The familiar form and look of a 1970s terraced house has been tastefully updated and upgraded, using timber and other biomaterials. When it came to the extension and renovation of his southeast London home, George Reed of TDUK members Price & Myers was in a uniquely well-informed position…
We knew we wanted to extend,” recalls George Reed, Associate Structural Engineer at Price & Myers. “The house dates from the late 1970s and not much had been done to it since then – we are only the second owners. While it gave us a reasonable amount of space, we had our second child on the way. In fact, he was born in our living room whilst the builders were building the extension!”
Extending into the garden – but not the way you think
A timber extension to the existing house allowed the different living area spaces to become much more accessible
The house, in Brockley, is unusual for a London property in being quite wide – nine metres wide with a generous garden. “This gave us a few options to play with,” George says. “It’s an end-of-terrace. There’s an alleyway down the side of the property and we back onto a park, so we’re exposed on three sides.”
“The architects, Whittaker Parsons, came up with the idea of a long single-storey extension down the side – along the length of the garden’s right-hand side – which secured us from the alleyway and lends a pleasant, enclosed feel to the garden. The extension is three metres wide, so we are still left with a wider garden than most London terraces.”
The proposed extension was a little challenging from a planning perspective. A council’s planning guidance might typically show a diagram of a Victorian terrace that’s around four and a half metres wide, and the proposed narrow, long extension was quite novel.
“They asked why we weren’t doing a three-metre deep extension? To which there was a simple answer: it didn’t work with the plot.” Planning did require a couple of attempts. But the new 14m extension passed, with its utility room, playroom, shower room and guest bedroom – all fitted out with plenty of thoughtfully designed built-in storage.
Using screw pile foundations
The design and construction of the extension was low-impact – the hempcrete blockwork and timber used in the extension’s structure is supported by screw piles, which minimised excavation and saved over two tonnes of CO₂ – around a quarter of the project’s total emissions.
“Adding 1.5 or 2 metre deep concrete strip footings seems very disproportionate for a single storey lightweight timber frame extension,” George points out. “Screw piles seemed like the logical solution. It was great to work with an architect sympathetic to that.”
“There are some tricky details that arise from having a suspended structure – there is a void underneath, effectively, which must be closed off. That was the learning curve with using screw piles: how to deal with the suspended space and how to close it off.”
They ended up with a half-skin brick garden wall along one side to close that space, with a small footing; and added similar works on the other side. A French drain was installed on the garden side, as it is clay soil and at the top of a hill. Water runoff was an issue as the site slopes significantly: the French drain works well in preventing ponding in the garden.
Cross section of the extension identifying the various materials and elements of the project. Drawing by Whittaker Parsons
The screw piles were installed in a day using a mini-digger with an arm attachment – for which having side access was of course very handy. “They were taken down to a depth where the ground is not going to move: they were in between three and four metres long, and the helixes on them are just below that point,” George explains. “We’ve seen no signs of movement in just over a year, and it does get very wet and very dry.”
George sent off the pile loads to the subcontractor; they created a design and that was submitted to Building Control: a straightforward process.
The extension allows a spacious open-plan lay-out
The extension: materials used
The extension features exposed Douglas Fir rafters, bespoke north-facing glazing and timber shutters. Woodfibre board, hempcrete walls finished in lime render and cork flooring create a breathable, tactile interior.
The extension is glazed (full-height) on the north side into the garden, with every third timber mullion – made of Douglas Fir – being load-bearing. Above these are hung attractive clay tiles, which resemble arrowheads or leaves, referencing the house’s original façade. The builders made up the windows themselves and fitted triple glazing cut to size.
The roof of the extension is exposed Douglas Fir, while the other sides, where the hemp-block infill is, use a standard softwood. The extension follows the incline of the hill slightly, and the roof has a very shallow, subtle pitch. There is a rainwater outlet, a single-ply membrane, and then a green roof on top.
Renovating the main house
The new porch, featuring distinctive arrowhead tiles, creates an attractive entrance to the home
At the front of the house, a new porch creates a handsome, sturdy entrance, while the reconfigured ground floor links open-plan living areas to the courtyard extension. Upstairs, the circulation space has been expanded into a generous landing with a calm, pastel-green family bathroom. Three well-proportioned bedrooms enjoy views across the sedum roof, extension and park beyond.
On the ground floor, the new extension has enabled a more spacious open-plan layout, with a living room/dining area next to the kitchen, which leads directly and logically into the extension’s utility room. The renovated kitchen area uses Douglas Fir for joinery. George fitted much of this himself, ordering the panels cut to size and edged from a supplier; they complement the Douglas Fir rafters above them. Timber is finished internally with Osmo Polyx oil.
Operational energy
The family took the opportunity of the extension and renovation to go all-electric. An air-source heat pump now supplies hot water and heating, while rooftop solar panels provide up to 50% of the household electricity. The retrofit has lifted the property’s EPC rating from D to A, with triple glazing throughout, thermal performance exceeding Part L requirements by 41% and a SCORS (structural carbon rating scheme) rating of A.
“The air source heat pump works very efficiently, even though we didn’t upgrade the insulation in the existing house,” George tells us. “Between the heat pump and the PVs, it has made a huge difference to our energy bills.”
Keeping things natural and breathable
Sheep’s wool was used in the floor between the joists; underneath which was wood fibre insulation and a breather membrane. The walls are hemp block in between the studs, with two layers of wood fibre insulation. “In terms of sustainability, we were on the same page as Whittaker Parsons from the start,” George recalls. “It was their suggestion to use hemp blocks and wood fibre insulation, and the sheep’s wool insulation in the floors. They pointed out natural breathable materials wherever possible.”
The extension is carefully detailed with exposed Douglas fir rafters
This article featured in Issue 11 of Designing Timber – the full magazine can be read here.
