Building Green: Chapter 9 – Cordwood
My friend, the author and cordwood expert Richard Flatuau, was nice enough to write this excellent short article on cordwood for the digital update to “Building Green”. He promises to blog here on occasion, so click on the link below to read the latest cordwood information.
Best Practices with Cordwood Construction
By Richard Flatau
Over the years the people in the cordwood field who have kept building, writing and helping have come to realize that there are several techniques that can be considered Best Practices to use with Cordwood Construction.
Like all building decisions there are continual cost/benefit/budget decisions that must be made before and during the construction of your home. There is no absolute right way to build your home, rather there are decisions that you must make based upon available money, skills, time, talent and preferences. When we built, one of our main goals was to come away from the project mortgage-free. Not everyone has that goal and so you adjust your purchases to meet your goals. For example, rather than buy expensive cabinets, we ordered birch cabinets from the former JC Penny catalog for 1/5th of the cost of regular cabinets in order to meet our goal. We didn’t scrimp and save on the safety aspects: wiring, plumbing, chimney, furnace, windows, but we did make monetary concessions on the plumbing fixtures, floor coverings, cabinets, etc. You too, will have to make decisions based on your goals and objectives. Take the following discussion on Best Practices with that in mind.
1. Foundations: Most cordwood builders use an insulated frost protected shallow foundation (FPSF). www.nahb.com Others are implementing Frank Lloyd Wright’s rubble trench foundation as an alternative to costly foundation work. Several are putting radiant-in-floor heat into the slab. It is, of course, possible to build cordwood with a basement or crawl space, and this adds to the cost of the building. If you prefer a basement and have that as a goal, put in a basement. Remember that even with an insulated slab you can frame out the floor and put in hardwood floors. Some cordwood builders have done this and used the 2” x 6” floor framing to run electrical, plumbing and heating.
2. Post and Beam: Most cordwood experts now agree that one of the advantages of post and beam framing is that you can put your roof on first. That allows you to do the cordwood masonry ‘out of the elements’, it also gives you a covered space to store all of your log-ends, tools and supplies. It affords the opportunity to build one section of wall at a time. If winter comes early, simply side up the sections that aren’t finished and finish them in the spring. Even folks who have chosen the stackwall corner are beginning to post and beam the walls in between the stackwall corners.
3. Build a Practice Building:
In order to find out if the alternative building technique you are enamored with is the “right fit” why not build a small (doghouse size) or large (garage) practice building. This way the system is researched, tested and evaluated. It can be an effective method of learning and deciding. Or you can do like Clarke and build a cottage using multiple systems.
4. Mortar Mix: The mortar mix must be one that will cure slowly and set up relatively slowly. There are about four basic mixes. Some will leave your walls smooth and others will have an adobe type quality. Before you make a decision it is wise to try a few of the mixes and see what they look and feel like before and AFTER you mortar. It is also good to see which ones crack more and which retain their color. The latest craze in cordwood is a Lime Putty Mortar (LPM) mix which is basically how the Romans did it. Type S hydrated lime, soaked for three days, mixed with mason’s sand in 2.5 sand to 1 LPM ratio. I will write an article and give all the gory details on how to use this new/old mix. Soaked sawdust and slurried paper have been used successfully to slow the set and cure of the mortar.
5. Wood Prep & Drying: The biggest problem with cordwood is the natural tendency of the mortar to separate from the wood. This is why it is so very important to dry wood to the minimum moisture content for your area. Here in Wisconsin that is 12% for air-dried wood. Your wood should have cracks and checks in it before you use it. Otherwise it will shrink in the wall and let air in. Borrow a moisture meter from a lumber yard, sawmill or a friend. Or buy one. Burn a piece of your wood and see if it spits and pops (if it does, it is still too wet.)
6. Split some of your wood. If you want your wood to dry faster, try splitting it. Splitting makes two things happen. The wood will dry faster and there will be no primary check to allow air infiltration.
7. Perma Chink & Log Jam: NO matter how dry your wood is, there will still be some pieces that loosen up or check. This is a cosmetic problem and can easily be solved by putting (slathering) PermaChink or Log Jam caulk on the mortar and the space where the log end and the mortar meet. In fact I was just in a house that had ALL the mortar PermaChinked. Believe me there was no air infiltration in that home.
8. Cedar and other softwood: Cedar is the ideal wood for cordwood. It is light, has a good
R-value, is naturally decay resistant and has a light attractive end grain. However, except for staying away from hardwoods (they have a tendency to swell and crack mortar joints) most of the other dry, insect free softwoods are suitable for cordwood building.
9. “Treat” the wood to a borate bath: It is becoming common practice to spray or soak the cordwood in a solution of borate (borax). The most preferred, economical method is to use 4 cups of 20 Mule Team Borax (borate) with a gallon of hot water. This can be sprayed on, or the logs can be dunked. This treated is a “three-fer:” an insecticide, a wood preservative and a fungicide. Commercially available products can be used: (Timbor, Shell-Guard, Pentatreat, etc.)
10. Large Overhangs & gutters: In order to keep the cordwood dry and free from splashback, it is a good idea to have at least a 24” overhang. It is also a good idea to gutter your roof eaves to prevent against splashback.
11. Build up off the ground: Most experienced cordwood builders recommend that you start your cordwood at least 12 inches off the ground, however, if your climate is especially prone to high water or straight-line rain, and then you will want to consult with local officials and apply what works for your locale. We have been using split faced block on the outside and inside with an extruded polystyrene thermal break in-between.
12. Code Compliance: One of the main thrusts of the Cordwood Conference 2005 was to establish a document that dealt with Code Issues. Fortunately the document
Cordwood & the Code: A Building Permit Guide was one of the gems produced by the Conference. It comes in a 54 page volume with an attached CD that will allow most owner builders to approach the code officials with confidence and success.
13. Build small now, add-on later: Some would advise building a smaller structure now, while leaving room to add on later as more resources become available. This is one of those areas that become a personal decision, but it is important to know that it is an available option.
14. Random Pattern: Don’t build with all one size wood, use a random pattern to give your cordwood building an attractive appearance. Step back from the wall every so often to see what you are building.
15. Use Energy Startm Guidelines: www.energystar.gov
• Energy Heel Trusses that allow R-60 in the ceiling and especially at the point where the top plate meets the truss.
• Energy Efficient Windows and doors. Much of the heat loss in a home comes from leaky windows and doors.
• Standing Seam metal roofs are long lasting; provide some fire protection and let snow and tree leaves/needles slide right off.
• Living Roofs are an important consideration and should be thoroughly researched if chosen as an option.
• Seal all electrical outlets
• Caulk all inlets and outlets (plumbing, electrical, etc) to keep the home as air tight as possible.
Cordwood Construction Resources
W4837 Schulz Spur Dr
Merrill, WI 54452