Tiny Strawbale/Cob Home Progress and Questions

Hi all, in another post many of you have helped me decide how to best build my tiny house. I'm currently still building the foundation. This is roughly what I have envisioned for it. A one and a half story cob house with straw bales wall interior for insulation on a rubble trench foundation.



Since it can rain a lot here, last week I decided it would be less hassle to build the roof first, which means I'd need to build wooden supports to hold the wooden shingle roof.



This is where I need advice:

If the roof connects to the wall ~4 meters off the ground, is a 5-meter long supports with 1 meter sticking into the foundation enough?

To prevent wood rot, I want to forgo concrete (maybe lime instead). Would burning the ends (Shou Sugi Ban) that lie in the rubble trench suffice?

If I go the burnt end route, how should I form the rubble trench around the poles? Is there a general recipe, like using more fine particle gravels instead of bigger rocks, or does it not matter as long as it’s in sturdy?

Is there anything else I need to bear in mind that I might be missing?

5-meter long poles without foundation



Otherwise here's the progress digging out the foundation and starting to fill it. Enjoy :)


The initial site


12-cubic-meters of various size rocks from the quarry






Finished digging the ~1.3-meter depth ring (future extension juts not visible)


Laying down the barrier between the rocks and the earth





Voila!


Future extension juts

What diameter is the house please? And where are you building?
Burning log ends is a good idea.
Fitting the poles into the gravel trench with what ever rocks fall against the post will be ok, a bit of air around the poles will do no harm.
Will you have the inside or outside of the strawbale wall?
Or fitted inside?
Have you thought of 4 or 6 poles and build a gabled or skillion roof, it may be easier?

The house is an oval house with an interior of 3 meters x 4 meters with the roof connecting to the walls at about 4 meters of height. The walls will be roughly 60 cm wide, that is 40 cm wide bales with 10cm of cob on both sides. I'm building it in Lithuania (about 55ºN).

I recently learned that building a cob house, you don't want to submerge more than half the width of the poles into the cob, hence I still haven't decided how I'll do that. Because, the house is already small, I'll most likely go with having them on the outside, however, since I'm using cob more as thermal mass than wall support, would it matter if I sandwich the poles between the straw bales?

I have considered other roofing options, however, I'm more interested in learning beautiful architectures, hence, I'm not looking for the easiest route, but the most rewarding one, whether that's in the learning process or the finished result.

**Random question** - I'm planning on installing solar panels onto the roof. Do I need to cover the area underneath with shingles like the rest of the roof or can I install the panels directly?

For solar panels on a roof at 55 N latitude, I think you really will need to have them sloped much more than the roofline shown. Thus they couldn't form part of the given roof surface. I too would prefer to use panels as the water-shedding surface, but I understand professionals discourage this idea.

I think for a roof with solar panels, you will get the best looking results with a steepish gable or shed roof facing due south; this will allow the panels to blend with the roof instead of sticking out like an afterthought. If you want heat energy from the solar panels, at 55 N I would consider putting them on the south wall rather than the roof. They will give much more output when heat is needed that way. If you only want electricity from them, and can stand not having much output in winter, the roof will work. How much power/how large a panel area are you considering?

You can always install the solar panels on the ground with a frame suitable.
And that frame maybe adjustable to allow the panels to be directed to the sun each month.
Having the pole as a door frame is an excellent idea.

You may want to research photovoltaic (sp?) shingles...please excuse my inability to provide more info - all I remember is I first heard of these several years ago. I recall they were pricey - but as they double as the actual roof, it may offset the cost.

With the shape/slope of the roof, actual installation of regular solar panels may prove challenging.

Thanks for the feedback everyone. I'll update the roof designs to reflect the steeper roof.

@Glen - I'm having trouble imagining what a gable or steep roof would look like on an oval house. Considering that the only fixed dimension of the house is the shape (as it's the only thing that's dug as of yet), I'm open to the idea of a different roof to facilitate solar panels. Have you any examples where I might look towards for inspiration? Secondly, since my entire property is a woodlands (on its way to becoming a forest), sunlight will be harder to come by, so I'm keen on raising the panels as high as possible. I'm considering 3-4 panels. My consumption will be minor, charge my phone, computer and power some lights.

