In Memory of Mike
Friend Mike helped a lot of people to avoid a life of economic serfdom, whether they built one of his earth-sheltered homes, or not. We kept up with each other over the years and visited each other in New York and Idaho. I sold a lot of his $50 and Up and Earth-Sheltered Solar Greenhouse books, for which I wrote the Foreword, ending with: “I’ve always prided myself on sharing information on low-cost green building techniques in my books, but Mike outflanks me every which way from a Mexican Sunday: the guy builds cheap, dirt cheap, and I say this with begrudging admiration. After too long a remission, the happy hippie hobbit surfaces once again to improve the nick of time.”
Mike will continue to resurface every time someone picks up one of his books. Incidentally, while all his books are well-written, his best and most entertaining literature is the wonderful One Mexican Sunday.
Jaki and I will miss you, buddy!
Rob Roy
Hi J.T.:
Last time I looked, it was still May, although we had July-like weather today. Jaki and I look forward to seeing you at the Cordwood Worksweek, July 15-19. We'll make sure all the cobwebs have been cleared out of La Casita. To all others: We still have room for this workshop, although the guesthouses are all booked. There is room for a single person in the Earthwood house on a B&B arrangement. Get info at www.cordwoodmasonry.com . Click on Workshops for descriptions, and Registration to register. Or call us at 518-493-7744. Rob (and Jaki) Roy, Earthwood Building School.
Paul Wheaton and Adrien of Permies.com suggested I start a new topic about our cordwood workshops this year. This is my first "new topic" so please bear with me while I try to put on some pictures to flesh out the text. Adrien suggests a new posting for each workshop, so that is what I am going to try to do. In the meantime, I can tell you that we have cordwood workshops very soon in Marcellus, Michigan (just 20 miles south of Kalamazoo) May 10-12. Also, cordwood and earth-sheltering workshops at Earthwood, West Chazy, NY May 24-27, July 15-19, and August 30-Sept. 2. Finally, we have a 5-day Comprehensive Workshop (Timber Framing and Cordwood Masonry) at Mondovi, Wisconsin (near Eau Claire) June 25-29. You can get all the Info (descriptions, tuitions, etc) at www.cordwoodmasonry.com Once there, click on Workshops for descriptions and Registration to register. More coming - including pictures - later today, I hope.
Thanks for the kind words about our Open House tour, Allen. It may interest Permies followers in the NE that we are doing another free Open House on Saturday, May 4th, 10 am to 4 pm. It is at Earthwood Building School, 366 Murtagh Hill Road, West Chazy, NY. You can see earth-sheltered housing and living roofs, about a dozen different cordwood buildings, a strawbale guesthouse, the masonry stove, bicycle-powered water system, off-grid solar system and an astronomically aligned stone circle. Directions are at the Newsletter page of www.cordwoodmasonry.com This will be the last Open House until October.
Hi Alice-Lynn:
Building a small practice building, like a cordwood playhouse for the kids, is a great idea. Make an inexpensive mistake there instead of a very expensive one on the main structure. It sounds like you are at the very beginnings of your researches, and, before you build, it would be a good idea to obtain either a book or a DVD on the subject, or both. Then, if all goes well, and you like cordwood, consider attending a workshop where you can learn to do it much more quickly and with a higher quality: balance, pointing, etc. Our Earthwood website is just one of several out there where you can get on the trail. Go to www.cordwoodmasonry.com Then click on Books and Media. Or Workshops.
Good luck!
Dear Alice -Lynn:
You say," I'm a little concerned about thermal bridging. If extra insulation is added on the outside, then it loses it's charm, but if it's added on the inside then there goes the thermal mass... Unless I'm missing something. I probably need to just buy the book. =] Also the bulk of the trees on the land are oak, birch, and white pine, and I vaguely remember reading somewhere that those are bad for cordwood building."
The log-ends themselves have characteristic of both insulation and thermal mass. There is very little thermal bridging. In the north, we like to use northern white cedar because of its high R-value of about R1 per inch of thickness on end grain. But other woods work well, too, such as white pine, spruce and quaking aspen. The mortared portion of the wall does not ahve any thermal bridging because of the insulated mortar space between the inner and outer mortar joints. Of the woods you list, the white pine is your best choice. And, Yes, that is a fine cordwood home that you give the URL for.
