Current state 2017/04/10
I have been pondering on a load bearing bare Strawbale Cabin for quite a while, after the tipi, yurt and geodesic dome the winter 2014/2015 something more solid: an easy to build and take down strawbale based cabin.

The main idea is to be modular and cutting as little parts as possible of common sized timber, like 3m and 4m long beams, and maintain bare strawbales, inside and outside and see how it does.

The main measures are based on the OSB/MDF, in my case I used 22mm thick 2050mm x 675mm OSB/MDF, and I ended up with roughly 4m x 6m, or to be exact: 3 x 6 x OSB 2050mm x 675mm = 6.15m x 4.05m floor size, the room height is around 2.20m.

Reminder for non-metric people: 1m (meter) = 100cm (centimeter) = 1000mm (millimeter)

Rough Sketch with 2 Options for the Roof

Floor Plan

Ceiling Plan

Roof Plan

Floor: 6.15m x 4.05m, ~24m2 (interior: 5.5m x 3.4m, ~18m2)
Wall Thickness: 45-50cm
Ceiling Height: 2.20m
Strawbales: ~140 pieces (apprx. 90cm x 50cm x 35cm per strawbale)
Features:
- 1x door (prefabricated)
- 2x windows (prefabricated)
Total Height: ~4m

Strawbales

~180 x small strawbales (90cm x 50cm x 35cm, apprx. 2-3 Euro/pc)

Solid Wood

20 x 4m x 7.8cm x 5.8cm wood beams (a 5.80 Euro/pc): floor and ceiling (14 used, 6 spare)
30 x 3m x 5.8cm x 5.8cm wood beams (a 3.50 Euro/pc): roof
50 x 4m x 4.8cm x 2.4cm wood struts (a 1.30 Euro/pc): floor and roof
30 x 3m x 4.8cm x 2.4cm wood struts (a 1.00 Euro/pc): roof

OSB

20 x OSB 205cm x 67.5cm x 22m (a 10.50 Euro/pc): floor (18 used, 2 spare)
25 x OSB 205cm x 67.5cm x 12mm (a 5.20 Euro/pc): ceiling (18 used, 7 spare)

Misc

24 x 2m x 0.91m bitumen roof (a 8.65 Euro/pc): roof
1x door with frame
2x windows with frame
7m x 7m PVC: to cover construction to prevent rain entering the strawbales

Prices as of 2014/10, wood & OSB from Bauhaus.info (Germany), strawbales from local farmer, door and windows were spare.

I started to plan the cabin with the idea for a single person to build it, and test some of the wall construction methods. Due to logistic issues like belated arrival of strawbales, the late fall and more humid and rainy days cut the experimentation period short and I had to accept help by two people.

Compressed Wall with Threaded Rods
The chosen method I ended up doing was "Compressed Wall with Threaded Rods", actually suggested by one of the helpers named Cyprian: compress 4 layers and the top 2 layers of the bales using threaded rods, which requires 2 people to position a bale, particularly at the edges: one positions the bale, the other one makes sure the threaded rod pushes through the bale and doesn't bend when resistance is met. This allowed to develop a rather stable wall, while still be "Load Bearing" and little wood involved in the wall construction itself.

I estimated the material cost about ~1500 Euro overall, given you have the basic tools for construction, and door and windows are already available.

It took 9x afternoons (~4 hrs), or ~4 1/2 days to raise the cabin with the roof complete, apprx. 2-3 persons worked on it. A single person might work 10-14 days on it, an experienced person a few days less.

So far this has been the most "solid" temporary building I did, and also the first were I had to accept help from others to actually raise the building, with domes, tipi and yurt, you can raise it as a single person (up to 6m diameter of those). With some patience and dedication one can build a strawbale cabin as a single person as well, e.g. by compressing the wall with cords instead of threaded rods as I did, and this way simplify the manual handling when positioning the bales.

2014/10/12 14:54

2014/10/30 16:51

2014/11/02 15:29

2014/11/04 15:34

2014/11/19 14:02

2014/11/19 16:03

2014/11/19 16:55

2014/11/20 15:44

2014/11/22 13:05

2014/11/24 13:13

2014/11/25 15:08

2014/11/27 14:28

The main disadvantages of constructing with bales are

the sizes are not even or regular, one has to account to margins and compensate accordingly
prevent water (rain) to enter the strawbales while you raise the building

whereas the main advantages on the other hand are

the bales are flexible and not too rigid, which gives 2-3cm margin on the side to jam things, e.g. window, door, or general unevenness (of the bales themselves)
light(er) bales might not be perfect for larger buildings, but they are easy to handle
rather inexpensive construction material
has good insulation properties

About the actual exposure of the bare strawbales as I plan, I can't say anything yet (2014/11/26), check later in a couple of months.

I'm more fond of circular and spherical structures, as the rest of this web-site tells, there were two reasons to go rectangular with the strawbale cabin:

the strawbales are rectangular
the bitumen roof sheets are rectangular

in particular the roof sheets were a strong reason to keep the rectangular shape. I thought first of a strawbale based dome, but the rain cover would have been very cumbersome, as the entire surface or most of it, to be properly sealed, as straw does compost quickly when exposed regularly to water and air. So, to minimize the roof I decided to go with vertical walls and due the assembly of overlapping bitumen roof sheets, I went rectangular overall.

Most up-to-date entry at top, first and oldest entry at the bottom respectively last page.

The farm and its land, where the cabin was built on, was sold, this meant it was time to take down the cabin again . . . after ~6 years occupying it.

strawbales were reused for horse boxes at the farm
roof was properly disposed / recycled (contains bitumen)
construction wood (strong beams) and floor were reused
scrap wood / broken beams put in a fire
clay walls & clay oven were hammered away and redistributed on-site where it came from

I took down the cabin in almost the reverse order it was built: windows, roof, ceiling, walls, floor; and I was able to do so all by myself with just an axe and hammer as tools. Most nails and screws used I collected again for future use.

