Sheathing Over Straw bales

I am going to build a small timber frame straw bale structure this summer. It'll be a precursor to building my straw bale home at a later time. I am mostly interested in using straw bales because of the R value and because it is a natural building material. Plastering and sheathing the straw bales with boards both on the exterior and interior appeals to me. It seems to me that plastering and sheathing would be a great deterrent to rodents. Has anyone here had experience plastering then sheathing the straw bales with wood?

What natural sheathing and what perm rating? Look at the MSDS it provides some info as to any hazardous materials.....You might check if they recommend a vapor retarder to protect their sheathing from constant vapor pressure, and if you are using a clay plaster it will retain and breath vapor pressure, add the ideal temperature and a food source in the sheathing and you create a fungi rot of the sheathing. The straw needs to breath or pass vapor pressure or it can rot, so trapping it in with low perm sheathing and/or membranes on both sides can be an issue. Typically sheathing in mainstream non-natural construction has a smart vapor (15- 20 perm) membrane or vent/rain plane between it and siding, interior vapor barrier behind drywall, so the wall dries outward. Not the case if you plaster direct to sheathing with clay on both sides.

Rodents can get into any wall without the proper detailing to keep them out I would let them drive me to sheath bales, there are plenty of them without sheathing. You get around r-30 and some mass effect with clay, some in cold climates like NE USA are wrapping frames (2xs) with blown in to get to r-50....they are following all the code rules for vapor retarders and barriers....They strap the interior bales to the frame to resist settling and the need for stuffing....Rodents can still get in if they leave gaps in the envelope.

I am thinking about framing a second wall on the exterior side of the bales and then horizontally strapping the 2X's. I would then use board and batten for the sheathing. Before the board and batten is applied I would plaster the bales.

I like the idea of possibly mixing loose straw with a clay or soil based slurry and then slip forming the mixture in to the walls. I wonder what the R value is for a straw-slurry mixture?

I'm not sure I know what you mean by "I would let them drive me to sheath bales, there are plenty of them without sheathing." Could you clarify.

Alfred, I was just saying before I added sheathing cost to keep rodent's I'd spend the money on "air fins" or mesh details and a good render to keep them out. Check this video out that discuss clay slip and anything in the way such as sheathing that can keep walls from drying out: https://permies.com/t/43345/straw-bale-house/Straw-clay-slip-video

Alfred Negri wrote:I am going to build a small timber frame straw bale structure this summer. It'll be a precursor to building my straw bale home at a later time. I am mostly interested in using straw bales because of the R value and because it is a natural building material. Plastering and sheathing the straw bales with boards both on the exterior and interior appeals to me. It seems to me that plastering and sheathing would be a great deterrent to rodents. Has anyone here had experience plastering then sheathing the straw bales with wood?

Hi Negri, et al,

I have been a student of these different modalities for some time...and yes...I have had experience/knowledge of mixing these different finishing modalities. First I would recommend reading SB Architecture and Pest Control.

Clay or lime plaster alone is not enough of a determinant in many areas from stopping some "infestors" from trying to make a home inside bales. I am also of the thinking...and have been for some time...that SB alone may not always be the best modality of infilling a timber frame, but a clay slip and straw or wood chip may be superior in many ways. I would also consider many of the traditional methods of "stacked wood architecture" (What friends of mine like Rob Roy like to call "cord wood") as an infill method, like the "Kubbhus" styles of Eastern Europe and elsewhere. These kubbhus, cob, and "clay wood chip" methodologies could present as superior in speed of construction and general design over many SB systems for some areas where trees are overly abundant.

Regards,

j

Terry Ruth wrote:Alfred, I was just saying before I added sheathing cost to keep rodent's I'd spend the money on "air fins" or mesh details and a good render to keep them out. Check this video out that discuss clay slip and anything in the way such as sheathing that can keep walls from drying out: https://permies.com/t/43345/straw-bale-house/Straw-clay-slip-video

Thank you Terry. That video was excellent. I think you'll find the videos at Riverstone equally as good: https://www.youtube.com/channel/UCL-Zp0bNYarqgFjgr7nHVkg.

Jay C. White Cloud wrote:

Alfred Negri wrote:I am going to build a small timber frame straw bale structure this summer. It'll be a precursor to building my straw bale home at a later time. I am mostly interested in using straw bales because of the R value and because it is a natural building material. Plastering and sheathing the straw bales with boards both on the exterior and interior appeals to me. It seems to me that plastering and sheathing would be a great deterrent to rodents. Has anyone here had experience plastering then sheathing the straw bales with wood?

Hi Negri, et al,

I have been a student of these different modalities for some time...and yes...I have had experience/knowledge of mixing these different finishing modalities. First I would recommend reading SB Architecture and Pest Control.

Clay or lime plaster alone is not enough of a determinant in many areas from stopping some "infestors" from trying to make a home inside bales. I am also of the thinking...and have been for some time...that SB alone may not always be the best modality of infilling a timber frame, but a clay slip and straw or wood chip may be superior in many ways. I would also consider many of the traditional methods of "stacked wood architecture" (What friends of mine like Rob Roy like to call "cord wood") as an infill method, like the "Kubbhus" styles of Eastern Europe and elsewhere. These kubbhus, cob, and "clay wood chip" methodologies could present as superior in speed of construction and general design over many SB systems for some areas where trees are overly abundant.

Regards,

j

The straw-clay modality really appeals to me now. So much so I think I'm going to shift from using straw bales to using straw-clay when I start building. The videos at riverstone were very persuasive: https://www.youtube.com/channel/UCL-Zp0bNYarqgFjgr7nHVkg.

What you are talking about doing can and has been done. Begin by stacking the bales so that the strings on the bales are visible and exposed. You can then slide strips of wood behind the twine as your furring strips. Plastering in addition to board and batons would be unnecessary, but a clay slip over the bales is recommended for fire protection I guess, which I would forgo. If your boards catch on fire you're toast anyway ha. The advice for the clay slip is recommended for when metal is installed over bales, in that case I definitely would do the slip. A good barn cat will do as much good as a coat of earthen plaster and be a heck of a lot cheaper:). It sounds like you want to do this project fast, easy and cheap and then on your next house pay a little more and spend more time on it. If that is the case, I think my advice is very applicable. Stack the bales, slide in some wood strips, nail up some lathe and install your boards seems like the easy fast way. Maybe not the longest lasting, most problematic proof way, but that's ok. Good luck and happy baling.

P.S. I read a story of a guy who laid some pallets on a gravel pad, stacked up his bales in the before mentioned way, slid in furring strips and put plywood over the whole structure for a quick, easy, affordable, and super insulated shop. What you're talking about is basically the same thing. Hope that gives you some inspiration, and ideas maybe. :)

How did the job come up in the end

I am of the keep your natural material wall breathable camp and would never have sheathing on both sides.  I have done experimental retrofit work here where I have put in light straw clay against existing sheathing making sure the inside wall was earth plaster and the existing external sheathing is moisture permeable, if I am saying that right, to the outside anyways.  So far we have seen no moisture issues from this, but I wouldn't do both sides and it is a waste of money and materials