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Strawbale Cabin

written by Rene K. Mueller, Creative Commons CC BY NC 2014, 2015, last updated Fri, April 14, 2017

2015/01/03: Snow Slide Down

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.

2015/01/01: New Year

2014/12/31: Week with Snow

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.

2014/12/27: First Snow

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.

2014/12/23: Walk Around

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.

2014/12/19: Fine Tuning

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.

2014/11/28: Sunny Afternoon

Today the sky cleared in the afternoon:

2014/11/28 12:26
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 17:27

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.

2014/11/27: Cleaning Up

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 14:28
2014/11/27 14:28
2014/11/27 14:29
2014/11/27 14:29
2014/11/27 14:29
2014/11/27 14:29
2014/11/27 14:29
2014/11/27 14:30
2014/11/27 14:30
2014/11/27 14:30
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2014/11/27 14:31
2014/11/27 14:31
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2014/11/27 14:32
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).

2014/11/26: Roof Complete

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.

2014/11/25: Roof Almost Done

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.

2014/11/24: Roof Started

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:

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

2014/11/22: Ceiling Done

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
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.

2014/11/21: Finishing 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.

2014/11/20: Continue Building the Walls

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.

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

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.

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