lessons from experience - the owner builder magazine corkin.pdf · lessons from experience how on...

22 THE OWNER BUILDER 205 February/March 2018 © www.theownerbuilder.com.au

Lessons from experienceHow on earth do you build a sustainable house?

Who were these people? How could ‘ordinary’ people do such extraordinary things? Houses are big, complicated technical things – surely most people buy them ready-made for good reason.

I can’t remember at what point I could say ‘I am an owner builder.’ It kind of

creeps up on you. People ask me how I started, where on earth I got the ideas from. Sorry but I still can’t answer that. No previous experience, no grand life-long dream… but I can answer some of my earlier questions about the people behind these extraordinary creations – they are ordinary people, like me, who had ordinary jobs, and then followed a passion and dared to step outside the box a little.

Having read The Owner Builder magazine for a few years, I was always so amazed by the creativity and sheer determination of the owners. Most articles are about the actual builds, the months of hard work, ingenuity, problem solving and milestones which I loved reading about in an abstract way – a bit like ‘armchair travel’ with glossy holiday magazines! But I wondered about the people behind these creations.

BY MIRANDA CORKIN

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THE OWNER BUILDER 205 February/March 2018 © www.theownerbuilder.com.au 23

Be careful – you could become one too! And once an owner builder, always an owner builder – or at least another potential one. I’ve taken my personal interest in sustainable building on to a new career in building design now. Others will stumble back into ‘ordinary life,’ dazed but happy. But as a life experience it’s up there with the best. I’d love to motivate and encourage others to give it a go.

So how do you get from house site, to house build, to completed home, and even to an award! Here are some lessons from my own experience about sustainable design and owner building, which I hope will be helpful to others setting out on their own building journey.

The brief and the budgetI wrote my own brief – and it went

way beyond just listing the number and size of rooms I wanted. I read books, went on courses, did site visits, asked questions, doodled sketches and edited and re-edited lists. My must-haves, my would-likes, my budget-is-no-object dream features, my maybes… (I still have that page – it has worked out not too badly).

I found A Pattern Language by Alexander, Silverstein and Ishikawa a fascinating book . I jotted down ideas for style, function and form that resonated with me and that I wanted to incorporate in my home.

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The absolute joy of designing and building your own home is that you can imagine your favourite things – and then make them happen. I’d always loved the idea of having a day bed in the sunniest spot in winter for reading, a pantry big enough to keep all my kitchen appliances in one accessible shelf rather than stuffed in drawers, a place to dry laundry inside in winter NOT in front of the fire in the lounge, feature windows framing a favourite tree or view.

And now I have them! Here’s what my brief looked like:

• special, individual, private, calm, curved, warm, welcoming

• sensitive to its bush environment• warm in winter, cool in summer• economic to build – both financially

and environmentally• energy, water and maintenance

efficient to live in• light, open, stylish, contemporary,

striking – with fun, playful factor• adaptable for teenager spaces, elderly

relatives, adult privacy• communal party and entertaining

spaces – indoor and outdoor• predominantly using recycled and/or

local materials• mud room/laundry, drying room, TV

snug, open loft, wood fire

• 3-4 bedrooms, 2-3 bathrooms• large garage and storage.

My goal was to build a modern, comfortable family house while still being very alternative, sustainable and efficient to live in.

The house is just over 300m2. It might seem extravagant in some ways, but I wanted to prove that it could be done for a similar budget as a ‘normal’ house. I wanted it to look stylish, contemporary and well finished. Owner building budgets are of course hugely influenced by the ‘free’ (hah!) labour and project management efforts you put in yourself – but I was aiming for, and achieved, under $2,000 per square metre.

