KEYNVOR

Area: 399m2 including Annexe

Procurement: Traditional

Contract: JCT Intermediate Building Contract with Contractors Design 2016

Main Contractor: ADD Sustainable Construction

As-Built SAP: 100A Environmental Impact: A Rated

Construction Stage Air Pressure Test: 1.44 m³.h^-1.m^-2@50 Pa

Statutory Body: Cornwall Council LABC (Plan Check and Inspections)  Local Authority Building Control (LABC)

As an LABC partner we have benefitted from a dedicated officer (Martin Pipet) who understands the way in which we design and specify, often using natural and recycled materials which can create challenges.  Early informal discussions during the design process and working closely through the detail ensured the best possible design results for this project and added value to the project.  Particular challenges included the inclusion of Approved Document M guidance due to the site being defined as “steeply sloping” and the design spread across multiple levels. This was made harder due to the use of the building as a holiday let and desire to retain the integrated landscaping scheme by Darren Hawkes Landscapes. This involved close consultation with Local Authority Building Control to agree an access strategy across multiple levels, multiple buildings and retaining the enhanced character and nature of the landscape and setting of the architecture.

Keynvor is a low-energy, Passivhaus-inspired coastal home designed to harmonize with its sloping site and panoramic sea views. Built by ADD Sustainable Construction, this 399m² dwelling features reverse-level living, sedum roofs, slate hanging, and timber cladding – all chosen for durability and coastal resilience.

With an EPC rating of 100A and an air pressure test of 1.44 m³/h·m²@50Pa, it delivers high performance and minimal energy demand. Integrated VR design and 3D modelling ensured seamless collaboration and precision. A separate annexe, biodiverse landscaping, and strategic solar shading complete this sustainable, landscape-sensitive retreat on Tedragon Road.

To replace the existing dwelling with a new sustainable architecture that captures the essence of the site capitalising on the spectacular views and natural light whilst providing a series of interconnected private spaces that allow for introspection. Enhanced biodiversity, replacing the existing lawn only approach is to run through the site binding together spaces informally and promoting interplay of internal / external relationships. Approach is key and through the use of denial / reward relationships enhances the journey through the architecture.

The building should nestle within the hillside and draw from the typology of the adjacent architecture whilst promoting a contemporary re-envisioning enhancing the area as a whole, and on the local scale redefining the bookend to Tredragon Road. Proposals are to improve where possible the views from neighbouring properties.

True sustainability sits at the heart of the Arco₂ ethos, minimising energy consumption, through a passive exemplary standard fabric first approach supplemented with renewable technologies.

• Site specific analysis with clear site wide strategy clearly defining:
• • Entrance to living space views.
  • View ribbons from the East entrance to the West pedestrian scale.
  • Public frontage to the west / private spaces to the east and between buildings.
  • Protection of sea views from Tredragon Road providing enhancement over existing.
• Massing and scale similar to that of the surrounding context ensuring proposals remain sympathetic, respectful to neighbouring buildings with minimal visual impact. Proposal at first floor is sited around a clear east to west axis capturing and framing the sea views across the bay. The ground floor is defined through a north to south axis maximising the length of the triangular plot whilst clearly defining public areas to the west and private to the east.
• Reverse level living capitalising on views and providing a clear hierarchy of open and closed private spaces.
• The existing building sat central with wide open grass external spaces on all sides. This provided little in the way of private amenity space. This has been addressed within the site through pockets of sunken areas to rear. This zone also provides a useful sheltered microclimate to enable this external space to be useful during windy periods in this coastal location.
• Solar shading strategy through strategic fenestration and overhangs, with flexible solar shading shutters provided tackling west-based solar gain whilst retaining key views. The defining first floor overhang provides solar shading and sheltered seating to the ground floor west elevation and circulations areas.
• Low maintenance and robust materials which are in keeping with the coastal environment and exposure, such as slate hanging, timber cladding and zinc fascia’s. Materials can patina with age to become harmonious with landscaping.  These materials were considered to enhance the local distinctiveness.
• Large-scale sedum roofs to both buildings providing reduced rainwater run-off during peak rainfall periods, improve biodiversity and nestle the development within the landscape. Due to the site topography, sedum roofs are viewed from multiple angles framing the sea views to surrounding properties and benefitting the locality overall.
• Control of surface water drainage via sedum roofs, permeable landscape and soakaways to minimise impact to the existing infrastructure network.
• Landscaped external areas designed by an award-winning local specialist. Enhanced biodiversity through a structured planting strategy areas utilising diverse native flora. A net positive compared to the existing blank lawn.

