How The First Little Pig Could Have Beaten The Wolf and Helped Tackle Climate Change

Constructing a load-bearing straw-bale extension. Source: Jakub Wihan, 2012. 

This blog was written as an assignment for the MSc Sustainability Adaptation and the Built Environment that I am studying at the the Graduate School of the Environment at the Centre for Alternative Technology, at Machynlleth in Wales. It's a brilliant course and I highly recommend it! I've been meaning to write a "what's so good about bales anyway?" blog for ages, so it was great to be able to do it with the access to resources and peer-reviewed journals that being on the course brings.

I debated stripping out the in-text references for easier flow of reading, but in the end I've left them in so you can choose to ignore them or check any statements I make.


When discussing straw-bale building with the unacquainted, the Three Little Pigs are often mentioned (representing structural concerns). If worries are based outside fairy tales people may ask “isn’t it a fire risk?”, “won’t it rot?”, or simply “Why?”

These are sensible questions. This blog will summarise the evidence and show that straw-bale construction can create safe, comfortable buildings, and contribute towards climate change mitigation and limitation.


Buildings and climate change.

The international community agree to urgently limit emissions; to prevent “dangerous anthropogenic interference with the climate system” by containing global temperatures at 2°C above pre-industrial levels (UNFCCC. COP, 2009).

The UK released 474.1 million tonnes of CO₂ in 2012 (UK. DECC, 2014). The construction industry can influence an estimated 47% of this, of which 83% is related to use of buildings (UK. DBIS, 2010). Creating buildings that reduce this is essential.

Sustainable construction must limit emissions from energy-use whilst preparing for uncertainties of climate change, energy security, and the potential need to withstand increased extremes of weather and temperature. 


Straw and carbon

Barbara Jones (2009) estimates unused wheat straw in the UK could build 423,000 3-bed (350 bale) houses a year. Straw is a waste product of monoculture agriculture, the sustainability of which is arguable; but it makes sense to use currently available waste rather than extracting virgin materials.

The embodied carbon of straw (amount of CO₂ released by its production) is 0.01 kgCO₂ per kg straw (Sodagar et al., 2011), or 1.21 kg CO₂ per cubic metre. The chart below compares straw with other structural and insulation products (straw-bales act as both); kgCO₂/m³ is used as it takes into account different material densities. (Click on the image for a larger version).

Comparing the embodied carbon of straw to that of some commonly used building materials.
* kgCO2e/kg - including other gases whose greenhouse potential has been converted to CO2 equivalent.
Data sources:
Calculated from ICE – Inventory of Carbon and Energy (Hammond and Jones, 2011). Median values used where range given in ICE.
Straw-bale density derived from construction-grade bale in Jones (2009), median weight 20.5kg, size 1.05m x 0.45m x 0.36m. Wood wool density data from Ty Mawr Lime (2009); Glass fibre density data from RIBA Enterprises Ltd (2014).

The chart shows straw-bales have significantly less embodied CO₂ than alternatives (though increased recycled content in standard construction products could reduce their embodied CO₂, and that of bales would increase if transported long distances).

Straw is a carbon sink: it absorbs CO₂ as it grows, storing it within its molecular structure. 1kg of straw contains 0.367kg of carbon; if burned or biodegraded this would re-combine with oxygen to produce 1.35kg CO₂ (Sodagar et al., 2011). So 1kg of straw stores 1.35kg CO₂. A standard 20.5kg construction bale would store 27.68kg of CO₂. A 350 bale average 3-bed house would have around 9688kg CO₂ sequestered in its walls (163.35 kgCO2/m³).

To avoid releasing sequestered carbon when dismantling buildings, materials should be reused – straw-bales removed from walls could be re-baled if required, sending little to be composted. Buildings should be designed with maximum possible lifespan.

Straw-bales used as external insulation of an existing building.

Insulation

Straw-bales can reduce energy-related CO₂ emissions as part of a super-insulated home. Straw-bale walls have thermal conductivity of 0.045 W/mK (Wimmer et al, 2000). The table below compares this with other insulation materials. (Click on the table for a larger version)

Temperature sensors embedded in straw-bale walls confirm that they insulate interiors from outside temperatures (Ashour, Georg and Wu, 2011.; and Straube and Schumacher, 2003). Combined with low embodied CO₂ this makes straw-bales eminently suitable for use in low-energy building. 


Fire risk.

