been looking into building a cordwood addition on to our log home. We have an abundance of osage orange trees. I read an earlier question about the osage orange being used and it said to treat it as any other hardwood. Osage orange does not rot even in the dirt or ground and I find older down trees from 10 to 30 years old laying over with the bark completely off and the tree is like stone when I cut it for firewood. I also have an abundant source for red cedar but it seemed like a lot of extra work to strip the bark from cedar.
A: We have just finished a workshop during which we used some very hard hardwoods (ohia and guava). Also Cook's pine. A house built in Hawaii 5 years ago used a variety of woods, and suffered no shrinkage or expansion problems. A local wood turner told us that the Hawaiian wood is stable because of the constant climate, and no fast and slow growing seasons.
Q: I'm building some cordwood walls in Jamaica, west Indies and would like to have your opinion on the best suited wood ( we have local cedar, mahoe) would I be better off to import some white cedar. Also how can I use driftwood in the wall for interest?
A: I would certainly go with local woods, as opposed to bringing wood in from off-island. Apart from economy, the local woods are likely to be more stable. Also, the importation of quantities of non-native species (and the possible bugs therein) could be very dangerous from an environmental standpoint. Yes, you can use driftwood as special features. Others have done so. I have even heard of one or two cordwood buildings (in B.C. and on the Mississippi, as I recall) that were done entirely from driftwood. You could use interesting shapes or worn pieces as special design features, and even install the wood "sideways."
Q: I would like to build a cordwood shed as well as a cordwood sauna, but all the trees on my property are white oak with a few pines. Is there a local supplier in Massachusetts for cedar? or can I use the white oak?
A: You would probably have to haul white cedar by truck 4 or more hours, depending on where you are in Massachusetts. Between the white oak and the pine, I would go with the pine. Do you know what kind it is? White pine is quite good, almost as good as the white cedar. If you absolutely must use the oak, start with the pine down low, first couple of courses. Then start introducing the oak. Read the dozens of posts in this column that tell about the special considerations for using dense hardwoods in cordwood masonry. Particularly, don't over-dry the oak, which could cause expansion problems later on.
Q: Is Blue Gum (Eucalyptus grandis) suitable for cordwood building. It has been given invasive species status here so availability is not a problem.
A: We have used Eucalyptus in Australia, but there are over 200 varieties. It wouldn't be my first choice, preferring a lighter-weight wood, but it can be used.
Q: We have well over 90 standing white ash dead from the ash borer. Can we use it to build a cordwood home?
A: Yes, if the ash borers have abandoned ship. I think they leave, once they have killed the tree, as they move on to their next stage of life, but you might want to check with your local co-operative extension or equivalent agency.
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