First rural affordable housing Passivhaus scheme supported by STYROFOAM-A


Parsons & Whittley architects employed Passivhaus design principles for a 14 dwelling Hastoe Housing Association rural affordable housing development in Wimbish, Essex, the first of its kind.

The houses, a mixture of homes for rent and shared ownership, are designed to be super energy efficient, and not only comply with Passivhaus principles but meet Level 4 of the Code for Sustainable Homes.

Passivhaus standard buildings retain heat created within the dwelling as well as from passive solar gain, eliminating the need for central heating and reducing fuel costs. The standard requires very high levels of insulation (in order to meet U-values of below 0.15 W/m2K for walls, roof and floor), a design that makes the most of solar energy and superb sealing throughout.

Parsons & Whittley’s design for the development is supported by FLOORMATE™ 300-A insulation running below the entire floor slab, solid aircrete external walls wrapped in over 250mm of foam insulation, and conventional insulated ceilings.

Construction details have been kept simple and effective in order that they can easily be replicated at future sites. Porches, meter boxes and Brise Soleil are independently supported to avoid penetrating the insulation overcoat. East-West orientation of the blocks facilitates passive solar gains, with careful attention to shading to avoid summer overheating.

The STYROFOAM Solution.

Key to effective insulation of the buildings was the specification of Dow Building Solutions’ FLOORMATE 300-A STYROFOAM™-A insulation to run below the entire concrete floor slab of the structures. Installing insulation below the slab helps create an ‘envelope’ of continuous insulation which minimises heat loss, requiring a material which can maintain strength and good thermal performance, even when used externally.

FLOORMATE 300-A has a design load of 130 kN/m2 and is highly durable with excellent moisture-resistance and compressive strength, enabling the insulation to perform outside the waterproofing envelope. Installing insulation below the slab also helps to avoid thermal bridges at floor and wall junctions and makes the most of precious internal space, meaning it is fast becoming recognised as an effective way of insulating new buildings.

A U-value of 0.07 W/m2K was achieved for the floors of the Wimbish development.

FLOORMATE 300-A is available in a range of thicknesses: 50mm, 75mm, 100mm, 125mm and 150mm.The material is manufactured using technology that takes CO2 from industry and uses it as a blowing agent in order to create insulation foam with a Global Warming Potential (GWP) of less than five.

For more details on FLOORMATE 300-A contact Dow Building Solutions by email on and one of the account managers will be in touch or visit

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