HEALTHY HOMES CASE STUDIES
Warren Clarke Architecture: 124 Bowhill Road, New Brighton, Christchurch
The Why
Designers own home
I have been designing beyond code houses for a number of years and quite often when I was discussing energy efficiency with clients, one of the first questions ask was; what does it cost, what are the benefits, what is the payback time. I decided that it was time to build a home to a budget, live in it for three years, collect the data, and then I would be able to tell people about the costs, benefits, and payback.
The Design
Design principals
The first consideration was that it needed to be a family home. Three bedrooms, two bathrooms, open plan kitchen/dining, lounge, and a media room that doubled as a fourth bedroom and office. 140sqm is the footprint of the home but the internal living area is 128sqm due to the thickness of the walls. The volume of living space is 332 cubic metres. The layout reduced redundant space as much as possible. One hall doubles as the laundry space, the media room is a bedroom and office. There is no walk in wardrobe. The master bedroom is entered from the lounge. The final design has plenty of space to live and the volume adds to that feeling of space.
The design is based on Passive Haus principals, but I never intended to design and build for certification. The wall to footprint value ratio is the best I could do given the size of the section and what I wanted to achieve for the home. It is oriented for North facing glass windows to allow passive heating of the slab foundation. The rear house is close to the boundary, so I modelled the winter sun to ensure that the house was never in shade at the equinox. It worked; the shade finishes at the edge of the lounge/media room external wall. The design need to be for NZ living, open plan, indoor/outdoor flow etc.
We then concentrated on airtightness and insulation.
A garage was given away, as a cost measure and also I think that transport will change in years to come..
Foundation: Given the land is classified as TC2, an engineered waffle slab was designed to compensate. There is 30mm of XPS Climafoam board around the perimeter and under the slab. The was then tanked and sealed to ensure no mositure entered the foundation. This would reduce the R-value considerably. Hydronic in slab heating was installed by WarmthNZ.
Walls: All external walls are 140 x 45 timber framing, with 6mm OSB board ridged air barrier on the outside then a Proclima Solitex wrap and then Superbuild Autoclave lightweight concrete panel on a 24mm closed cavity system. Plaster finish. The close cavity gives R0.7 to the overall R-value of the wall. On the internal side of the timber framing is a Proclima Intello wrap, then a 50mm service cavity, then the final GIB lining. The 140mm framing has Knauf Jetstream blown insulation, R4.1, and the service cavity is filled with 50mm of R1.2 insulation. Overall R-value of the wall is R6.0.
Windows: The windows are a fibreglass extrusion imported from North America. The extrusion is brought in, in a raw state, cut and assembled then painted and glazed. Mostly site glazed. The windows aren’t recessed into the insulation layer, but they perform as well as recessed uPVC windows. Massey University have used the windows in a study of thermal efficiency of windows in NZ and these windows outperform standard, thermally broken aluminium and standard uPVC joinery. The glazing has LowE film, argon gas and layered for acoustic reduction.
And, yes, we do get condensation on our windows, except it’s on the outside of the window!
Roof: hyJOIST rafters span the roof with a ribbed colorsteel Maxx cladding. Under the purlins is a Proclima wrap then 6mm plywood, then rafters, then Proclima Intello wrap, ceiling battens and GIB. In the living and kitchen area is an acoustic HushPanel ceiling for noise reduction. Part of Homestar10. Jetstream insulation fills the rafter cavity and the Hushpanel has an acoustic batt that absorbs the sound but also insulates to a degree. The finished R-value of the roof is R7.0.
Heating: is provided by hydronic pipes in the slab. There is an air sourced heat pump externally of the dwelling which heats the hot water in the hot water cylinder internally and then a small pump under the hot water cylinder circulates water through the pipes. It is a closed loop system, we don’t use the domestic water. We run this system during the day because we have photovoltaic panels on the roof, so while the sun is creating the energy to run the heat pump, we heat the floor. Then at night it’s turned off and the floor radiates the heat into the living space.
