Passivhaus Classic – Howe Park Wood, Milton Keynes

The Parks Trust set a challenging brief to develop a home on a derelict, vandalised site. The site is next to a site of special scientific interest that resulted in exacting environmental standards. As a charity the client needed the home to generate a good financial return on initial investment, without compromising its environmental principles. Following preliminary discussions the goal of building Milton Keynes’ first Passivhaus was set, along side additional targets for high levels of water conservation, use of low impact materials and using the project as an education tool. The result is an award winning, highly sustainable, five-bed, executive rental home, which has provided a consistent income since 2012.

The high quality design and attention to detail throughout the project resulted in the Howe Park House achieving full Passivhaus certification. This accreditation reliably demonstrates the project’s environmental achievements in terms of thermal performance and build quality.

A Passivhaus is a much healthier home thanks to the MHVR system which draws fresh air into the house without the risk of draughts and controls the level of humidity. This in turn reduces the risk of condensation and mould growth. The filters within the system remove pollutants and odours from the air which leaves occupants happier and healthier. Additionally residents benefit from a greatly reduced heating bill.

The most airtight building in the UK

Overall the greatest triumph on this project we feel is the achievement of such a high level of airtightness, with air changes down to 0.07 per hour at 50 pascals. This was accomplished through quality control, excellent workmanship and a high level of detail. The level of airtightness has greatly reduced the heat losses, a 19% improvement on Passivhaus minimum requirements.

Airtightness plus the MVHR help to deliver the comfort experienced in Passivhaus buildings. Fresh air is efficiently delivered throughout the home and there is no sitting in drafts. Comfort is the main advantage of Passivhaus design. By designing a home according to this standard we created a place where occupants are comfortable all year round without the use of traditional space heating systems.

Building materials were selected by their environmental credentials for their longevity, low toxicity, low embodied carbon, re-usability and recycled content. Natural materials were used where possible. A very visible example of this is the Kebony cladding, a soft wood treated via a natural process to achieve the longevity of hardwood.

The design includes a laundry room on the first floor, which incorporates an MVHR extract allowing clothes to be dried internally without additional energy usage or a risk of condensation. The location also keeps dirty laundry out of the kitchen and closer to its point of use.

One particular innovative approach we took during construction was to eliminate the sole plate at the base of the timber frame walls. This reduced the cold bridge at the junction with the floor and reduced possible settlement issues. We felt this new approach was a cost effective way of cold bridge elimination.

Another key element of the scheme is the approach taken to landscaping: Howe Park wood is a designated Site of Special Scientific interest, valued by English Nature for its wildlife, therefore it was imperative to protect the site’s inhabitants.