Earthen building needs some tlc before it falls apart! Advice?

Last year I bought a property that has a lovely little earthen building on it.  It is made of a combination of straw bale, rammed tires, wood, cement floors, and i think some clothing in some of the walls.   I have made it a guest house/tiny house.  The exterior is weather worn and crumbling apart.  I dont know what was used as mortar but I'm guessing it is local clay and dirt from the property.  The walls seem pretty unstable inside and out  on one side and I'm hesitant to add anything over what is there for fear it will fall right back off!  One idea I had was to cover what is there with plywood and just start a new layer with  lime plaster .  Another was to build up the bottom and sides with stone and lime mortar, possibly over the plywood.  But it is so lumpy and uneven there would be significant spaces behind the wood for the mice to live in.  Any great ideas? I'd love to preserve how cool it is!

Does this building have any bond beam on top of the walls and columns within the walls? If it does then I would be replacing eroded parts section by section using cob and then plaster it.
If it does not have any frame and the walls are just holding everything then it's a different and more complicated story because the walls that are supposed to be weight bearing are crumbling.

What a sweet shack! I can see why you want to preserve it's character. According to this online site straw bale can be used alone  as a structural wall for smaller buildings like yours. It looks to me that the 'plaster' layers are coming detatched. What sort of climate are you in? Maybe if there is not enough overhang the walls have been getting damp. Damp clay will quickly be destroyed by temperature extremes I imagine. Hopefully someone can give some rectification advice, it would be a pity to start again, but at least natural materials like straw can be added to the garden if neccessary!

Welcome to the forums!

That is a really cute building so I can see wanting to preserve it.

If that were my building I would want to do something asap.

The chickenwire reminds me of the way stucco is added to buildings.

Depending on your resources and what you want to do you might want to decide what kind of finishes you want to use.

Some suggestions would be cob, stucco, plaster, etc.

Here are some threads that you or others might find of interest:

https://permies.com/t/72946/Questions-earthen-plaster-render-dry

https://permies.com/t/181213/Lime-earth-based-plasters

https://permies.com/t/35079/Cow-Dung-Cob-house-Plaster

https://permies.com/t/47234/Questions-straw-bale-foundations-exterior

I would say there is not near enough overhang all around, and the first thing I would do is extend all eaves a foot or so. The exterior walls are obviously getting wet regularly, and you will not be able to fix the issues without keeping them dry. They probably want to sit exposed and sheltered for some hot weather too, so they can dry internally.

Finding out if there is any structural frame beside the bales would be a good first step to repairs.

The space is small enough that I would not want to add any more than a surface coating to the inside walls. If you add a structural layer of any sort, I think you would be basically encapsulating decay.

I hope you can save the building, it is a sweet place.

Such a wonderful building to learn, practice and develop earthen building skills!
Looking at the interior, protected area of the space with a magnifier on the photo, I don't see any wall cracks which suggests that the bales are supporting the weight of those lightweight corrugated roof panels. I see that the 2 x 4 pine rafters are notched into a board at the top of the bales forming some kind of distribution of roof weight, along the bales.
Outside on the overhang, I see what looks like water erosion from a short overhang and agree with Nancy and Glenn that an extension of those roof panels would really help.

If it were my cottage, I would focus on the shed roof extension. Extend the overhang rafters (match the pine 2x4, notch and bolt new lumber on existing rafters and panels under the existing distal edge at least a foot as Glenn noted). Definitely pay the minor cost for proper gasket sheet metal self-tapping roof screws and place those screws on top of the ridges rather than the trough where the water runs as in the picture. Others might replace all the rafters on the long side of the shed roof, and add purlins. Others might replace all the roof panels beyond the A-frame cottage on the shed-roof. It depends on your budget and skills and assessment of leaks.
Once the roof is tight, I'd re-plaster using mud and builder's sand. The trick is to get the mud to stick to the building materials without a gap. Anne's provided some helpful sources. If you have more questions about using mud plaster on straw, chicken wire, wood, dry mud and non-mud materials after reading the permies threads, please ask.

Thank you to all of you for your input!  Yes, I will definitely be extending the eaves.   From your advice,  I am hoping to be able to get enough material to slowly add layers and build up the wall, adding stone in the hollow parts.  Plumbing was recently intalled in the room in the photo, requiring jackhammering to get some cement up from the floor, and the vibrations caused some inside cracking. I also will be putting better roofing on that side of it.  Again, many thanks!!!

