Green Oversite



My House

Measures Taken to Improve Energy Efficiency

Bruce Barbour - July 2019

A brief overview of my house construction and measures taken and features installed that impact on its thermal efficiency and the total energy used in the house.  For comments on actual household energy use refer to the Photovoltaic page.

Site and orientation

The site on which the house is constructed is not ideal for solar passive design. The block fronts the street facing approximately South and is 12 metres wide. The block is 30.5 metres deep. The block orientation is offset from true North South by 20 degrees. This is not an ideal block for solar passive design. The reason for this is that very few blocks are subdivided with the requirements of passive solar design in mind. A block that is suitable for passive solar design either happens by chance or else is a larger block that allows more flexibility in the placement of the house on the block to ensure better solar access and limit shading from houses and trees on the adjoining blocks.

Site Plan

There are a couple of reasons I did not choose a larger block which would have allowed full passive design. Firstly larger blocks in the area that I was interested in were more expensive - and I was on a budget. Secondly the larger blocks on the subdivision had minimum house size covenants meaning that I would have had to build a house at least 50% larger than I wanted. This would add considerable expense. The last reason is that I did not want to have to maintain the grounds of a larger block. Refer to the Subdivisions page for further commentary on issues relating to subdivisions.

Given that I had chosen this non ideal block I had to make the best of it. I located the living rooms to the North facing rear of the house and the bedrooms and service rooms to the South facing front of the house. Consequently the house is designed so the living rooms at the rear of the house benefit from solar access, and bedrooms etc. at the front of the house getting little direct solar access.

See below for reflections on how the design could have been changed to allow solar access to the front bedrooms.


Foundations and floor

Because the site slopes to the rear two different foundation types are used. The front of the house is constructed on a concrete waffle pad sitting on the ground. The rear of the house is constructed on a suspended concrete slab. It is insulated under the slab with R4 insulation. The floor slab is the main thermal mass in the house.


The walls are a timber framed with rendered 50mm thick Hebel panel veneer. Hebel is manufactured as Autoclaved Aerated Concrete (AAC). It has a lower weight and a higher insulation (R0.5) compared to brick. I also used R2.5 polyester batts between the wall studs bringing the total wall insulation up to approximately R3. The walls are painted a light colour.

Windows and doors

Double glazed windows. There is an inert gas (argon) between the panes which adds a bit to the insulation of the windows. Also a low emissivity (Low-e) coating on one of the glass panes. The window frames are Aluminum. The windows and the doors have excellent weather seals on them, lowering infiltration. I have used casement windows where possible which will allow the maximum ventilation rates when opened for summer cooling.

There are two 2.0 metre  high by 1.8 metre wide windows / glazed door on the north facing rear wall of the house. These windows are the primary windows for controlled solar access to the house. The windows are under a shade structure designed to allow solar access during winter and to block it during summer.

Three of the east or west facing windows are fitted with roller shutters to block the sun during summer. No roller shutters on other windows. Note that there are no eaves on the house.

Roof and ceiling

The roof is a light coloured Colorbond corrugated metal roof. The light colour should assist in maintaining cooler temperatures during summer. It is underlain with one layer of reflective foil.

I used two layers of R3 polyester batts (total R6) in the ceiling, although the contractor that installed them did not do a very good job meaning that R6 may not be achieved over all of the ceiling.


The house itself has an energy rating of 7.2 stars and uses some passive design principles, although full implementation of passive design was restrained by site restrictions, as stated earlier. Effectively the rear of the house uses passive design principles, the front of the house is just well insulated. The floor size is 130 sqm, not including the attached single garage. This is a lot smaller than most new housing which aids in limiting energy usage.

Equipment and accessories


A 4.3 kW photovoltaic (PV) system was installed at the start of March 2019. See the separate article on the photovoltaic system for further details.

There is no gas connected to the site so all heating, cooling and cooking is by electricity (or passive solar gains for some heating).


Primarily used batten fix lights for main room lighting. Most contain light emitting diode (LED) light bulbs, although there are some compact fluorescent lights (CFL) in low use rooms.

I did not extensively use downlights. Even though downlights are now primarily LEDs they still require creating holes in the ceiling insulation which would result in heat loss in winter and heat gain in summer. Besides I prefer the look of batten fix lighting.

There is a solar powered "skylight" in the laundry. This has a small PV panel (separate to the main PV system) which powers a square (300mm x 300mm) LED ceiling light. The amount that this is lit depends on the amount of sunlight hitting the dedicated PV panel. It works well and looks like a standard skylight without compromising the ceiling insulation.

Heating and cooling

Daiken Reverse cycle split air conditioner - 1 kW - was installed. It heats / cools the living room areas. There is no heating or cooling for the bedrooms.