Cj: I am unclear as to whether you are asking for pics of Earthwood or of Yone' Ward's house. At any rate, I don't know how to put pictures on these posts. But our Earthwood website, www.cordwoodmasonry.com , has several photo album pages that might be of interest to you, including pics of the various buildings at Earthwood Building School. See also our Earthwood Building School Facebook page, which my wife, Jaki, maintains with more current stuff.
Frances and CJ: Under Green Building, I have posted replies on the following topics during the past 2 or 3 days: Cordwood - Green Buiding, Earth Sheltered Houses Questions for Rob, R-values, Building One's Own Home, and Poplar. I assume that it is best to answer questions in their specific topics, so that is what I have done. I am new at this website! But if you want to see hundreds of cordwood questions and my replies, go to http://greenhomebuilding.com/QandA/cordwoodQandA.htm . At Green Home Building, I have done a long-running Q and A on cordwood masonry.
Hi Jay: Thank you for the very interesting post! As for the part that portland cement (or concrete containing portland) plays in the discussion of cordwood masonry, it is, once again very important to differentiate between horizontal log construction and cordwood masonry on end-grain. They are like apples and oranges. Moisture can certainly be trapped between chinking and horizontal logs, as you point out, but not so in a properly built cordwood wall, and certainly not in any of dozens of cordwood buildings I have been involved with over the past 37 years. My mantra to keep it that way is: (1) Use sound (not punky) wood in the first place. (2) No log-ends touching each other (wicks moisture). (3) Use a good overhang. (4) Debark the log-ends. and (5) Keep the cordwood masonry clear of the ground.
Hi Frances: In my (perhaps biased) view, cordwood masonry has a unique and wonderful combination of insulation and thermal mass. In terms of comfort and performance, what we observe is a house which keeps a steady temperature. It takes a long time to change the temperature of something so massive. We normally think of this as a heating advantage during our long North Country winters, but the house can also store "coolth," my made-up word for heat at a lower temperature, a handy characteristic which helps keep the house cool during our short North Country summers. I don't know what "thermal mass leverage" is, but the effect of the mass is substantial. If you are looking for facts and figures, the best I can do for you at the moment is to say that a cordwood masonry wall, including the double mortar joint and insulation, will weigh somewhere between 40 and 60 pounds per cubic foot, depending on the density of the wood, the percentage of mortar, the thickness of the mortar, etc. The value of thermal mass is hotly debated by intelligent people. All I can say is that it seems to work for us.
Victor and Walter: Firstly, it is important to know what wood we are talking about when we say poplar. There are tulip poplar, Lombardy poplar and - in the north - quaking aspen is commonly called poplar. In Northern New York, the quaking aspen is called "popple." To be clear, its scientific name is Populus tremuloides. This is the one I say is good for cordwood masonry. Wikipedia says: "Populus tremuloides is a deciduous tree native to cooler areas of North America, one of several species referred to by the common name Aspen. It is commonly called quaking aspen, trembling aspen, American aspen, Quakies, mountain or golden aspen, trembling poplar, white poplar, popple, and even more names. The trees have tall trunks, up to 25 m (82 ft) tall, with smooth pale bark, scarred with black. The glossy green leaves, dull beneath, become golden to yellow, rarely red, in autumn. The species often propagates through its roots to form large groves."
We have been using quaking aspen - which I think is what you are both referring to - as cordwood for over 30 years without a problem. Scores of other builders in Canada and in the US have used it for a long time, as well, including a number of "black and white house" built in Manitoba in the 1930's. Used the way we do in cordwood masonry, showing the end grain on both sides of the wall, the breathability of the poplar is exactly what protects it from rot. I think it was Mac Wells who said "Ventilation is the best preservative we've got." Rot is caused by fungi. If the constant damp conditions necessary to its propagation are not present, the fungi cannot get a foothold. Concrete does not cause rot in wood. Constant damp - and fungi - is what causes rot. Actually, two log-ends touching each other trap moisture far more than a lo-end touching its mortar matrix. I believe the popular (not poplar!) misconception in this regard, expressed by Walter's comment - Contact with concrete will speed up the rotting vs simply sitting in a wood pile - is based upon bad experiences where concrete forming boards, when left in place too long, rot out. They rot out because moisture is trapped between the concrete and the poorly breathing side grain of the forming boards, generally down at ground level.
