Straw bale granny flat, #161 - The Owner Builder

6971086. Roof mounted solar hot water with electricboost – part of the living lightly plan.7. Kitchen layout works really well despite itsmodest size.8. Not your average store-bought letterboxand front fence!9–10. The chook shed was constructed withthe left over bits from the build.Far left: The granny fl at in various stagesof construction: plywood platform fl oor;hardwood ladder frame bottom fi lled withgravel; straw bales installed; walls are amixture of stud frame and load bearing strawbale; rendering externally and internally.50 • THE OWNER BUILDER • 161 October/November 2010© www.theownerbuilder.com.au • 02 4982 8820

We designed the granny flat so thatwhen all the buildings on the site arecompleted people can stay there andbe private from the main house. Thisnecessitated orientating it to the eastbut we have still managed to get anortherly aspect for the living areas. Itwas to be functional, well ventilated,with lots of light and due to it being asecondary dwelling, under 70m 2 . Weachieved this by maximising the livingarea and having a second bedroomin the loft. This has created a ‘Tardiseffect;’ when seen from the front it isquite low but it opens out to a doubleheight space.As my father, also Kurt, is a semiretiredbuilder he helped us out a lotand we didn’t have to jump throughall the owner building hoops that wenormally would have had to do. We alsoreceived a lot of help from my father-inlawJohn during the building processand we could not have completed itwithout their help.Construction basicsThe granny flat is built on galvanisedsteel stumps with a hardwood framedfloor. We decided to create a workplatform out of plywood to allow us tobuild a lot easier and safer. As we weregoing to put some type of hardwoodtimber floorboard over the top, thisworked very well as we didn’t have toworry about damaging the floor.We wanted to minimise waste so wechose to use radial sawn weatherboardsas cladding. Unfortunately thesewere not available locally so we hadto source them from Radial TimberSales in Victoria. They were sustainablyharvested and the company has a strongenvironmental policy. The boardswere cheaper than if we bought new orsecond-hand ones locally. We specifiedsemi wobbly logs to give the naturaleffect but still make them easy to putup. When using these logs we found itbest to cut the ends off and then lay thecomplete log out on the ground. Thisallowed us to easily maintain the correctpattern and discard unsuitable planks.The secret to getting them lookingcorrect and level is to make a mark ateach end that is level and let the middleof the log do what it wants.We used load bearing straw baleconstruction on one side of the roof.The bales are supported on a recycledhardwood ladder frame bottom, filledwith gravel, and tied together usingthreaded rod which was also used forcompression of the top plate. As weneeded the rods for wind tie-downsanyway, we thought it was easier to keepusing them throughout.We had a plastic rain shield to coverthe top of the bales, which we droppeddown every night or when it rained.This it did as soon as the bales werestacked up. The rain shield worked wellexcept at the top. There were gaps wherethe tie down rods went through the topplate and water got in and tracked downthe bales. We had to pull a few bales outof the wall. We managed to remove allthe wet straw and rebuild. The plan forthe main house is to build a roof firstso we have a dry area to store and workwith the straw. The bale walls will thenbe infill rather than load bearing.We rendered the bales with threelayers of lime render as the soil on ourblock was not suitable.The lime was very easy to use as itwas very consistent and we had madethe lime putty when we started building.We added fibreglass mesh after the firstlayer to hold it all together. My fatherrendered and I mixed and it was hardwork. The wall has been standing nowfor nearly three years and there areno cracks, even with the whole placeshaking when the washing machine goesinto the spin cycle!Material choicesAll the timber windows were sourcedfrom second-hand and demolition yardsat a large cost saving. We managed toget a few matching ones, which was abonus. As some of the windows andour sliding door were of a large size wewere required to get a glazing certificate.For us to get this the glass needed to besafety glass. As the budget was comingto an end we went for the cheaperoption of putting a safety film oninstead of changing the glass.We bought hardwood floorboardsat an auction only to find out when weunpacked them that they had groovesin them. They were not floorboards buthardwood tongue and groove liningboards. After the shock we decidedto use them for the eaves linings andas an entry feature. We were not tooconcerned as they only cost 70c a metreWe ended up putting in a bamboofloor, which we have found to be a biton the soft side as it scratches easily.It is solid bamboo so can be sandedback and resealed in the future. Thefloor went down when the weather hadalready heated up and we needed fourpeople to lay it as the glue we were usingwas setting very quickly.Plasterboard was chosen for internalwalls due to price and ease of installation.We tried a lightweight foam board forthe ceiling but had problems with thecardboard breaking through the fixings.We will be using ECOply for the house.The internal temperature is verystable. The granny flat is orientated tocatch the cooling summer bay breezesand we have a ceiling fan to keep uscool. In winter we use a small oil heaterwhen required to take the chill off theair. When it is 1–2 degrees outside inwinter the inside temp doesn’t dropbelow 14–15 degrees. We have beenvery happy with the performance ofthe straw bale wall, which is on thewestern side, and the stud walls are wellinsulated as well.Essential servicesOur goal one day is to be water andpower self sufficient. To this end wehave installed two 23,000 litre polywater tanks that catch water from theshed and granny flat. To fill them all weneed is one good rain storm and theyare overflowing. First flush divertersand leaf guards were installed on alldownpipes. These need to be cleanedout regularly due to all the trees andshrubs around the block.There is now a council requirementfor new houses to have a minimum 500litre water tank connected to the toiletand washing machine. We currently usethis water for the garden and drinkingwater but we are not able to have itplumbed to the house. In Brisbaneyou are not allowed to plumb tankwater to any outlet that could be usedfor drinking or dishwashing. We havebeen drinking this water for over two© www.theownerbuilder.com.au • 02 4982 8820THE OWNER BUILDER • 161 October/November 2010 • 51

