Straw Bale Shed - The Owner Builder

Straw balebuilding updateThe Australasian Straw Bale Building Association (AUSBALE)promotes the use of straw bale construction. This issue, Angus Stephenshares his experience of building a straw bale shed.The shed comes firstPractice building in straw bale before tackling the houseBY ANGUS STEPHENAs the Secretary/Treasurer ofthe Australian Straw Bale BuildingAssociation (AUSBALE) and a licensedbuilder, I receive quite a few emailsfrom people keen to know more aboutstraw bale buildings and in particularwhat it costs to build. The stockanswer on the cost question has been‘somewhere between brick veneer anddouble brick’ (it should be relativelyeasy to get a rough guide on whatthese cost in your area). The problemwith comparing costs from project toproject is that the work I do as a smallresidential builder and the work you,as owner builders, do falls into thecategory of prototype work – one-offbuildings that are rarely repeated.Jane and I moved with our youngfamily to the Southern Highlandsof NSW in May 2007 and receiveddevelopment approval in February 2008to demolish the existing house andbuild a straw bale and weatherboardhome and adjacent straw bale garage/workshop. The 300m 2 home is twolevels, the upper level having externalwalls 900mm high with bedroomswithin the 35 degree pitched roof. The100m 2 garage/workshop is L-shapedand has a 30 degree pitched roof. Thepassage of our DA through councilwas pretty painless, although we wererequested to provide a report from ourengineer on the weather resistance ofthe straw bale walls (mildly humorousgiven we have verandahs infilledwith weatherboard to the southernand western elevations, a glazedconservatory dominating the northernelevation, and a three metre verandahto the east).As so many other contributors to thismagazine have experienced – the shedcomes first! There is no budget to buildthe house and the shed serves as a testrun to help you iron out some of theissues prior to the main event. And so ithas been with us.This article has been written tooutline what it cost us to build the shed– a simple hybrid straw bale structurewith a small number of openings. Ihope it will allow people to get a betterhandle on what it might cost them toput the ‘six sides on a box’ if they wantto build a simple building, withoutgetting too involved in the costs ofthose elements that are common to allforms of housing (i.e. internal walls,bathrooms, a kitchen etc.). I haveignored any plumbing and electricalcosts for this reason.The slabWe poured the slab in mid April2008. Our slab was expensive. Welive in an area of class H soils (highlyreactive clay sites) so our shed had900mm deep x 450mm wide trenchfootings and chewed up 36m 3 ofconcrete. I had a local contractor do theexcavation and another come in to dothe edge boards, tie the steel, place andfinish the concrete.The frameAs a hybrid straw bale building,the engineer had specified a total offourteen posts in the perimeter of theProud builders – resting between tasks.34 • THE OWNER BUILDER • 153 June/July 2009 © www.theownerbuilder.com.au • 02 4982 8820