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It took me apprx. 10 days to dismantle the cabin, about 4-5 hours per day. A thin layer of straw was left on-site which eventually would decompose in the spring.

It has been a gift to be able to live this experiment with a low impact, low cost strawbale cabin for the past 6 years.

A small side project: earth oven, next to the cabin:

subsoil (beige colored) collected around the cabin (below the brown humus), soaked in water for 1-2 days
mixed with a bit sand and straw, stamped with the feet until it was keeping form while still be formable (no photos as my hands were full of earth)
used some cardboard boxes, cut into shape so a nice bow room achieved, second box for the front, taped together
apprx. 5-6cm thick layer plastered around the form
apprx 2-3 hours preparation, 1.5 hours plastering and mixing 3 batches on a piece of tarp

2017/04/02 14:36

2017/04/09 10:53

2017/04/09 12:28

I let it dry for 2 weeks and then fire the interior, and it will burn away the cardboard - update posted later.

Nature changing now quickly: warm weather with a bit of rain.

2017/03/22 17:25

2017/03/25 13:03

2017/04/02 14:38

2017/04/04 15:16

2017/04/10 15:18

Nature, here north of Switzerland, seems 1 month ahead of its usual schedule.

An excerpt of 25 photos of a sequence taken 2017/03/05 ~12:45 every 30 secs

Sunny day 2017/03/05

After weeks of sub-zero Celsius all day long, it rather quickly jump to 5-10°C, and today reaching 15°C - usually end of February is the coldest time of the year here at north of Switzerland.

Also most of the trees and bushes have been trimmed, some longer straight branches I put aside for some new smaller constructions:

bow based tent-like shelter
small tipi

Asleep garden (February 2017)
2017/02/23 14:15

New projects . . .
2017/02/23 14:15

The last days below zero Celsius during the day, some snow fall (~5cm / 2"). Cold dry weather doesn't affect the strawbales, so I don't expect any significant changes during the next weeks and months.

I've have been pondering on invest some more time to improve the cabin the coming spring:

plaster the interior: reduce interior dust, brighten the interior
get electricty from the grid (apprx. 150m away)
heat transfer to store energy (warm water or electricity)

The last days below zero at night (frozen ground) and rain during the days (4-6C). With the additional floor insulation it feels warmer, temperature droppings and raise aren't so quick, but actual detailed temperature measurements required.

The garden has calmed down, flowers and grass stopped growing; the cut apart left over slowly decomposing.

Two years ago around the same time I just finished the built of the cabin itself, it was mild and dry before it began to rain.

Photo: November 19, 2016 - around 15:30 already in the shadow of the trees / forest in the west, sun not yet set over the ridge farther west.

Last night rain turned briefly into snow, just a bit of snow - a few patches over the grass, which melted during the morning away; 6 weeks earlier than in 2015.

I decided to upgrade the floor insulation for this coming winter 2016/2016 with 35mm thick pressed china grass insulation (198cm x 35cm or 28cm), it is solid enough to serve as floor without additional wood. I also insulated the door with the same parts.

Additional 35mm thick Floor Insulation

I harvested the rest from the garden (pumpkins, tomatoes) and removed the small tomatoe shelter, 1/2 of the tomato harvest didn't finish to ripe on-site but now in the warm kitchen.

After weeks of warm weather the temperature fell from 25C to 15C rather rapidly within 1-2 days, and regular fog in the morning arrived. Not much rain yet which otherwise is usual in October and November in this region.

The exposed raw strawbales doing fine after nearly 2 years, another month the 2nd anniversary is reached when I will take detailed photos of the strawbales again.

2016/10/12 14:10

2016/10/12 14:11

2016/10/12 14:12

The garden does well, so far the moisture of the ground is still sufficient for the garden - no additional watering was required so far - posting photo as comparison for previous month.

Until ~14:00 the the sun doesn't reach the front of the cabin, and it's nicely cool inside the cabin, yet, once the sun reaches the front the inside warms up significantly, through the windows (the shades are inside).

Summer has been hot and wet, the surrounding has been blooming, grass has grown significantly compared to summer 2015.

The grass around the cabin slowly reaches the strawbales, and insects might more easily reach the bales - so I likely will cut the grass around.

Also the small garden began to do well, planted vegetables are growing well - assuming the soil has been balancing itself:

tomatoes: growing well
potatoes: growing well
zucchini: late planting (seed into the soil) grows well, others vanished and did not grow well
rhubarb: growing slow, next year possible to harvest, not this year

Since the soil in front of the cabin is humid I did not have to water the garden at all.

All 4 photos were taken apprx. 1.5m off the ground:

West side (sunny)
2016/05/22 15:50

North side (shade)
2016/05/22 15:50

East side (shade)
2016/05/22 15:50

South side (shade)
2016/05/22 15:51

There is a slight dark shade on the strawbale, at the close up the "shade" is made up by small dark spots on the straw. So the change is very minimal, more long term exposure is required to estimate the longevity of the bare strawbale cabin.

West side (close up 4x)

West side (close up 16x)

Btw, the green tone of the "East side" comes from the grass behind the cabin reflecting green to the strawbale wall.

Looking at photos of last year around May 2015, and one sees how fertile and green nature looks around. The grass is high and dense.

After a period of 10 days with a lot of rain and lower temperatures of 10-15°C sunny days with up tp 25°C.

I started a small garden in front of the cabin, but the earth with horse manure isn't mature yet for vegetables:

rhubarb: does well
squash/pumpkin: too early to tell
zucchini: doesn't do well, some leaves turned yellow despite sufficient water in the ground, new leaves are green again
tomatos: too early to tell

each bed has 3 layers

sand/earth mix layer at the bottom
horse manure mixed in
loose straw on top

the base is a moist or wet ground.

