Cold Bridging

‘This ‘gap’ may occur where the structure is required to penetrate the thermal line, examples include projecting balconies or roof overhangs’

SOLID’s 1% Better Every Day mission endeavours to explore better, more sustainable, solutions for modern residential and country home construction. We are finding new ways to reduce carbon emissions and build solid structures across every sector that are better prepared for the effects of extreme climates.

Our next sustainability subject for the year is cold bridging (or thermal bridging). A cold bridge is, simply put, an area of a building where a gap occurs in the thermal envelope, so a warm area of the structure meets a cold surface – allowing heat to escape and possible condensation to accumulate. This ‘gap’ may occur where the structure is required to penetrate the thermal line, examples include projecting balconies or roof overhangs or where vertical masonry wall bear on foundations lines. For a property to maintain a high level of energy efficiency, as many cold bridges as possible need to be removed.

‘A cold bridge is, simply put, an area of a building where a gap occurs in the thermal envelope, so a warm area of the structure meets a cold surface – allowing heat to escape and possible condensation to accumulate.’

Throughout our projects we endeavour to keep cold bridges to a minimum and are often researching new methods of construction to help achieve this. With the need for designs to be low carbon, following passive house design principles helps ensure energy efficiency before concentrating too heavily on using energy from renewable sources to power the property. Passive House principles include creating a thermal bridge-free design by implementing continuous insulation. This allows the property to be air-tight, bar the necessary filtered air ventilation. 

We have recently been looking at a case study based on the Entopia building in Cambridge which offers an insightful look at the ‘deep green’ retrofit of a six-storey telephone exchange built in the 1930s. The retrofit upgrades the building into one of the world’s most sustainable properties and provides a benchmark for others to follow. Whilst many opt to build new in an effort to create a zero-carbon property, retrofitting an existing property effectively reduces the emissions from that building without adding the huge quantity of carbon that is associated with constructing a new-build property. (It is believed the Entopia building saved between 50 and 70% of carbon compared to building new).

The Entopia building, home to Cambridge University’s Institute for Sustainability Leadership, has successfully adopted a fabric-first approach to ensure that it maintains passive house levels of insulation. Not only has this been achieved, but it has also been delivered at a cost that is competitive to a conventional office refurb. The Institute for Sustainable Leadership wished to create a sustainability exemplar – showcasing how a future proof building can be achieved without requiring an exponential budget. They state “Sustainable buildings should not be any more expensive. As a principle, it’s about design development, it’s about the team thinking collaboratively and getting value for money.” The design development took into consideration the ‘whole life perspective’ to ensure any decisions made would be resilient throughout the lifetime of the Entopia Building.

The Entopia building is situated in Cambridge

A primary challenge in creating an airtight shell around the building was that the Entopia building falls within the conservation area of Cambridge City Centre. This means that it had to maintain the appearance of the original facade. Therefore, the design team decided to construct an ‘internal exterior wall’ made from timber stud with triple glazed windows inserted into it, creating airtightness. The glazed area was increased by 60 percent compared to the original building, controlling solar heat gain and maximising daylight. Bio based products were used including wood fibre insulation, timber studwork and line and cork plaster.

Throughout the course of the build, the inevitable issues arose that are commonplace in older properties, but despite these, the project still came in at a reasonable budget and achieves the required sustainability. By implementing a fabric first policy 84% carbon was saved per Meter Square compared to a standard office refit. 62,332kg co2e was avoided in construction materials. 21,000kg of CO2e was saved through reclaimed materials for example the PV rooftop canopy, furniture, and lighting, including 350 recycled LED lights. The SOLID team enjoyed learning about the Entopia Building and look forward to implementing further energy saving techniques in our own designs over the coming months.

Learn more about the Entopia building here