After the roof extensions I would a lime plaster thinly to the patches that require attention, and build up the thickness as required.
People forget that earth buildings need regular inspection and maintenance.
Looks great anyway.
PS when you extend the roof, install a gutter to catch water so it does not splash against the wall and use that water.

I saw a lot of buildings like this before and during my career as a builder. This one looks like it was fashioned from materials found and on hand—rammed earth tires for footings, different kinds of roofing materials and windows, and different wall materials from straw bales to stones to cotton.  As a small structure, it may have been exempt from structural review if building codes/permits are required in that area.  And it may have been built without much awareness of then-current best construction practices for building with bales and framed roofs.  This may not have mattered if its original function was a chicken coop or garden shed or just a hands-on opportunity to learn about building an inexpensive shelter with mostly natural, found, and low-cost materials.  

I agree with the recommendations for larger roof overhangs.  You don’t say where this building is, but clearly something has been eroding what looks like an exterior earth plaster (although I have seen crumbling lime and cement plasterers that look very similar).  It may be that deep snow piled up at the building’s base (after sliding from the roof) contributed to this as well, and larger eves would help deposit snow further from the wall.  

I also agree that without knowing more about the structure (post and beam or load-bearing?) it’s difficult to tell what’s going on, and what the failing exterior plaster might mean for the entire structure.  

It looks like a charming, funky building that may be worth salvaging if you’re committed to making this a comfortable guest space.  Or it could be a tear-down, with some of it salvaged for another building, and as Anne said, some of it composted.  Start with evaluating the walls.  If it’s a post-and-beam structure and the framing is in good shape you could lengthen the roof, replace any damaged bales, take care of the edge and flashing details, prep the walls for plaster, then apply a suitable plaster.  If it’s load bearing and the bales are in bad shape....

If you decide to salvage this, a few other observations:  

Window sills.  One photo shows windows that might be set into floating window bucks (in a load bearing wall)...or they might be mounted to framing that extends from the sill plate to the top plate (what Cristobal called a “bond beam”).  Either way, the bales below the windows were at one time protected by a plastered sill which has now eroded and possibly lead to some straw bales being damaged—hard to tell if the discoloration is mud or decomposed straw.  I repaired a lot of these during remodels—turns out that plaster isn’t a particularly durable sill material if exposed to water.  Moisture collecting on the sill soaks through the plaster into the bales below.  Using 15 lb. building paper under the plaster would help prevent bale damage, but exposed building paper will also soon succumb to the forces of nature.  A peel-and-stick membrane would be a better choice under a more durable projecting sill.

Current best practice today is to use a material like tile, concrete, stone, or wood to direct water away from the area below windows; sloped sills should project at least a few inches away from the wall so water drops hit the ground and not the wall.

Mesh/lath.  I’m guessing that the “chicken wire” used on the bales was just that...chicken wire?  Although this material was commonly used early in the straw bale building revival (late 1980s through 1990s), it’s not a great choice for the application.  Chicken wire is made of a lighter gauge steel (usually 22 ga.) than stucco netting (usually 17 ga., 16 ga., or 14 ga.), and has a correspondingly thinner galvanic coating.  This protective coating is sacrificial—the thinner it is, the less it protects the steel from repeated wettings. Over time it begins to rust.  When I have torn into ten- and twenty-year old straw bale walls that used chicken wire for lath/mesh and had been subjected to seasonal wetting it just turned to dust—crumbled to the touch. Unless it was well attached through the bales it also caused heavy plasters to sag.  Some builders report that using any steel mesh with clay plasters is asking for trouble since clay holds onto water and water corrodes steel, though I think that’s mostly a concern for exterior plasters that experience seasonal wetting.  I use polypropylene mesh (deer fencing) when I use mesh at all on a clay plastered straw bale wall.  The bale surface supplies sufficient lath or “tooth” for all plasters, and mesh of any kind is only needed when a straw bale wall plays a structural role like resisting in- or out-of-plane forces.  

Today’s best practice is to use a mesh (and lath) suitable for the plaster type, and to attach it properly, according to its designed role in the wall.

