Materials in the past:
Technology has come a long way since I first started as an apprentice carpenter and joiner 46 years ago. The same can be said for the materials that we now use on our home extensions. Long gone are the 2 storey extensions with the cheap and nasty hardiplank, timber weatherboard or rendered blueboard popped up on top of the existing house that performed so poorly in our Melbourne weather. I can remember when going back to complete the first floor fix out (hang all the doors and install the architraves & skirtings) how extremely hot it would get up there in summer, it was just like being in a sauna. Great way to lose weight but not that comfortable to live in too say the least. Needles to point out, that in winter you would need to run the heater at full bore to keep warm. With the cost of utilities today that would be wasting money and in turn have a negative effect on our environment. I am sure you could think of better ways to spend your money.
These days we have more options open to us when considering an upper floor extension. My preference is to use a 75mm polystyrene cladding system that is screw fixed with an approved washer system to the face of the wall framing of the extension, and then a cement render coating is applied with the colour of your choice to the face of the 75mm polystyrene. It looks great and has a rating of R2.6 with the wall wrap (insulation paper) We also use R2.5 wall insulation between the wall studs as well. This performs really well, not like the good old days. Never thought I would actually ever say that! All jokes aside it is no doubt a much better system in the way it looks and performs in our Melbourne weather.
If you would like more and improve on that, you could upgrade to 100 mm polystyrene cladding system which increases the R value to R3.0 including the wall wrap. This is a little more expensive to use, and on the average size 2 storey extension this would add around $2,000 to the cost depending on the size of the extension.
Combining polystyrene render finish and weatherboard:
You can combine the polystyrene render system with weatherboards to break up the look of your 1st floor extension if you prefer (my preference is to use the James Hardie Scyon linea weatherboard system because of its durability and good looks) more about that another time. This will ultimately depend on your final design & the requirements of your house extension.
Can you use a polystyrene render system in a bush fire area?
In most applications this system can be used in a bush fire prone area, depending on the assessment of the BAL (bushfire attack level) for your local council area and first-floor extension. It is very important to ensure that the system selected complies with the Australian standards, building regulations, local council or any other authorities that may have jurisdiction over your home or your bushfire level area that is in force at the time.