 As one enters the site from the upper east boundary road, they descend down a series of broad width stone steps winding down through the landscape detaching you from the built-up surrounding area with partial coastal views across an expansive sedum roof set against the natural aesthetic of slate hanging and recessive coloured timber cladding.

The main entrance welcomes visitors at the first floor with a dark grey aluminium feature entrance door in keeping with the surrounding dark timber cladding. Accent naturally coloured timber cladding within the entrance seating area and eaves offset and define the building forms and signal the level of quality and attention to detail throughout.

Entering, a double height light filled space contrasts with the dark exterior. Natural fluted oak vertical oak panelling feature walls extend upwards to the vaulted ceiling reinforcing the loftiness of the space. Curated linear views through the hallway draw you into the space.

Progressing, one enters the single story with mezzanine over open kitchen and dining space providing a human scale activity space within a high-quality and fully integrated designer kitchen. Views across the bay open up and progressing further are now within the main double height living space, greeted by expansive fenestration capturing the view across the bay and headland. The offset orientation of the first floor becomes apparent in its design in crafting the most special of views uninterrupted and panoramic, visitors become lifted within the space and the brilliance of bay is heavily imbued upon them.

The mezzanine above provides an elevated view of the living space below retaining the views outwards. The mezzanine accommodates a private office and storage space that can be separated from the main living spaces below.

Adjacent to the main living space, is smaller and recessive snug with access out onto a private balcony space. Separated by a feature room dividing ethanol burner set within a striking copper feature surround providing a tactile and beautiful patina.

The staircase to the ground floor is separated by vertical timber screening with gunslit windows behind capturing glimpse views across the sedum roof. Ground floor accommodation promotes a rhythm through fenestration that is at the essence of the building as a whole. Externally, this is accentuated through the anthracite grey external sliding shutters. Four bedrooms of accommodation with two en-suites are provided in a linear fashion with each capturing the westward sea views.

The linearity of the ground floor separates the private and public amenity spaces. Externally a sunken patio area is provided to the perimeter of the building. This provides a relaxed delineated external space adjacent to an expansive lawn area.

A separate two-bedroom annexe is provides alternative accommodation to the north boundary of the site separated by an intense human-scale landscaping planting scheme. A series of rhythmic vertical slatted oak sleepers are strategically located providing privacy to both.

The building is constructed on a cast in-situ reinforced concrete edge thickened raft foundation and ground floor slab. All ground floor construction has a 65mm screed with underfloor heating pipework clipped to 200mm high performance rigid insulation.

First floor construction consists of posi-joists to receive MVHR ducting and services, interstitially insulated to acoustically separate floors. A pre-routed structural deck allows for integration of underfloor heating within a low-profile build-up overboarded as required to receive floor finishes.

Retained walls consist of a reinforced shuttered concrete wall lined internally with 200mm water-repellent glass mineral wool insulation and internal blockwork leaf tied back using low-thermal conductivity basalt fibre wall ties. Internal blockwork leaf received an airtight parge coat with service cavity and finishes over.

Walls generally consist of two independent timber frames spaced 400mm apart, but not joined.  This allows for maximum recycled newspaper insulation and no cold bridging through the walls.  Sheathed internally with an OSB based airtightness layer, taped and sealed, with service cavity and finishes over, this provides a robust and continuous solution throughout.

The roof consists of engineered I-joists which use less timber, span further than solid timber and have minimal cold bridging.

The basic principles employed during the design, specification and construction are to ensure that the building has low embodied CO₂ content.   Materials were selected that have not required a large amount of energy in their sourcing, processing or transportation.  The solutions include:

Warmcel Recycled Newspaper Insulation: Warmcel is a natureplus® certified product. This is a standard for products that meet the highest standards from raw material sourcing / extraction, to low emissions and clean production methods.  Warmcel is manufactured from recycled newspapers, these are collected from offices, schools, overruns from printing companies and kerbside collections. Manufacturing processes use very little energy, the combination of the cellulose fibre properties and its specific manufacturing process gives Warmcel an extremely low Global Warming Potential of -1.5 Kg Co₂/m².  The CO₂ sequestered within Warmcel is then locked into the building and is actually less than the CO₂ produced in the manufacturing process.  Unlike other insulations, Warmcel is an inert material with no off-gassing of Volatile Organic Compounds (VOCs), making it the best insulation for a truly healthy home.

Glass Mineral Wool Insulation: Manufactured using ECOSE® Technology with no added formaldehyde and the best possible Eurofins Gold Certificate for Indoor Air Comfort. Knauf Insulation products are certified to BES 6001 (BRE Framework Standard for Responsible Sourcing), a BREEAM-recognised responsible sourcing certifications scheme.