@Lorinne - Yea shingles would be nice, however I think we're still quite far away from that here in Lithuania. I'll wait for the technology to work those prices down and their way over here.

Glen, I played around with some roof alternatives, attached below. Is this doable, or would I be attempting something way over my head? Any thoughts?

Regarding this roof - because the roof is angled at ~50º to support 2 solar panels, I’d like to have the roof hang over the walls but not at such a steep angle. Is it possible to have the overhand roof at a smaller angle than the roof structure, like a '\_' ?

That looks like a practical roof layout, and interesting too. I assume you have the elements to correct scale for the panels you would use. I don't think there would be any reason to extend the rafters or roof below the bottom edge of the panels, while maintaining a decent overhang to protect the wall surface. The gables would allow a nice pair of windows for view and cross-ventilation.

A simpler roof might be to have the gable running east-west, with the southern face steep for panels and the northern face shallower to allow more usable loft space, and windows on the east and west ends. The gable doesn't have to be centered on the structure; you could move it north or south to give more steep surface or more interior clearance, as desired. This simple gable would allow more clear width for panel mounting.

Reviewing your sketches, I see that there is not a gable end on the north, so you would not have standard windows for cross-ventilation. You could still alter the finished profile to allow that, or use roof windows/skylights for cross-ventilation.

I would rest those long sloped rafters on the beam supported by the posts at the bottom of the panels, only extending the rafters enough to give sufficient overhang to protect the walls. You could also crank the roof profile below the panels to give more overhang with less drop as you suggest. This would complicate the structure some.

Putting the panels on an east-west gable would allow them to be at the highest point of the roof for best solar exposure and least shading from trees as they grow. I would proactively thin trees to the south, southeast and southwest to allow continued solar exposure. You will probably want some garden space, and sun is important for that too.

Not a builder, here, but I find myself pondering...is there any reason that you could not put a squared room, atop the round walls? Cantilevered "floor joists", by a few feet, all the way around.

I would think this would seriously simplify the roof/solar system, from both a cost and installation perspective; as these items tend to be generically dimensional, and in rectangles.  It could be extended/elongated over the door, to create a covered/sheltered entrance.

I would also think that construction of a square upper floor would be much simpler, faster and likely cheaper; especially roofing, siding and window installations, along with internal fittings such as flooring, shelving, cupboards...

As an added advantage, one could increase the square footage on the second story, and if the "box" cantilevered, say 2 feet beyond the round walls of the lower story this would provide exceptional protection for the lower structures round walls, and some handy covered storage areas...as heat rises, the less insulated upper floor might actually prove to be a bonus.

Again, I am not a builder, just sharing my random thoughts...

Thanks for the suggestions Glen, I've updated the designs to reflect my understanding of them. Is this what you had in mind? I plan to have a window in the horizontal triangular roof top. Would this suffice for cross-ventilation? And yes, I foresee having to trim trees in the coming future.

Lorinne, I considered a square building and a square building on oval foundations feels illogical and needlessly complicated, plus I want fewer corners and more rounded shapes to reflect my living style (they say your home is a representation of yourself after all). With that said, I'm not looking to build something fast and cheap but something authentic, practical, and I want to learn from mistakes and opportunities. Hopefully I'm not biting off more than I can chew, we'll see.

Regarding the frame construction, any recommendations for joints to hold it all together?

That looks very cool, very complicated, and with even fewer ways to get cross ventilation.

What I was talking about was a regular gable roof with a north slope and a south slope, and walls up to the peak at the east and west ends. This allows regular windows and a maximum amount of south surface for panel mounting. The edges of the roof would not need to be square; they could be rounded or angled to better follow the wall footprint.

Timber framing joints are the last thing you need to think about after deciding on the actual plan. What you have shown would require extremely complex joinery with scarcely a right angle in the lot. I would strongly advise against trying to learn timber joinery on this frame. That said, looking up timber framing resources would be your best bet; it is not practical to describe how to do any such thing in a forum post.

A tweak on the gable roof would be what is called a gabled hip roof (called "Dutch Gable" in this chart.)