The Daikin reverse cycle system installed was smaller than recommended by the installation company - who suggested 1.5 kW. I had done the calculations on the house heating energy usage and had determined that 1 kW was a sufficient size. This has so far proven correct though it is still early days. Of an evening once the room has reached temperature it operates using between 200 to 300 Watts. However if the house has been unattended for a number of days and the thermal mass (mainly the floor slab) has cooled then the reverse cycle air conditioning system can struggle to bring the room quickly up to temperature - not an issue most of the time. I also only heat the main living area and not the bedrooms - a closed door slows the loss of heat to the rest of the house. I insulated (R1) the walls between the living area and the rest of the house during construction. I set the temperature of the air conditioner to about 20 degrees (winter) in the living area in the evening which is fine for me so long as I have a jacket on, but may be too cool for some. Often I find 18 degrees is adequate in the morning (winter).

Hot water system

Heat pump system from Sanden. For further information on the hot water system see the Photovoltaic page. I added additional insulation to the water pipes running between the heat pump and the tank. I insulated the pressure relief valve on the tank making sure not to disrupt its operation (very important).

I added additional insulation to the hot water supply pipes from the tank to the tap, where possible.


The refrigerator I use is a LG 300 litre. It is rated at 4 Stars with a rated energy use of 279 kWh per year, an average of about 0.75 kWh per day - though I measured a daily consumption of 0.66 kWh with my power meter - that may have been due to the measurement being taken in winter. It is about 6 months old (at July 2019). It is interesting to note that my previous fridge was rated at over 500 kWh per year and only had a storage volume of 200 litres. It was over 20 years old when I changed it over. Refrigerator technology has come a long way. The new fridge uses 50% of the power of the old fridge and is 50% larger. Even considering embodied energy it is probably worthwhile upgrading if the fridge is old. Financially it should pay back in under ten years.

Washing Machine

I use a front loading washing machine on cold setting. This is quite efficient. If I used hot water the energy usage would be many times that of the cold setting. (I did measure it once but have forgotten the figures.)  The machine has an internal water heating element so the energy usage would be high. I try to dry the clothes on the outside clothes line though in winter this sometimes does not dry the clothes 100%.


I don't have a dishwasher at present. I wash the dishes by hand in the sink. This would be quite energy efficient as the hot water used comes from the heat pump hot water system largely powered by the PV system. Most dishwasher machines I saw when I investigated this a few years ago had an internal heating element, so bypasses the heat pump hot water system. If I used the machine on a sunny day most of the power should come from the PV system (depending on power draw) which is a bit better but energy use would still be more than sink washing, even if more water was being used in sink washing (as claimed by the dishwasher machine manufacturers). I may still get a dishwasher in the future for the undoubted convenience. I will see.

Water Tank

A two kilolitre water tank was installed under the rear decking during construction. The tank supplies water to the toilet cisterns and the garden taps, utilising a.small electric pump. Installation of a water tank was mandated by regulation - if a new house was not connected to reticulated "natural" gas where available, it had to have a minimum 2 KL water tank. As I did not want gas I had to have a water tank. This is a strange regulation as the two are totally unrelated. If the regulation was not in place I may not have opted for the installation of a water tank - the economics, the pay back period for water tanks, is really quiet poor. However now that I have a tank it will save some water and means I will be able to water the vegetable patch over summer with a clear conscience, while the tank water lasts. If the tank water runs out it automatically switches over to mains water.

Aspects that could have been improved

Security system - I had a security system installed in the house. This was a decision made on the run with no investigation into the best system. The house had been broken into during construction and many items taken. Consequently I asked the electrician to install a security system. It was only after installation that I discovered that it uses 18 Watts of power. This would have been fine if it was just using this power while the system was switched on and doing its job of detecting intruders. However it uses 18 Watts 24 hours per day whether on or off. This amounts to 0.43 kWh per day. It is approximately 50% of my total "phantom" load of around 36 Watts. Unfortunately it would be too expensive to replace with a more efficient system or at least one with a lower standby power use. It is disappointing to me that companies are still allowed to sell system with such high standby power loads. It is clear to me that the companies won't address this issue by themselves so there needs to be regulations in place to tell them what to do.

My other phantom loads are from the PV system (using 5W after the sun goes down) and the television, recorder/DVD player and washing machine. Also two security lights on sensors and two hard wired smoke detectors.The total phantom load of 36 Watts amounts to over 0.8 kWh per day which is often greater than 10% of my daily energy usage - reasonably significant. I will endeavour to address this usage by turning appliances off at the wall where possible. (I can't turn off the security system at the wall socket when it is not needed as it has battery backup and will trigger the alarm if it loses power for a time.)

