When We had a whole-house heat pump installed to replace an EoL gas furnace the installation also included an energy efficiency audit. There were some places (like blowing foam at the foundation/house joint to suppress air leaks, and insulating exposed ducts in the attic) that made a significant difference. And this was for a house built 14 years ago.
Easy low-cost low-disruption insulation should be done, typically for the UK draft-proofing, and loft/cavity insulation.
But very high levels of insulation may never repay their carbon (and financial) cost when a home is heated with a heat-pump from a very low-carbon grid. It's the next part of my research programme: "understanding first" vs "fabric first".
Of course, but with a heat pump you get the combo of lower demand and much higher efficiency. In Germany for example due to high electricity prices you really need COP>3 or so to beat fossil fuel for heating economically.
German has made some absolutely brain dead energy policy decisions over the last 30 years. Choosing to decommission their fleet of nuclear reactors, not investing in developing enough wind and solar generation, building a bunch of oil pipelines to Russia.
Depends where you are, and what your start point is.
I've looked at improving old houses in Australia, and you would usually be better off putting the cash in the bank. (After heat pumps, and sometimes a battery).
Real question: As I understand, good insulation in your home helps two ways: Keep the heat inside in the winter, and keep the cold inside in the summer. Do I have that right? If yes, I understand there are lots of places in Australia with very light winters (or none at all), so they are mostly focused on cooling with A/C. Are you saying that installing significantly better insulation is not economically efficient for many Australia homes?
The area I'm in, Victoria, goes from about -4 overnight at the coldest, to 45 at absolute peak (Celcius). Energy wise we are a "more heating" area, but comfort wise I personally prioritise cooling.
It's a big place, the north is essentially a cooling year round climate.
Most of the older places have very little insulation, lots of airflow, single pane leaky windows.
Usually the areas you need to fix are air leakage, better windows (double glazing), then in ceiling insulation. In order of impact.
Our construction industry is pretty much broken, and considers double glazing advanced luxury alien technology... So it can cost so much to replace the old windows that you can run heat pumps as much as you like with the interest on the sum.
And without that the improvement from more diy insulation upgrades don't really achieve much in a monetary sense.
On the other side, we have a much better solar and battery uptake, and the cost to install is fair. So a typical house might be a leaky wooden crate, but with enough solar and battery to be comfortable anyway.