I like quaking aspen because it has a good R-value. If not seasoned properly in single ranks, covered on the top, but not the sides, the ends can blacken, thus the "black and white" houses. The black is bacteria digesting the wood sugars. After curing, the black can be eradicated with a 30% bleach solution. Problem with that is that the log-ends are also "bleached" of some of their natural cream color. A better solution, I have found, is to clean them with a 4500-rpm circular sander. Makes the ends look very nice indeed. In either case, the black will not return.
Finally, with aspen, I prefer using a variety of different sizes of rounds, as opposed to split log-ends. Here's why: The axe makes a nice clean cut on the side of the log it enters, but, by the time it exits the log, 16" or so later, the split is ragged, not clean. Makes it hard to point the mortar. Hope this helps clarify.
Hi C. Green:
Your pine would be the best choice for cordwood.
We do workshops here at Earthwood Building School in West Chazy, NY in late May, July and late August/early Sept. For complete information, go to www.cordwoodmasonry.com and click on Workshops, then Register for Workshops. We are located near Plattsburgh, NY, about 5.5 hours' drive from Avon, CT, where my brother lives.
We have lakefront land for sale on Chateaugay Lake, about a half hour's drive west of Earthwood, in case that is of interest to you. 56 acres, 1500 feet on the lake. Beautiful land and lake.
Rob
C. Green: Cordwood Building: The State of the Art discusses various techniques which have worked all around the country; in fact, all around the world. From place to place, there are basically two different variables: climate and species of wood available. These variables are discussed in a generalized fashion: warm climate versus cold. wet versus dry, dense woods versus light and airy woods. Obviously, at workshops, we can answer specific questions. If you tell me where you live, and what woods you have, I might be able to help a little more.
Oops! Typo city. My recent reply said 400 SF actual usable. It is actually 2400 SF, now corrected above (I hope!) Sorry about that. Your home seems very energy-efficient, indeed!
CJ: The gross square footage, footprint including thick walls, is 2800. But we lose 400 SF in the 16-inch thick walls, so the actual usable area, that you can run around in, is really about 2400 square feet - or "round feet." (It is, after all, a round house.) We use a bit more than four full cords (about 12-plus face cords where the logs are cut to 16 inches.)
I notice that you are in Vermont. We are right across the lake in Northern NY. You would be welcome to come to our Open House on Saturday, May 4th, 10 am to 4 pm. For more info, go to www.cordwoodmasonry.com Click on Newsletter and scroll down for directions.
Thanks for your kind comments, Brian. Yes, comfort is subjective. To be more specific, we keep our house to around 72 degrees throughout the year. (We’re in our 60s!) The house mass means the temperature is very slow to change, up or down. It is a giant capacitor.
Most of our students are owner-builders – or potential owner-builders - who generally want to build their cordwood or earth-sheltered (or combo) homes out in the country, all climates, from Georgia to Alaska. They may or may not have to go through the local permitting process, but, if they do, it is not usually a problem. They are generally not involved with serious energy code issues. Once again, the bottom line – for me - is fuel use. To clarify, the $600 is roughly what we spend on firewood each year, some years a little more, some a little less. We use only wood and passive solar for heat.
I know of no home in Clinton County (New York’s northernmost county) that gets by on a half a cord of wood per year, but I do know of a beautiful 1800-SF double-wall cordwood/earth-shelter built near us by our former students Bruce Kilgore and Nancy Dow, which is very “comfortably” (sorry!) heated with a about a cord. Incidentally, both Bruce and I burn our wood in massive masonry stoves, the most efficient means of burning wood, in my opinion.
As to finishing the walls with dry-wall or plaster, I have only seen two examples of this (plaster) where it was done well, one in Washington State and one in Ontario. I would certainly not do this until the log-ends have transpired their sap moisture. This could take a year or more. If infiltration is the issue, there are cheaper and easier ways to attend to that. Jaki and I have not found infiltration to be a problem at Earthwood, or at Mushwood, or summer camp. But we were very careful about the log-ends we used.
There are lots of successful cordwood homes in northern New England and New York. Earthwood is near Plattsburgh, NY, just across Lake Champlain from Burlington, VT. The keys are using the right cordwood and mortar ... and following best practices.
