Jeld-wen’s low u value windows specified for energy efficiency refurbishment project

Exceptionally high performance windows from JELD-WEN, one of the UK’s…

Exceptionally high performance windows from JELD-WEN, one of the UK’s leading manufacturers of timber windows, have been specified for their exciting ‘Retrofit for the Future’ HeatPod project in Penzance that has recently been completed.


Working with Penwith Housing Association (a member of the Devon & Cornwall Housing Group), JELD-WEN supplied its revolutionary new DreamVu™ windows, which were triple glazed and achieved a market leading U value of 0.7 W/m2K.  


Denys Stephens, Sustainability Manager at Penwith Housing Association, said: “We wanted to replace the existing PVC-U windows with timber and it was essential that we could achieve a really low U value.  JELD-WEN was one of very few companies which were able to supply us with a bespoke window solution that could meet our very exacting requirements and we are delighted with the results.”  


The property, which is on Atlantic Crescent in Sennen, had been built in the post war period and typical of local authority houses of this time featured a cavity wall construction with traditional concrete tile window subsills, which provided significant cold bridges across the external wall. To remedy this situation, JELD-WEN’s windows were positioned to overlap the outer face of the external wall, which was done to allow the windows to span the joint between the existing masonry and the new wall insulation, and JELD-WEN subsills were fitted. This detail greatly reduced cold bridging at the window reveals and eliminated the need for insulation around this area, which is required when the frames are set further back in the opening. 


Following the fitting of the 100mm layer of external insulation, the final render stop beads were sealed against the window frames to provide a weather and draught tight seal.  


JELD-WEN’s top hung, fully finished DreamVu™ windows were specified, which retain the aesthetics of the street scene and complement the architecture of the property.  


The fact that they were factory finished means that the housing association will benefit from a superior appearance to the windows, with less need for maintenance.  All JELD-WEN’s fully finished windows come with a 10 year guarantee on paint finishes.


Denys Stephens continues: “This was a great opportunity for us to trial different techniques of upgrading and refurbishing our properties.  We have many properties of this type where cold bridging can be a problem and the solutions trialled here and the innovative approach to window design and installation means that we expect to have significantly increased the thermal performance of this property.  We also hope to be able to replicate this in other properties in the future.”


Retrofit for the Future is a Government initiative managed by the Technology Strategy Board, designed to find practical and affordable ways of transforming old inefficient properties into very energy efficient homes, requiring minimal heating and which can be retrofitted with new, innovative technologies to test low carbon building technology.  


The property will be tested for airtightness and monitored for a period of two years by the housing association and the Energy Savings Trust to assess the amount of energy and carbon saved from the refurbishment. It is hoped that this will aid future research into lower cost implementation of energy efficient measures into the UK’s social housing stock.


Tony Pell, Business Development Manager at JELD-WEN, said: “It was great to be involved in developing a specification for upgrading existing homes that could provide a blueprint for future refurbishments.  This project demonstrates our technical ability and bespoke service, as we were able to deliver the very low U values required to meet the client’s exact sizes and specification.  We are really looking forward to finding out what the energy savings will be for this property in the future.”


As well as being very energy efficient, the windows were also fitted with espagnolette locking systems to enhance security. 


JELD-WEN’s timber windows supplied to Penwith Housing Association had full Chain of Custody certification, which meant they originated from well managed forests with strict reforestation programmes.


Other energy saving features included the replacement of a solid fuel heating system with renewable heat from a ground / air / solar / source heat pump (an innovation in heat pump systems developed as part of the project), which is expected to further enhance the energy savings and reduce the carbon footprint of the property.


For more information on energy efficient windows, contact JELD-WEN on 0845 122 2890, or visit the website


The work reported here has been funded by the Technology Strategy Board under the Small Business Research Initiative (SBRI) under the Retrofit for the Future programme.  This project is one of nearly 90 projects funded under the programme.  Further information on the programme can be found at:



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