Cobwood walls

I plan on building a timber frame and using cobwood for the walls. Is the only problem of using green wood for the cobwood walls, that I will have to go back and fill in the cracks?

Hi Doug,

After reading the below links, let me know if I can further assist.

https://permies.com/forums/posts/list/45465#362042

https://permies.com/forums/posts/list/38854#302985

As for the "only problem," I am not certain that I would even discribe the "green" nature of the wood a "problem" but a possible challenge depending of system of kubbhus that is employed for a particular project. This is a varied and multifaceted system of building, with walls as thin as 300 mm and as thick as 1 meter. I am glad that it is being utilized as an infill method rather than "free supporting," which can and often does have many challenges. Some of which that may not manifest themselves for a few years.

Regards,

j

Hi Jay,

People have different definitions of what "dry" wood is, haha. This tends to get a bit confusing. I am looking to build a small home, so that I can live on my property while I build a slightly bigger home. I have a lot of Spruce that I can use for the cobwood walls. If I use them before the 6-12 month( maybe longer?) recommended drying period, am I facing any other issues other than having to reapplying cobb? Especially since I am only looking to have this be a primary residence for under 5 years.

Thanks,
Doug

Wood Associations based on testing consider wood to be "dry" below 19% moisture content (MC), above 29% pores are saturated no place to dry out (check). Below is the ability to reach "Equilibrium Moisture Content" (EMC) or balance to Relative Humidity (RH) in the surrounding air if you will of different building materials at different RH and % MC by weight. It peaks at 85% RH then exponentially increases fast! Spruce is listed, it absorbs fast in the grain direction. Desorption or "drying" is close to the same given the same conditions. Capillary up take is also faster along the grain, Cap desorption can be slower depending on gravity, pressures, etc......Perhaps why "drying" gets a little perplex but a mositure. meter does't lie

Soil around or in contact or a path to wood does not make sense to me, termites, but who knows. I wouldn't do it in the wild, wild, termite west and I can think of better ways to insulate wrap Timbers and keep them in the sweet MC spot.

Thanks to John Staube for the materials properties.

Hi Doug,

Yes, the "wet and dry" aspect can be confusing for a novice. Even many "experts" I met have very narrow and/or limited understanding of these methods. Much of "folk" and vernacular systems of building (and understanding natural materials) has either been lost, or misrepresented in text. ​

I have seen many modern Kubbhus, like my friend Roy that I have corresponded with over the years that are built more on "theory and experimentation" than actual historical knowledge and research. I have "debated" this topic with a few "cordwood building experts" that had only a limited understanding of the method as they new it from examples in Canada and the "New World" but had no experience with the foundational elements from Eastern Europe, the Middle East and Southern Asia.

If of an unstable species of wood and very "green" (i.e. wet) you can get an over amount of checking and movement, though this isn't insurmountable if a more traditional method of application is employed. If to "dry" a wall can actually push itself over and or a frame apart.

In your planning process to build small than larger, I would suggest that the smaller one if possible becomes an augmentation of the larger. Often on DIY projects this lack of "forward" planning can either cause a waste of materials and/or a loss of optimal use.

Spruce isn't the best species, but far from the most challenging as well. It is totally fine if not leaving expose and plastering over or covering in some way, on the outside. I also tend not to recommend the "round" method unless well versed in the modality of building and going with an extra thick wall.

If I use them before the 6-12 month( maybe longer?) recommended drying period, am I facing any other issues other than having to reapplying cobb? Especially since I am only looking to have this be a primary residence for under 5 years.

Well now we really get into the "expert debating points" on this subject. Again, each species is going to react differently, and the method of application is also a major contributing factor. One year or ten doesn't really equate into the method I would recommend...for the most part. I just do not recommend to novice (nor do I myself) go with "single course" thickness walls. I would strongly recommend a minimum of 300 mm. I also would not, unless an historical restoration project, ever build with this method minus a timber frame. Since you are using a timber frame, I feel you are very much on the correct path. So....

Since you are using a timber frame, I personally do not believe you need to age the wood much beyond even 3 months...if at all. I am writing this with the caveat that I very well may have an image of design and context application outside what you intend. Seeing a "sketchup" model of your plan can give me more insight into being of further assistance.

Regards,

j

Hi Jay,

I just started to get in some of the books from the list you have, so I have a lot of reading ahead of me. I am looking to do some preliminary drawings soon. I was just trying to see how much of the resources I have available to me on my property that I could use to build the house. I am not looking to build a round house, something more along the size of 20x30, but I am still waiting on some books to further flesh out the framing. As for the thickness of the wall, I was planning on something thicker than 300mm. I would defiantly be planning to cob the outside of the house. I also have a lot of different types of trees available to me, so Spruce doesn't have to be what I use. I have an 8 acre wooded lot in central Maine. A couple of the books I bought have great sections on wood characteristics, so again, lots of reading ahead of me. Thanks for all your help, Jay!

Doug

Hey Doug,

I am super excited for you...!!

I am sure as you get into the "book list" I suggested you will have many more questions, and new ideas.

I am not looking to build a round house, something more along the size of 20x30, but I am still waiting on some books to further flesh out the framing.

This is a good thing in my view. "Round" architecture is aesthetically pleasing and very romantic in concept...seldom does it work in practicality for living and/or having a "working home" as most farmers tend to require. Some of my better teachers and mentors suggested that "rectangular" works for permanent architecture, while round fits the "transient," forms best...I now tend to agree.

As for the thickness of the wall, I was planning on something thicker than 300mm.

I'm also very please to read your plans about the wall thickness. You are close enough that I might have to come for a visit. If you haven't started experimenting with "Sketchup" for a method of modeling your design, please begin. It will motivate me to finish some "cobb-kubbhus" designs I have sitting in the "concept file." If I may also suggest, start a blog to record your progress and keep a photo archive of your progression. Send me an email soon...

Regards,

j