GSEducationalVersion

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Offi ceLaundry

Bathroom

Bedroom

Bedroom

Bedroom

Deck

MORNING SUN

SUMMER MORNING SUN

CROSS VENTILATION

THROUGH VENTILATION

N W WINDS

THROUGH VENTILATION

NORTHERN SOLAR ACCESS

NORTH

sunrise

sunrise sunset

summer

sunset

winter

AFTERNOON SHADE

SUMMER SHADE FROM EAVES

TREE SHADE

Kitchen

Porch

Dining

Living

Floor plan showing passive solar ventilation

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Arrow letters refer to photos

PLAN

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The design

Solar passiveIt almost goes without saying these

days thankfully, that solar passive design features are a prerequisite for new buildings. The aim is to build a house that you can live in comfortably in the local climate without the need for energy-guzzling heating, cooling and ventilation. In winter in my previous, uninsulated house, despite heating being on in the evening, by the next morning you could see your breath smoking in the cold kitchen. Definitely a motivating factor in getting this house right.

Solar passive design uses the building itself to help keep us warm in winter, cool in summer and maintains fresh clean air inside our home.

ClimateI discovered that you really need

to know your own local site climate – including winds, seasonal storms, shading, sun heights and yearly rainfall patterns. Although our site is below the hilltop line on the opposite side of the valley, we still get very strong funnelled winds hitting us, which I thought we’d be sheltered from.

The Building Code of Australia classifies eight different climate zones, and we fall into ‘Mild Temperate’ along with much of the south coast of NSW. But at the top of the Blue Mountains, with an elevation of 1050m, we have winter snow, regular frosts and hot dry summer days often well above 30°C. Even NATHERS more detailed 69 zones rate us the same as Canberra – which has an elevation of 560m and quite different monthly data to Blackheath.

I didn’t get too technical about every R-value (energy efficiency rating) of each material during the design, but I did plan overall for a house that would be toasty warm in winter – and it’s worked so far.

OrientationDespite coming to Australia nearly

25 years ago from the UK, I still have to remind myself that the sun is in the NORTH here, not the south. I got it right for our house site which was chosen partly for its northerly aspect – both my previous homes had wonderful views but to the south, so the main living rooms were oriented to the cold and shady side. No such mistake this time.

My design is basically rectangular (with some funky curves and shapes) with the ridge beam running east-west with all the living rooms facing north and the bathrooms, utilities and office to the south. Again, as with the R-values, I didn’t get too literal about angles. We actually face slightly west of north, and with curved walls and a curved roof, the windows all have slightly different aspects and heights under the eaves, so I found it impossible to work out exactly the eave overhangs required to shade out the hot summer sun for every window. But I made up for that with glazing options and blinds.

Thermal mass and insulationNothing worse than bare feet on a

cold tiled floor in winter ; and nothing nicer than lying like a lizard on a warm stone wall in the summer sun. When it came to the materials we used for our build, we got a lot of advice from expert and experienced builders and we now have a wonderfully eclectic mix of all sorts of sustainable building methods and materials. But the criteria for all the exterior walls was consistent with the principals of thermal mass and insulation: in winter, let the warmth of the sun in and keep it in; and in summer, keep the hot sun out and let hot air out.

Our site slopes downhill, so we have one main ground floor and ‘half’ a lower floor below, cut into the slope. We have concrete slab floors, partly suspended and partly on ground. The loadbearing walls on the lower level are recycled tyres rammed with earth from the site, and in situ concrete built up in formwork.

The upper floor has all external walls made with timber framing, straw bale infill and then hand rendered with cob made from the site soil and straw offcuts. The outside is weatherproofed with lime/sand render – all done by hand – and the interiors are finished with finer lime and clay renders, with smooth steel trowel finishing. The result is a beautiful textured finish to 500mm thick walls – think wide, warm, sunny windowsills to sit on… Added bonuses are that these walls are fire rated to bushfire attack level BAL-29 and, because of the lime and organic renders, the walls are breathable – which means they allow air vapour through and this maintains a comfortable air humidity inside.

The core of the house has its own passive temperature regulator in the form of a 5m high solid cob wall – just mud and straw – which creates a dramatic feature wall in the main lounge. Together with a curved cob wall along the corridor to the bedrooms, this helps maintain the heat in winter and the cool in summer through the middle of the house. The wood fire and its flue back against the cob wall so it becomes a central heat bank and keeps the house warm overnight. Despite the high ceilings, the room temperature only drops approx. 3 or 4° overnight – no more smoking breath on cold winter mornings!