I began to prepare some garden beds in front of the cabin as I thought to take advantage of the muddy and humid ground.

Since the cabin is located on the west slope, the sun reaches the roof and garden beds around noon - will see how it does once I planted some veggies. I also collect some rain from the roof, yet, without dedicate rain channels as for now.

Between March 23 and April 12, just 3 weeks, the change in nature is significant:

in the background the forest is significantly more green
the grass in front of the cabin is grown significantly

The last weeks it remained 5-10°C during the day, and a few times below 0°C. For 1-2 days it snowed ~5cm but melted away right away - the winter skipped, and spring time coming slowly.

Rotting strawbales due leak of the covering tarp
Some of the strawbale I piled up outside covered with a tarp I checked, and some began to rot due a small leak of the tarp - so I had to dispose the bales and scattered the open straw near by to provide some soil soon for gras on the slope behind the cabin (see photo). One remaining pile of strawbales seems doing fine.

I leaned a small wheelbarrow on a pile of covered strawbales, with apprx. 5-10cm space between bales and the wheelbarrow - it began to rot just at that space; microclimate with lack of proper air circulation seems to affect bare strawbales greatly.

April is a rainy month in central Europe - so once April and part of May passed I photograph the bales of the cabin close-up and compare with previous photos I made.

Mid of February, and the past weeks hardly any snow, rarely below 0C, more humid and rainy wheather. The straw is still doing fine as far I can tell, but will review carefully when spring approaches and temperatures raise over 10C.

About 10 days ago we had a winter storm "Susanna" approaching from south-west, 80-100km gusts over period of ~18 hours on and off, and the cabin maintained itself.

After warm and humid (rainy) weeks finally the temperature fell below 0°C and snow fall started.

The straw on the north side is a bit darker due the humid weeks - will see if it will reverse due the drier and colder days ahead.

The mild fall has continued, hardly any rain; the small upgrade I did a few days ago paid off, less mice on the roof as they used the gap to explore the top of the cabin. Since the fall has been so warm, so little rain, the strawbales aren't really tested much in regards of mold.

A bit more than a month until lowest sun path (December Solstice), before the daylight extends again.

After a hot summer, with days with over 35°C and hardly going below 20°C at night, fall approached, which until November did not have a lot of rain but quite some foggy days around 5-10°C.

I noticed the northern side of the cabin slightly darker, with some slight mold; the west and southern side still like color as in the summer.

A small "upgrade" I did a few weeks ago: closing the gap at the back (east-side) just at the roof/wall junction, which otherwise was open straw compressed between the ceiling beams, and now a ~6cm line of wood:

The straw did quite well through the winter and spring, humidity did not affect the straw as far I can tell. The rest of the summer was rather hot, up to 38°C for days, very unusual for this region.

Snow is gone, the dome I had to take down as the snow and storms - so far the cabin did very well through the winter time, let's see how the rest of spring time will affect the exposed straw bales.

Snow Gone
A low pressure system with strong winds and rain went over the region last night, and decimated most of the snow, but left the soil very damp. The temperature raised up to ~8C° in the sunshine. The snow which slid from the roof remained in front and in the back.

Heating
The gas heater I obtained isn't doing the expected: it heats the air quickly, but it won't last due the minimal thermal mass as I realized. The insulation of the cabin isn't as tight as I planned (still needs work), but this is just part of the problem. A real oven radiates the heat off its thermal mass, and carbin monoxide mostly exits through the pipe, whereas the gas heater leaves carbon monoxide inside the room and needs proper supervision. So a real oven would have been more suitable, even for just 2-3 months use during winter time, after that it won't be of use for me. Ideally would be a light stove with sufficient thermal mass, e.g. using water for the thermal mass instead of heavy stones.

Gas Heater: very light (2kg), inexpensive (EUR 70), no pipes, easy source of propane gas (11kg = EUR 20)
Ordinary Oven: heavy (80kg mininum), variable price (free - EUR 600), requires pipe system, easy source of wood (1 ster = EUR 50)
Light Oven: light, inexpensive (DIY), requires pipe system, easy source of wood (1 ster = EUR 50)

1 ster = loose 1 m³ wood

A "Light Oven" I envision a brick based rocket stove, which can be assembled on site and disassembled when taking down the habitat again, and only transport the pipe system. The thermal mass would increased with heat resistant water canisters positioned close to the oven.

Last night around 22:00, the snow slid down first on the front (steeper west-side), and 40min later at the back (east) in one go. After an afternoon with positive Celsius temperatures, and some rain. I was a bit concerned how much water the rain will capture before it slides down - but since I made the roof quite steep, steeper than the suggested 25° for this region, as stated on the flyer of the bitumen roof sheets. The actual angle of the roof is about atan(1.3m/2m) ~ 33°. I estimate about 300-400kg snow piled up until it slid down.

December 31, 2014

A week with sub zero Celsius degrees of temperature - the snow piled up on the roof. The heating isn't working as ideal as I envisioned, several factors:

just 10cm insulation of the floor
loose straw filling the gaps of the ceiling construction, a compromise to increase overall static

The next weeks I gonna try to fix the weak points of the insulation.

One night was -15C, and inside the temperature dropped to approx. -5C and liquids froze in the bottles, definitely something I did not expect to happen.

The next days positive Celsius degrees are expected, with rain - it will be important for me to observe how the melting and slide down of the snow ice combo of the roof occurs, e.g. the weight will first increase of the snow, until the ice underneath detached of the roof and perhaps ice and snow in one go slides down.

First snow of this winter season - it started to snow this morning, apprx. 10cm, humid and rather heavy snow; first test of the roof which I made rather steep for excactly this use case.

