This is an interesting article about the emerging policy on the carbon effects of retrofit vs rebuild.  It makes the obvious point about whether retrofit can make a profit, and that this is dependent on the price paid for the land.

Whenever planning policy is uncertain it is natural that developers will seek to exploit loopholes in the policy and will be encouraged to offer a greater value for the land than might otherwise be the case.  In the early days of affordable housing policies many developers got burnt fingers by ignoring the policies and buying land at values that were greater than could sustain the required affordable housing.  Only when it became clear that affordable housing policies were going to be applied vigorously, notwithstanding the price paid for the land, did this sort of practice peter out.

We seem to be in a similar position at the moment with the issue of embedded carbon.  The science is getting more precise about the calculation and impact of embedded carbon, but policy is still not clear in what circumstances buildings can be demolished or not and that, of course, encourages speculation.  If Government is serious about the issue of embedded carbon then its policies need to be specific, so that the market can take account of the policy in establishing land values.   Once planning policy and the market are in synchronisation then development will happen.

Of course, such a policy will have an effect on the appearance of the built environment.  That is where developers will be able to demonstrate their ability to innovate and to distinguish themselves from their competitors.