24 May 2016

Garden plot provides perfect spot for sustainable build

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When Architect, Bernard Tulkens, bought his home in Hackney, there was a piece of land at the bottom of his garden accessed by a gate. From the outset, Bernard knew it was an ideal infill plot for a self-build scheme, with direct access to the roadside and in a residential location.

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Bernard’s original plan was to use the project as a test ground for his interest in sustainable design, while building a home that his children could one day move into. While the scheme has achieved the first of those objectives with a certified Passivhaus build and a quirky, contemporary design, the property is now the home of Bernard’s in-laws who have brought a lifelong interest in antiques into the modernist space to create a stunningly eclectic home.

Explains Bernard: “The house is not a self-build in the traditional sense because I didn’t build it so that I could live in it myself. However, I was the architect, the project manager and the client on the scheme.

“What I hadn’t anticipated was building a home for a retired couple, which, potentially could have influenced the design. Building it as an experimental project for my children meant that I had much more freedom to explore construction methods and put sustainability to best practice with very contemporary styling.

“As it turns out, the energy efficiency, impressive U-values and bare interiors have provided an ideal home for the in-laws because the blank canvas and industrial feel of the interior creates a dramatic contrast with their antique furniture, while the Passivhaus specification gives them a comfortable living environment and extremely low energy bills.”

Passivhaus challenges

When Bernard started designing the house, one of his biggest goals was to ensure that it delivered a high standard of sustainability and he looked at various sustainability standards to provide design cues.

“The problem was,” Bernard continues, “many of the standards are not really measureable in terms of outcomes and I didn’t want a situation where the project’s environmental credentials were not as credible as they first appeared.

“I started to look at Passivhaus accreditation as a best practice standard for sustainability. Not only was it tried and tested, it was also measurable. And those measures are very exacting with clear targets for air tightness and U-values delivered through the integration of a considered ventilation strategy and a ‘fabric first’ approach.

“However, as I was already involved in the project as an architect, client and construction coordinator, I made the decision to appoint accredited Passivhaus designer Peter Rankin to help with the PHPP (Passive House Planning Package) calculations and review the design against Passivhaus standards. This collaboration was critical to the project’s success in achieving Passivhaus accreditation.”

In fact, the house is one of only five Passivhaus homes in London and the first to be built in Hackney, despite the borough’s reputation as the ‘coolest’ in the capital. The Passivhaus Institut was established to promote and control Passivhaus standards some 20 years ago, therefore Bernard felt confident in using them as the basis for his design.

In many ways, however, the plot was not ideal for a Passivhaus build. Located in a conservation area, it was subject to planning restrictions on the height of the property. As a result, Bernard designed the house as a two-level home with a basement and ground floor and a topsy-turvy layout that features the bedroom and bathroom on the lower ground level with the living/dining and kitchen areas on the upper ground floor.

Bernard comments: “Passivhaus usually relies on maximising the thermal value of solar gain with high-performance insulation. However, the south elevation is overlooked by a four-storey building so the house relies on a reduced level of solar gain from the west, with only a small window on the south-facing wall and a triple layer of Gutex wood fibre insulation.

“As a client, this might have made me nervous, but as an architect the additional challenges made the project exciting because it was all part of creating a design strategy that could work with the limitations of the plot and still deliver a great home to Passivhaus standards.”

Impressive U-values

Because Bernard was Architect, Project Manager and Client while still operating his busy architectural practice, Tectonics, the build process took several years and numerous design revisions. Planning was secured in 2010, with excavation and drainage following in 2013 and construction beginning in earnest in 2014/15. It was 10 years earlier, however, that Bernard had first come across the building material that was to become pivotal to his approach to both building the structure and insulating it.

Bernard explains: “It was back in 2004 that I was first introduced to CLT (cross laminated timber) as an engineered timber product with good structural properties and low environmental impact. It was over 10 years later that I used it for the first time on my own build!”

CLT provided an ideal approach for the above ground section of the build because it meant that the structure could be constructed with minimal joints, aiding air tightness. It is also a breathable material fabricated from raw wood, which complemented both the Passivhaus goal of a diffusion open structure and the idea of using renewable resources.

It was the CLT supplier that signposted Bernard to the insulation strategy for the property, which is fundamental to a fabric first approach to Passivhaus certification. Bernard worked with environmental building products specialist, Ecological Building Systems, to develop the specification for this part of the build.

Explains Senior Technical Engineer at Ecological Building Systems, Niall Crosson: “Our portfolio of products has been handpicked to enable the construction of more energy-efficient homes based on a fabric first approach. We work with specifiers and self-builders to help them determine the best combination of products to achieve their designed U-values, which, in this case, was a pro-clima airtight vapour membrane followed by a triple layer of Gutex single ply wood fibreboard insulation.”

Following the CLT assembly and installation of high-performance windows, the pro-clima DA airtight, weather-resistant vapour layer was used to completely encase the ground floor structure and taped to seal joins, preventing the free movement of warm air and vapour out of the building, while reducing the risk of condensation. Joins were sealed using pro-clima VANA tape.

The Gutex insulation was then adhered to the structure in three layers of varying thicknesses: a 140 and 120mm Gutex Thermosafe Homogen and a 60mm weather-resistant Gutex Ultratherm board. The system was secured using 500mm HECO Topix screws installed, as per Niall’s calculations, to satisfy the significant suction and shear loads such as depth of insulation and cladding creates.

Niall continues: “The Passivhaus standard for thermal performance is no more than 0.6 ac/h @50pa and the house has achieved 0.29 ac/h @50pa overall, with a U-value of 0.10 W/m²K for the upper walls where the Gutex insulation was installed. Bernard started with a target U-value and we helped calculate the specification from there, with the completed structure checked and verified by the project’s Passivhaus Consultant, Peter Ranken.”

The CLT and Gutex build-up sits neatly on top of the basement level concrete structure and the house is clad in a ‘raincoat’ of continuous zinc above ground level. The dark zinc finish of the external walls echoes the black single ply flat roof.

Scalable success

The stripped back look of raw materials and exposed services continues inside the house. Bernard decided to leave the wood and concrete finishes on the walls and ceilings and the ducting and pipework for the high-performance MVHR (Mechanical Ventilation with Heat Recovery) system is also on show.

Bernard continues: “The house tells the story of its sustainable construction in its interior. The MVHR unit extracts air from the warmest parts of the house – the kitchen and bathroom – and uses it to pre-heat incoming fresh air. Combined with solar gain and high-performance insulation, this means that the home remains at a comfortable 21°C all year round, with the only additional heat coming from two electric towel rails. When your specification has achieved that and ensured that heating costs are less than £14 per month, why not make a feature of it?”

With the one-bedroom house totalling just circa 100m² (94m² for the Passivhaus measuring method) it’s easy to assume that it’s the modest size of the house that’s keeping the heating bills so low. However, Bernard states that the U-values may actually be improved in a scaled up property using the same high-performance insulation and ventilation.

He adds: “As my first Passivhaus scheme, this was definitely a labour of love, but I am now looking at a new project in South London and would definitely take a similar approach and work with experts like Ecological Building Systems and Peter Ranken again.”

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