House 8

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Before renovation

House 8, belonging to an adult couple and their university student daughter, was one of the first homes built in Papakowhai, having been constructed around 1965.  Downstairs is split level, with the higher part, used for a gym, added in 2004.  The gym includes two double glazed windows and a part concrete slab floor and part timber suspended floor on an enclosed concrete block footing.

The lower part of the split-level downstairs area has timber framed windows and a timber suspended floor. It contains the fourth bedroom, a rumpus room and the laundry. Upstairs in the lower part of the split level is an open plan lounge, dining, and family room. In the upper part are three bedrooms, a bathroom and a toilet. Both parts of upstairs have a timber suspended floor, with the exception of the foyer on the lower split level on the upper storey. The garage has a concrete slab floor and is attached to the upper split level on the upper storey, but is not internally accessible.

The house is well-maintained, and the majority of the windows have recently been replaced with tinted single glazing with aluminium frames. The upper part of the house is clad mainly in weatherboards, with some sheet materials below the apex of the long-run iron roof. The lower part of the house is clad in sheet material, and the back wall of the gym is concrete block.

There was ceiling insulation throughout, with holes for recessed halogen lights in the bathroom and the living areas. The walls were uninsulated, aside from the exterior walls of the downstairs gym. The underfloor was entirely uninsulated.

Underneath the house, subsidence around the new rumpus room addition had caused a clay downpipe sump to break, leading to a small stream of water trickling under the house and pooling underneath the rumpus room and fourth bedroom.  A waste pipe under the house was also leaking a little.

The home was heated with two nightstore heaters, one in the hallway of the bedroom wing upstairs, and one in the rumpus room downstairs. There is underfloor heating in the family room.

The family wanted to achieve capital gain on their property as well as reduce their energy costs through solar water heating.  The home was also quite damp, with three dehumidifiers operating.

The renovation package

House 8 was received a moderate to high thermal retrofit with a solar hot water system and some other small scale improvements, including:

  • re-laying ceiling insulation and adding a second layer of R2.6 over existing insulation and across ceiling joists to remove thermal bridging and raise insulation to approx R4.0
  • adding R2.4 insulation to the rear wall of bedroom 4 and gym
  • insulating timber suspended floors with R2.0 foil-backed bulk insulation
  • laying under-floor polythene
  • installing solar water heater with 300L cylinder
  • fitting double glazing panes into existing aluminium frames
  • installing a showerdome to address condensation and mould in bathroom
  • a plumbing maintenance check
  • a worm farm


Improvements as a result of the renovations

An easier home to heat

Temperatures in the family room and main bedroom stayed fairly similar between the 2006 and 2008 winters; however, the home required substantially less energy to heat.  Temperatures increased between the 2006 and 2007 winters but dropped again in the 2008 winter.  Overall, mean temperatures in the living room dropped 0.9°C and there was a slight decrease in mean bedroom temperatures, both decreases because of a reduction in heating within the home.

Temperatures are given as averages (mean), and as the overnight temperatures are still low, it brings the average temperature down. 

The most common temperature experienced in winter in the family room has stayed the same and the most common temperature in the main bedroom has had a ~2°C increase. The temperature most often recorded in the family room both before and after renovation was 18°C.  The most common temperature in the bedroom increased from 16°C pre renovation to 18°C after renovation. 

Relative humidity levels were tested in July and found to be above 70% about a fifth of the time.  Given that the significant moisture sources in the home (bathroom, kitchen and under-floor) were being managed, these relative humidity levels can be explained by the low temperatures.  If the home had been adequately heated, and clothes drying behaviour modified (commonly clothes were dried indoors) then relative humidity levels would be expected to improve.

Summer overheating

Given the extra insulation in this house, summer temperatures were also monitored.  The frequency of higher temperatures increased substantially and lower temperatures were eliminated.  While the highest temperatures in the home experienced were around 27°C and this did not change, the frequency in the main bedroom increased substantially.  The design of this house means there is largely no shading of northern or western windows, and the house was not mechanically cooled with window opening being the main cooling behaviour.

Lower power bills

The family’s electricity use reduced quite a lot - with reduced heating and substantial reductions in hot water energy use. The solar hot water system has been the main driver of energy efficiency, despite an increase in hot water use between the 2007 and 2008 winters.  Overall, they used significantly less electricity to heat their water with a reduction of 70% in hot water energy use during winter.

Significant space heating savings were also  made despite making no changes to how the home was heated (two electric night store heaters and an under-floor heater). The ceiling and under-floor insulation and double glazing has helped retain the warmth in this home from the use of the family’s heaters. Overall, they used these 15% less energy in the 2008 winter.

These factors contributed to an overall reduction in their electricity use of ~33% over both the winter period and the whole year.


What the family found

The family reported a marked improvement in the comfort of their home. They needed to heat the home less and noticed significantly reduced electricity usage despite increasing hot water use.   The house is drier too, with reduced use of their dehumidifiers.

An additional benefit for the family has been peace and quiet.  Members of the household no longer hear train noise filtering up from the main trunk line.

The family have been so impressed with the impact of insulation that they would prioritise insulation in the roof and the floor in any future renovations, and install solar water heating.


Our analysis

The family’s electricity use has reduced to 13,400 kWh per year but this is still high with their electric heating a big contributor.  The benchmark for electricity use is 7,300 kWh per year.   We suggest the family install an efficient heating system.  Their night store and underfloor heaters are big users of electricity.  If they want to retain an all-electric house, our recommendation is a heat pump.  Heat pumps can be up to four times more efficient than the heating methods they are currently using and, because of the way they heat, they may well see major electricity savings as a result.  Alternatively the family could look at installing a pellet burner or wood burner.

The temperatures in this home in winter are still lower than the HSS High Standard of Sustainability® benchmark.  The average minimum winter overnight temperature was 14.4°C in the main bedroom and the average minimum winter evening temperature in the living room was 16.2°C.  Our benchmarks, based on World Health Organisation recommendations, set a minimum of 16°C overnight in bedrooms and 18°C in the evenings for family rooms.  The decreased heating in the second year may be a type of “reverse takeback”, where the household decided to revert to the pre-retrofit temperatures and comfort, and gather further energy and cost savings from reduced heating.

Futher gains could be made in heat retention by installing heavy thermal curtains and pelmets, draught stopping remaining wooden windows, and installing wall insulation - starting first with the bedroom and south facing walls. 

Relative humidity, the percentage of moisture in the air, is recommended to be between 40% and 70% but is still high in this house.  Humidity is linked to cold indoor temperatures, as cold air holds far less moisture than warm air.  In cold temperatures, the moisture naturally in the air settles on cold surfaces such as un-insulated walls, ceilings and windows as condensation.  Our strongest suggestion is that the family stop drying clothes indoors.  This is a major source of moisture in a home, and may be a reason why they need to use their dehumidifiers so much.  It’s more energy efficient to use a dryer (vented to the outside) to dry clothes, than it is to use a dehumidifier for this purpose as dehumidifiers are large electricity users.  We also suggest the family upgrade their bathroom extract fanso that it is ducted to the outside.


Apart from the plumbing check and the change to solar hot water, no measures were undertaken in this house which would be expected to impact on water use.  The household’s average water use was 265 litres per person per day.  The HSS High Standard of Sustainability® benchmark is 180 litres per person per day.

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House 8, Papakowhai