Brookwood Farm, Woking

Development of 12 new Code level 5 low carbon homes

Developer: Woking Borough Homes

Contractor: William Lacey Group

Status: Completed September 2010

As forward-thinking housebuilders and developers seek to build new homes with significantly smaller carbon footprints, finding a model which is realistic and cost-effective has been one of the biggest challenges.

Woking Borough Homes found the ideal building envelope to meet its low carbon homes objectives with the ICF Tech system, in conjunction with high performance windows and doors from Litchfield Group sister companies, to provide a thermally superior envelope to roof height.

The RSL (Registered Social Landlord) developed 12 new family homes at Brookwood Farm near Woking to level 5 of the Code for Sustainable Homes.  This means the new four and five bedroom semi-detached houses have heating and power efficiency which is 100% better than Approved Document L’s 2006 requirements.

The new homes are amongst the UK’s most eco-friendly and built using an integrated external building envelope delivered by ICF Tech walls, Sheerframe windows and from The Litchfield Group.

See how the construction took place in the photo gallery.

Getting the maximum ICF benefits

Woking Borough Homes is part of the Thameswey Group, owned by Woking Borough Council.  Contractor William Lacey worked closely with the technical team from ICF Tech to design homes which would offer optimal thermal and low-carbon performance.

The 12 homes were constructed using insulating concrete formwork (ICF).  This provides excellent structural strength and thermal performance along with outstanding air-tightness, but also offers exceptional levels of acoustic insulation; plus the system is quick, clean and low cost to construct.

With U values as low as 0.11 W/m2K and air infiltration as low as 0.74 m3/m2/hr @ 50Pa and a Y value of just 0.04, Code Level 6 and PassivHaus standards are made possible, and repeatable, using the ICF Tech System.

Buildability combined with performance

In choosing ICF Tech, William Lacey Group's architect could provid a strong proposition to Woking Borough Council’s clerk of works in terms of the system's buildability and inherent performance characteristics.

The system's double leaf polystyrene forms are connected by high strength polypropylene webs that the installer can screw directly into, with witness lines identifying their location beneath the bright white insulation. These enable the erection team to attach the bracing alignment system which aligns the wall prior to a pour.

While the ICF system provides for two wall widths plus internal and external corners, a special floor down-stand unit and a base profile, it is the cavity closer which completes the picture from an energy point of view.

Traditional looks, next generation energy efficiency

The ICF Tech system is designed to accommodate high performance Sheerframe HED casement windows with a U-value of 0.8 w/m2K.  These windows represent a step-change in thermal performance with their ultra-low U-values.  Current Part L requirements for windows to achieve a U-value of no more than 1.8 W/m2K are surpassed significantly to a level normally only seen in imported, often expensive hybrid window systems with long lead times.

Sheerframe HED’s mainstream look is a crucial consideration for house builders who recognise that more unusual green building components are not always going to sit well with traditional British architecture.  On closer inspection the subtle attention to detail is evident, with the frames’ slim sightlines and additional beading to hide unsightly mastic.

Up to six side-hung, triple glazed casement windows are fitted into each property to match the typical brick-built 20th century styling of the homes.  The PVC profile is lead-free, calcium-organic stabilised and UK-made and fully reinforced using Thermlock.  This provides windows which are thermally superior and robust enough to meet the requirements of Secured by Design to gain maximum Code points.

Window installation at Brookwood Farm was completed using a new technique to allow the properties to 'breathe'.  This is a achieved through a new three-part perimeter sealing system involving injected foam, an advanced silicone sealant on the inside of the window and a different specification sealant on the exterior.  By allowing the moisture to escape from the homes without water ingress, this plays an important role in reducing the risk of condensation.

Doors to combine style with performance

The combination of advanced technology and traditional styling also underpins the door-sets at Brookwood Farm.  These are Lifetime Homes-compliant Masterdor Thermal door-sets which utilise a 54mm thick engineered timber door leaf with a foam core to provide a U-value (including frame) of 0.9 W/m2K.

As every Masterdor is made-to-measure, the architect’s exact requirements could be accommodated from the outset, including the tightly radiused curve on the triple glazed units and non-standard colour finish.  Like the windows, these Masterdor door-sets are also Secured by Design certified for enhanced security performance.

Key to meeting Code 5 is a high level of airtightness and Masterdor Thermal doors achieve this through a unique triple weatherseal design.  The doors have been supplied to site as a pre-finished complete door-set incorporating a PVC outerframe system that is colour matched to the Sheerframe HED windows.

The Brookwood Farm project provides an exemplar case study for the Zero Carbon Hub - see full details.