If you want to get a really good look at what’s going on at the exterior straw bale wall surface you might want to remove all the plaster beneath the windows and what seem to be other areas impacted by moisture.  Check the mesh condition (is it rusting through?), see if there’s water damage to the bales (surface, or through-and-through?), and look into replacing parts of or all of them.  If it the mesh looks OK and it appears to be pinned or tied through (to the other side) and the bales have only minor deterioration at the surface, you might leave everything in place and re-coat the walls with new plaster—at least two coats.  The first coat will have a lot of depth variation (typically ¼” – 1 ½”), and a lot of cracking because of it.  The second one can be more uniformly thick (typically 3/8” – ½”), and will likely crack less if it’s a good mix, i.e., the right balance of binder, aggregate, and possibly fiber.  If you want to use earth plaster you need larger roof overhangs if that’s the cause of the existing plaster erosion.  Lime plasters will be more durable, but larger overhangs are still a good idea because lime plasters saturated by wind-driven rain (or rain/snow sitting on a plastered sill) will readily wick moisture in towards the bales.

Where plasters stop (edges).  It looks like the exterior plasters didn’t have a defined stopping point—they just ran onto whatever the mesh was stapled to at the wall’s top, bottom, and around windows and doors.  I saw a lot of this on straw bale structures built up through the early 2000s. The problem is that straw and wood have different thermal and moisture expansion-contraction characteristics.  Wood moves with seasonal humidity changes, and a crack forms where plasters have been applied over wood unless a slip plane was inserted between the two. Or there’s A LOT of straw or other fiber in the plaster to supply tensile strength.  Best practice is to use two-ply stucco paper there, lapping it several inches onto the bales to cover this junction, then installing a lath (burlap, fiberglass, metal) over the paper so plaster sticks to it.  Without doing this the plaster over wood and near edges can crack and chip off.  I also like to "capture" plaster fields with wood trim or metal screed and bead that protect the plaster edges and creates a very clear stopping point.

Window Flashing.  The windows have no flashing (which can be challenging to apply over floating bucks in a load bearing wall).  This is a peel-and-stick tape that seals the window mounting fin to framing, makes that joint more air-tight, and keeps water from getting behind the tape and into the window and wall, potentially ruining both.  Best practice is to do this on every window and door, but with large enough roof overhangs you may not need to worry about this.

Roof flashing.  One picture shows a small shed roof (what is sometimes called a “rooflet) positioned between a window and the ground.  It’s not clear what this roof is protecting, but there’s no flashing between it and the wall it’s attached to.  It looks like any water running down the window will drain down behind the roof—and remain on or in the wall.  Best practice is to have wall-to-roof flashing here—a kind of “Z” flashing where one leg of the “Z” extends up the wall (beneath the plaster siding) and the other laps several inches over the gap at the roof/wall junction.

Ceiling insulation?  It looks like the ceiling isn’t insulated, and that the rafters are possibly 2 x 6?   It’s not clear if this was meant to be a conditioned space with a vented roof, but if the interior picture shows the underside of the metal roofing, there there’s no insulation in the space, so it probably gets cold in the winter, and warm in the summer?  If it can be a vented roof, then the rafter depth minus at least 1” of vent space would offer about 4” for insulation...or around R-12 to R-15 for the rafter bays (thermal bridging at the rafters will drop the overall ceiling insulation to around R-10).  R-39 is the minimum ceiling insulation requirement for temperate climates like where I live in S. Oregon, and that usually requires at least a 12” deep space for insulation.  If you want to insulate the roof to make the space more comfortable, you’ll also need some kind of ceiling to keep inhabitants from breathing insulation particles that float down.  2 x 6s may not be able to carry these added loads across that span, and you’ll need to explore ways to re-do the way the roof/ceiling is supported.  Know that whatever you do must carry the greater weight of insulation and a ceiling like sheetrock or T&G wood.  If the latter, note that T&G isn’t air-tight.  I have been in plenty of “mostly natural” straw bale buildings that used fiberglass or rockwool or denim insulation in the ceilings. Where only T&G separates the living space and the insulation, on windy days I have seen dust particles (bits of attic insulation) floating down through gaps in the T&G.  Use some kind of air barrier there, or people will be breathing insulation dust.  I like the looks of T&G but would use sheetrock under it because it’s a better air and fire barrier.

Good luck!

Jim Reiland
Many Hands Builders

Wow this is all such great and valuable information! Thank you so much to everyone!  Eventually I will update with progress reports!

My advice would be to try and preserve the character as best you can, but also think of the insulation safety of those inside. You can start by repairing the walls with cob and lime plaster, and then add the plywood if needed. Make sure to check the eaves and make sure they are properly extended if more protection is needed from the elements.