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Strawbale Cabin

written by Rene K. Mueller, Creative Commons CC BY NC 2014, 2015, last updated Thu, January 5, 2017

Updates

Wed, November 18, 2015: A year in the cabin.

Wed, November 26, 2014: Roof finished, ready to move in.

Wed, November 12, 2014: Strawbale details, more plans and wall building plannings.

Sat, November 1, 2014: Starting with the diary, documenting the first steps doing the insulated floor.


Current state 2017/01/05
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)

Plans


Rough Sketch with 2 Options for the Roof

Numbers


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

Material

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.

Reflection

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.


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