Wetland wonder


Simon Roberts and Sarah Bruml managed to achieve their innovative, sustainable and flood-resilient cabin on a highly sensitive site next to a tidal creek and natural wetland in Southwold, thanks to a bedded-in design


Serendipity led Sarah Bruml and Simon Roberts to buy a modest holiday cottage on the east coast, and to later relocate from London and make the area their permanent home. “We’d been looking for somewhere to spend our weekends when we came across Southwold, a small seaside town with a harbour,” explains Simon. “After viewing a property there, which wasn’t quite right for us, the owner mentioned a friend with another cottage for sale just up the road.”

At first, GP Sarah and industrial physicist Simon had been somewhat deterred by the proximity of a busy road, but were swayed by the one acre plot, nestled in a hollow within a shallow valley and beside a tidal creek which attracts all manner of birds and wildlife. “There were no immediate neighbours, and the location really swung it for us, so we bought the old cottage back in 1997 and enjoyed many happy times there over the years,” continues Simon.

Originally two 19th century reed cutters’ cottages, which were later combined to form one property, the building had stood empty for years after being flooded in 1953. The previous owners had rectified damp issues by the time Sarah and Simon purchased the property. “We’d been thinking for some time that we wanted to improve the layout and overall performance, possibly by building a replacement house, but we weren’t clear what restrictions might apply,” says Simon, who has a long-held interest in energy efficient buildings. 

The site is in a prominent position on the road into Southwold and was not an obvious choice for redevelopment. Located in internationally recognised wetland, and an Area of Outstanding Natural Beauty (AONB) in the Suffolk Broads, it stands adjacent to a creek, reedbeds and a salt marsh which is designated as a Site of Special Scientific Interest (SSSI), creating a perfect storm of potential issues from a planning perspective. Any new building would also require a flood-resilient approach to construction.

Simon and Sarah therefore needed to meet a demanding brief: to create a new building which would enhance the surroundings, respect the environment, and deal with the risks from flooding, while meeting exceptionally high energy standards appropriate to the 21st century and sustainable into the future. “We asked if someone from the council planning department could advise whether it might be possible to build a house on stilts, to keep us above any potential flood water, and the planners then asked to see a design,” says Simon. “We took the decision to start big, so that we could always reduce the house size later as part of any negotiation.”

Using an online 3D design tool, Simon produced a drawing of a large, elevated house, which the planners responded to with a long list of policies with which the building would need to comply. At this point, in May 2013, Sarah and Simon invited several architects experienced with low energy buildings to visit the site and discuss their ideas.

“We chose architectural practices who understood the principles of sealed buildings and Passivhaus design, and whose websites also showcased interesting buildings – not just blocky ‘passive houses’ with small windows,” explains Simon, who trained as a Code For Sustainable Homes assessor, a now discontinued environmental assessment method for rating and certifying the performance of new homes. 

“Our first designer didn’t fully grasp our ideas,” says Simon, “so in 2014 we began working with prominent architect Jon Broome, who wrote The Green Self-Build Book and is highly experienced in working on Passivhaus projects, as well as being a self-builder himself.”

Simon and Sarah collaborated over a period of 18 months to build up their design with Jon Broome and Sam Brown, his assistant. Featuring an undulating green roof to mimic surrounding fields and reduce the building’s visual impact, Creek Cabin explores the possibility of creating a low impact home for the future while also conserving surrounding flora and fauna. The result is a building which sits within its unique site with the grace of a living object and is largely constructed with local, natural materials.    

Covering 287 m2, the layout includes an open plan upper floor of living, dining, and kitchen space with extensive views in all directions and across the creek. A pop-out pantry and larder have been clad externally in corten steel. Below this is a mezzanine with a bathroom and two bedrooms – one of which is a bed-sitting room with a balcony – and separate external access. 

Instead of standing the house on stilts, as originally proposed, Jon Broome suggested infilling this potentially wasted undercroft space to create a flood resilient ground floor to include a snug and live/work office. A pneumatic lift for ease of access is expressed externally, with a full-height curved, triple glazed window.

Window positions have been located to frame views to the adjacent wetland and woodland, providing different vistas throughout the year, and the building features three raised terraces to maximise views of the surrounding AONB and provide blended inside/outside living, maximising the modest footprint.

“Suffolk is actually quite enlightened in encouraging modern architecture, and the planners appreciated that the house has a strong design element and convened a design review,” says Simon. “A panel of architects and other experts visited the site and listened to the case presented by our architect, to assess the proposal. The only real alteration they wanted was to replace the mezzanine flat roof with an additional wavy one, which we were happy to do.”