UK Building Regulations require dwelling-walls to resist spread of fire for between 30 and 60 minutes, (UK. DCLG., 2013). In recent tests a 3m by 2.6m plastered straw-bale wall survived 135 minutes without failing (Strawbuild, 2014).

The furnace test-rig hydraulically compressed the wall to simulate real-life loadings, while subjecting one face to 1000°C. Timbers embedded in the wall’s centre reached 90°C maximum. The test ended after 135 minutes when “fireproof” boards protecting the hydraulics burned through (Strawbuild, 2014). 


Moisture

Studies of moisture in straw-bale walls agree they have low risk of decay, provided external plaster and protective detailing is well executed. (Lawrence et al, 2009.; Ashour et al, 2011.; Straube and Schumacher, 2003.; Wihan, 2007).

Laurence et al (2009) monitored straw-bale moisture content of a building in Bath, UK during a period of frequent rainfall (828mm during test period). Microbial decay needs bale moisture content of 25% to 120% (Lawrence et al, 2009). Despite the walls having little chance to dry out, moisture content ranged from 8% to 20%, well within the safe range.

Monitoring of a straw-bale house in Germany found humidity variations inside and outside had little effect on moisture within the wall. Straw samples removed after 5 years showed no signs of decay, even within the bathroom wall (Wihan, 2007). 

Structure and longevity.

The oldest known load-bearing straw-bale house was built in 1903 in Nebraska, USA. It is in good condition despite being unoccupied since 1956 (Chiras, 2000). One nearby has been continuously occupied since 1925 (Huxley, 2010). In Europe the oldest straw-bale building is a 2-storey straw-infilled timber-frame house in France, built in 1921 and still in good condition (CNCP, 2013).

1921 newspaper article about La Maison Feuillette from ‘La Science et la Vie’ No. 56. Source: CNCP, 2014. 

A number of studies tested load-bearing strength of straw-bale walls. The walls safely withstood between 19.2 kN for an un-plastered bale wall (Walker, 2004) and 40kN/m for a plastered one (Faine, M. and Zhang, J., 2002), compressing as little as 55mm (Walker, 2004). In practice compression is usually forced before plastering, to minimise future movement. Wall failure is “unspectacular”, involving some detachment and cracking of plaster (Faine, M. and Zhang, J., 2002).

Testing in Bath found prefabricated straw-bale panel walls could safely withstand hurricane force winds of 120mph (University of Bath, 2014).

A Load-bearing straw-bale building has even been subjected to a simulated Mw 6.7 earthquake (University of Nevada, 2010). It was damaged, but in no danger of collapse (Ibid). The video of the test is worth watching 

Conclusion. 

Currently straw is abundant. Building sustainably involves choosing materials with the best balance of positive properties and least harmful repercussions, from those available at the time.

If first little pig had used plastered straw-bales, it could have saved itself and its siblings, boiled the Big Bad Wolf in a cauldron of hot water heated with no risk of burning the house down (or damaging it with steam), and lived away its days in a comfortable home handed down to its descendants – all while storing away several tonnes of CO₂. 

References. 

Ashour, T., Georg, H. and Wu, W. (2011) ‘Performance of straw bale wall: A case of study’, Energy and Buildings, 43(8), pp. 1960–1967. doi: 10.1016/j.enbuild.2011.04.001. Elsevier [Online]. (Accessed: 12 November 2014).

Chiras, D. D. (2000) The natural house: a complete guide to healthy, energy-efficient, environmental homes. White River Junction, Vt: Chelsea Green Pub.

CNCP (Centre National de la Construction Paille) (2013) La Maison Feuillette | CNCP. Available at: http://cncp-feuillette.fr/maison-feuillette/ (Accessed: 26 November 2014).

CNCP (Centre National de la Construction Paille) (2014) Article ‘La Science et La Vie’. Available at: http://cncp-feuillette.fr/wp-content/uploads/2014/03/Article-la-science-et-la-vie.jpg (Accessed: 7 December 2014).

Faine, M. and Zhang, J. (2002) ‘A Pilot Study examining and comparing the load bearing capacity and behaviour of an earth rendered straw bale wall to cement rendered straw bale wall.’, in International Straw Bale Building Conference, Wagga Wagga, December 2002. University of Western Sydney, Australia. [Online] Available at: http://naturalbuildingcoalition.ca/Resources/Documents/Technical/two_storey_lb.pdf (Accessed: 21 November 2014).

