Advice needed for first time build in Perth

there is a standardized energy testing of new home designs. I believe rn its a 7 star minimum. Upgrades to insulation are not overly expensive either so you could go over an above. Sound is another matter. There is no real way to ensure an off the shelf design will meet your criteria, because there's many variable considerations that don't form part of an off the shelf design.

Build quality is a factor of price, that s true, but there are also many premium builds out there that are just as bad. The key is making sure you have the works inspected independently throughout the build and stay on top of the builder to ensure they rectify. This is by far the most annoying part of building because there is a lot of variability between site supervisors and how much BS you get fed throughout the process. Consider that you can either approach it from a position of ignorance and everything is fine, or spend some time learning about the process, verify everything you are being told and lots of research. That being said, as a general rule of thumb, don't be led down the garden path by builders sales people. They don't care, they often lie and often b the time you realise, its too late. So if something doesn't sound right, get it in writing so you can use it later if necessary.

What I meant by limitations/variables is that its hard to tell how much noise needs to be accounted for for your specific needs. What is not enough, just right, or overkill. Like realistically you would probably want to avoid spending 10's of thousands on something that could be addressed with heavy drapes, you know?

So in that regard, things you can do that help with acoustic dampening in the home that may be over an above:

1. double or even triple glazed windows (many builders offer double as standard, some don't. Even those that do, their double glazed units may not be as well rated as some better quality ones. You'd have to ask.) To put this in perspective, Some double glazed units i experienced in a New York hotel facing times square entirely killed any sound. My double glazed units at home, somewhat effective at limiting neighbor noise. bear in mind triple glazed windows are not generally considered in Australia, and their prices is insanely more expensive in comparison to a single/double glazed unit. Some manufacturers will have acoustic testing data you can use to compare between products. However if upgrading windows, you may find an upgrade to commercial windows more cost effective than triple glazing. I'm not 100% sure though.

2. Soundcheck plaster in key areas

3. special acoustic rated insulation

4. insulating internal walls or between floors if you go go two story

5.Propper draught sealing of external doors. You can add additional seals to the frames yourself to further limit any draughts and sound that travels through the same gaps.

6. Heavy Drapes. Don't forget pelmets too. This will help with energy efficiency as well as sound.

7. Anticon roof blanket. This is a thermal insulator, but also deadens noise. This needs to be installed by the builder and is usually an upgrade.

Alternatively if your council allows for it, I understand Hay bale construction would address both your needs very effectively and somewhat more economically, though I don't know what you'd get for your budget, I've not been tracking build costs for years.

any one of these will help. but i don't know where the diminishing returns will start. So you'll have to explore what is right for you. Just don't forget you want some nice finishes too, so don't spend your whole budget on sound treatments that you may not need.

In Sydney that is now the price of a 60 sqm granny flat ( almost). But you get your 2 bedrooms