Introduction

The promise

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My house was built in 2010 in Canberra (Australia). It was a knock-down-and-rebuild, architect designed, and built by a reputable builder. The construction cost about $700k.

We thought we were building a comfortable and energy efficient home. There were huge north-facing windows to capture winter sun, all double glazed and with timber frames. A concrete slab floor for thermal mass. Insulation in the roof and walls; even some insulation under the slab apparently. Some of the walls were lined with compressed waste straw board for extra insulation. Yep, we were pretty smug…

How bad is it?

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Winter

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On 19th June 2023, at 9am as I was sitting down to work in my study, the temperature was 13.7°. In fact the temperature in the study never went above 16.9° that whole day.

This wasn’t unusual. The next day, the temperature in the study hovered around 12.5° all morning until early afternoon. And the day after that was similar. Looking at one full year of data, there were 97 days when the temperature fell below 16°. And 13 days when the temperature never reached 18°.

We have solar panels, so we generally run the heating (in-slab hydronic heat pump) during the day. Here is our energy use on that day:

The study is at one corner of the house, so it has more exposed surface area than other rooms, but it does have a big north-facing window.

At the other end of the house, also with a north-facing window, we have Bedroom 3. Here there were 65 days when the temperature fell below 16°. And 12 days when the temperature never reached 18°.

Summer

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Canberra usually has a big diurnal range: the nights are cool even on hot summer days, allowing passive cooling by ventilation. But not always. Here is an example of a summer day with a not-cool night.

On this day the study (which is also supposed to be a guest bedroom) reached 28.9°.

Looking at that full year of data again, there were 89 days when the temperature in the study exceeded 26°. In Bedroom 3 there were 52 days over 26°, and 26 days that never fell below 22°.

Awakening

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I was aware that our house was uncomfortably cold or hot a lot of the time. But I grew up in a similarly cold draughty house so it didn’t seem that unusual.

In January 2021 we changed our in-slab hydronic heating system from a gas boiler to an electric heat pump. This had the immediate effect of making our heating energy use visible in real time (via a solar app).

Previously we had been burning vast amounts of gas, but it was not something we thought much about until the winter quarter gas bill came in. Now that our heating energy use was visible, we monitored it and tried to align it with our solar power. We made sure it was off at peak tariff times (morning and evening), and kept it off overnight. (It is required to be off overnight for noise reasons.)

Also, the electric heat pump ran at a much lower temperature than the gas boiler had. (There were a couple of times with the gas boiler when the concrete slab floor became almost too hot to stand on! - the thermostat being based on air temperature instead of slab temperature.)

As a result, I was very aware that we were using tons of energy to try to be warm, or at least not utterly freezing, and more often than not, failing. So I had to face up to the fact that there were serious problems with our home’s thermal integrity.

I was so depressed about being cold all the time that I felt I had no option but to retrain as a home energy assessor so I could (a) know what to do about it, and (b) save other people from the same fate.

How did this happen?

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We as clients

did not know enough about what was possible for thermal comfort; what was standard practice in more advanced countries; we were stuck in 1970s thinking about “solar passive” design;

An architect

who designed a beautiful house, but didn’t prioritise thermal integrity of the building envelope;

A home energy rater

who made significant errors, and did not advocate for good practice;

A building certifier

who did not ensure the correctness of the energy rating, and of the insulation install;

NatHERS

the National Home Energy Rating Scheme which failed to recognise or represent these problems;

A builder

who created an amazing structure but did not prioritise thermal integrity of the building envelope, especially with air leakage and insulation details;

A building industry and culture

that did not take thermal comfort or efficiency seriously;

Building laws

which encoded poor standards, and crucially, did not verify the outcome - there is no accountability for air leakage or failed insulation.

A roofing company

that - when the roof was replaced after hail damage - did not check the ceiling insulation properly (I did ask them), missing the opportunity to rectify it before it was covered with solar panels again making it inaccessible.

Improvements

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The awful truth is that the temperature readings above were after I had made major efforts at improvement. Here are some of the works I had previously made to the study:

• adding insulation board to openable shutters;
• adding secondary glazing to the windows and doors;
• draught-sealing windows and doors;
• filling many gaps;
• making heavy drapes and pelmets;
• fixing insulation board to internal side of blockwork wall;
• insulating upper section of wall adjacent to roofspace;
• insulating the edge of the concrete slab (one side only at that point in time).

These and more are described on the following pages.

One thing I had not managed to do much about at that point was the ceiling insulation. See the ceiling insulation page for details.

See the conclusions page for the final* results and thoughts.

* it’s never final really.