I was away a few days and when I came back today and the two PVC domes (LC 3:3:2 and 2V geodesic) nearby crashed due the weight of the snow; I gonna fix them tomorrow or so.

Temporary buildings need on-site presence to take care of them for severe weather conditions, the strawbale cabin definitely is more solid and requires less "care" on-site.

A brief 3min walk around, no spoken comments, getting a sense of the size of the cabin, texture and feel of the bare strawbales, a brief view of the inside etc.

The last two weeks I fine tuned or adjusted the insulation, patched gaps, and made a small door for the attic, and removed the temporary poles inside the room, they were used to support the ceiling while working on the ceiling & attic. Also I haven't noticed any further compression of the bales the last two weeks.

I bought a gas heater (EUR 60) as I didn't want to install a wood stove / oven; but since it was rather mild the last days (5-12C) and partially sunny, there was no need to heat yet. The gas heater is for exterior use mainly so I have to be carefully to use inside (carbon monoxide poisoning) and properly vent. Two tests I did of heating the room within 10-15min from 5C to nearly 18C, so I assume with lower temperatures the period of running the gas heater will be around 30min or so per day at sub zero (Celsius) days outside, to reach 15C interior; will document this later.

Last week I had the first mouse entering the cabin, from the top, where loose straw was used to patch the gap from the wodden beams under the ceiling - so I added more straw and compressed it further. It was a compromise I made, it increased the ceiling stability, but introduced a gap where loose straw was required to be used (8cm thick portions of a bale).

A few days ago some brief windy rain occured and did wet the south-west side of the cabin, after a few hours it dried off again. It will be interesting to observe change of the color and material (straw) over the period of weeks and months - one of the main aims of this project to observe long(er) term use of bare strawbales in construction.

Today the sky cleared in the afternoon:

2014/11/28 12:26

2014/11/28 12:27

And I continued to close the ceiling / roof gap with OSBs, here the south side:

2014/11/28 15:57

2014/11/28 16:27

By chance, without planning actually, the height of the triangle is 1.30m or ~ 2x 0.675m so two lanes of OSB fit nicely - the left over I reuse for the north side. The details of the rain runway below the OSB triangle I will do tomorrow - it's very important that rainfall reaching the triangle flows down, and then over the strawbale and not into them.

Afternoon I spent cleaning up the surrounding and collect left overs of the construction, patch some more holes between the bales and make some more photos:

2014/11/27 14:28

2014/11/27 14:29

2014/11/27 14:30

2014/11/27 14:31

2014/11/27 14:32

I spent the last night in the cabin, and it sensed some straw dust, also visible with the LED light. Also at the morning it's a bit too dark for my taste, coming from translucent PVC canvas of the geodesic dome, and hearing nature direct whereas the cabin is almost like a sound studio, completely sound proof. To light up the interior, I'm pondering on some ways to plaster the inner walls with some bright or white surface, in a manner which if the cabin is taken down, the strawbales can be still used again - so some rather natural material then.

So far I haven't decided on the actual details of how to seal the air triangle under the roof, the south side might be sealed well, as it's the main "weather" (wind & rain) exposure. The north side with the door and its roof triangle I like to keep accessible, e.g. with a small door. Most storms come from south west or north west, since the slope the cabin is east to west down, so the east side is quite well protected from winds or storms.

The backside of the cabin, the 6m long wall is a bit wobbly at the center, e.g. gives in apprx. 2cm with some pushing, the ends near the corners / edges do not move at all. Since the windows are at the front, where winds or storms will reach the cabin, they actually provide some stability with the threaded rods so close by (see illustrations/plans for details).

Roof finished

Today was again Cyprian at work, one of my helpers, he is experienced with roof building, and so the east slide of the roof he finished quickly, especially the last lane was tricky to attach (see photos).

As next we moved the China Grass matts, which I have had available, but I could have used also layers of compressed straw evenly distributed over the OSB ceiling.

East slide of roof continue
2014/11/26 13:42

Near finish of the roof
2014/11/26 14:49

Roof finished
2014/11/26 15:08

Arrival of the China Grass matts used for ceiling insulation
2014/11/26 15:38

China Grass matts as ceiling insulation
2014/11/26 16:16

It was a foggy day and no rain, only in the only early morning, but not while construction.

What's left to do externally, which I do myself, is

closing the triangle gap below the roof and the ceiling, as strong winds might otherwise lift the roof away, so I need to block the gap, and
perhaps put a small door so I can enter up there later as well.

After some measurements the main skeleton of the roof was done, mostly using 5.8cm x 5.8cm x 3m beams. A 10cm extension was required for the horizontal support of the roof, as the walls slighly "V". The smaller 4.8cm x 2.4cm horizontal 4m + 3m supporting wood was aligned with 20cm spacing, a bit narrow for my taste, yet, one of the helpers recommended it - at the rather steep angle I thought 30cm would be sufficient, and enough space to slip through whole attaching the bitumen sheets. Once the skeleton was done, the bitumen sheets were attached, west slide: 2m + 1.2m bitumen sheet, 10cm overlap, and 5cm extension above and below => 3.0m. We just finished the west slide around 17:15, with some LED light attached the last sheet, and covered the east side with some PVC for the night.

