The U-Build system utilises modern materials and fabrication methods that minimise weight, waste, transport, plant and the requirements for skilled labour. Structural efficiency is designed in by the cellular form and the stiffening effect of the cells’ face panel. The resulting structure is exceptionally lightweight and stiff, yet tolerant of movement.
Start on site March 2021 | Completion November 2021 | Gross internal floor area 127m2 | Construction cost £280,000 | Construction cost per m2 £2,204 | Architect Studio Bark Client Francine and Stephen Burns | Structural engineer Structure Workshop | M&E consultant Atamate Building Intelligence | Quantity surveyor Studio Bark Projects | Project manager Studio Bark Projects | Principal designer Studio Bark | Approved building inspector Quadrant | Main contractor Studio Bark Projects | CAD software used Vectorworks/Rhino | Annual CO2 emissions 5.99 kgCO2/m2 | Carbon consultant Looper | Groundworks contractor Peter Antonius
The house’s operational energy is also very low, owing to key moves such as orientation to benefit from solar gain; use of second-hand photovoltaic panels, which also serve as awnings; and user-responsive infrared heating, which dispenses with any need for radiators and pipework. A green roof and extensive planting strategy support biodiversity, which was important to the clients, who are keepers of rare native breeds. Choices of materials such as the zero-carbon linoleum floor and butyl for the roofing help the project’s eco-credentials further. Sarah Broadstock, associate at Bark Studio, speaks of ‘environmental rigour’ or being ‘forward-thinking in environmental terms’. But a building’s sustainability is only as good as its client’s.
This is an unconventional detail, its main purpose being to determine how we could omit the use of concrete from ground up, while providing level access throughout, on a very sloped site.
First, we stabilised the ground with a series of reclaimed railway sleepers. Groundwater springs were found during the groundworks phase, so two new land drains were installed behind the retaining wall and a further one installed under the building pad below the compacted hardcore level. Once the foundation level had been achieved, recycled hardcore (from less than a mile away) was used to create a compacted hardcore raft. This was levelled to ±20mm. Jack pad foundations were then positioned on the pad (with 50mm adjustment) before inserting the structural timber base frame (using C24 treated spruce). Once installed, a DPM was positioned between the timber base frame and U-Build floor boxes, which were bolted together with central stiffeners to create a super-stiff raft on top. U-Build wall boxes were then installed to get to wall plate height. Four birch plywood beam boxes completed the structural frame. U-Build roof boxes could then be bolted together on top of the beams to complete the shell. Pre-tapered PIR insulation from Xtratherm (since rebranded as Unilin) was used to insulate the roof and taped for airtightness prior to the installation of a further DPM and then the butyl one-piece roof covering on top.
The build group
When we first approached Studio Bark we were not confident we would get planning consent but their approach to the brief and willingness to communicate positively with the planning officers increased our confidence. We are delighted with the result – our home, which is not only ideal for my needs as a disabled person, is also so suited to its rural setting. We are proud to have been part of this innovative project and feel we have made a new ‘family’ with the student team involved in the building work. We know they will all go on to achieve great things in their careers.
Francine Burns
Source: Jim Stephenson
Inside the Nest House
This strategy is made possible by good levels of insulation and airtightness in the building envelope. The heaters are controlled by occupancy and temperature readings, reducing the amount of time energy is used for heating and so reducing the overall demand.
U-Build parts are CNC-cut from sustainably sourced plywood. They fit together to make modules for walls, floor and roof that are fixed manually, with nothing but a drill and a mallet. The external walls are wrapped in a breather membrane, insulated with sheep’s wool and, in this case, clad with timber slats of varying widths, in step with the rhythm of the windows.
Week one of construction
Source: Jim Stephenson
Source: Studio Bark
The designer, Studio Bark, was founded in 2014 with the express purpose of delivering eco-friendly buildings. It’s a mission that got Periscope House, one of Bark’s first projects, featured on Channel 4’s Grand Designs. The studio has created something of a niche for itself by navigating the Country House Exemption, Paragraph 80 of the National Planning Policy Framework – delivering houses of ‘exceptional quality’ on rural sites where a refusal might have been expected.
Once the roof was finished, all the walls were wrapped and taped with an airtight breather membrane, before vertical Douglas fir battens and cross-battens were installed ready to accept the Douglas fir cladding (using stainless steel ring shank nails). All of the cladding and decking was set out on a 100mm grid, except for windows and doors, where the grid changed to 50mm to help break up the proportions of the elevations.