For Brian: Richard Flatau's 30-year-old cordwood home in Merrill, Wisconsin, a cold climate, passed a blower test with flying colors. His cordwood walls are 12" thick. We can talk R-values and infiltration until the cows come home, but the essential questions really are these: Are the houses comfortable? And: How much fuel is required to keep them that way? I can report that our 2400-SF (actual usable; really 2800 SF gross) round two-story cordwood home is very comfortable indeed through our 9000-degree day climate on a fuel use of about 4 full cords per year. We buy most of our firewood and spend about $600 a year for fuel. For fair disclosure, it must be said that 40% of the cylindrical walls are earth-sheltered. (16" thick surface-bonded concrete block walls below grade.) The impact of thermal mass in combination with insulation value is still hotly debated, at least as far as fuel consumption is concerned. After 31 years inside of our 240-ton Earthwood house, I can tell you that I am a great believer in thermal mass, as long as there is good insulation between the mass and the ambient. Incidentally, I try to be conservative with my R19 estimate of our 16" white cedar walls with their insulated mortar matrix. I am only using R1/inch for the white cedar, although it is rated at R1.5 on side grain. I take a two-thirds value because of the greater heat transfer along the end-grain, and infiltration. My 2/3 factor may be a little high or a little low. Dr. Kris Dick, a P.E. in Manitoba, has tested a 24" single-wall cordwood wall, with the insulated cavity, and yielded results of R35 or R1.47 per inch. This seems high to me, as I'm sure it does to you, but he is the engineer, not me.
For Cindee in Alaska: You say, "I like the idea of putting an air space in the middle---cool idea. Or maybe straw/clay in the middle. That breathes." An air space, by itself is not quite useless, but almost. Engineers normally assign it a value of R2, like a double pane window. Not much help. When the space is filled with an insulation with an R-value of R3 per inch, a 12" insulated space would yield R36, plus R2 twice for the heat transfer through the two mortar joints, so: R36 + R2 + R2 = R40. As opposed to R2 + R2 + R2 = R6 for the double mortar joint with just an air space. For Alaska, I would recommend 24" cordwood walls. The mortar joints can be 5" wide, which would give you almost 14 inches for the insulation. As for the straw/clay in between, you would need to get some kind of estimate for its R-value per inch in order to do the calculations. Incidentally, we have had no deterioration in the sawdust insulation at Earthwood after 31 years. About ten years ago, and again last fall, I had occasion to go inside the cordwood walls (once for an expanded window, once for a vent for a gas clothes dryer). The sawdust insulation, treated with builder's lime, was as light and fluffy as the day it was installed. We treat the sawdust with lime at the ratio of 12 parts of sawdust to 1 part of lime, and always pass the sawdust through a half-inch mesh screen, to get rid of bark, grass and other junk.
Hi Julie: Indeed, Ianto Evans and Linda Smiley stayed with Jaki and me at Earthwood for a few days several years ago, and, while they were here, we built together a cordwood masonry panel in our garage, about 4 feet by 6 feet. Instead of our regular mortar, described below, we used cob as mortar. We did insulate the mortar joint with sawdust in the central cavity, as usual. Ianto and I had to go out and search for good clay to build with, as there is none at Earthwood. We found it where a contractor friend was doing an excavation about15 miles away. The cob mix was about 80% coarse sand, 20% good quality (quite pure) grey clay. We used chopped hay/straw as reinforcing binder. An easy way to do this is to come down on top of a flake of hay or straw with a rotary lawn mower. Presto, nice 2-inch pieces of chopped reinforcing binder. Linda finished the wall with a thin coat of cob without the reinforcing. This panel has held up very well, but it is well protected with a 3-foot overhand and it is well off the ground. Chapter 20 (More Cordwood and Cob) of my book Cordwood Building: The State of the Art, goes into more detail about this project and others, and has a picture of Linda and Jaki working on the panel. You can get it at our Earthwood site, www.cordwoodmasonry.com or, maybe, win one here on Permies.
Over the years, Jaki and I have developed a very successful cordwood mortar using portland cement, lots of builder's (hydrated) lime, sand, and soaked softwood sawdust. The mix by equal volume (shovelfuls) is 9 mason's sand, 2 portland cement, 3 lime and 3 sawdust. The softwood sawdust needs to be passed through a half-inch screen and completely soaked overnight. The soaked sawdust acts as a cement retarding agent, preventing mortar shrinkage cracks. If the right sawdust is not available, use a commercial cement retarder, such as Sika Plastiment, Daratard-17 from W.R.Grace, or equal, usually three ounces per wheelbarrow load. Do not mix sawdust and commercial retarders.