Main roof junction
2014/11/25 13:32

Roof beam connected with ceiling "foot"
2014/11/25 13:35

Using a cord as reference
2014/11/25 14:15

Continue with the roof beams
2014/11/25 14:19

2014/11/25 14:27

Horizontal support wood for the roof (4m + 3m = 7m total, apprx. 35cm extension on both sides)
2014/11/25 15:04

West slide of roof skeleton complete
2014/11/25 15:08

Completing roof skeleton
2014/11/25 15:20

First lane of bitumen sheets put up
2014/11/25 16:13

2014/11/25 16:18

Covering the west slide of the roof
2014/11/25 16:35

It was 7-8C with high fog and some north wind, fine to work like that. Tommorrow alike weather is forecast, but then some rain is expected the day after tomorrow - definitely time to finish the roof. What's left to do: east slide of the roof finishing, and then China Grass matts for the ceiling insulation. I will eventually close the south side of the roof, and make a small door on the north side, so I potentially can reach under the roof and above the ceiling later, not that I will use it as storage space, as the China Grass matts are quite fragile and won't last when stepping on them. And then the internal setup, with a bed, a desk, perhaps part of a kitchen section.

Yesterday cleared the inside of the cabin, and patched some of the gaps in the wall with small bushels of straw. Today we measured the details for the roof, and the ceiling is slightly off by 10cm, slightly a trapez than a rectangular, so in order for the bitumen sheets to align properly, these 10cm off had to be accounted for and compensated. Perhaps it would be possible another way, yet, Cyprian recommended to have exact perpendicular edges so the alignment of the roof tiles remains intact and no gaps show up.

Feets mounted for the roof beams
2014/11/24 16:28

2014/11/24 16:29

Precision at work
2014/11/24 16:29

Fixating support vertical beam for horizontal support of the roof
2014/11/24 17:02

I decided on the final roof design:

west slide: 300cm (wood) + 10cm sheet overlap + 5cm bottom extend + 5cm top extend = 320cm (200cm + 120cm)
east slide: 265cm (wood) + 10cm sheet overlap + 5cm bottom extend = 280cm east side (200cm + 80cm)

Since the bitumen sheets are 200cm long, and overlapping is 10cm vertically (water running down direction), I cut 8 bitumen sheets to 8x 120cm + 8x 80cm.

The roof extends about 35cm over the main beams on the top, which compress the bales, plus about 5cm over it. The roof is essential to make sure as little as direct rainfall exposed, yet, it can be fully prevent as heavy winds and rain storms - so this will be the main experiment: how does a bare strawbale cabin maintain itself in moderately humid climate like flatland of Switzerland (apprx. 700m above sea level).

Yesterday was all day long fog, today sunlight most of the day, and then some clouds covered the blue sky - the brief sunlight warmed up the inside of the cabin and it was noticeable warmer inside than outside, the ceiling not yet insulated.

I'm definitely curious how good the actual and final insulation works I decided:

floor: compressed straw => apprx. 10cm thick
walls: bare strawbales (95cm x 35cm x 50cm) => apprx. 50cm thick walls
ceiling: compressed China Grass matts => apprx. 15cm thick

Today we finished the compression wood on top, fixated the door and added the supporting beams which hold the OSB composed ceiling, 18 x 2.05m x 0.675m. The walls were slightly twisted, which meant the corners aren't prefect right angle anymore - with a proper supporting structure this would have happened, but the walls were off about 3-5cm with 210cm height. Also, the threaded rods didn't go up straight, as we often moved the strawbale a bit to fit best and so misaligned the rods a bit. The vertical support for the back and front wall helped a lot, perhaps next time also proper edges would have to maintain the right angles consistently.

While building, Cyprian changed his mind, and meant that the agreed plan for the supporting ceiling structure needs to be changed - which meant a slightly higher ceiling, and some spaces which required bushels of straw to fill - so I agreed with the idea, as it meant additional 5cm ceiling height, yet, some lose straw required to fill the gaps. Again, we started around 13:00 and finished 17:15, and covered all with a big PVC cover again. All day long we had fog, just after 17:30 I could briefly see dark blue sky the fog barely vanishing.

2014/11/22 13:05

Realign the compression beam, realign the windows properly
2014/11/22 13:54

2014/11/22 13:55

Line up the supporting beams for the ceiling
2014/11/22 14:59

Composing the ceiling with 18 x 2.05m x 0.675m x 12mm OSBs
2014/11/22 16:19

Tomorrow I work alone again, and likely prepare things so Monday the external part of the cabin is finished - it took much longer than anticipated, mainly because small details which show up during the construction needed to be addressed and good solution to be developed. I definitely benefit from the expertise of the two helpers in regards raising the walls.

Foggy morning, walls raised, no ceiling yet

I decided to go with 6 layers, 35cm x 6 = 210cm height, quite exact actually, plus 5cm thickness of the supporting wood on top, and then the OSB based ceiling. The 7th layer could have been possible, but I decided against it: as my first strawbale house and experimental approach using the threaded rods as stabilizers, a slightly low ceiling would be ok to have a smaller volume to heat up for this coming winter 2014/2015.

My helpers are only available in the afternoon, and there was a bit rain in the afternoon, which slowed down the work today, but we succeeded to finish the wall, and put the final wood at the back and front to compress the 2 long walls. I didn't photograph the final state of today as it was already dark - so far the insulation above the windows are done as well.

6 layers of the back-side done
2014/11/21 14:30

4m + 2.20m wood (7.8cm x 4.8cm) compressing the 6m long back-side wall
2014/11/21 15:50

Last partial bale inserted (1)
2014/11/21 16:30

Last partial bale inserted (2)
2014/11/21 16:30

Working on front-side wall, finishing insulation above the windows
2014/11/21 16:31

Tonight some possibility of brief rain exist, so I covered the entire structure with several PVC canvas. I expect the ceiling to be done by tomorrow evening, and Sunday I likely work alone for the roof. By Monday evening I expect the cabin to be finished externally.

Today we did continue raising the walls, finishing the first bottom 4 layers and compress them with 4.8cm x 2.4cm laths.

Cutting a small ridge so the laths sink well into the bales, so the 5th layer lays properly on the 4th and the lath is well embedded - without the ridge the lath would introduce instability for the next layer. In other to continue layer 5, Cyprian decided to mount vertical support laths, so the next layers properly align vertically - they will be taken away once the wall is finished and the ceiling is mounted. Also, the two heavy windows we mounted, rather jammed between the bales with threaded rods near by, and I used two wodden pins and hammered them into the bales, which worked quite well.

