House 10

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This house does not have a heat transfer system, so supplementary space heating in the bedroom (not separately monitored) paired with increased insulation levels are the most likely cause of the increasing overnight temperatures in the main bedroom.

Before renovation

House 10 belongs to a family of five and was built in the early 1970s. The family bought it as a ‘do-up’ - it had been poorly maintained, with rotten timber window frames, drainage problems, and leaks in the building envelope. The current owners have progressively been relining parts of the house, and have installed double glazed window units in the bedroom wing during the summer of 2006-2007.

The upper level of the house contains an open plan kitchen, dining and family room wing, connected by a sunken foyer to the bedroom wing containing three bedrooms, a laundry and a bathroom. The lower level of the house contains a fourth bedroom or rumpus room, a storage room, and an internally accessible garage. The upper level of the house is clad in sheet materials with timber framed windows. The floor of the living areas is unusual in that it is concrete, while the rest of the upper level has timber suspended floors. The lower level has a concrete slab floor, and concrete walls. The roof of the house is concrete tiles.

The ceiling cavity had some older batt insulation which has been lifted and piled up in places leaving large areas without insulation. The walls were uninsulated apart from downstairs, where battening and new plasterboard lining has provided an air gap which provides a small amount of insulation to the concrete walls of the downstairs bedroom or rumpus. The floor was uninsulated throughout.

The house was heated with an older recessed enclosed woodburner in the lounge, and oil column heaters in the bedroom wing.

The family were already planning extensive renovations and had already double glazed their children’s rooms to combat the cold. They were most concerned with cold, damp and mould in the home.


The renovation package

House 10 was renovated witha high thermal retrofit with efficient heating and a solar hot water system,   including:

  • insulating and lining the flat roof above foyer with R3.6 mid-floor batts
  • putting two layers of R2.6 over old insulation, with the top layer over ceiling joists to remove thermal bridging.
  • stripping walls, insulating with R2.4, and re-lining throughout house, except for downstairs bedroom
  • insulating timber suspended floors above subfloor and garage with R2.0 foil-backed bulk insulation
  • laying under-floor polythene on sub-floor
  • replacing inefficient woodburner with new high efficiency woodburner and wetback pumped to hot water cylinder
  • installing solar water heating system on foyer roof.
  • replacing rotten window frames with double glazing units and window frames in living areas
  • using compact fluorescent bulbs for main lights
  • installing extraction fans in bathroom and laundry
  • draught-proofing a garage door
  • a plumbing maintenance check led to fixing a leaky tap
  • a worm farm    

Improvements as a result of the renovations

A warmer home

Temperatures in the family room and main bedroom improved significantly as a result of the renovation.  Average winter temperatures in the family room increased by 1.4°C.  Average winter temperatures in the main bedroom increased by 2°C.

The most common temperature experienced in winter in the family room has stayed the same at 17°C, but there has been a reduction in the coldest temperatures.  The picture is even better in the main bedroom where there has been a ~4°C increase.  The temperature most often recorded in the main bedroom before renovation was 13°C; after renovation, it was 17°C. There has also been a big reduction in the frequency of cold temperatures.

The heavy insulation and double glazing has helped retain the warmth in this home from the use of the wood burner and portable electric heaters. 

Lower power bills

The family’s electricity use reduced quite a lot - largely as a result of the improved efficiency of the solar hot water/wetback system, and the improved thermal performance of the home.  Overall they used significantly less electricity to heat your water with a reduction of ~70% in hot water energy use during winter. Although the solar hot water system is providing nearly 100% of hot water needs in summer, the family has also had significant benefits in terms of increased hot water use - their hot water use has increased by 25% since they got the new system.

The solar hot water and insulation contributed to an overall reduction in their electricity use of ~23% over winter and ~30% annually.  However, a ~45% reduction in total reticulated energy use in the 2007 winter was reversed in the 2008 winter with a ~39% increase in total reticulated energy use.  Most of this extra energy use came from portable heaters and appliances.  As a result, a significant component of electricity savings from the change in hot water heating methods was taken back in other electrical services within the home.


What the family found

The renovations met the family’s expectations of greater warmth and comfort, and the unexpected benefit were the very considerable cost savings they were able to achieve with solar water heating and the wetback. The family say they were originally sceptical about solar water heating but, if they were faced with the same situation again, they would place solar water heating at the top of their priority list. They felt heating combined with insulation had the most impact on temperatures.

The bedrooms no longer feel cold to the occupants; although when it gets really cold, they do run supplementary heating in the bedrooms.  They commented that, while the wood burner was very efficient, it can’t get heat down to the other end of the house, so a heat transfer system is needed and this is something they plan to do at some stage.  Overall they noticed that temperatures have risen in the house during winter, with the morning temperature “much higher”.  The family found it too hot in the house over several weeks in summer, but opening the windows and doors solved the problem.

Dampness had gone in the main living areas and the extractor fans in the bathroom and laundry were “excellent”, especially when combined with new windows.  Although the family did use dehumidifiers when they first moved in, they no longer need them.

The most unexpected consequence for the family was the enormous sense of well-being derived from being able to progress the renovations and improve their living conditions. The warmth, in particular, and the reduction of noise from the double glazing and window repair have been particularly appreciated.   They report having a lot less colds, runny noses, and flu”.   They commented that they all felt more relaxed,  that being warmer makes them happier, and that “We are doing our job as parents by keeping the house healthy for the kids”.

The family acknowledge that they are using more water, now that they no longer worry about the water left in their cylinder.  “As the family have grown we don’t have to worry about the water - we used to boil water on the fire and share the bath with the kids”.

Our analysis

The family’s electricity use is quite low at around 5600 kWh per year, compared to the benchmark for electricity use of 7300 kWh per year.

The solar water heater is performing very effectively for the family, especially given their hot water use has increased and given the monitoring period was over the winter months (May-September).  The panels were well oriented for winter sun. The systems used were of a high specification – with panels twice the size of an installation undertaken under the EECA subsidy scheme, and therefore not a common practice installation.

As a result of the improvements, winter temperatures come very close to meeting our HSS High Standard of Sustainability® benchmarks.  The mean minimum family room temperature in the evenings is 17.8°C and the mean minimum in the main bedroom overnight is 15.8°C.  Our benchmarks, based on World Health Organisation recommendations, set a minimum of 18°C in the evenings for family rooms and 16°C overnight in bedrooms.  This house does not have a heat transfer system, so supplementary space heating in the bedroom (not separately monitored) paired with increased insulation levels are the most likely cause of the increasing overnight temperatures in the main bedroom.  We suggest the family considers installing a heat transfer system to ensure that heat generated in the family room is more effectively spread around the house.

A reversal of temperature improvement in the family room has occurred despite an increase in space heating energy.  The family found it difficult to keep an even temperature from the wood burner during the first winter, suggesting that learning to operate the wood burner optimally may be helpful.

Because of the extent of thermal improvements we made to this home, we also looked at summer time temperatures.  These have increased, particularly in the bedrooms,  with the highest temperatures around 27°C.  We suggest installing sunshades on western windows to provide late afternoon shading.

Humidity, the percentage of moisture in the air, is recommended to be between 40% and 70%.  Humidity levels at times exceeded these levels.  Given the measures taken to reduce moisture in the home, this may be largely due to under-heating of the home leading to elevated relative humidity levels.


Apart from the plumbing check and fixing the leaky bathroom vanity, no measures were made which would be expected to improve water use in the home.  The family’s average per person water use was 151 litres/pp/day compared to the benchmark of 125 litres/pp/day.

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House 10, Papakowhai