Hot water system - It is interesting that even on days when I don't use any hot water, the hot water system still uses between 0.75 and 1 kWh of power during winter. The energy use will probably be less in summer. The energy use must be due to heat losses from the tank during the day and night. I may investigate adding more insulation to the tank to lessen this heat loss - it would be worthwhile if I can halve this loss..

In my situation each shower per day adds between 0.75 and 1 kilowatt hour to energy use, so decreasing the amount of hot water used per shower can have a significant effect. I measured (with a bucket and stop watch) the flow rate from the shower head that I am currently (July 2019) using at 6 litres per minute. This is higher than the flow rate at a previous residence, with a different shower head, which I measured at 4.5 litres per minute - and I still got a satisfactory shower. That shower head was a cheap head - at around $20 - from Bunnings. I will try to decrease the flow rate from my current shower head by blocking some of the water delivery nozzles. I am hoping to be able to block at least a quarter of them without adversely effecting the feel of the shower.
Note on shower head rating: Both of these shower heads were rated that 9 litres per minute - the legal maximum. This rating relates to the maximum flow rate and not the flow rate at which it is possible to have a nice shower. I would think that few people would have a shower with the flow rate set to the maximum - I certainly don't. Consequently I doubt the usefulness of buying a 7.5 litres per minute rated shower head. These usually sell for prices much higher than warranted and would not guarantee (unless they specifically provide the guarantee) that you would end up using less hot water than a cheaper shower head. However if you have someone in the family that insists on turning the shower water flow up to the max then it would be a worthwhile investment - if education does not work.

Hot water pipes - during construction the plumber installed a line of hot and cold water pipes down the centre of the house for the whole length of the house and then ran branch line to each of the taps. This approach may be alright for cold water but would have been very wasteful for hot water as the hot water would have to run through many additional metres of pipe to get to the tap. I pointed this out to the plumber and he changed the arrangement. However the layout of the hot water pipes is still not optimum. Ideally the hot water pipe should run to each hot tap by the shortest possible route. And the smallest allowable and practical pipe diameter should be used.

Floor tile colour - the tiles in the living area are light coloured. Ideally for passive design the floor tiles in areas that receive sun light onto the tiles should be black or a dark colour. The dark colour would allow more solar energy directly heating of the concrete slab during the day meaning the slab would be warmer going into the evening. With light colour tile a greater proportion of the light is reflected off the tile. This reflected light would more heat up the room during the day, and less for direct slab heating. This is OK so long as the room does not get too hot. However it means the slab will be cooler going into the evening.

Window frames - the window frames are unbroken aluminum. Aluminum has high thermal conductivity which is not ideal. I can feel how cold they are at night during winter. Should have used a broken aluminum or even timber would have been better (though it requires maintenance over time).

The window shade structure at the rear of the house was installed lower than I wanted. However because the levels were not documented in the house construction contract document there was nothing I could do about this - without large expense. It means that I lose about 150 mm of solar access through the  northern windows during winter which is regrettable but not disastrous.

Perhaps I would consider the use of eaves if I was to design another house.

There is a fluorescent tube (36W) in the garage. On reflection I could have installed batten fix LEDs instead of the fluorescent tube. This will be overcome when LED replacement tubes become more widely available.

Pelmets and Curtains - The current window curtains are unlined, single thickness fabric. Pelmets are yet to be installed. Installation of pelmets and lined curtains on the windows should improve overall thermal efficiency. Note that windows are still the weak link in a house's thermal performance. Even with double glazing it is likely a window without curtains would have an R value of under 0.4. This compares to a typical wall which in newer houses should have an R value of over 2.0. Even with double glazing the R value of windows is still less than 20% the value of the wall's R rating. This means that the conductive heat flow through a square metre of window would be five times that of a square metre of wall. Adding curtains and pelmets will increase the R value of the window by a couple of points however the overall R value will still be substantially less than walls. However it is a worthwhile improvement.

The water tank is currently only connected to two roof down pipes. It would be relatively easy to connect a third down pipe. (A fourth down pipe would be more difficult but doable.) If done this would have no impact on winter water collection - there is an excess to requirements with only two down pipes - however it should extend the availability of tank water over summer.

Larger possible design alterations to improve solar access

As mentioned the bedrooms at the front of the house do not get any solar access. This could have been addressed if I had been willing to consider using a split level design. The site slopes from the front to the back so it could have been possible to have the floor level of the rear of the house at a lower level than at the front. This would have allowed the placement of windows in north facing wall of the raised front of the house. However it would have meant having stairs between the two sections of the house which I wasn't keen on. Another possibility would be the use of clerestory windows for the front section of the house - a feature that again I am not keen on.

Considering that I did not do this, if I want to use these bedrooms for other than sleeping in winter I would have to install auxiliary heating - probably a multi-head split reverse cycle air conditioner. This can still be done post construction though I have no plans to do it at the moment.

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