The concrete floors get warmed by the winter sun falling well into the north facing rooms, and for the rooms where the sun doesn’t reach, we have underfloor hydronic heating coils on a low thermostat setting which gently warm the slab.

To wrap up the rest of the house, we sprayed a thick layer 150mm of Easy Foam Icynene as the roof insulation; while hard to rate exactly for R-value (approx. R-2.5 for 100mm thickness), it also has the extra benefit of sealing all air gaps in the roof and the top of the bale walls.

The windows are all double glazed and uPVC framed with very efficient airtight closures. To counter the difficulty of shading out all summer sun with the eaves due to the curves, I have internal blinds which sit neatly within the frames, and can be drawn ‘top down’ or ‘bottom up’ – so the sun can be blocked from shining directly on the floor from the lower half of the window, while keeping the blind open at the top to still see out for daylight and the view. Other passive design features include airlock entrance rooms for the front and back doors and smaller windows to the west to limit the hot afternoon summer sun.

VentilationCareful planning for good ventilation

keeps the house cool in summer. With outdoor temperatures over 30°C, the inside rarely gets above 24°. We close the windows in the daytime and open them at night, and they are positioned to allow cross ventilation through the house. Hot air accumulated during the day rises to cathedral ceiling in the lounge and a floor vent draws cool air up from under the slab behind the tyre wall below. Vents and openings through the loft room above


the middle of the house allow air to flow at ceiling level, right through the length of the house and out of high clerestory windows. This natural convection of hot air means we have no need for air conditioning. Large reversible ceiling fans also assist with moving the air.

As well as the solar passive design features, there are two other significant aspects of the sustainability of the house.

Energy efficiencyPart of my brief was that the house

should be efficient and low cost to run. I decided against any gas supply, so everything runs on electricity including hot water and central heating. I estimated our monthly power usage of all appliances and LED lighting.

At the time of installing a 5kW solar PV system, the cost of storage batteries was still prohibitive, so we have a feed-in system to the grid. Without overnight storage, we still ‘buy in’ some electricity at night and on cloudy days, but over a whole year, we are approximately ‘energy neutral’ as we export more than we use in the summer.

We have one Sanden air heat pump, (which is very efficient in our cold climate) that gives us constant hot water in a 315-litre tank; two other heat pumps run the underfloor hydronic heating plus two wall radiators. I designed a small drying room next to the laundry for winter clothes drying, which is warmed by the manifold for the floor heating. No more laundry draped in the lounge room!

MaterialsThe slab floors seemed to have a lot

of steel and concrete go into them, but that was the ‘cost’ of the sloping site and need for a suspended slab. It is however the finished floor surface, so apart from tiles in the bathrooms and cork boards to soften the kitchen floor, we minimised the use of purchased and manufactured flooring materials as much as possible.

From the site excavations we had plentiful soil, which fortunately has a good clay content for cob. Stones were sorted and used in the landscaping and about 50m of dry stone walling. Trees cleared for the build were felled, milled on-site and cut for all the main framing – no transport or material costs. Recycled tyres were salvaged free from local garages and rice straw bales were purchased from western NSW. The in situ concrete was made with our site soil, recycled crushed concrete from the local council and cement. Lime and natural renders on the internal walls minimised the need for plasterboard lining and paints. Wherever possible we kept to natural oils for timbers, low VOC paints and finishes.

To wrap up, it’s a joy to live in! There is a huge sense of achievement and satisfaction with living in a fantastic warm, comfortable family home, which hasn’t cost the earth to build. u

Miranda Corkin won the major award category, Residential Sustainable Building Design, for the design in the 2017 BDA National Design Awards.

Links & resources

u MKC Building DesignEncouraging sustainable home building in the Blue Mountains.

0438 552 939, www.mkcbuildingdesign.com.au

u Easy FoamEnergy efficient spray foam insulation.

02 9820 9021, www.easyfoam.com.au

u Sanden Hot Water Heat Pump SystemUsing less electricity to heat water.

1800 146 123, www.sanden-hot-water.com.au

u A Pattern LanguageBy Christopher Alexander, Sara Ishikawa, Murray Silverstein. ISBN 9780195019193. Offers a practical language for building and planning based on natural considerations


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