When it came to awarding contractors, Jon Broome stepped back and his assistant, Sam Brown, transferred to MAP Architecture – a young, forward-thinking architectural practice based in east London – to progress to construction. 

“This project was about finding a way to live in harmony with the surrounding environment,” remarks MAP Architecture partner Robert Mawson. “The local area is rich with biodiversity, and a sensitive approach to all areas of the building has led to a home that not only sits within, but interacts with, the local wildlife.”

During Covid, monthly site meetings were conducted virtually, and Simon and Sarah divided their build into two phases – enabling them to continue to use the original cottage every weekend, then live on the building site during 2020. Once phase one had been completed, the cottage was demolished, and the couple moved into the new part of the house while the other section was built.

“We had a great relationship with our main contractor, MS Oakes, and although living onsite made the build and insurance cover slightly more complex, it meant that when Covid hit we could remain in Suffolk for lockdown,” says Simon. “We rented out our London home and basically never went back.”     

From the start of the project, Simon and Sarah hoped to create something more than just a home for themselves. They wanted a building which would have a light impact on the environment and would benefit the surrounding AONB, walkers, and visitors to the area. To achieve this, the house has been built into the existing bank, far back from the road to reduce its impact. Sunlight studies showed that the original cottage was in prolonged shade, and so the new house was positioned to minimise shading from large trees and to maximise sunlight and passive solar heating.

Situated within a flood risk zone, the building needed a flood-resilient approach to construction, and the ground floor was designed with a solid concrete floor slab and brick and block wall construction. Bricks needed to be selected with a low moisture absorption, limiting the choice of local options, and Cambridge Gault was chosen.

First floor cladding is Kebony, a sustainable softwood processed with an environmentally friendly bio-based treatment, which densifies the wood for long term stability and develops a natural silver-grey patina after exposure to sun and rain. The first floor was designed to sit above the one in 1,000-year flood event level and allows for climate change. A terrace bridging to the adjacent bank provides a safe evacuation route.     

The curved living roof, with an integrated irrigation system, was original to this project and unseen elsewhere. Created using only straight sections of engineered timber joists, to avoid an overly complex structure, the tops of the timbers were boarded with three layers of 6 mm ply, flexed to follow the curved surface of the joists. The depth of the overhang increases as the roof height rises, to provide shading and prevent overheating in summer.

Creek Cabin required a bespoke glazing solution, and the GreenSteps Scandinavian Slimline timber/aluminium triple glazed system was chosen for a crisp, modern appearance. Unusual features include a four metre curved triple glazed window, Signal Yellow coloured opening sashes, and special installation detailing to allow completely hidden upper frames in the clerestory glazing. 

Another challenge was the requirement to achieve high levels of thermal comfort while keeping the embodied carbon low – achieved using a mostly timber structure, with sheep wool and wood fibre insulation on the upper levels.     

Throughout the detailing it was important to avoid thermal bridges, and this led to a highly insulated structure, including the ground floor slab, which sits on Isover IsoLohr loadbearing insulation formwork, manufactured offsite. The external walls at first floor level were constructed using Steico insulated joists, with wood fibre insulation fixed to the outside to complete the thermal envelope. 

The project was a technically complex challenge for the couple, with Sarah and Simon requiring a range of off-grid energy systems and innovative features. “Although we built to Passivhaus guidelines, we chose not to be restrained by seeking full Passivhaus certification, so we did install a boiler, which makes up for having so much glass,” Simon asserts.

Even the family pets were considered in the design, with a thermally broken and digitally controlled petWALK pet door installed through the ground floor wall, allowing them to come and go without increasing the heat loss of the house. “Costs did go up and up,” says Simon. “We went for an open book arrangement because the build was so complicated, and the final cost was around £1,950,000.”

The annual energy demand for space heating and lighting has been optimised using Passive House Planning Package (PHPP) software, which also modelled the risk of the house overheating in summer.     

A PV array is sited near the south east boundary, facing the adjacent field where it is not visible from the road or the footpath alongside the creek to the north. Top-up
heating and hot water are provided by a wood pellet boiler, sited outside on the bank above flood level.

“We were extremely involved with every element of the build, and even mocked up our kitchen with chipboard, balanced on dustbins, to check spacing,” says Simon. “Passive houses really should be the norm, and we wanted to show that low energy buildings can still look great.”