Hammond, G. and Jones, C. (2011) ‘Inventory of Carbon and Energy (ICE)’. Sustainable Energy Research Team (SERT) Department of Mechanical Engineering University of Bath, UK. Available at: http://www.circularecology.com/embodied-energy-and-carbon-footprint-database.html (Accessed: 28 November 2014).

Huxley, E. (2010) The Bozeman Straw Bale Project - History of Straw Bale. Available at: http://www.bozemanstrawbale.com/strawbalehistory.html (Accessed: 26 November 2014).

Jones, B. (2009) Building with straw bales: a practical guide for the UK and Ireland. Totnes: Green Books.

Lawrence, M., Heath, A. and Walker, P. (2009) ‘Monitoring of the Moisture Content of Straw Bale Walls’, in Howlett, R. J., Jain, L. C., and Lee, S. H. (eds) Sustainability in Energy and Buildings. Springer Berlin Heidelberg, pp. 155–164. [Online] Available at: http://link.springer.com/chapter/10.1007/978-3-642-03454-1_17 (Accessed: 19 November 2014).

RIBA Enterprises Ltd (2014) 511 Paper Faced Glass Fibre Roll - Mayplas, 511 Paper Faced Glass Fibre Roll. Available at: http://www.ribaproductselector.com/Product.aspx?ci=27722&pr=Mayplas-Roof-Insulation511PaperFacedGlassFibreRoll (Accessed: 7 December 2014).

Sodagar, B., Rai, D., Jones, B., Wihan, J. and Fieldson, R. (2011) ‘The carbon-reduction potential of straw-bale housing’, Building Research & Information, 39(1), pp. 51–65. doi: 10.1080/09613218.2010.528187. Taylor and Francis Online [Online]. Accessed: 3 November 2014.

Straube, J. and Schumacher, C. (2003) ‘Monitoring the Hygrothermal Performance of Strawbale Walls’. Available at: http://www.ecobuildnetwork.org/images/PDFfiles/Straw_Bale_Test_Downloads/monitoring_the_hygrothermal_performance_of_strawbale_walls_straube_schumacher_2003.pdf (Accessed: 26 November 2014).

Strawbuild (2014) Strawbuild | Fire test 2014, Strawbuild. Available at: http://www.strawbuild.org/firetest_2014.html (Accessed: 12 November 2014).

Ty Mawr Lime (2009) ‘Wood wool board - data sheet.’ Available at: http://www.lime.org.uk/downloader?publication=86 (Accessed: 12 July 2014).

United Kingdom. Department for Business, Innovation and Skills (DBIS) (2010) Estimating the amount of CO2 emissions that the construction industry can influence: supporting material for the low carbon construction IGT report. [Online]. Available at: https://www.gov.uk/government/publications/low-carbon-construction-igt-report-co2-emissions-influenced-by-the-construction-industry (Accessed: 27 November 2014).

UNFCCC. Conference of the Parties (COP) (2009) ‘Report of the Conference of the Parties on its fifteenth session, held in Copenhagen from 7 to 19 December 2009 - Addendum - Part Two: Action taken by the Conference of the Parties at its fifteenth session.’ [Online] Available at: http://unfccc.int/resource/docs/2009/cop15/eng/11a01.pdf (Accessed: 28 November 2014).

United Kingdom. Department for Communities and Local Government (DCLG). (2013) The Building Regulations 2010: Fire safety. Approved document B: Volume 1 - Dwellinghouses. 2006 edition, incorportating 2010 and 2013 amendments. [Online] Available at: http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partb/bcapproveddocumentsb/bcapproveddocbvol1 (Accessed: 20 November 2014).

United Kingdom (UK). Department for Energy and Climate Change (DECC) (2014) 2012 UK Greenhouse Gas Emissions, Final Figures, Revised March 2014. [Online] Available at: https://www.gov.uk/government/statistics/final-uk-emissions-estimates (Accessed: 27 November 2014).

University of Bath (2014) BaleHaus: innovation in straw bale building | Research | University of Bath. Available at: http://www.bath.ac.uk/research/case-studies/balehaus-innovative-straw-bale-building (Accessed: 19 November 2014).

University of Nevada (2010) Seismic Performance of Innovative Straw Bale Wall Systems. Available at: https://nees.unr.edu/projects/straw-house (Accessed: 18 November 2014).