I-Joists: Engineered timber joists made from small sections of timber and timber by products. They offer many design and performance advantages over conventional structural products including a composition which resists shrinking and warping, an excellent strength to weight ratio straight and uniform dimensions. The joists also have FSC & PEFC Accreditation & Labelling, Life Cycle Assessment and ISO14001:2004 Environment Management System.

Timber: Recognised as one of the most sustainable building materials, all timber has been specified carefully ensuring that the chain of custody is clear.  This protects against irresponsible sourcing and irreversible damage to delicate ecosystems. Where possible, we advocate the use of European timber (FSC & PEFC).

Glulam Beams: Small sections of timber from sustainable sources glue laminated to provide a larger structural grade timber. Used throughout within floor construction and timber frame elements to provide for larger openings without the use of steelwork.

Timber By-Products: Such as the Bitroc bitumen impregnated fibreboard to the external sheathing and orientated strand board (OSB) airtightness layers, have also been incorporated in order to utilise further waste products.  Additionally, these products have lower chemical content in terms of adhesives and binders than composite materials such as chipboard and medium density fibreboard, both of which have reported harmful binders which can cause a health hazard when working with the materials.

Designed as a breathing shell (vapour permeable) which is not susceptible to condensation build up and significantly reduces the risk of associated respiratory illness.  As it breathes the structural frame is less prone to decay and offers greater longevity:

• Bitroc: naturally emulsified bitumen impregnated fibreboard made from Scandinavian recycled chipped softwood together with waste newsprint to provide a breathable sheathing board to the external walls and roof.
• OSB: Oriented Strand Board made from thinning’s from managed plantations (FSC); the process utilises 95% of the wood, discarded bark being used for fuel in horticulture.  Used for internal racking walls and first floor sub-deck.
• Wood Treatments: Selected to limit the amount of chemicals utilised within the building.  OSMO polyx hardwax-oil rapid for clear internal applications was selected because it incorporates natural wood wax oils which are solvent free
• Green Roof: Extensive sedum green roof incorporating mixed vegetation allowing a broad range of locally drawn upon species providing a low maintenance supporting a biodiverse and integrated roof makeup. Furthermore, this roof also assists the drainage of the building by slowing down the runoff of water from the roof prior to entering a drainage system.
• External Joinery: High specification triple glazed windows were specified to help reduce heat loss.  Aluminium windows were chosen to reduce maintenance due to the aggressive coastal environment.
• Rainwater Goods: Zinc rainwater goods were selected because of their quality, durability, minimal maintenance, and recyclability.

The biodiverse landscaping and planting scheme envisioned is a harmonious blend of ecological principles and aesthetic appeal. With a focus on promoting biodiversity, the scheme incorporates a diverse array of native plant species, creating a resilient and broad ecosystem. The design prioritises the use of indigenous flora to support local fauna, fostering a balanced and thriving environment.

The landscaping scheme integrates spatial layers providing a series of informal interconnected spaces that allow private and sheltered interaction with the views within a highly built-up area. This is incorporated with strategic feature seating, local materials and rhythm that encourages a stillness within the space.

In essence, this biodiverse landscaping and planting scheme strives to be exemplar in the marriage of environmental stewardship and aesthetic design, creating a vibrant and sustainable landscape for both nature and people to enjoy.

Construction is based around a fabric first Passivhaus approach with u-values achieving Passivhaus where possible. Coupled with a good airtightness value, passive design and sustainable technologies the building achieves an exemplary SAP/EPC as a result.

Both buildings maintain consistent comfort levels throughout the year requiring minimal heating through supplemental sustainable technologies, PV with battery storage and air source heat pump.

U-Value Summary (Constructed)

External Walls

Twin-Skin Timber Frame                           0.12 W/m2K

Roofing

Pitched Slate Roof                                      0.08 W/m2K

Pitched Timber Clad Roof                         0.16 W/m2K

Sedum Flat Roof                                         0.12 W/m2K

Flooring

Ground Bearing Floor Slabs                      0.09 W/m2K

Soffits (Kooltherm K110 Plus) 126mm     0.14 W/m2K

Balcony                                                            0.18 W/m2K

External Joinery – Raynaers                 Average U Value – 0.12W/m2K

Lockdowns during Covid provided complication within the design team due to working at home, also with the client, both overcome by regular teleconference meetings. Further challenges on-site included, self-isolation of the workforce and sub-contractors, lockdowns, additional PPE, staffing, programming, material cost increases, difficulties in obtaining products due to manufacturing constraints all as a result of Covid.