Tighten first 4 layers of the wall (1)
2014/11/20 14:07

Tighten first 4 layers of the wall (2)
2014/11/20 14:08

Vertical support (front & back)
2014/11/20 15:07

2014/11/20 15:22

2014/11/20 15:44

Cut a ridge with the motorsaw into the bales, for the strut which compress the 4 layers
2014/11/20 15:46

Putting in the window (not openable)
2014/11/20 16:40

Using wooden pin (25-30cm long) to fixate window near the bottom
2014/11/20 16:40

2014/11/20 16:40

Compressing the 4 layers together took quite some, as the bottom layers needed to be align quite well so the overall walls remain stable. Once the 4 layers were compressed, it took just 30mins to mount the 5th layers (no photos as it was already too dark). In other words, once you have a good start of the wall, actually positioning the bales goes rather quickly. The door and windows yet demand 1/2 or 1/3 or custom sized bales, which take some time. Since the bales aren't precise, one has to bind the custom bales on site and on demand.

Also, a small note, the corners are very stable, they won't tilt even an centimeter when pushing them any way, whereas the wall between the windows is quite wobbly, as well the 6m long wall at the back. The expectation that once the ceiling is mounted, the stiff structure which allows to mount the ceiling, gives the overall cabin more stability, in particular the parts which are still a bit wobbly - we will see.

Tomorrow overcast with brief rain is possible, which poses some risk while raising the wall and have the bales exposed. I have to quickly respond cover the entire structure with a cover.

Done for today, 4 hours work

After more than a week of partially rainy days, today I was able to continue with two helpers (Cyprian & Claudio):

threaded rods (M10 x 1m) anchored on the floor
laying out first strawbales at the corner, and working to the center of each side, and fill remaining with partials of a strawbale
we decide to make 4 layers around the 2 windows quickly, so they can be mounted without support
the door frame was moved slightly, now 1m away from the back; 1m is roughtly the width of a strawbale
there are some gaps seen, which I gonna fill manually with small straw bushels

First corner M10 threaded rod (25cm / 25cm from the edge)
2014/11/19 13:15

Covering the inside with newspaper and straw on the floor, to protect the floor while construction
2014/11/19 13:53

Preparing first strawbale
2014/11/19 14:02

First corner strawbale
2014/11/19 14:29

Proceeding quickly, two layers done, preparing window water slide away
2014/11/19 16:03

Threaded rods to use with 4.8cm x 2.4cm lath and with M10 nut compress the first 4 layers at the window section
2014/11/19 16:46

Done for today, 4 hours work
2014/11/19 16:55

2014/11/19 16:55

Detail of water slide away
2014/11/19 16:55

Door frame
2014/11/19 16:56

2014/11/19 16:56

Covering work for the night, humidity falls and tomorrow fog expected all day
2014/11/19 17:06

Sunny afternoon was pleasant, it warmed up and I started to work in the t-shirt only - around 16:00 the sun set behind the small mountain ridge and it began to cool off quickly. Around 17:00 we stopped as it quickly darkened. The next days are expected with no rain but fog, and likely no direct sunlight reaching the ground.

I took the afternoon to sort all ~180 strawbales:

heavy and compact bales first to use (layer 1)
good strawbales, a bit ligther as next (layer 2-5)
moderate good strawbales, light, well bound (layer 6&7)
and putting aside bad strawbales (~10 bales)

A few strawbales I fixed by re-binding, using additional cords to make it strong again. As mentioned, since I didn't instruct the local farmer to press bales for actual building, the bales are quite light (~15kg) and not that strong.

The advantage of light bales is that the decided procedure using threaded rods to compress bottom 4 layers and then top most (7th) layer again - that the rods can penetrate the strawbales with a bit effort and keeping them straight while pushing down (M10 x 1m are ok, perhaps M12 x 1m would be better choice for next time).

Today I drew some more detailed plans how to proceed building the cabin:

Level 1,3,5 strawbale wall

Level 2,4,6 strawbale wall

Ceiling plan

Detail ceiling foot / roof plan

Rough sketch of roof structure

Options to build Strawbale Wall

Rainy days prevented me to continue, but it gave me more time to plan putting up the walls.

Options:

putting bales straight on top of each other: highly unstable, 3-4 layers might work
putting bales half-way shifted or staggered on each layer (like putting together a brick wall), 4 layers might work
putting bales half staggered half-way, first 4 layers tied together, next 2 layers tied on top of 4th layer: 6-7 layers might work

Some of tests I made:

Shifted wall with no support
2014/11/12 11:20

Shifted wall with 4 layers combined
2014/11/12 11:33

Shifted wall with 4 + 2 layers combined
2014/11/12 11:53

Shifted wall with 4 + 2 layers combined + 1 layer
2014/11/12 11:57

Yet, even the last option gave some improvement, I decided to go with following solution:

Stabilize the wall each 2m distance 3m long M10 threaded rods (total 30 x M10 x 1m, Euro 1.40 / pc) vertically positioned and using nuts at the bottom and top: under the floor, and on top a long piece of wood which presses then the 6 or 7 layers of bales together.

It keeps the bales and wall therefore in position, and gives the possibility to compress the layers together in a controlled way (height-wise). It's a bit more overhead than I anticipated, but I think it makes the cabin sturdy and less prone to become unstable.

