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Dow Building Solutions - Effective insulation key to England's first certified Passive House

STYROFOAMTM-A from Dow Building Solutions has been used to extensively insulate the first certified Passive House in England, Underhill House – a project recorded for the latest Channel 4 Grand Designs series.

Produced at Dow’s facility at King’s Lynn in the UK, distinctive blue STYROFOAM-A products FLOORMATE™300-A, ROOFMATE™SL-A and PERIMATE™DI-A insulate the floor, roof and basement walls of the structure, and played a vital role in the house getting Passive House certification.

Underhill House is entirely glazed to the south. The rest of it is earth-sheltered and highly-insulated, creating the perfect passive solar design.  The structure of the underground house is constructed from concrete, much of which has been left exposed internally to exploit the benefits of its thermal mass. 

“In order to meet Passive House standards we needed insulation which could maintain good thermal performance outside of the waterproofing envelope, as this would allow us to expose concrete within and make the most of the internal space,” said architect Helen Seymour-Smith who now lives in the building with her family.

“Insulation that can perform effectively in its environment for the expected lifetime of a building is key,” she continued.  “There’s no point installing photovoltaics or a ground source heat pump if you’re still leaking heat through the building fabric!”

The process of extruding polystyrene foam generates a mass of small, homogeneous closed cells which gives STYROFOAM-A products high design loads, low water absorption and excellent insulating properties. Such features mean the material can be installed outside the waterproof envelope, the right design choice when aiming for an ‘envelope’ of continuous insulation that minimises heat loss:

  • Chosen for its high moisture-resistance and compressive strength, FLOORMATE 300-A was installed below the vast concrete floor slab, helping to avoid thermal bridges at floor and wall junction and achieving a U-value of 0.1 W/m2K.
  • The extensive green roof, insulated and supported by rot resistant ROOFMATE SL-A boards, is a major feature of the building design and delivers an incredibly low U-value of 0.097 W/m2K. 
  • The insulation was used in combination with a waterproof but vapour permeable separation layer, ROOFMATE MK, in a system known as ROOFMATE MinK - this allowed the architect to reduce the amount of insulation required to address the so-called ‘rainwater cooling effect’.
  • Below-ground walls were covered with tanking membrane before being surrounded by FLOORMATE and then PERIMATE DI-A boards and backfilled. PERIMATE DI-A boards have vertical channels cut into one face, to drain water away, with a filter fabric bonded to the face to prevent soil particles blocking the channels. A U-value of 0.11 W/m2K was achieved.

“We believe that as regulations around the thermal performance of buildings become tighter in the drive towards more energy-efficient buildings, insulation that can perform for the long term in such demanding environments will play a vital role,” said Matthew Dyke, Account Manager for Dow Building Solutions.

“Underhill House is a fantastic demonstration of how a combination of effective materials and an architect’s vision can result in a beautiful yet practical family home that directly addresses environmental issues.” 

STYROFOAM-A products are manufactured in the UK using technology that takes CO2 from industry and uses it as a blowing agent in order to create extruded polystyrene foam with a Global Warming Potential (GWP) of less than five. They offer lightweight yet robust performance, high strength and excellent moisture resistance, making it ideal for below-ground and exposed roof-top insulation demands.

To find out more visit the website and architect’s blog for Underhill House at www.aipassivhaus.com. Contact Dow Building Solutions by email on FKLMAIL@dow.com or visit www.styrofoam.co.uk.

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