Raising building standards in Eastleigh

Five new warm and comfortable Passivhaus on Woodside Avenue in Eastleigh form part of a larger development, just shy of 100 new build homes. Designed by PHT member Architecture PLB, the terrace of three bedroom houses has been recognised by Inside Housing Development Awards, shortlisted for the Build to Rent category. The 94 homes built for Eastleigh Borough Council, in partnership with the developers Vivid, are a combination of family houses and apartments.

Leah Gardens | Architecture PLB

Local authority taking the lead

Eastleigh Borough Council’s planning department allocated the site for the development of housing with a detailed Development Brief back in April 2009, and took what was at the time a forward-thinking decision to require 5% of the development to be built to the Passivhaus standard, as well as achieving BREEAM Communities ‘Excellent’ and Code for Sustainable Homes Level 4 across the whole site. With certifcation achieved for the five Passivhaus homes in January this year, the target succesfully delivered the second multi-unit Passivhaus scheme to be completed and certified in Hampshire.

Predicted energy performance

Thermal Energy demand (≤15kWh/m2.yr):

Thermal Energy load (≤10W/m2):

Primary Energy Renewable Demand (PER):

Primary Energy Renewable Generation (PER):

Leah Gardens Passivhaus plaque | Architecture PLB

Not long after, it was followed by Hatch Farm, a development between Eastleigh Borough Council and Radian Homes, which achieved Passivhaus certification for 6 of the total 98 homes in September this year. The team for this project included PHT members Greenbox Associates and Green Building Store.

Hatch Farm, Eastleigh | Greenbox Associates

Hatch Farm, Eastleigh - photo Greenbox Associates

The borough’s new local plan, currently under examination, takes their ambitions a step further, encompassing not only their own projects but all future developments in the borough. All new developments above 500sqm will be required to achieve either Passivhaus certifcation plus BREEAM ‘very good’ throughout, or BREEAM ‘excellent’ including at least 1% of residential units with full Passivhaus certification.

How do the Passivhauses differ?

Key facts

Build start date:

Date of certification:

Date of occupation:

Number of PH homes:

Total number of homes:

Cost/ m² (GIA):

Form factor:

TFA:

September 2017

January 2019

February 2019

£1,656

2.48

432 sqm

Construction and house type was standardised as far as possible across the site, with the five units that were assessed as the most beneficial in terms of heat loss form factor, orientation and shading selected to be taken all the way to Passivhaus standard. For these homes, the layout had to be varied slightly to accommodate the MVHR unit. This was located at first floor and central to the plan, minimising duct routes but also positioning the unit close to the thermal envelope. Its design and installation was well conceived and coordinated between the MVHR and timber frame designers, and commissioning went smoothly.

Elemental u-values

Wall:

Roof:

Floor:

Windows (uninstalled):

Doors (uninstalled):

Window g-value:

0.187

0.138

0.184

0.77

0.85

0.55

All dwellings were built using an off-site manufactured timber frame with external brickwork cladding to ground floor, and blockwork with a cementitious panel to the first floor. The Passivhaus homes needed extra attention to achieve the airtighness target. While the main contractor was experienced in building to Code for Sustainable Homes levels 5 and 6, the additional airtightness demands of Passivhaus were new to them. But they found the airtight OSB used gave a robust basis for the overall airtightness strategy, and the final test came in under 0.6 ACH/hour.

Costs

The five Passivhaus homes were built at a total cost of £811,490, or just over £160k for each 3-bed home (excluding utilities, fees and prelims). Working out at £1,656/sqm against gross internal floor area (GIA) or £1,878/sqm against treated floor area (TFA), this represents just a 13% uplift over the non-Passivhaus dwellings on the same site. This is a good result for what is a first-time Passivhaus project for client, contractor and Passivhaus Designer, as our recently published costs analysis shows. If the same team build on their experience, we can expect them to achieve an even better result on future Passivhaus projects.

Leah Gardens back | Architecture PLB