Sourcing locally considerably lowered the building’s embodied carbon. The project is free of concrete foundations or structural steel. The Douglas fir used for cladding and decking came from the nearby Whitney Sawmills. In addition to bringing warmth, it gives the house a sense of belonging. Groundworks and retaining walls are made from reclaimed railway sleepers from Ross-on-Wye. The structure is raised on jack pads made from recycled plastic.
A protective fleece was then laid, followed by a lightweight recycled plastic drainage layer with geotextile membrane, before laying the organic substrate and then finally the sedum matting. All perimeters were protected using a generous border of riverstones.
Source: Studio Bark
Ventilation is provided by a demand-control system that only ventilates spaces when CO2, humidity and VOC levels drift out of range. This minimises the amount of ventilation provided, which reduces the amount of energy needed to run the house. Fresh air is provided to the habitable rooms such as bedrooms and living rooms by automated trickle vents in the façade. Air is extracted from the dwelling by a fan integral to an exhaust air heat pump. This provides mechanical extract ventilation via a ducted system from wet rooms such as bathrooms and kitchens and discharges air to the façade. This unit also generates and stores hot water by performing a heat pump cycle on the extracted warm air stream and ensures that heat is recovered all year round, and hot water is generated at a high coefficient of performance.
• Reclaimed railway sleeper retaining walls
• Very local recycled hardcore, compacted to accept the foundations
• Re-usable, recycled rubber and steel jack pad foundations
• Modular U-Build construction system, made from sustainable spruce plywood
• KLAR triple-glazed timber/aluminium-clad windows
• Thermafleece sheep’s wool insulation (pre-cut to size)
• Illbruck airtight breather membrane
• Sky Garden sedum roof system on butyl one-piece membrane
• Forbo Marmoleum natural flooring system
• Locally sourced ash timber sills and worktop
• Battens, cladding, decking joists and decking were sourced locally from Whitney Sawmills.
Sarah Broadstock, associate architect, Studio Bark
The building is surrounded by Douglas fir decking sitting on Douglas fir joists, all installed with stainless steel fixings for longevity.
Wilf Meynell, director, Studio Bark
With Nest House, Studio Bark challenges us to go further. The generosity with which they offer up their processes dares us to do better, if we’re brave enough.
Ewa Effiom is a London-based, Belgo-Nigerian architect, writer and producer
Lightweight structures can result in complications due to the risk of overturning, but the pragmatic plan at Nest House develops a compact form that is inherently stable and avoids requirements for additional ballast or tension anchors. And the modular layout results in pragmatic load paths and avoids the need for long spans or transfer structures where steel or engineered timber beams might be required.
Through consideration of context and astute material choices, Nest House, in the picturesque Wye Valley, challenges preconceptions about sustainability while embedding itself into its scenic milieu.
Resource efficiency was a key driver for the project, with the aim of keeping things affordable both financially and environmentally. Concrete was banned from the site, replaced by an innovative jack pad foundation system, coupled with a series of raised decks to provide level access. In order for the building to ‘nestle’ in the landscape, significant groundworks were required to get to foundation level. An innovative reclaimed railway sleeper retaining wall and planter system was developed in collaboration with the groundworker and engineer, saving huge amounts of concrete and steel.
Percentage of floor area with daylight factor >2% Unavailable (daylighting studies not carried out) | On-site energy generation 22% | Heating and hot water load 50.85 kWh/m2/yr | Total energy load 73.44 kWh/m2/yr | Carbon emissions (all) 9.99 kgCO2/m2| Annual mains water consumption 45.6 m3/occupant | Airtightness at 50Pa 2.82 m3/hr/m2| Overall thermal bridging heat transfer coefficient (Y-value) 0.06 W/m2K | Overall area-weighted U-value 0.19 W/m2K | Embodied/whole-life carbon (RIBA Stage 4, estimated): 215 kgCO2eq/m2; (RIBA Stage 5, actual): 268 kgCO2eq/m2| Predicted design life 60 years
The building also makes use of a photovoltaic array and battery system to generate and store electricity. This allows a proportion of the building’s energy demand to be offset.
Josh Shimmin, consultant, Atamate Building Intelligence
The courtyard acts as a lightwell, adding a wash of natural light to what might otherwise be a dark space. It assists cross-ventilation and enables views from within uninterrupted by circulation. The home is completely wheelchair-accessible and this makes for generous interior spaces that have an affinity with the broad surrounding landscape. This home is both an ode to its context and a celebration of pastoral living.
