Eco-refurbishment challenge part 2

Guest post from Robert Prewett at architect Prewett Bizley, who is designing the eco-refurbishment of a Victorian house which featured in a previous post in January

In around six months time, works to a Victorian terrace house in Hackney will be complete. Though a modest project in terms of scale, it’s an exciting one for anyone interested in the current debate about reinvesting in our existing building stock – the adjustments that are now underway will not only result in much more convivial layout but also an enormous reduction in the energy required to run the house.My practice Prewett Bizley has been working on the project since mid-2007, when our clients

Inside of eco-refurbishment in Hackney

Robert and Bronwen Cohen engaged us soon after they bought the house. Since that date, we have been on quite an odyssey: dealing for months with a planning authority whose default position is to maintain the status quo; reviewing attempts by others to deal with the same issues; researching into the latest forms of insulation and glazing technology; redrawing and modelling repeatedly the internal spaces; and conducting meetings late into Friday evenings. Occasionally these meetings required with a bottle of wine or two to supplement all of our spirits, but the time spent will be well rewarded.

The clients

Robert and Bronwen have been different from most usual clients. The first time we met they uttered the phrase ‘extreme sustainability’ which was a defining moment when choosing to work with them. Like true pioneers they have not given an inch since then which is rare if not unique. When the Planning Authority treated their ambitions with disdain they bravely stuck to their guns and trusted us that we would win through. Thankfully their bravery and trust paid off.

The scheme

The final scheme includes a compact extension made by stepping the rear wall of the house towards the garden at lower levels. Small it may be but it will transform the previously tight interior spaces. It will be formed using reclaimed bricks but this time incorporating a 200mm layer of insulation and high performance triple glazed windows imported via ‘Double Good’ from Germany. At the same time the front elevation will receive remade sashes with micro double glazing, as well as its own substantial layer of insulation to the wall – a new system which has been developed with the manufacturer Knauf. During the summer, the inside of the house will be reconstructed using reclaimed timber and a new air tight sheathing layer. A mechanical system with a high efficiency heat recovery unit will ensure that almost all of the energy contained within the air will be transferred into the fresh air being fed to each room. Together, these measures add up to an 80% reduction in energy required to heat the house. Initial calculations using the SAP software were encouraging and these have been lent further authority by modelling the house using the ‘Passivhaus’ software developed in Germany.

Eco-bling ban

At the same time, we’ve always agreed that overt displays of Eco add-ons were neither appropriate nor cost effective. From the street the smart front facade will apparently be as it has been for over 150 years – an attractive flat-fronted early Victorian terrace that has merited designation within a Conservation Area. Even from the rear garden, the extensions may seem like so many other varied accretions that houses of this type seem to accept so well. Perhaps on entering the house, one might notice that the hallway and living space beyond are both somehow more generous than one might expect. Further investigation will reveal a well proportioned kitchen and dining space downstairs that leads directly into the leafy garden. And at the top of the house a study nestles into the roof structure behind the familiar V roof profile. The interiors will be fresh and light even with the windows closed. Occasional benches set within the deep window reveals will be comfortable and draught free, while radiators will be dispensed with altogether. Both old and new materials will be visible, brought together using details and proportions that befit the original.

Our involvement continues to be intense, tweaking the design as the real uneven form of the existing walls becomes more evident, revising connection details as we find out what really lurks behind areas previously hidden, and chanting our mantra about air tightness

Latest update

Right now, two months into the operations on site, there’s still a long way to go to achieve this vision. The house is a shell, with just three walls and a roof (see picture above), and the builder is completing the steel frame. Work so far has been fiddly and done with painstaking care so as to save as much material as possible for re-use. Our involvement continues to be intense, tweaking the design as the real uneven form of the existing walls becomes more evident, revising connection details as we find out what really lurks behind areas previously hidden, and chanting our mantra about air tightness – a mantra that the builder and his team are now harmonising well with!

Robert Prewett is a director at Prewett Bizley.

Related posts:

1. The refurbishment challenge: air tightness Guest blog by Robert Cohen, technical director at Camco, who...
2. The existing challenge – the builder’s tale Third in a series of posts on the ambitious refurbishment...
3. Green refurbishment the hard way Guest post by Robert Cohen, technical director at Camco, who...
4. The green refurbishment, part four Continuing the series of guest posts on a refurbing a...
5. Refurbishment Question Time First in a series seeking free advice for my upcoming...