Walker, P. (2004) Compression load testing straw bale walls, test report. Test report. Bath: University of Bath. [Online] Available at: http://people.bath.ac.uk/abspw/straw bale test report.pdf (Accessed: 19 November 2014).

Wihan, J. (2007) Humidity in straw bale walls and its effect on the decomposition of straw. MSc. University of East London.
 

Wimmer, R., Hohensinner, H. and Janisch, L. (2000) ‘Heat Insulation Performance of Straw Bales and Straw Bale Walls’. GrAT (Center for Appropriate Technology) Vienna University of Technology. [Online] Available at: http://naturalbuildingcoalition.ca/Resources/Documents/Technical/heat_insulation_performance_strawbales.pdf (Accessed: 21 November 2014).

Bale Frenzy Part 2: Hairy Bungalow

Here's the second half of the primary bale-work photos, now from several weeks ago.  I'm still trying to catch up with this blog and get it up-to-date.  I'll try and finish that this week.  In real-time: the extension now has complete roof-structure (looks amazing!) and I'm learning basic timber-framing to build the structure that will hold up the conservatory/back-porch roof and form its window openings.  I'm trying to do it properly, jointed timbers and dowel pegs rather than walloping it together with nails or screws.

By the way, in all the blog posts, if you click on a photo it should open a slideshow with full-size images, although the captions aren't displayed then (if anybody knows a way to make it show the captions in slideshow mode, please tell me).

Coralie and Sam checking the bale walls are straight and vertical

Using the Persuader to correct any bales that aren't in line

The inside of the wall plate (timber structure on top of the bales walls, that the roof is attached to) is insulated with sheepswool insulation.  Long hazel pins are driven through the plate to pin it and the bale walls together

Over on the bungalow wrap, the angle grinder with wood-carving blade is used to cut a groove for the hazel poles (part of H-clip used to clamp bales to existing wall - see Bale Frenzy Part 1 for more on these)

First few rows of wrap bales, against clay-plaster to level the wall.

Truckers' straps, ready for compression of the new bale walls

These run over the wall-plate and under the base-plate, securely hooked together

Coralie directs from above

Notches were made in the base-plate before it was fitted to allow the straps to be passed through, folded around a baling needle.  There's a channel between the inside and outside of the baseplate formed from flattened drinks cartons with the ends cut off, secured to the timber with gaffa-tape.  The smooth inner surface of these coupled with the strength of the card allows the straps to glide through and be easily removed afterwards.  Apparently before this innovation the straps frequently became trapped after compression as the LECA aggragate in the baseplate was squashed onto the straps forming a vice-like grip.

Packing strap and buckle is used to provide a permanent tie between wall-plate and base-plate and maintain the compression

To compress the walls, the ratchet straps are tightened in sequence until the required (and even) amount of compression is achieved.  This is checked by using a site-level and a tape to check how far the top of the wall-plate has dropped during compression.

Finished bale walls! (well, apart from render, and windows, and...)

After the compression the walls are incredible strong.  There's less air in there, and the whole thing becomes tight and rigid.  It also starts to have a satisfying hollow "thump" sound when thumped.

Linda and Kuba fitting bespoke small-bales under the front window

The bottle jacks and steel-plate compress the penultimate row of bales down.  Bale-height bits of wood are then used as temporary props at each end to hold the plate down while the last bale is slotted in.  This keeps the wrap compressed, dense and strong.

The steel brackets holding on the window boxes are covered in clay plaster to regulate moisture and reduce condensation within the bale walls.

The angle grinder sucked in lots of straw while squaring bales and cutting notches.

After a clean-out, now fitted with patent Straw-Ingress Prevention Device (the wrist of an old pair of work gloves) over the air-intake

Compression to fit last bales under the eaves

On the gable wall, two timber wall-plates allow for compression of the bales here

First of the insanely large, over-specified glulam beams for the hips of the extension roof is bodily hefted around and into place.  No machines available for this one!

Perhaps Kuba is trapped beneath?

And another one... It took a while to work out where to cut these and what angles etc.  I was very impressed by Mike and Tim's calculations as both beams slotted in perfectly first time.

Up the gable

Hip beams in place

Slim timbers holding the steel-plate and compression on the gable, after bottle-jacks removed, before bale slotted in and plate removed.

Hairy bungalow

And the rain returns... At this point I re-organised the tool room and cleaned the rest of the bungalow which was in a bit of a state by the time volunteer weeks were over.