This (built much steeper) would allow east and west windows in each upper gable end, with roof below to protect the east and west walls and avoid having to build two-story-high strawbale walls.

Thanks for the feedback Glenn. I looked into Dutch gables and the dilemma I run into is that the hip is at less of an angle then the roof, whereas I'd want the opposite, because I'm in a northern climate and my panels will be around 50º, I don't think the hip is of any help. To achieve cross-ventilation it looks like I'll have to go with what Lorinne advised all along.

I've updated the designs, if you could let me know if this is in the right direction and if I'm missing anything. I added center supports in the third design for stability.

That looks like an eminently practical roof structure. All you need to do is extend the ridge on both ends a bit and make little gables. This would give you more space upstairs and allow for windows on north and south ends. This would give less solar panel space than what I was describing, but fits the oval well.

I don't understand what you said about the east-west ridge with hips giving less slope... you can make both parts (the main roof faces and the lower hips) any slope you want. This with a 50 degree slope would certainly make a high peak in the middle of the upstairs, but not so high as to be stupid, as long as the point where north and south faces meet the walls is as low as you can make it while giving door and window placement access. For that matter, the ridge doesn't have to be centered; you could move it south a bit so there is good window exposure on the ground floor south side, and a low wall without windows on the north side. A standard hip roof has its lower edge the same all around, but this is not required either. You can extend it or cut back as desired for your purposes.

I don't have sketchup, so I butchered your drawing to give an idea of what I mean.

Hi there!

I have a question if you don't mind. I am currently in the process of exploring Cob options in my area and it seems grim when it comes to building codes - but I am leaning on just building it anyway. Did you go through your county? If so, did they give you any trouble on approving this? Or are you doing this on your own? Thanks!!

The house under discussion here is in Lithuania, so not really applicable to American code questions.

I can't tell you how grateful I am for your feedback Glenn. I'm poor with directions so I added directional markers going forward. I've updated the mocks to reflect my understanding of your sketch. If this is correct, what kind of joins will I use to connect where the corners all connect (See top end of the yellow part in the last photo)

There are many ways you could frame this, but given that it is on an oval wall structure, the corners of the hips project farther than necessary to protect the walls below them. I would make a gable roof with the main roof beams extending to form the overhang, and separate beams with braces to the main posts to support rectangular "hip" roof sections. I would add triangular roof sections to join the corners of these parts, giving a somewhat octagonal plan to the whole roof.

This would make for simple framing joints. I would run the main gable beams over the post tops, with posts tenoned into mortises in the bottoms of the beams. I would tenon the "hip" support beams and their diagonal support braces into mortises in the sides of the posts. I would probably also add support braces for the gable beams' overhangs since those will be fairly long.

What kind and size of timber do you have available to use? The larger and stronger the frame members, the simpler the bracing can be. You will need diagonal bracing on all posts at the corners of the wood frame to keep the roof steady before the walls are built. This will also be beneficial in the finished house, taking wind load stress so the strawbale walls don't need to. With hefty enough posts and frame members, the frame could be self-supporting without sinking the posts deep into the rubble trench, reducing the potential for rot in below-grade wood. Wind loads during construction will be a major consideration here.

Looking at your gable-v2-1 sketch, I would make the four horizontal beams half-lapped at the corners over the posts, with long tenons on the posts rising through both parts of the lap joint to secure it. The beams parallel to the ridge have little load, and I would put them as the lower part of the lap (or else just tenoned into the other beams), and extend the beams that are in line with the gable beams to tenon into the bottoms of the gable beams to form triangular trusses.

Here is an exploded view of the framing joints I described... very rough and not to scale.

Hey Glenn, lots to process here but very helpful information. Regarding the tenon connections I want to make sure if this is what you had in mind. Regarding your question what I have available, thus far I only have the poles that will go in the ground. I've burnt a meter off the ends in preparation for impregnating them via the Shou Sugi Ban method, and they're long enough that I'm not worried about sticking them deep into the foundation. Otherwise, I will look to acquire whatever lumber fits best, though I'd prefer less processed logs wherever they'd fit.