The door I use is exactly 210cm in height, its frame to be precise, so I pondered on follow options:

6 layers give apprx. 210cm height, when compressed going near 200cm, and missing 10cm: making door open to outside instead of inside, having 10cm reach over the bales on top.
7 layers give apprx. 240cm height, when compressed going near 230cm, still well over 210cm of the door frame, ability to keep the door opening to the inside - filling the expected gap above the door frame of 10-20cm with straw and/or wood.

and I likely go with the 2nd option using 7 layers, as 6 layers with resulting 200cm ceiling height is a bit low for my taste, and I have sufficient amount of bales spare.

With apprx. 23 bales per layer, and 7 layers I reach total of apprx. 161 bales (2.4 tons).

Today, after weeks of delay, the strawbales arrived - so called "small" strawbales, as nowdays "large" 400kg heavy strawbales are sold. I've got apprx. 180 strawbales in this shipment:

~180 Strawbales
2014/11/09 14:00

Frontside of Strawbale
2014/11/09 14:01

Headside of Strawbale
2014/11/09 14:02

Backside of Strawbale (9 layers)
2014/11/09 14:02

Width ~90cm
2014/11/09 14:02

Depth ~50cm
2014/11/09 14:03

Height ~37cm
2014/11/09 14:03

Frontside of Strawbale
Numbers of a Strawbale:

Width x Height x Depth: 95cm x 38cm x 58cm (0.21m3)
Cords: 2 (blue)
Weight: ~15kg (rather loosely pressed)
Year of Straw: 2013 (2 years old straw)

I call the "Frontside" where the straw is bent, and "Backside" where the straw is cut and the hollow diameter of the straw exposed - the backside will likely reside inside of the cabin, whereas the frontside outside.

The strawbales are made from 2013 straw, and did cost Euro 3.00 per bale, which is rather expensive, as 1-2 months ago straw 100kg was Euro 8 which are 4-5 heavy bales (Euro 2.00), or ~6 light bales (Euro 1.35). I've got also got rather light bales, apprx. 15kg. The farmer informed me, if I told him ahead, he would have pressed heavier and compacter bales for me.

About 10% of the bales are misaligned, and the two cords no longer straight, so I expect to "fix" some of the bales again. Based on the photos you see about 9 layers pressed together - the farmer told me he pressed based on 100cm and the final length of ~90cm came from compression. I also expect about 2cm loss of height when compressed per layer.

So, based on the measure of a sample strawbale I need:

Width 615cm / 90cm => 7 bales x 2 = 14 bales
Depth 405cm / 90cm => 4.5 bales x 2 = 9 bales
which results to ~23 bales per layer
Height ~210cm / 35cm (compressed) => 6 layers

which results in 6 x 23 bales => 138 bales, about 5 x 3 bales are not needed for door and two windows, which makes 123 bales in total, or apprx. 123 x 15kg = 1.8 tons weight.

Now, the coming week are 1-2 dry days, other days it's exected to rain, so there is enough time to raise the walls, as I expect as my first strawbale cabin I require apprx. 2-3 consective days without rain and fog to raise the wall and assemble the ceiling. The roof can be postponed for a few days.

Taking out wet straw insulation, and replace with dry one

I had to open 2/3 of the floor in order to replace two insulation parts. It's definitely the weak point of this floor setup: any water penetrating the floor is not running away or through, but stays with the straw insulation. The plus point is though, that there is no humidity coming from underneath into the straw and then the OSB floor.
Last night it began to rain intensesivly, and one of the bitumen parts bent so some rain water leaked on the new floor and through to the straw insulation, and due to the humidity blocker, could not run away - so I relieved it by poking some holes into the PVC. Yet, I have to remove some OSB and replace the humid or wet insulation straw, before I can continue. The next days will by foggy and partially also rainy - let's see how things go.

Today it was slightly covered sky, apprx. 15-20C warm, and it was possible for me to work longer than just a few hours, but the entire afternoon.

I positioned the OSB as perfect as possible, there were some 1mm gaps at max but mostly I could pushed them closely together, and drilled 35mm screws on the 4m beams underneath, 4 screws per OSB. As next I cut off the PVC left over and wrapped it under a bit. In order to prepare for the next 1-2 days with some rain expected, I used the bitumen roof parts to cover the floor, as the PVC cover has some holes which would leak water on the floor.

Position the OSB closely, with hammer and a piece of regular cut wood
2014/11/04 14:07

Floor finished, PVC wrapped underneath
2014/11/04 15:34

2014/11/04 15:34

Closeup
2014/11/04 15:35

Look underneath with the blue cords
2014/11/04 15:35

2014/11/04 15:36

Covering with bitumen roof parts, protecting for the expected rain
2014/11/04 16:46

Tomorrow are finally the strawbale expected, hopefully - yet, the weather as mentioned won't be supportive to continue with the construction, so I wait for 2-3 day window to raise the walls. Once the walls (and door and 2 windows) are raised, the ceiling can be done quickly, and then, so far my plan, construct the roof on top of the ceiling within a day.

Adding and removing some straw to level it properly, and roughly position the OSBs:

Starting to lay it out
2014/11/03 14:18

2014/11/03 15:02

Roughly positioned, not yet fixated
2014/11/03 15:48

Covering it up for the night
2014/11/03 15:56

2014/11/03 15:56

Since the wooden strut as enforcement turned out too thick under the floor insulation, I came up with the idea to use cords to wave a kind of net in between, then the PVC cover, and then the pressed straw layers:

Using a cord to wave a tighter or closer support
2014/11/02 13:16

Cord net finished
2014/11/02 14:02

Cord net finished (closeup)
2014/11/02 14:02

Vertical end strut
2014/11/02 14:36

2014/11/02 14:40

Refilling the straw layer
2014/11/02 14:41

Looking underneath
2014/11/02 14:42

Continuing putting pressed straw layers
2014/11/02 14:52

Some layers are compact, but still fragile to handle (tend to fall apart)
2014/11/02 15:07

Almost done for today
2014/11/02 15:29

I'm going to loose the pressed straw layers so they use up more volume, yet, the OSB can easily press it again, to make sure entire dedicated space is filled with straw.

