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Even prefabs can be made warm, comfortable and energy efficient

Posted by Tom Bradley on 13 March 2014 at 3:01 pm

Following the second world war, new homes were urgently needed to replace those destroyed or damaged through the war. One of the options the UK government took was to use the wartime manufacturing and organisation structure to roll out prefabricated housing. 156,623 prefabricated homes had been completed by the end of 1951. These properties were usually made of concrete and metal. They were incredibly quick to produce and only intended to last about 10 years.

Decades after the project, there are many thousands of these properties remaining. They have lived well past their original intended lifetime, and thus need many improvements. A large number of these were inherited by the social housing providers, but also many homeowners now own these properties. Low levels of insulation, difficulty in insulating (they have no cavity wall), cracks between panels allowing draughts in, and thin walls mean these are exceptionally expensive to heat. However, measures such as solid wall insulation can be used to improve the properties. 

Can prefabricated buildings be turned into warm comfortable homes?

Here at the National Renewable Energy Centre (NAREC), we recently finished a project looking at how much residents in social housing save from renewable and energy efficiency improvements. The project (funded by the European Regional Development Fund) was carried out with Homes for Northumberland, South Tyneside Homes, and project managed by NAREC. The project included improving 328 homes, many of them prefabricated, and then quantifying the improvements. Additionally, many of the houses had solar photovoltaics installed as part of a separate project funded by the housing associations.

The prefabricated buildings in the project were Tarran Newlands and Wimpey No Fines type houses. The improvements included external wall insulation, new windows, roof insulation and heating systems improvements. We used residents’ bills, questionnaires, air pressure tests, thermography, and data loggers to measure the improvements.

So, what did we find?

For the Tarran Newland properties (which had minimal insulation before the work) the electricity usage decreased by 38 per cent and the heating demand by 56 per cent. For Wimpey No Fines properties (which had been retrofitted with new windows and some loft insulation prior to this project) the improvements were 19 per cent for electricity and 13 per cent for heating. We had the air infiltration (essentially, how draughty the buildings were) tested by an independent company. They found improvements of up to 32 per cent. After the works the properties were almost Part L compliant for air infiltration.

Looking in more detail, the Wimpey No Fines had external wall insulation installed to all properties. Additionally, properties had loft insulation topped up if needed and other technologies including gas saver energy efficiency units installed. The total cost per property was approximately £11.5k (this varied; the mid terraces were cheaper, the end terraces more expensive). According to questionnaires, this reduced the average gas bill from £906 to £789 (13 per cent). Taking the questionnaire results at face value, and assuming energy prices will increase by 9. 11 per cent per year (the 2010-2013 average); this would give a payback time of under 25 years. 

However, socio-economic factors impact the amount of energy people use in their homes, so this can not be considered a representative example for all homes. For example, estimates from Which! using Energy Savings Trust calculations suggest that a typical gas-heated semi-detached three-bedroom house with a heating bill matching the UK average would save £490 a year from external wall  insulation. With the current 9.11 per cent yearly rise in gas bills this would pay for itself within 14 years.

Ultimately, insulation measures can turn a prefabricated house into a comfortable home to live in. The cost of installation will take time to pay back, but throughout the years that the costs are being repaid, you will be living in a comfortable, warm home.

Please click here for more details on the work carried out in the Social Housing Energy Management project.

More information

YouGen guide to insulation

YouGen guide to energy saving

From the blog

How to get the best out of solid wall insulation

Old House Eco Handbook: a review

Photo courtesy of NAREC Distributed Energy

About the author: Tom Bradley works for Narec Distributed Energy, which is part of the UK National Renewable Energy Centre group of companies.

If you have a question about anything in the above blog, please ask it in the comments section below.

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1 comments - read them below or add one

EnergySavingGrants.orgComment left on: 19 May 2017 at 9:22 am

External Wall Insulation makes a massive differenece to system built (prefab) properties. As well as making them more energy efficient, it also helps to increase the value of the properties and in some cases can even make them mortagable (as unfortunately some mortgage companies will not provide a mortgage for some system built properties).

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