You are understanding the tenon post-beam joint correctly, although the tenon should be smaller so the beams can have more strength with smaller holes. I was expecting that you would use round poles for the beams, flattened as much as necessary at the joints.

I would not notch the rafter as that weakens it significantly; rather, I would extend the beam as a tenon, with a mortise in the rafter.

I didn't flatten them at the joints as I plan to do when I construct it, however I take it this is what you had in mind with the long tenon.

You could do the tenon that way, though it wouldn't be very strong at the rafter connection. I would extend the horizontal beam that is in line with the rafter so that it tenons into the rafter, with a tall thinnish vertical tenon, then cross-drill and pin the tenon to the rafter. (Look at the details of the exploded view I posted.) This makes an independent triangular truss frame sitting on top of the posts.

I would advise making the horizontal beam connection a mortise and tenon rather than half lap, as the beam shown in the exploded view has much more load than the one (not shown) at right angles to it.

I strongly advise studying some timber framing resources to understand the best dimensions and practices; you can get better information that way than I can give in words on a forum thread. Here is one that looks good: https://timberframehq.com/joints-and-joinery/

And a specific detail for the beam-to-rafter connection: https://timberframehq.com/double-mortise-and-tenon-joint/
The extra tenon from the right-angle beam adds some complexity to this. There may be a better way to do that part.

Thanks for the resources Glenn, I studied the site, however it looks to be geared away from round timber framing joints. It's made clearer the connections regarding braces, however, I've still some uncertainties.

I've updated the designs to reflect the correct distances between the poles as well as the corner post shapes to reflect materials that I have (they're square now instead of round) and I've updated the tenons. I would very much appreciate confirmation whether the corner tenon & mortises are ok here and how to connect the gable posts.

Again, no builder here... could you not run the angled gable beams all the way to the ground to act as braces, instead of leaving the free floating?

Hi Lorinne, the poles would need to be about 6.5 meters long, so if I could find 4 such suitable poles then yeah, it's an option, though it might make getting around some corners of the house difficult as there are trees nearby and the posts would descend into the area between the house and the trees.

I found an invaluable series where two guys construct a round-wood timber shed using handmade tenons and mortises which is proving helpful. Futhermore, now that I'm learning more terminology I can better search for existing examples, like this here which shows how they construct a support for the gable.

Here's what I'm edging towards now. Any feedback would be greatly appreciated.

Edit: I don't have it shown here though I'm still considering how best to cover the ovular parts of the house that will stick out, whether that means extending the gable posts or something else.

Here's some progress on the tiny house. With a lot of guiding from Glenn, I discovered the style I want to build the house in. I found Ben Law and his round-wood timber framing materials which answered the biggest questions I had regarding how to build a gabled roof using the fir trees from the forest nearby. I spent all summer digging and filling a rubble trench foundation.



Before I launch the photos I'd like a second opinion on the order of building, regarding flooring and insulation. I'm building this house with only reclaimed, donated materials, hence I'm avoiding buying synthetic materials like for insulation, so I'm wondering how best to insulate the floor, and when to do it. Ecologically, I only know of clay slip & straw insulating but I don't know if this is viable for floor insulation, and I don't know how thick to insulate. I think, I'd add the insulation once the roof is built to prevent rot. Anything I'm missing.

Here's the rubble trench filling progress:

More photos...

Progress report?  

Progress report… I returned to my Vilnius apartment where I kicked my roommate out to build a workshop, and I've been practicing how to make log tenon & mortises

I'm getting ready to order tarps, a container to store all the tools I've acquired for the upcoming construction and if anyone wants to take part, I'm actively searching for help :)

More updates to come once the snow melts and I can do more on the land!

Maruf Miliunas wrote:Progress report…!

Maruf, I cannot be of any help because I'm nowhere near you but I just wanted to say that even 10% of something is better than 100% of nothing so keep moving forward and you will get there! It will be worth it!

Thank you for the support!

Maruf, how is your project going?

https://permies.com/t/189786/Seeking-advice-attach-roundwood-rafters#1562415

https://permies.com/t/190711/Alternative-cylindrical-oak-pegs-securing