The air is mechanically exchanged via an energy recovery ventilation system. As the system removes the stale moist air from the home, the incoming clean cold air passes this air and the heat is recovered back into the house. We recover about 80% of the heat back into the home. This system won’t heat the home, but it means the home remains healthy with minimal heat loss. An extra fan is installed in both bathrooms that is activated by a motion sensor as you enter the space, this runs the fan for 15 minutes to help remove the extra steam from those spaces. A further fan is installed to the underside of the ceiling in the loft. This fan is connected to a slot in the roof the opens to the underside of the iron roof, so when the roof heats up during the day we draw air from under the iron and have it pass through the energy recovery system, there by extracting the heat/energy from this air while dumping the air outside again.
Homestar10: I had been studying the Living Building Challenge.
https://www.livinghouse.org.nz/living-building-challenge which is very much along the lines of New Zealand Green Building Council’s Homestar rating system. As I worked more closely with the builder and discussed what we were trying to achieve, the question was posed, ‘what would the house get now’ and what would it take to get a ‘10’. Turned out there were only three things to consider, grey waste recycling, acoustics, and energy reduction. So, the challenge was laid down. We have achieved the ‘10’ and am one of three Homestar10 homes in New Zealand.
Homestar is not an energy rating indicator, it is a holistic approach to building better than the New Zealand Building Code. If you are considering building or renovating, do research the website and include as much of what is suggested https://www.nzgbc.org.nz/homestar
The Outcomes: The data; over the first twelve months of living in the home, we averaged a daily temperature of 21.88 degrees. The house never dropped below 18.5 and when it was 32 degrees outside, we managed to maintain 27 degrees inside, without mechanical cooling. The radiant floor means that the temperature at floor level can be same temperature as at ceiling height. The energy cost for the year, just under $1,500.00 per annum. I’ve had people tell me that they can spend that in just three months.
I think the greatest unsung benefit of a healthy home, is just that health. We don’t have winter and summer duvets or winter and summer PJ’s. It’s the same temperature in every room. If fact, it took a few months to adjust to having to put on so many clothes to go outside in the winter. A winters day, it’s bright and sunny outside, it’s 21 degrees inside, you step outside, it’s 10 degrees!
Discoveries
The greatest discovery was acoustics. Acoustics is the last thing people think about, and more often than not, not even considered. As a designer, I’ve tried to incorporate it into specifications but usually cost and not truly understanding the benefits meant it was soon dropped. Having now lived with it for three years, I can honestly say it should be much higher in the consideration list of any home. We have entertained 37 people at one time, in our little home, and everyone could be heard, it was just amazing to have experienced it.
Heating: I don’t think I could have any other heating type. One thing you have to remember, is, it’s not instant heat, you don’t turn it on and off as the temperature ebbs and changes. Once that thermal slab temperature builds up, it just feels great.
One of the aspects of an energy efficient home, is that keeping the heat in, is the easy part, getting rid of the heat when you don’t need it, is the hard part. Cross ventilation and passive air movement is very important. Next time is would have special venting windows. I also would design more window shading; we ran out of money for the Breeze Soleil over the French doors and I think it would help a lot with the passive heating control.
Skylights: I’ve always like skylights because I’ve always thought that we should, as designers, get as much natural light into spaces as possible. But I had forgotten the benefit of the natural ventilation. Part of the trick of keeping the house cool was to open the windows on the south side of the house, close the blinds of the skylight (to reduce solar gain) and crack the skylight by 15%. Worked amazingly well. Blinds in skylights are a must though, the solar gain is more than you realise.
For me, the benefits clearly out way the costs. When I look at the housing stock today, and what is still being built every day, I can’t help but wonder what the cost to the NZ economy is from the poor health of New Zealanders, the loss of workplace productivity due to health, the asemia rates in our children and think how different it could be if we all had warm, dry, healthy homes. Everyone needs to build beyond Code.