Finally, I think the use of cob and cordwood together - which we call "cobwood" - is only appropriate if you have a source of good quality clay close top the building site. Once, we did a workshop in North Carolina using North Carolina red "clay" in a cob mortar. The wall went up beautifully, but we learned from our hosts that later, when the wall had dried, the cob mortar was crumbly. Probably not the best clay. We have had no such problem with the wall we built at Earthwood.
You are unlikely to find a contractor who has experience in building cordwood. The good news is that you can do it yourself at a very low cost, although it is labor intensive. May I invite you to register for one of our 3 or 5-day workshops this year. Go to www.cordwoodmasonry.com for info. Once you get there, click on Workshops, then Register for Workshops.
In a seismic zone, it is absolutely imperative to do the cordwood masonry within the confines of a strong post-and-beam timber frame. This compartmentalizes the cordwood into small sections. This feature was insisted upon by the code enforcement officer at an Earthwood house that was built in Carlsborg, WA, about 20 years ago. This was a Seismic 3 zone. The house never suffered from earthquake damage, to my knowledge, but I don't know what kind of quakes it has endured, on the Richter scale.
Red cedar is quite a bit more dense than northern white cedar, only about two-thirds of the R-value. So walls must be thicker to get the same insulation quality. Also, red cedar shrinks more than white cedar. It really performs more like a hardwood. Rot is rarely a problem with any species of wood, because of cordwood masonry's unique breathability.
There are several kinds of red cedar, including aromatic red cedar, used in cedar closets to discourage moths in the woolens. Be careful using a lot of this, as the aroma can be overwhelming. One lady I heard of had a sauna built for her out of red cedar boards and she could not use it; at 150+ degrees, you could not breathe in the room. It was not cordwood, but cordwood would not have been any better, maybe worse.
Finally, to conclude on a positive note, I know of an excellent Earthwood type cordwood house in North Carolina built out of red cedar that was brought down on a flatbed from Maine. Beautiful, very successful home, no aroma issues, an unqualified success.
Great question, Tracy, and one that I deal with in Earth Sheltered House. Maybe not well enough!
Laying blocks with a 3/8" mortar joint is a very skilled job, and labor intensive. Surface bonding, I find is much easier, and several times stronger against lateral pressure.
We discovered - after four courses of dry laying - that our corner blocks had a one-sixteenth inch bias, one end of the block to the other. So after four courses, we were one-quarter inch out of level (because we laid them all in the same direction. Once we discovered this, we simply laid the blocks the other way for four courses and - presto -we were back on track.
The best way to take out burrs and irregularities in blocks to put on a pair of rubber masonry gloves and slide or scrape the block over the pallet of blocks, both sides. This will usually make them fit upon one another without a wobble. If a slight wobble is perceived, put a thin metal shim under the appropriate corner to take the wobble out. Use your level to find out which corner to put the shim under.
R-value of cordwood masonry and air infiltration: two very important questions.
First, R-value. There is a popular misconception that the mortar of a cordwood wall (which can be 40-50% of the cross-sectional area of the wall), goes all the way through, from interior to exterior. This would be a thermal disaster! The mortar would conduct the heat right out of the house. Thankfully, this is not the way we build cordwood masonry walls. There are two separate mortar joints - an inner joint and an outer joint - separated by an insulated space. In a properly built cordwood wall, the R-value of the mortared portion of the wall is actually greater than the wooden portion. As an example, our Earthwood house in Northern NY (9000 degree day climate, like Montreal) has 16" northern white cedar cordwood walls. On end grain, the cedar is good for R1 per inch, so R16. However, the mortared portion of the wall, with six inches of sawdust between the inner and outer mortar joints, is worth R22. The average value of the wall meets NY's R19 energy code requirement. But, of course, the thermal performance also benefits from the exceptional thermal mass.
