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Passivhaus versus Code on £15m Oldham housing scheme

Contour Homes is building a mixture of Code Level 3, Level 6 and Passivhaus homes at a housing development in Oldham to learn what works both in construction and once the tenants move in.

Client Contour Homes (Part of Symphony Housing)

Contractor Bramall Construction (Keepmoat)

Architect Nicol Thomas

Cost £15m

When Contour Homes took on the £15 million redevelopment of St Mary’s Way in Oldham, the company decided to use the site as a test bed for a range of different low-carbon and sustainable housing styles.

Once completed, Contour will be closely monitoring the houses to see how they perform in use and plans to gather the data to inform the company’s future building programme.

Of the 93 houses on the site, 87 have been built to Level 3 of the Code for Sustainable Homes, four have been built to Level 6 – the highest level – and two have been built to Passivhaus standards.

Contour secured funding from the Homes and Communities Agency and the former Oldham Housing Market Renewal Pathfinder to support its own capital investment and get the project off the ground.

A great opportunity

Contour Homes senior project manager Louise Marsden had specific responsibility for the Code 6 and Passivhaus houses, and on site the team also has a dedicated manager looking after the buildings.

“With a need for more homes that have less environmental impact and lower running costs, this approach at St Mary’s has provided us with a great opportunity,” Ms Marsden says.

“We have a unique chance to explore, compare and develop more sustainable construction methods, as well as help our tenants save money on their energy bills and tackle fuel poverty.”

“We wanted to be in a position to understand, compare and contrast the different standards”

Louise Marsden, Contour Homes

Ms Marsden’s role involved helping co-ordinate the design, working with main contractor Bramall Construction to decide on materials, keep costs in check, ensure the scheme meets Contour’s standards and liaise with housing management teams and tenants.

This is the first scheme of its kind in the North-west, so there was the added pressure that comes with a flagship development.

It was also a first for many of those working on the project, meaning the team had to learn and work together to understand exactly what was required to reach each different standard.

Exceptional level of detail

“The sheer amount of design work that went into detailing every aspect and every junction of the Passivhaus was amazing,” Ms Marsden says. “It was the most technically interesting aspect of our work on the development.

“There was a lot to consider even in deciding the location of the two Passivhaus houses. We looked into the orientation of the units and how the overshadow from the buildings opposite would affect the daylight calculations. The level of detail we went into was amazing.”

The requirements for Level 6 of the Code compared with Passivhaus are quite distinct, meaning everything from the materials used to the orientation of the houses was different.

“The Code is more holistic and takes into account issues such as waste management, whereas Passivhaus is all about the building envelope and airtightness,” Ms Marsden says.

To reach Level 6 under the Code, a property’s environmental performance is assessed against nine indicators, including water consumption, waste management and the use of sustainable materials.

“The knowledge and skills base to design and build these homes was not so readily available”

Louise Marsden, Contour Homes

Applying the two standards alongside one another was enlightening. “In order to meet the challenge of carbon reduction and achieve the energy credits under the Code, we decided to adopt a fabric-first approach on the Level 6 houses too,” Ms Marsden explains.

The Level 6 houses have solar PV panels on the roof, a sedum roof, mechanical ventilation heat-recovery units, a highly thermal-efficient building envelope, triple-glazing, A+-rated electrical appliances and low flow-rate sanitary ware.

The Passivhaus houses also have MVHR units, but as the core focus of Passivhaus is dramatically reducing the need for heating and cooling, the properties have excellent thermal performance and airtightness.

It’s hoped that Passivhaus residents will only need to pay around £70 a year for heating costs, while customers should be able to save more than 40 per cent on annual fuel bills in the Level 6 homes.

The team were aiming for an airtightness of 0.6 cu m/h/sq m@50 Pa on the two Passivhaus houses, but they actually achieved 0.36 on one and 0.38 on the other. On the Code 6 houses they achieved an airtightness of 2.7 and on the Level 3 homes the airtightness was 10.

Steep learning curve

The technology, skills and knowledge required to build to these extremely high levels and requirements are not always easy to find, so the design and construction team on the St Mary’s development had to learn quickly to get up to speed.

“Code 6 and Passivhaus are not new standards,” Ms Marsden says. “In fact, Passivhaus is a very popular construction method on the continent, but there are not many types of either in this country and certainly none in the North-west.

“As such, the knowledge and skills base to design and build these homes was not so readily available. It was a steep learning curve for the whole team and we gathered a lot of information from previous schemes elsewhere in the country.”

The team also worked closely with the BRE, who carried out the final assessments, and sought expert advice from Mark Siddall at the Low Energy Architectural Practice and the Green Building Store.

“The sheer amount of design work that went into detailing every aspect and every junction of the Passivhaus was amazing”

Louise Marsden, Contour Homes

But getting the design right is only half the battle, as the teams on site must also understand exactly what is required, particularly when it comes to the extremely strict airtightness targets on the Passivhaus buildings.

“Passivhaus in particular must be built on site exactly as it is designed,” Ms Marsden says. “There is no room for error or for changing any construction details on site, as every change has an effect on the Passivhaus Planning Package.

“The team knew how important it was to maintain the airtightness of both the Level 6 and Passivhaus buildings onsite, and dedicated site manager Tony Kavanagh was appointed to oversee the eco homes.”

Mr Kavanagh was tasked with ensuring all the relevant trades knew what they were trying to achieve and how important it was to produce quality work on site.

He facilitated all the trades working closely together and made sure high levels of quality control were adhered to at all times. “This made all the difference to the project,” Ms Marsden adds.

The team also engaged with the manufacturer of one of the blocks used for the building of the Code 6 houses, Wienerberger, which carried out toolbox talks, gave demonstrations and was on hand for advice when necessary.

Learning from experience

The scheme was always going to feature some Level 6 units, but Contour was keen to try something new on the site to increase its understanding of sustainable building and new construction methods.

“The Passivhaus concept is a fast-growing sector now in the UK,” Ms Marsden says. “As an organisation, we have always been interested in exploring different construction standards and methods, and the scale of the St Mary’s development presented us with an excellent opportunity to trial the Passivhaus standard for ourselves.”

Aside from discovering new construction techniques, the company is also very keen to learn how the two different standards work when in use, how the tenants find living in their homes and how the different approaches affect energy bills and use.

“We wanted to be in a position to understand, compare and contrast the different standards. We are keen to learn from our experience and also to share this learning,” she says.

Post-occupancy evaluation

The most important learning will come from the two-year post-occupancy study that will monitor factors including air quality, energy consumption, heat loss and water use in each property type.

Contour is working with Queen’s University in Belfast and Low Energy Architectural Practice on the evaluation.

“We’ve installed data loggers and secondary meters for the gas, water and electricity in the Passivhaus, Level 3 and Level 6 homes so we can monitor our tenants’ energy usage and make sure they are achieving the reductions we anticipated,” Ms Marsden says.

Low Energy Architectural Practice will then analyse and interpret the data and carry out a full study into the cost/benefit analysis of the unit types.

It will also assess the challenges in the design stages and on site, while also carrying out building-user surveys with the tenants.

“We aim to use this information to inform our future building programme; as a result of the studies, we will be in a position to know what elements of the different construction types are the most practical, give the most benefits and provide the best comfort standards for our residents,” Ms Marsden says.

“We will also be in a good position to disseminate the information we gather to the building sector as a whole.”

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