Retrofit or start from scratch - how to cut carbon in buildings
Sustainable homes will be a key component in the drive to reduce society's carbon emissions, but what should we do with existing homes with their drafts, leaks and energy-hungry heating systems?
But even as far down the line as 2050, if we keep following current trends, 70% of the houses we will live in then have already been built.
That creates a huge headache for those who would like to see a big cut in emissions from homes.
It raises a question with three answers - is it better to leave existing homes as they are and focus on new build, retrofit the existing housing stock to improve efficiency, or knock it all down and start from scratch?
At energy trade show NEMEX last week consultant Gary White of the Crichton Carbon Centre presented research that attempted to provide an answer.
"We all recognise that in terms of the allocation of greenhouse gases that the residential sector is one of the top three. Our buildings are a really good place to start looking at efficiency," he said.
"In terms of our new building stock we'll probably get there."
He said that there is an argument saying we need to be looking at knocking down existing buildings because they are horrendously inefficient and replacing them with new buildings.
The study to see if the argument held water looked at full lifecycles including construction and maintenance cost as well as operational energy.
"We took a very simple model of a typical house in the Scottish Borders and looked at replacing it, doing no work on it and refurbishing it," he said.
Doing nothing, as might be expected, did not turn out well in terms of carbon - Mr White acknowledged it is very difficult to heat 'very leaky buildings with wind blowing through'.
But the retrofit results were impressive, he said.
"A fairly moderate amount of embodied energy in upgrading that building led to a pretty radical reduction in operational costs," he said.
"What was really interesting was that actually, when you start to think about knocking this building down and replacing it even with some really quite high tech low carbon buildings we could see that what we're gaining in operational savings we're actually losing [from the] need to knock these old buildings down."
On balance, he said, retrofitting was the most carbon-efficient - and probably the cheapest, solution in most cases.