Zero carbon building – 30 years easier than it sounds

May 27th, 2014 by

 

Homes constructed by Salford Council more than 30 years ago, and using conventional construction techniques come close to the 2016 ‘zero carbon’ standard. Here’s how. 

As the construction industry begins to find its feet after the longest recession since the war, interest in very low energy, low running cost and zero carbon building is starting to return.

It’s a moot point whether the current government has any intention of sticking with the ‘zero carbon’ standard due to come into effect in 2016. For a whole host of reasons I believe they should and hope that they do. Much depends on the outcome of the 2015 election.

Zero carbon building 30 years easier than it sounds

SE aspect of the Salford low-energy houses, 1980. Image: University of Salford

One of the concerns often raised about imposing such a standard is that achieving it is very complicated, ergo the industry needs more still time to prepare. (But let’s not forget that in the time the UK has been discussing a zero carbon building standard America went from JFK’s speech to putting men on the moon).

So is it really that difficult to design and construct very low energy buildings?

There is plenty of evidence to suggest that it isn’t. Take the example of the 2 bed terraced and semi-detached homes built by a local authority over 30 years ago. Not only do they outperform current (2013) Building Regulations, but they get pretty close to the proposed ‘zero carbon’ 2016 standard. In a somewhat understated way they demonstrate that the key to really low energy buildings is combining insulation, thermal mass and controlled ventilation in the right quantity and the right order.

What become known as the Salford Low Energy houses were designed and built in response to the oil crisis in the mid-70’s. The 40,000 dwellings owned and rented out by Salford Council were proving too costly to heat and problems such as condensation, and mould were commonplace.

In 1975 Salford Council approached the University of Salford for advice on designing a new low energy dwelling with the stipulation that:

  • The cost should be within social housing cost yardstick limits.
  • The design should use established construction methods.
  • The dwellings could be used ‘normally’ by tenants.
  • Maintenance costs should not exceed those of existing housing, and,
  • The dwellings should be adaptable to different types of fuel and heating appliances.

What resulted were dwellings that looked, to all intents and purposes, like conventional council houses of the time. The cost was unremarkable too, the average being 107% of the yardstick value +/- 8%. But is it what lies beneath the conventional looking brick exteriors that makes these homes different.

Zero Carbon Building - 30 years easier than it sounds

Cross sections of the Salford Low Energy House. Image: University of Salford

As you would expect insulation levels are good. Two hundred millimetres of glass fibre in the loft, 200mm of polyurethane under the floor with 173mm of the same in the walls. It is they way this has been combined with heavy materials that gives these homes very high thermal storage capacity helping them to stay warm in the winter and cool in the summer.

The internal walls are constructed of dense concrete blocks. This and floors made up of concrete beams with block infill, topped-off with sand and cement screed give each home four times the thermal capacity of traditional homes constructed at the time. And crucially the mass is on the inside, that is on the warm side of the insulation.

Mechanical ventilation is limited to extractor fans in the kitchen, bathroom and toilet. Trickle vents were fitted to the heads of double glazed, timber framed windows. The production houses were heated with just one, or sometimes two balanced flue gas convector heaters in the living room and hall to give between 1.5 and 2.5kW of heat.

Compared to many of the examples of very low energy and ‘zero carbon’ homes being constructed today these homes look decidedly low tech, and unremarkable. But, as testing by Salford University in 2010 confirmed, 30 years on they still do exactly what they were designed to do, really well.

It’s all too easy to get lost in the design details of low carbon buildings at the expense of the big ticket items. What the Salford Houses demonstrate is that the right application of heavy materials, insulation and ventilation it is possible to construct very low energy, and low running cost homes affordably following conventional approaches to design and build.

Zero carbon building - 30 years easier than it sounds

Wall details from Salford Low Energy Homes. Left, internal walls, middle, exterior walls, & right, ground floor. Images: University of Salford

Links and resources

The Salford low-energy house: learning from our past. University of Salford 2011. Click here to download.

Six principles of low carbon design. Click here.

Thermal mass – flipping marvellous. Click here.

An introduction to self-heating and self-cooling buildings. Click here.

Images courtesy Salford Housing and Urban Studies Unit, UK. http://www.shusu.salford.ac.uk/

Written by

Environmental consultant, facilitator, founder & Director of Climate Works Ltd.