Source: Andy Billman
However, for all that there is something poetic about people coming together to build with materials from the land to which the structure is ultimately destined to return, this project is not the golden ticket to sustainable construction at scale. Architecture will not find redemption through a series of single-occupancy rural homes. But it is a start. Nest House poses important questions, the most important of which is: which parts of this methodology, framework and outlook could be the start of something bigger?
Source: Jim Stephenson
Masonry construction with large, glazed openings creates buildings that are heavy and brittle. These typically lead to conservative foundation solutions, such as mass concrete strip foundations or piles that guarantee minimal settlement. The lightweight, flexible nature of the U-Build system means it is possible to use low-impact solutions – perhaps less conventional but entirely appropriate. At Nest House we employed compacted stone foundations, lined with a geotextile to prevent fine aggregate washing in or out. The superstructure is supported directly onto the stone using recycled-plastic jack pads to raise the timber off the ground.
The house was built using U-Build, Studio Bark’s open-source flat-pack timber construction system, which it designed with engineering design consultancy Structure Workshop. All parts are fully demountable and therefore portable and re-usable at end-of-life. The circularity of the system was important to the clients, who are keenly aware of their impact on the landscape and wanted an architecture of the lightest possible touch. They didn’t need convincing of the importance of sustainability.
As you approach the site, you’re met with a breathtaking view of Herefordshire hills. It is a view so engaging you could be forgiven for not noticing the 127m2 single-storey timber-clad house embedded into the hillside. The east elevation, which you encounter first, is, if anything, understated. Maroon-coloured window frames, though not out of place, are the only standout features. As you enter the house, you’re reacquainted with that view, this time framed dramatically by large, west-facing windows.
The house’s rectilinear doughnut plan is organised into two complementary ‘L’ shapes wrapped around a central courtyard. Upon entering, you find yourself in the ‘L’ that includes the kitchen, dining and living rooms. This assembly of spaces looks onto the adjacent fields, a reminder of the site’s agricultural past. The rooms throughout are clad in spruce plywood and, except for some of the furniture, which has been moved in from the clients’ previous home, the utilitarianism of the materials at work here would make Bentham proud. The second ‘L’ shape houses the bedrooms and bathrooms; the master bedroom at one end also overlooks the fields to the west. Despite their equivalent overall size, it’s clear that these spaces are ancillary in the arrangement. The clients speak enthusiastically of east and west wings in relation to the sunrise and sunset and their effect on their day-to-day; the subtlety of the plan is not lost on them.
The project’s embodied and operational carbon counts are notably low due to fabric-first principles, local and natural materials, high levels of natural insulation, good airtightness, on-site renewables and a ‘smart’ infrared heating system. It was built using the following pallet of materials with environmental impact at the front of mind:
Nest House is an all-electric building. This includes the heating system, which uses infrared (IR) heaters integrated with the fabric of the building. The IR heaters predominantly work by heating the occupants directly in a similar way that we receive heat from the Sun. This provides thermal comfort in a different way to traditional convective heating systems and allows the room temperature to be slightly lower, reducing the building’s energy requirements.
Nest House’s orthogonal simplicity was the perfect test-bed for NBAU and U-Build. The clients concede the result is ‘not for everyone’ but, with a construction cost of £280,000, it does call into question the argument often put up against sustainable construction – that it is prohibitively expensive.
Minimising embodied carbon is now a key consideration in structural design. One of the biggest challenges is below ground, where high-carbon concrete has a monopoly due to its strength, versatility and durability. By designing lightweight, movement-tolerant buildings with pragmatic load paths, alternative foundation solutions can be considered, providing huge savings in the total amount of embodied carbon used.
Alastair Barnard, senior engineer, Structure Workshop
Under construction
Clients Francine and Stephen Burns outside the Nest House
Studio Bark Projects, the firm’s contracting arm, was the main contractor overseeing construction. The house was built in a little over 12 weeks in the summer of 2021 by a dozen students, who camped on site as a part of the first No Building As Usual (NBAU) initiative, launched by Studio Bark. NBAU is a not-for-profit collaborative venture that seeks to bring together different parts of the industry to encourage environmental literacy and diversity in construction. It gives students from disparate backgrounds and at differing points in their education hands-on experience of working with consultants, dealing with budgets and clients and running sites. Gracious, one of the Nest House students, acknowledges a degree of privilege is required to participate in the unpaid programme but says: ‘To gain some site knowledge this early in a career is something I don’t take for granted.’
Source: Andy Billman
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