Using mini-straw-bales for interior walls

Hello Chris and thank you for coming to Permies!

I have a question regarding a lesser-known option for straw bale homes. Have you ever heard of anyone else using half-width "mini-bales" to create the interior partition walls of their straw bale building, and what do you think of the idea? Although I got the notion from a book about straw bale architecture, it was only a brief mention, and it was an old book as well. Having never heard anything else about it anywhere since, nor encountered anyone else who has, I have begun to suspect that I may be the only one doing this, and wonder if that isn't for good reason. To provide background: I have a passive solar straw bale home in South Carolina, currently about 75% complete, in which I am crafting nearly all interior partitions from bales. This is, of course, in addition to the exterior walls, which are fairly conventional using full-sized bales.

To make the mini-bales, I retie both strings of a standard 18"-wide 2-string bale to make it as compressed as I can manage by hand. Then I fit it into a homemade cutting jig: basically a snug box of scrap wood and OSB with an open top and an open channel on the bottom in the middle. Then I zip right down the middle of the bale with an electric chainsaw. About 85-90% of the time, the results are two 9"-wide 1-string bales. The other 10-15% of the time, the result is an explosion of straw, LOL! I have learnt through misadventure that it is better to do it this way. For a while I attempted to create more solid and manageable mini-bales by retying four strings around each original bale, so that the two mini-bales it produced would themselves each have two strings. But I found the results were just the opposite: unless each of the two strings were exactly equal in tension, they would twist the resulting mini-bale into a banana from which it did not want to return.

The partition walls are framed with double stud 2x4s every 36-40", between which a column of the mini-bales is stacked vertically to the ceiling. No running bond necessary. I use paired external bamboo pins to secure the bales prior to plastering, and no mesh of any kind in most places. At first, I used 8' lengths of vertical bamboo notched into sill and top plates and corseted into the bales with loops of twine stitched through the heart of each course; a fairly conventional arrangement, just as I used with the exterior walls. Since then I have wised up: it is much easier to use shorter lengths of bamboo running horizontally, one pair per course of bales. They are notched into the left and right studs and corseted with loops of twine and baling needles in the same way.

My reasons for eschewing the normal stud-framed gypsum board partition walls were threefold: 1) to continue the theme of maximizing natural materials and minimizing pre-manufactured materials further throughout my home; 2) to create partition walls with greater sound isolation between rooms; and 3) to make the partition walls aesthetically consistent with the exterior walls. I must admit that reason #3 was probably the most compelling reason for me, and given the labor expense inherent in natural construction, I have begun to question the practicality of my decision now that I am halfway through. Having toured another completed bale home and experienced the jarring incongruity of rectilinear gypsum board walls juxtaposed with undulating organic bale or cob walls with my own eyes, I still yearn for my bale partitions. But I yearn for a solid gold toilet, too. Alas, there are some things you just can't afford in this life!

So, am I indeed the only owner-builder foolish enough to invest in such a technique? As I said, I would be fascinated to learn if there are others out there doing the same, and to hear of their experiences.

Hi Matthew,

You're definitely not the only person to use mini bales or half bales for interior walls!

As with all things in design and building, my first step is to assess the owner's criteria, and from there figure out what makes the most sense. You've listed your criteria, which is helpful. Definitely the mini bale walls will help reduce sound travel between rooms and keep the plastered aesthetic set by the exterior walls.

There are two main drawbacks to using bales in interior walls. The first is that it is more difficult to run plumbing and electrical services through a solid wall like a bale wall. It's do-able, but it can be a pain, and definitely takes longer. The second is the loss of interior floor space, as even the half bale walls are at least three times as wide as a stud frame wall.

One way that we go about matching the convenience of stud framing while keeping the hand-plastered aesthetic is to use old-style wood lath on the stud walls and then use the same kind of plaster we've used on the bale walls to cover the lath. To manage sound in certain rooms, we'll use cotton batt insulation between the studs. In this way, we end up with fairly typical sizes for the walls, use all natural materials and don't have to worry about the labour involved in cutting bales, stacking, pinning and routing services through it.