came and was a damp drizzly day, but thethree guys hooked in and got the roof on,although the ridge capping was left foranother afternoon. We used Zincalume– the council’s heritage consultant hadrequested galvanized iron in preferenceto Colorbond, but the galvanized ironwas about 40 percent dearer than theZincalume.With a (almost) weatherproofstructure, it was time to staple thehessian to the inside of the fasciaboard along the western and easternelevations to minimise erosion of theclay render from wind driven rain. Thiswas staked out using baling twine andsome hardwood stakes that I had. Weused the hessian in preference to plasticas plastic tends to flap and tear in thewind, whilst hessian will let some of thebreeze through but slow the rain.The renderingWe ran another workshop withFrank over the Australia Day weekendthis past January. This gave us a coupleof months to get around to jobs suchas installing the window, door jamband door reveals in the garage dooropenings. We used a second-hand door($45) and window ($0).We had about eight to twelve peoplefor this workshop and we managed tospray two coats inside and a secondcoat outside in three days. We mixedthe clay 1:1 with yellow brickies sandto ensure that the rendering clay wehad ordered for the first workshop‘went the distance,’ as the sand wasavailable locally for roughly half the costper tonne of the clay. A 5mm squarefibreglass mesh was trowelled into thesecond coat of render to provide crackcontrol and extra strength. We spent themorning of the fourth day showing afew interested participants how to cut aniche in the wall, trimming up the truthwindow and having a bit of a clean up.With the workshop over, I then hadto put a final coat of render inside andout in preparation for painting. Thiswas a different clay, mixed 1:1 withtiling sand to give a smooth finish to thewall. All up, it probably took me aboutfive or six days to do that final coat,spread out over a month.The paintingWe decided to use Volvox claypaints, as an alternative to lime renderexternally. These German made paintsare natural, non-toxic and containno VOCs, so there is no offgassing aswith more traditional types of paints.More importantly for our clay renderedwalls, they allow our walls to retaintheir breathability and are suitable forexterior application. As the shed has alarge exposed western wall, I am lookingforward to seeing how this productperforms over the next few years, witha view to using it on the house, ratherthan lime, if it performs well.The instructions said to allow one litreper 8m 2 of wall area, to wet down thewall prior to painting and that the firstcoat of paint could be thinned with fivepercent water. I tried wetting the wall,but the roller pulled a few lumps of clayrender off the wall so I decided to skipthat tip. I ended up thinning the firstcoat with 10 percent water and it wenton reasonably well. With the clay renderbeing so porous, we got coverage closer toabout 4m 2 per litre. I bought new rollersand brushes as suggested. The productis lovely to use and comes in about 120colours, but at approximately $20 perlitre it is expensive. We found that we gotbetter coverage inside from the lightercolour. I have put two coats on outsideand one inside and that has taken methree days. Just one coat to go inside!The rendering – what we spent:Timber $204 Door, jamb, garage door revealsSand $250 Yellow brickies and tiling sandPump hire $1350 3 daysFibreglass mesh $560 4 rollsTop coat clay $180 1 drumThe painting – what we spent:Volvox paint $1,599 Two coats inside and outRollers/brushes etc $75The final costSo what did it cost us?Stage CostSlab $16,000Frame $2,507Straw walls $5,346Roof $9,824Rendering $2,544Painting $1,674Total $37,895So two-thirds of the cost was in theslab and the roof – elements that arecommon to all forms of construction.Nearly a year has passed since wepoured the slab, and we still have toinstall the garage doors and connectup the power. If you put a couple ofrecycled doors in those door openings,you would have a dwelling at lockupstage for around $400 a square metre.In this example, please remember thatplumbing and electrical have beenignored, and I have not priced mytime. The more labour you have tohire would have an obvious effect onthe price per square metre. I hope thatsome of you who are considering strawbale will find this useful in terms ofwhat it might cost and how long eachof these stages took. ■• AUSBALEThe Australasian Straw BaleBuilding Association is an organisationthat promotes the use of straw baleconstruction as a sustainable buildingmaterial.www.ausbale.org, or contact BohdanDorniak on 08 8344 8170• Angus ConstructionsAngus Stephen offers a broad range ofservices from assisting the owner builderto full project construction, focusedon delivering comfortable, practicaland energy efficient homes with a highquality finish. License Number 172670C.Master Builders [NSW] Member.02 4869 3950, 0400 887 870,angusstephen@bigpond.com• Yesterday-Today-Tomorrow StrawBale ConstructionTaking you on a journey from a dreamto a home come true.Builder Licence No 115643C0408 415806, www.strawtec.com.au36 • THE OWNER BUILDER • 153 June/July 2009 © www.theownerbuilder.com.au • 02 4982 8820

12 31. Help from friends and family withrendering is always appreciated!2. The tops of straw bales were coveredeach evening, to protect them from rain.3. The L–shaped truss roof includes threehip ends but still went up easily enough.4. Fourteen recycled hardwood posts formthe perimeter frame, spaced to minimisebale cutting and retying.5. The Zincalume roof was installed by threelocals in a day.© www.theownerbuilder.com.au • 02 4982 88204 5THE OWNER BUILDER • 153 June/July 2009 • 37