Can be used to retro fit an existing home. You may take off the existing cladding and include strawbale or natural materials instead. It's work we've done many times, however we don't retro fit for clients these days.
How much to renovate or do an extension?
It depends on how many wet areas you want and kitchens, if you're in any building zones (flood, bushfire), the size of the addition. Per square metre the cost is usually higher than a new house because you're usually building less than a normal house. Roughly, you could allow $2500 per square metre for a builder to do your extension.