We have, on occasion, used bales for interior walls, particularly if the wall is curved. In that case, the bales can actually make it easier, especially if we've planned to keep plumbing services out of that wall. As you've noted, there is a lot more labour that goes into doing this! The studs with lath and plaster are every bit as fast as studs with drywall.

Hello again Chris,

How fascinating to learn! Thanks for the info. I would love to hear more details about other people are doing mini-bale walls if you could share some or point me to more resources on the topic or the people who have done it.

You are absolutely right, of course, regarding the two drawbacks of bale partitions: difficulty plumbing and wiring, as well as floor space consumed. Since I had planned on these partitions from the drawing board on, I made sure that I was happy with the usable dimensions of the resulting rooms. I also ran all plumbing beneath my slab (monolithic concrete slab-on-grade) so that none of it needs to pass through my walls, and ran all wiring through the attic. Nonetheless, both solutions still pose difficulties. Mapping out (PEX) plumbing runs so that they stick up from the foundation precisely beneath a future fixture installation leaves little room for error, and of course it will be extremely difficult to service the lines in the event of future problems. Running wires through an attic is easy enough, but my building official required each one to be fully encased in conduit, later to be covered by plaster, from where it emerges through the ceiling all the way to the fixtures at floor level. Working with the plastic conduit and recessing it into the surface of bale walls has NOT been fun.

Those drawbacks, of course, being in addition to the primary drawback I already mentioned: additional time and expense during construction.

Your proposed solution - using wood lath to create an "old style" plastered stud wall, which can be insulated for soundproofing - is a good one. I already have such lath, and have counted on using just that approach in one small area. I am with you all the way up until you wrote "studs with lath and plaster are every bit as fast as studs with drywall." Having now completed many a linear foot of bale wall with three coats of plaster, I just have a hard time supporting that statement. Plastering is difficult, and it takes a long time! I am sure that plastering over lath, which I have not yet done, will be easier on the scratch coat compared to plastering over bales, but it is still a long and costly process. As with everything in natural building, it is all about the man-hours! So, I am eager to hear you elaborate on this point. Do you perhaps know some plastering tricks that I do not? If so, please share : ) FYI, I mix my own plaster in a small rotating-drum cement mixer using river sand, chopped straw, and (for the exterior walls) soaked lime putty for a binder. Plaster for the interior wall surfaces is the same, except that I am using a 50:50 lime/clay binder featuring bagged white kaolin. I had originally planned a pure kaolin interior plaster, but after a few first-coat sections I just missed the solid feel of my lime plaster, so decided to spike my mix with half lime from now on.

Incidentally, the small section in which I plan the plaster-over-lath finish separates a bathroom from a walk-in closet (actually a roll-in closet, since I am in a wheelchair, but no matter). On the "reverse" side, since it forms only the back of a closet, I will just finish the partition with gypsum board. On the "front" side, one third of the wall will be finished with cement backer board and tiled floor to ceiling in order to form part of a shower stall. Nothing too fancy, just plain discount white tile, but I will include the occasional unique homemade tile for accent. The remaining two thirds of that wall surface are to receive the plaster-over-lath. Recently, however, I have wondered if I might not finish this section of the wall with tiles as well, so that one wall of my bathroom would be completely tiled, wall to wall and floor to ceiling - like an accent wall - a portion of which extends into the shower stall. Having not yet done any tiling myself, I don't know: do you think this will be considerably more difficult and/or time consuming than the plaster work it would replace?

Thank you again so much for your input!

P.S. Having read portions of your wonderful book, I can already hear you saying "monolithic concrete foundations are too energy intensive; not a green choice!" You chose not even to discuss them in your book for just that reason. Well, for the record, I agree. In a perfect world I would have loved a tamped earth floor inside a grade beam foundation, or maybe a slate floor, and either would have worked with my passive solar design. But the truth is that few of us in this world have the luxury of unlimited budgets, and few of us on this continent have the luxury of exemption from building code jurisdictions. Therefore we must pick and choose our battles. I was pleased to read this logic expressed in your book more than once; I find that green building authors tend to conveniently gloss over these inconvenient realities far too often. For myself, I am content in having designed a home (assuming I ever actually finish it) in South Carolina without need for air-conditioning, which I am not installing.

