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GST: 'Making walls thicker could save £425 on build cost'


Adding extra layers of thermal mass in housing projects could save enough money to boost housebuilding or help reduce fuel poverty, according to new research by Broadway Malyan

A study carried out by the practice as part of Open City’s Green Sky Thinking programme concluded that using additional thermal mass on house walls could help reduce the amount spent on traditional wall insulation.

According to its calculations, installing a thick thermal mass layer inside the home could save around £425 on the cost of building an average semi-detached house.

Speaking at the launch of the report, Kevin Leahy, technical director at Broadway Malyan said: ‘This saving could mean that for every 158 homes you build, you could have one for free. The London plan is committed to building 300,000 homes, so when you scale it up it is a huge extra number to build.’

Speaking afterwards to AJ, Leahy said that most homes are now built with lightweight walls.

He said: ‘Virtually all internal walls now use plasterboard. Quite often external walls are built using timber frame or steel stud systems.

‘We have an image that external walls are built in block work but it is rare these days.’

He added that even if the principle was only applied to internal walls, the results would still result in two thirds of the savings highlighted in the report.

He said that the use of an internal thermal mass layer would enable a reduction in traditional insulation from 100mm to 80mm.

The study modelled internal clay wall layers because they retain heat better than concrete, Leahy said.

However, if the full traditional insulation remained in addition to the thermal mass, less heat would be lost, resulting in lower fuel bills.

‘This is not just about cost – perhaps a way of using the thermal increase is to start to tackle fuel poverty. If you take the temperature we can gain using thermal mass, it could save 20 per cent on your heating bill.’

Leahy said that councils would need to be persuaded to accept thermal mass complies with existing building regulations.

He said: ‘The regulations are very simple – you start with reasonable compliance. As long as local authorities will engage and allow us to take this route – which includes more complex modelling - that would be a major first step.

‘The second step would be for the client – it might be a local authority – to define a target – it might be two degrees and allow us to model it.’

Also speaking at the event, Jim Owen, principal building control officer at the London Borough of Wandsworth, welcomed the research.

He said: ‘It is a debate already in place in among local authorities. It is recognised that the method of just insulating boxes has reached its limit. Everyone is looking for some way of getting some 20 per cent increase in efficiency.’

Andrew Barraclough, group design director and pre-construction director at construction firm Waites, said that the savings on offer could be of interest to private sector rented developers responsible for fuel bills.

The research was modelled using data on thermal performance at Broadway Malyan’s Erith Park regeneration scheme in the London Borough of Bexley.

Thermal mass studies by Broadway Malyan

Thermal mass studies by Broadway Malyan

Source: Broadway Malyan

Thermal mass studies by Broadway Malyan



Readers' comments (2)

  • There could be resistance to this from developers who think that the greater the external wall thickness, the less the marketable floor area.

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  • Back to a future of 11-inch foam filled cavity walls, with an inner leaf of LBC flettons.

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