top of page
  • Writer's pictureBBSN

Sustainable House - Retrofit Unit

Updated: Oct 7, 2018

By Malcolm McKelvie

This is a 2 bedroom unit built in approx. 1980’s that has had an energy makeover. We have opened this one to show it is possible to achieve really good energy efficiency and comfort results from a pretty poor start. When a previous tenant moved out, we decided to take the opportunity to do the retrofits for a variety of reasons; to walk the talk not just in our own home and to practice some energy retrofit skills.

Building shell materials before the retrofit:

Floor- concrete slab.

Walls- brick veneer, foil only.

Windows- non thermally broken aluminium frames, single glazed, sliding windows. No pelmets.

Ceiling insulation- 100mm thick glass fibre batts with incomplete coverage. Estimated R value of 1.5

Roof- tiles

Energy Freedom Retrofits done:


We replaced the lounge room light fittings with LED oysters, left the kitchen strip fluoros and replaced other globes with LEDs

Draught proofing

A blower door test before we started showed 18 ACH50 which was improved to 9 by weatherstripping the doors, caulking around architraves, some pipe penetrations, some penetrations in the wall top plates in the roof space and fitting draft stoppas over the exhaust fans, repairing holes left by removing the heaters and filling in the open vented toilet window, which was also secondary glazed.


I filled any gaps in the ceiling insulation then rolled out R3.5 earthwool batts perpendicularly to the existing ones. The access hatch was too small to get them in so I had to lift some tiles, cut a section of the batten out and slip them in the hole. The hard to reach parts close to the edge were managed by lifting that row of tiles and doing it from above.

The walls were insulated with spray foam by SprayITsolutions. They drilled multiple holes in the brickwork, sprayed in the foam then filled the holes with mortar. They estimate the R value would be 2-2.5.


I got a quote from Magnetite to do all the windows which came back bw $8-9000. That caused me to wonder if I could do it myself. I ordered acrylic sheet, aluminium strips and magnetic tape. That system worked well for the smaller windows in the toilet, bathroom and laundry but not the bigger windows which needed some extra support to hold them in place. The kitchen and one lounge window were left to allow for easy cross ventilation. Secondary glazing raises the insulation value from about R0.18 to 0.5. Windows are usually talked about in U values which is the reciprocal of R values but I find it easier to conceptualise the problem with windows by using the same term.

I also fitted clear acrylic sheet pelmets above the curtains to reduce draughts.

Appliances and cooking

The existing gas cooktop and oven was replaced with a Belling induction cooktop/ oven combo unit that, annoyingly, was about 20mm wider that the old one so I had to move one section of the kitchen cabinetry a little. Then it also became necessary to redo the tiled floor…..

Heating and cooling

An old gas wall furnace that had not been used for years was removed and the large hole in the wall filled. That removed another big source of draught. The other gas space heater was removed, the holes again being carefully filled and a Daikin US7 heat pump installed.

Hot water

The old gas storage hot water service was removed and replaced with a Sanden heat pump unit. It’s timer was set to run only during the middle of the day when the solar PV would be producing power.

Energy monitoring and control

There is no monitoring device installed other than being able to check usage on the Powershop account or Ausnet’s MyHomeEnergy.

Solar power

A 4kw system has been installed, half on the east and half on the west facing roof. The neighbouring property has some trees which have grown taller and are probably causing some afternoon shading issues.

What’s it like to live here?

Our tenants report that it is very comfortable. “Living here is very comfortable since is very well insulated. You can feel the difference as soon as you walk into the house even when the reverse cycle is turned off. The solar panels are also a great perk, on an average day of winter we spend around $2.50 and $1.50 in summer”.

Their family members who have visited have since requested home energy assessments and some retrofit work done by BBSN as a result which has been gratifying. We don’t have access to the energy use data.

What did it all cost?

Solar PV- current costs with the Vic Govt rebate could be $2500 ish

Top up ceiling insulation (DIY labour) $1001

Sanden HWS (installed) $4162

Electrical work for new oven/ cooktop, HWS, wall insulation $1769

Weatherstripping materials (DIY labour) $161

Plumbing contractor (removing gas appliances, installing new toilet) $486

Secondary glazing (DIY labour) $1415

Daikin US7 (installed) $4150 (should have been less than this!)

Wall insulation $4631

LEDs and new fittings $187

Belling oven / cooktop $1800


The Scorecard assessment done after the retrofit gave a 10 star result for efficiency but only 1 out of 5 for the hot weather rating. The building shell rating was 3 out of 5- this is a proxy indicator of winter comfort.


So, all the energy freedom principles have been followed other than an in home display. Gas has been disconnected, so no more supply charges. Electricity use is minimised by improving the building shell and installing efficient appliances and the solar PV system can generate more power than is consumed. Any electricity bills to pay are a result of the supply charge and the discrepancy between import and export prices. Further improvements could be made by addressing shading issues on the PV panels, installing external blinds on the east facing windows and considering a battery when the prices are more reasonable.

25 views0 comments

Recent Posts

See All


bottom of page