In this regard, there is another aspect of the green building literature that I would like to bring up. I would love to hear your take on this point, as I've not yet read your book closely enough to know your position on it. That point being that green building authors, in my opinion, spend too much time talking about embodied energy without acknowledging that the energy embodied in a building's materials is ultimately dwarfed by the energy consumed by operating that building. My understanding is that only 11% of a building's lifetime cost is represented by the construction materials. This statistic I got from The Green Architect's Lounge podcast, and I don't know where they claim to have gotten it. Now, I believe they are measuring in dollars, not joules; but in the big picture, dollar cost is often a decent approximation for energy consumption. I also believe that they are averaging together residential and commercial buildings. Still, it is an impressive statistic. As I said: I would love to hear your reaction to this observation...

Hi again Matthew,

I definitely think that studs, lath and plaster are much faster than bales and plaster, especially since you're also framing a stud wall to go with your bales. In my course a few years back I had a team of three drywallers and with them we did the majority of the interior of a house in lath and clay plaster, and they were surprised to find that it was faster than they could drywall. There is no comparison between plastering over a flat, lathed surface compared to going over bales. Way less material and time!

I'm not very judgemental when it comes to how people decide to build. If somebody asks my opinion before they start building, I will make the case for the least intensive materials that meet their criteria, but if somebody chooses a concrete slab who am I to criticize that choice?!

I'll refer you to an article I just recently posted on the Endeavour web site http://endeavourcentre.org/2014/02/embodied-energy-is-it-important/ about why I think embodied energy is important. There's more to say than I want to re-type and post here, but check it out and see...

Thank you, Chris, for the link to your excellent article. A lot of good info. 1/20th to even 1/50th some people calculate?! Wow, that is an even bigger difference than I had heard. Still, your point is well taken that there are many choices in the course of building a home in which one can easily substitute lower embodied energy materials with ease. In that regard, I was surprised to learn that there is so much variation in embodied energy even among "off the shelf" conventional material choices. As in a difference of many orders of magnitude. I didn't know this, for example, when I chose to blow cellulose into my attic, but now I'm even more glad that I did. A good question to consider: why didn't I know this? Why is such important information not included on product packaging?!

I am also amazed and fascinated to read about your past experience with the dry-wallers plastering over lath. I still find it hard to imagine that it could go faster with a full three-coat wet plaster than with hanging and finishing gypsum board, but I'm sure those professionals would know the difference! And we know that, since both lime plaster and gypsum boards are relatively inexpensive materials to start with, faster equals cheaper. In that case, I am confused about somethings, something I had thought I understood, and am wondering if you can illuminate a bit of history for me: why did gypsum board walls become the industry standard if they were not in fact cheaper to achieve than the plastered lath walls they replaced?

In terms of embodied energy, it's important to remember that although older buildings might be 1/20 or more in terms of EE to overall energy use, as we make more and more energy efficient buildings, EE's share of the energy inputs will rise dramatically. A net zero energy home could see the majority of it's energy impacts be at the EE level.

I think drywall overtook wet plasters because it takes less skill and it gives a more standardized appearance. Sheet goods delivered much better results when energy was cheap... as they took over the market, the costs were well below what it cost to pay people to do the same work. However, the price of sheet goods has been rising consistently ever since, and we're getting close to the point where human labour costs are getting closer to being on par. However, we've lost the skilled trades and the aesthetic that went with human-made building systems, so there's more than just cost factors holding them back. For somebody holding a conventional building mortgage, the bank will give them a certain percentage of their total budget for drywalling. But in most cases, they wouldn't give an owner a penny towards lath and plaster. So drywall wins...