As for air infiltration, it is important to season the wood to minimize log-end shrinkage. This is a big topic, and species specific. so impossible to address here in a short answer. We spend about 45 minutes on this topic at our workshops. If the wood does shrink, you can caulk the gaps with a good siliconized clear caulking. Best to wait a year or so, at least through one heating season, before doing this. You don't want to do it twice. Incidentally, we have done very little caulking on our various buildings at Earthwood, because we have usually seasoned our white cedar for a year before using it.
First off, thanks to all of you for the warm welcome onto the Permies site. My good friend Mike Oehler, of underground houses fame, has told me what a wonderful site this is, and it seems that he is right on the money with his evaluation. Some of you have asked some specific questions in this welcoming email, and I will do my best to address them now, although it seems that these questions are better discussed in specific threads.
Jonathan Allen asks about permitting issues. Great question. This varies tremendously from jurisdiction to jurisdiction. Good idea to feel out the local code enforcement officer before spending a lot of money. The good news is that over the past 30 years, I have only known of 2 or 3 people who were unable to build the cordwood building they wanted to build because of intransient code officials, this out of hundreds of applications. Lots of good things came out of the 2005 Continental Cordwood Conference in Merrill, Wisconsin, but the best may have been a document called Cordwood and the Code, edited by myself, Dr. Kris Dick (PE), Alan Stankewitz and Richard Flatau. Wisconsin's top code official, the guy at the peak of the pyramid, called it the finest document he has seen concerning any of the alternative (natural or green) building systems. While it will not answer every last question an official might have, it will address the large majority of them: R-value, flame-spread, structure, etc. It is available at our Earthwood website: www.cordwoodmasonry.com
Marianne Cooper asks about a cordwood sauna. Perfect! Cordwood has a wonderful combination of thermal mass and insulation for the perfect sauna. We have been using cordwood saunas for 35 years and our present round one at Earthwood has been in use since 1982, almost every Sunday in winter. Putting water on the stones creates instant loyly - the sacred steam - but the end-grain of the log-ends soon brings the atmosphere back to dry. Wet, dry, wet, dry: this is the authentic Finnish sauna. See my book, The Sauna at www.cordwoodmasonry.com.
Peri Gordon asks about the use of cordwood masonry as a retaining wall. Sorry, Peri, I cannot recommend this. Cordwood needs to breathe through the log-ends on end-grain to prevent fungal growth (rot). Plus, it needs to be protected from above by a good overhang.
Lake Bleeker asks about the use of wood ash in the mortar. I'm afraid I have no experience in this, so I cannot comment intelligently. Over the years, my wife, Jaki, and I have developed a very successful cordwood mortar using portland cement, lots of builder's (hydrated) lime, sand, and soaked softwood sawdust. The mix by equal volume (shovelfuls) is 9 mason's sand, 2 portland cement, 3 lime and 3 sawdust. The softwood sawdust needs to be passed through a half-inch screen and completely soaked overnight. The soaked sawdust acts as a cement retarding agent, preventing mortar shrinkage cracks. If the right sawdust is not available, use a commercial cement retarder, such as Sika Plastiment, Daratard-17 from W.R.Grace, or equal, usually three ounces per wheelbarrow load. Do not mix sawdust and commercial retarders.
Amanda from Texas asks about pine as cordwood. Generally, it is good, but there are lots of different pines. You want to use the lighter, airier pines, such as white pine (in the north) and loblolly in the south. Southern yellow pine is very hard and dense and performs more like a hardwood. You can use it, but more caution must be taken.
Chad asks about the use of telephone poles as cordwood. I would only use them if they are untreated. Sometimes, the base of the pole, the part that goes in the ground, is treated, and the rest is not. You can derive 20 feet or more of good dry untreated wood from the part above grade.
Jami McBride says: "Depending on the type of wood, wood used in cord-wood projects will shrink, split and crack this isn't because of lime in cement though." Jami is absolutely right. How to minimize this shrinkage and checking is a whole other topic, however. For the moment, we need to discuss wood deterioration. It is true that wooden posts in the ground will rot, particularly at ground-level, where we have the perfect combination of food (the wood), and the air and moisture to promote fungal growth: rot. The reason that this does not happen with a cordwood wall is that the wood is breathing through the end-grain longitudinal fibers. Moisture, the bane of rot, is not trapped. The wood gets wet, dry, wet, dry, ad infinitum. The conditions for rot - fungal growth - are not present. Little baby fungi cannot propagate.
