MELLALUE

SAP: 73C  Environmental Impact: 75C

Air Pressure Test: 1.93 m3/(h.m2) @ 50pa

Planning Constraints: Close proximity to AONB, AGSV, Cornwall Nature Conservation Site & SSSI, Badgers

Mellalue is a contemporary replacement dwelling in Polzeath, Cornwall, designed to harmonise with its sensitive coastal setting and accommodate multi-generational living. Replacing a thermally inefficient dormer bungalow, the new home features a curved sedum roof, panoramic sea views, and a strong linear concept defined by a central spline wall. The three-storey layout includes subterranean bedrooms and a games room, entry-level living spaces, and a master suite with rooftop terrace.

Constructed using a 300mm I-stud timber frame insulated with reclaimed sheep’s wool, the building achieves excellent airtightness (1.91 m³/(h.m²) @ 50pa) and low U-values throughout. Materials include breathable Bitroc sheathing, FSC-certified timber, and locally sourced concrete with secondary aggregates. A high-efficiency MVHR system, LED lighting, and a clean-burning wood stove support low operational energy use. Despite its bold form, Mellalue gained support from neighbours and the Parish Council, demonstrating our commitment to context-sensitive, sustainable design in protected coastal zones.

The client brief was to construct a low energy contemporary home which could accommodate a family with teenagers and elderly parents on the entrance level.  The building should also be in harmony with the landscape and large garden.

One of the key design considerations was to retain the sea views of the neighbouring building behind and to improve their outlook.  The existing building dormer windows faced towards the rear and overlooked the private amenity space of the neighbour’s house.  The house was designed with a curved roof to maximise space, minimise impact with the same ridge height as the existing building.  The curve has been covered with a green roof so that the neighbours’ outlook is enhanced.  Although maintaining a view is not a planning policy consideration ARCO₂ always try to retain and enhance neighbours views wherever possible.

The design concept was to create a spline wall which separates public spaces such as lounge, kitchen, dining and private spaces such as plant room, utility and bathrooms.  The spline wall begins at the site entrance and draws you in to the front door providing perspective and preventing you from seeing the full extent of the view, with only glimpses of the views through slot windows.  The spline wall cuts through the heart of the building and the strong linear concept can be read through the length of the building.  When entering the entrance lobby you are then faced with the panoramic coastal views through the open plan kitchen, dining and lounge

The seamless transition between Architects and Construction was possible due to the client deciding to work directly with the Architects sister construction company Ecofab Ltd.  This kept all the design, project management and construction skills in house.  The client’s trust in their Architect also ensured that the original design concept was fulfilled.

The building is constructed using a 300mm I stud to the walls and roof which are insulated with sheep wool.  The external fabric has a hardboard interior sheathing to create airtightness with all joints and penetrations taped and sealed.  A services zone has then been added with 2 layers of plasterboard to provide thermal mass.  Externally the walls are sheathed with a breathable board with ventilated cavity and render board with silicone render finish, natural stone or timber cladding.

The air pressure test was 1.91 m3/(h.m2) @ 50pa which is a very good result given the complicated junctions with part of the building being underground.

The basic principles employed during design, specification and construction is as follows:

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:

1. Reclaimed sheep wool: a by-product of wool based industries in our region. The material is waste and previously discarded. It is untreated and has no embodied energy in terms of processing and only limited transportation requirements all being sourced from within the region. The material also has benefits in terms of its hygroscopic properties enabling it to act in harmony with changes in atmosphere, humidity and the seasons in general. With regard to handling, the material is safe with no off-gassing present in proprietary insulation materials. Additionally there are no damaging fibres and therefore no irritation is experienced by site personnel.
2. Jablite Premium 70:  Jablite insulation products are made from EPS (expanded polystyrene) which has an A+ rating in the BRE Green Guide.  It has a Global Warming Potential (GWP) of less than 5 and an Ozone Depletion Potential (ODP) of zero.  The blowing agent used during manufacture is pentane which has zero ODP and a GWP of less than 5.  Jablite insulation products are manufactured in factories which are ISO 14001 certified and Jablite purchases raw material from suppliers who are ISO 14001 certified.  Jablite insulation products are 100% recyclable. Jablite collect waste from building projects and recycle it, the product is 100% recyclable.  98% of the material is air and therefore extremely resource efficient. The lightweight nature of the insulation means that less fuel is used when transporting from factory to building site. (EPS is a plastic that is obtained from oil. In Europe, the percentage of oil used in manufacturing EPS is 0.1%. No CFC’s (chloroflourocarbons) or HCFC’s (hydrochloro-fluorocarbons) are used in the manufacture.
3. Rockwool: insulation to acoustic walls and floors (where breathability is not required).  Stone wool is made by melting naturally occurring volcanic diabase rock and recycled briquettes, made with carefully selected by-products from Rockwool’s own and other industries – diverting them from landfill.  Most of Rockwool’s building products achieve A and A+ ratings, according to the BRE Green Guide to specification.  Rockwool is 97% recyclable and during its long lifetime, a typical Rockwool insulation product saves more than 100 times the energy invested in its manufacture, transport and ultimate disposal.
4. I-Joists: Engineered timber joists made from small sections of timber and timber by products (see below). 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.
5. 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 together with locally sourced green timber such as western red cedar and Douglas fir for external claddings to reduce processing and transportation energy costs.  Locally grown Douglas Fir was used for cladding to landscaped walls, garden store, gate and fencing.
6. Timber by-products: such as the bitumen impregnated fibreboard to the roof (Bitroc), orientated strand board (OSB), and hardboard (air tightness layer) 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.
7. External Joinery: High specification triple glazed windows were specified to help reduce heat loss to the large north facing glazed areas which take advantage of the panoramic sea and beach views.
8. Wood treatments: have been selected which limits the amount of chemicals utilised within the building.  Clear wood treatments such as OSMO polyx hardwax-oil rapid for internal applications have been selected because they incorporate natural would wax oils which are solvent free.
9. Wall membranes: have been eliminated from construction. This serves to provide a breathing shell (vapour permeable) which is not susceptible to condensation build up and significantly reduces the risk of associated respiratory illness.
10. Floor membrane: Visqueen Eco Membrane: Manufactured from 100% post-use polyethylene, diverting more waste from landfill.
11. Green roof: consist of varieties of succulent called “sedum”.  These are extremely tolerant of dry conditions, have limited growth but also replenish themselves readily year-on-year.  This provides little requirements for maintenance and control and promotes a range of wildlife as well as looking spectacular year-round but especially in late spring during the main flowering season. This roof also assists the drainage of the building by slowing down/holding up the run off of water from the roof prior to entering a drainage system.
12. Green roof membrane: Hertalan EPDM Membrane is the most environmentally friendly roof membrane compared to all other roofing systems and is re-usable.  The membrane is root resistant and exceeds the expected lifespan of the vegetation layer.
13. Rainwater goods: Copper rainwater goods were selected because of durability, minimal maintenance and has infinite recyclability.

The construction project had to contend with badgers on the lower part of the site, their setts and habitat were cordoned off during construction and the garden area retained as before.  The remaining garden areas have seen huge ecological benefit including varieties of plants that encourage bees, insects and wildlife.  Wild grasses, shrubs and trees were chosen for their robust nature in such an exposed location.  New Cornish hedging has provided suitable habitats for invertebrates, birds and small mammals.  The landscape architect paid particular attention to ensuring the site has ecological enhancement and improved wildlife habitat.

U-Values

• Lower ground floor slab: 170mm Under screed Jabfloor premium 70 rigid floor insulation: 0.15W/m2K (BRE Green Guide A+)
• Upper floor slab: As above: 0.15W/m2K
• I stud walls 300mm Sheep Wool: 0.13W/m2K (BRE Green Guide A+)
• Curved Sedum roof with I studs and 300mm Sheep wool: 0.16W/m2K (EPDM membrane flat roofs achieve BRE Green Guide A)
• Velfac triple glazed aluminium clad timber windows and doors: 1.2W/m2K (average)

The contemporary design is very different from the neighbouring buildings but at the same time is in keeping with the surrounding environment.  The majority of buildings within Polzeath are white rendered and maintaining common materiality was a fundamental consideration.  The key challenges were to gain the approval of the neighbours to the rear and to convince the Parish Council that this modern design was in keeping with the area.  We were pleased to discover that the Parish liked the design and the immediate neighbours were also in support.