upper roof line1voidentry2livingsliding doorcovereddeck5study7diningladderupup8760Upper floorNumbered arrows refer to photosloftlower roofkitchenLower floorl’dry/bath.8947bedroomPLANS: COURTESY STUDIOGREEN ARCHITECTSyears now with no ill effects and thetaste is far superior to our tap water.Hopefully one day they will change therules then we can disconnect the watersupply. When we construct the mainhouse we will be installing a 46,000 litreunderground tank.Hot water is from a roof-mountedsolar system with electrical boost. Wehad to orientate it to the west so needto use the boost when the weather isovercast in the winter. We expected thisto happen and the system on our housewill face north.The block is not connected to asewer so our wastewater is treated bya Biolytix system with the water beingused for subsurface irrigation in ourfood forest. As our water usage is verylow, only 90 litres per day for the fourof us, not much water makes it to theirrigation area (approx. 250m 2 ). Thefood forest is doing well and we are verywary of the products we use as we knowthey will end up being eaten by theworms in the system and then used bythe fruit trees.We would have liked to go solar forour power as this was one of our goals,but we could not afford the expensewhen building our granny flat. Weare connected to the grid but whenwe build the house we will once againinvestigate solar power.Restored energyWe have been very happy with theway the granny flat turned out andwould only change a few minor things ifwe were to build it again; these changeshave already been incorporated intothe house design. We have learned agreat deal about building and are nowcomfortable using straw bales. Once wemoved into the granny flat we sat downand redesigned the main house to makeit smaller and simpler to build.All up the build cost us just under$1000 a square metre. It is amazinghow all the little bits and pieces you buyfrom the hardware store quickly add up.We realised how hard it was to buildourselves and how much it takes outof your life. While all our friends weregoing away on holidays and barbeques,we were slogging away day and nighton the flat to try and get it finished.We were completely knackered at theend of it and have needed our two yearbreak to get our energy back, and arenow ready to start building again. Wehave been doing other projects aroundthe yard and are especially proud of ournew chook shed, which was constructedwith all the left over bits from thegranny flat construction.The overall build took us six monthstill we could move in. The best advicewe can give is to finish as much aspossible before you move in, becauseonce you are in all those little finishingoff jobs never get completed. Too manyother projects come along to keep youoccupied… ■Kurt’s company is Studio Green Architects.He can be contacted on 07 3245 2898,0434 884 633 or via his website:www.studiogreen.com.au• Huff ‘n’ Puff StrawbaleConstructionsStraw bale constructions and workshops.02 6927 6027, 0412 116 157,www.glassford.com.au• Biolytix Water AustraliaThe BioPod treats householdwastewater to secondary standard forsub-surface garden irrigation.1300 881 472, www.biolytix.com.au• ECOplyECOply structural plywood is a layeredpanel made from radiata pine veneersfrom 100% renewable plantation pine132 321,www.chhwoodproducts.com.au/ecoply• Radial Timber SalesRadial sawn timber products, includingweatherboards, decking, flooring andscreening.03 9768 2100, www.radialtimbers.com.au52 • THE OWNER BUILDER • 161 October/November 2010 © www.theownerbuilder.com.au • 02 4982 8820