At the gable, the bales need to be compressed sideways as well as down, to ensure that they are fitted tightly against the underside of the slope of the roof (using a scissor-jack because bottle-jacks won't work sideways).  I was doing this bit on my own, involving much head-butting of bales, precarious balancing of timbers and the like.  The worst moment was shortly before this photo was taken: holding the scissor-jack and wood in one hand and attempting to wind the jack with the other.  They pinged out sending the timber flying inches past my head, I ducked just in time to avoid the falling steel plate, stumbled backwards and narrowly eascaped tripping backwards off the temporary scaffold.  I resumed operations with increased caution...

Primary bale-work complete!

Bale frenzy - part 1: The extension rises

Here are the first half of photos of the bale building weeks with the wonderful team of volunteers.  Probably I could be more selective, but despite appearances this is already a paired-down selection.  An awful lot happened very quickly and I want to show all the stages.  I've been busy since most of volunteers went home finishing the wrap at the gable end (this got complicated on my own, I had to use my head to hold up bales and push them in while my hands balanced jar-jacks and bits of wood - this probably makes no sense but hopefully the photos will explain, though maybe in part 2).  I'm also trying to make sure all the openings that will take windows and doors are ready to be measured by the window company on Tuesday; in some cases this just means fitting timbers around them, in the case of the conservatory it means trying to bring it into existence...

More on those once I've got this blog up-to-date - for now here's Bales part1.

James Herriot manoeuvre.  Kuba stuffing loose straw twisted together into any spaces between bales

Joe modelling a hazel staple, used to bind the corners together on each course

Staple hammered home

A notch cut in the window posts at the height the window sill will be (ideally, a height divisible by bale depth: eg, one bale high)

Coralie using the window sill (fitted into the notches) to compress the bale underneath by hammering in folding wedges.

The wedges are then cut flush with the post

Coralie and Kuba

Marcin and Joe debating

More sill fitting and compression

Fairy cakes by our friend Penny, rock cakes by my mum.  All scrumptious.

Kuba bashing a stake in.  The fourth layer of bales is pinned to the rest with long hazel stakes.

The first wall-plate sections arrive from Darren's workshop.  Aksel, Joe, Mark and Kuba (and me behind the camera) take in how big and heavy they are, and contemplate how to get them up on top of the walls.  Cursing of structural engineer's over-engineering begins.

Walls!  They weren't there when I went out to buy screws (at least, that what it felt like)

Marcin and Civita battle it out

The first week's team (a good number stayed for second week and were joined by more).  Front row: Darren, Kuba, Anna, me, Julia, Civita, Tim. Back row: Luke, Marcin, Aksel, Mark, Joe, Robert, Sam, Jonny, Mike.

Meanwhile, over on the wrap: timber baseplate fitted ready for bales (timber for all baseplates, wallplates, window/door posts and sills, is UK Douglas Fir - good durable timber that will take a long time to rot even if it gets wet.)

Walls at full height

window-containing boxes for the wrap, so that the new windows can sit in the line of the bale insulation (windows will be fitted flush with the outside edge of the timber)

Kuba setting up his time lapse camera.

More wall plate, squeezed in to Darren's workshop.  It's a big workshop but the wallplates only just fitted.  He said moving them around was like playing Tetris.

packing strap, passed through eyelets in the wall...

...the strapping passes over two verticle hazel poles which are slotted into the ends of a horizontal timber, forming a big 'H' which is clamped back toward the wall using the ratchet tensioner on the strapping.  This secures the bales to the bungalow wall and helps compress them.

The baseplate is (intentionally) set up so the space above is slightly less than the number of bales we need to fit in.  The penultimate row of bales is then compressed downwards using jar-jacks and a steel plate, the last bale is squashed in, resulting in a dense, strong, compressed bale wrap.

Joining the sections of insanely unwieldy wall-plate in situ.

The wall plate was resting on temporary bales above the height of the window and door posts, so we could join it all together.  Here we're starting to lower it into place (lots of people on scaffold lifting, other people pulling or pushing the support bales out, then all lowering it down)

Kuba finally turns into a bale

A tricky moment

The dog poses while in the background we try to get the window and door posts to slot through the holes in wallplate

The last door post is slotted through, signifying complete walls for the extension.  Everyone clapped and cheered, which surprised me, but was lovely.  Mum said it was a proud moment, and Dad would have thought so too.  We both got a bit weepy for a brief moment then pulled it together.

Pleased and relieved.

Look at my lovely bale walls