It's quite foggy at mornings, around 12:30 to 13:00 the sun penetrates the fog and disolves the remaining fog, until 15:30 I have direct sunlight, afterwards the sun sets behind the trees and humidity falls on the surface - so limits the time to work on the cabin to about 2-3 hours per day.

Today I laid a strong PVC canvas over the grid, and laid some straw over it - the pressed straw layer from a large strawbale (1.5m x 0.8m x 0.6m ~ 400kg) is about 90cm wide, and 8cm thick pressed, ideal for my use case. I used 3 layers for one "lane" of my grid. Some additional support is required which I will do with cords tomorrow.

PVC canvas as humidity blockage underneath
2014/11/01 14:34

Single layer of pressed straw
2014/11/01 14:34

One lane of the grid with straw layers filled
2014/11/01 14:39

Testing with OSB over it
2014/11/01 14:46

Supporting strut, but it's too thick
2014/11/01 14:46

I finished the supporting grid for the insulation, and tested with some China Grass based insulation matt - unfortunately it's a bit too thick for my use case:

Floor grid finished
2014/10/31 14:00

Testing with China Grass based insulation matt
2014/10/31 14:01

2014/10/31 14:10

Making it fit, but it's too thick
2014/10/31 14:23

I used smaller struts and attached them beneath the main floor beams, to prepare the floor insulation:

Aligning the beams before fixating
2014/10/29 15:01

2014/10/29 15:01

2014/10/30 15:18

2014/10/30 16:51

The idea is to use some plastic and then put the insulation on it and then the floor 22mm thick OSB.

The strawbales should arrive within the next week, so I decided to continue with the floor construction:

precisely aligned the beams, properly parallel with perpendicular alignment for the OSB, +/- 1cm correctness is mandatory, as I don't have much margin
fixated the 4m beams with 80mm long screws

Laying on the main floor beams (7 x 4m long)
2014/10/24 13:27

Testing with OSB
2014/10/24 13:44

Needs to be pretty exact (+/- 0.5cm)
2014/10/24 13:57

2014/10/24 13:58

2014/10/24 14:11

Where I am there are spare insulation material, apprx. 3m x 1.2m and 30cm thick and soft, when transporting they tend to "break" - I gonna try these, and if they don't work I gonna use loose straw to fill the space.

3 x 7 ground poles rammed into the ground, leveling the floor

Base Plan
I decided to ram poles into the ground, apprx. 30-40cm deep. This has the advantage of strong and solid footing, and also not sealing the ground at all.

It was a bit tricky to ensure perpendicularity, but it was achieved by measuring with a cord the diagonal both ways until they were the same length. The distance between the poles were easily to measure. Once they were rammed into the ground, either hammered further or cut and then with a 4m beam leveled until it fit. It was a bit time- and physical strength consuming but forth the efforts.

The next steps I had to postpone as the strawbale delivery was delayed and I planned to build the cabin within a few days with sun and no rain, so I don't have to cover up the unfinished construction.

Some notes of mine on paper (also for my own reference):

Rough sketch of cabin
2014/11/03 09:39

Some details of floor support
2014/11/03 09:39

Single slide roof sketch
2014/11/03 09:40

Optimizing size of cabin based on strawbale size & OSB size
2014/11/03 09:40

and electronic counterpart:

Base/Floor

Floor

Ceiling

After some pondering I defined the base or floor size based on the OSB and main beams which are 4m long, which made the depth, the width I came up 3x OSB length-wise 3x 2.05m = 6.15m and 6x 0.675m = 4.05m - perfect.

Strawbale Cabin

Plans

Numbers

Material

Reflection

Diary

2020/01/07: This Is The End

2017/04/12: Earth Oven (1)

2017/04/09: Spring

2017/03/05: Sunny Day

2017/02/23: Pre-Spring

2017/02/15: Icy Morning

2017/01/05: Winter Arriving

2016/11/19: Cold & Humid

2016/11/07: First Snow

2016/11/03: Upgrading Floor Insulation

2016/10/12: Fall Approaching

2016/08/14: Summer Time (2)

2016/07/25: Summer Time

2016/05/22: Bare Strawbales After 18 Months

2016/05/21: Summer Approaching

2016/04/12: Preparing Garden

2016/03/23: Spring Approaching

2016/02/18: No Winter

2016/01/16: Winter Arrived

2015/11/18: One Year of Cabin, Mild Weather Continued

2015/10/29: Fall

2015/06/26: Summer Time

2015/04/30: Springtime

2015/01/04: Warm Day

2015/01/03: Snow Slide Down

2015/01/01: New Year

2014/12/31: Week with Snow

2014/12/27: First Snow

2014/12/23: Walk Around

2014/12/19: Fine Tuning

2014/11/28: Sunny Afternoon

2014/11/27: Cleaning Up

2014/11/26: Roof Complete

2014/11/25: Roof Almost Done

2014/11/24: Roof Started

2014/11/22: Ceiling Done

2014/11/21: Finishing the Walls

2014/11/20: Continue Building the Walls

2014/11/19: After Rainy Days, Starting Strawbale Walls

2014/11/18: Sorting Strawbales

2014/11/14: Planning Procedure

2014/11/12: Planning the Walls

2014/11/08: Strawbales Arrived

2014/11/07: Fixing Floor Insulation

2014/11/06: Rainy Days

2014/11/04: Floor Finished

2014/11/03: Floor (Continued)

2014/11/02: Floor (Continued)

2014/11/01: Floor (Continued)

2014/10/31: Floor (Continued)

2014/10/30: Floor (Continued)

2014/10/24: Floor

2014/10/12: Ground Poles

2014/09/24: Planning