WILDWOOD

Wildwood, Lanhydrock, Cornwall

GIFA: 224m²

Procurement: Main Contractor

LABC: Cornwall Council (Plan Check and Inspections)

Wildwood is a sensitive refurbishment and extension of a converted chapel and Sunday School near Lanhydrock, Cornwall. Originally modernised in the 1980s, the building required extensive upgrades to improve thermal performance, eliminate damp and radon, and reorganise internal spaces. Our revised design replaced unsympathetic dormers with a single vernacular slip dormer and introduced a timber-framed sun room with a biodiverse green roof and pyramid rooflight.

Unexpected structural issues led to partial demolition and a new high-performance timber frame shell, enabling airtight detailing, underfloor heating, and improved insulation. A new staircase, gallery, and feature log wall were added, while the chapel windows and heating system were upgraded. The project also includes photovoltaic panels, a radon barrier, and a rainwater management system.

Natural materials such as FSC-certified timber, lime render, and Iroko cladding were chosen for low embodied carbon and durability. The result is a low-energy, breathable home with enhanced biodiversity, rural character, and long-term resilience.

The existing property was converted in the 1980’s and required modernising, re-organising, refurbishing and extending.  The brief was to refurbish the existing chapel and Sunday School, convert the Sunday School loft and replace the existing conservatory with a sun room.  Our clients approached ARCO₂ with an extant planning approval by another Architect.  The previous designs’ mass and volume dominated the south east elevation. The scale of the dormers was unsympathetic and obscured large amounts of the south eastern elevation of the chapel. The previous designs’ twin dormer windows provided a limited addition to the floor area in the attic space.

To create a larger single vernacular slip dormer which obscures less of the Chapel, improves natural light and views and provides added value to the internal spaces. The intervention is subservient, respectful and sympathetic to the existing building, offering a sustainable, high performance solution that uses natural materials. The sunspace extension will have a green roof and timber frame structure. The previous designs’ south west elevation shows the sunspace stepped in from the eastern wall, which creates a staggered, unclear language on the façade resulting in over-domination of the existing chapel.  The new design concept aligns the sunspace with the eastern wall and creates a clear symmetry to the design. The sliding doors on the southern façade of the sunspace create flexibility and allows for dramatic views to the south. A roof light in the sunspace above the extended kitchen area creates a light open airy feel.

During the removal of the existing Sunday School roof a bat ecologist was present, 2 bats were found and taken to the mitigation provided in a newly constructed garage and store building.  Once the roof of the existing Sunday School had been taken down it became evident that the 3 remaining external walls had been constructed on a budget, perhaps by volunteers with each wall being of a slightly different masonry construction, no doubt using whatever materials that could be obtained at the time.  Two of the walls had started to lean and the structural engineer instructed the walls to be taken down on health and safety grounds.  The decision was made to construct a timber frame shell which would be located inside the remaining wall.  The gable wall would have a new ventilated cavity with lime render and the final wall being predominantly internal was designed to complement the sun space.  This new structure enabled the thermal performance and air tightness to be greatly improved.  The suspended timber joists were mostly rotten and required removal.  This provided the opportunity to introduce a radon barrier, radon sump, concrete floor slab, insulation over slab and underfloor heating within a screed.  This greatly improved air tightness which was linked to the timber frame walls and roof and reduced the risk of radon and heat loss.  The first floor joists were replaced with I joists to create additional headroom within the loft and allow for acoustic insulation also aiding thermal separation.  The new roof incorporated a ridge beam to simplify construction, provide good insulation levels and maximise head room.

The new Sunday School accommodation enabled a new staircase to serve the 1^st floor with a short secondary flight serving the loft bedroom.  The large first floor gallery was reduced in size, trimmed with glulam beams and modernised with a sleek contemporary cantilevered glass balustrade.  The chapel windows were replaced to improve thermal performance.  The wood burner was replaced and a bespoke feature storage wall with log storage was constructed around the wood burner.  The damp walls were improved by digging away the external levels and installing a French drain to a new soakaway.  To further reduce damp the surface water design was improved to ensure moisture falls away from the building and a new kerb deflects surface water run-off from the road.

The external access was improved and vehicular parking area increased with a high efficiency condensing boiler serving underfloor heating and radiators.  The house also benefits from electricity generation via photovoltaic collectors.  To further improve efficiency a new freshwater pump and filtration system was installed.

The conservatory was replaced with a Sun/Garden room extension providing a lounge area leading onto an external terrace and the garden.  The new kitchen and dining area spill into this space but are separated via a split level accessed via 4 steps.  The fabric consists of over slab insulation with underfloor heating located in the screed.  The floor finish is a hard finish so as to retain thermal mass from the underfloor heating and solar gain.  The walls are timber frame with a steel goal frame around the main windows.  The mono pitched roof is also constructed of timber frame with a sedum roof and pyramid rooflight.  This extension was designed to improve thermal efficiency by buffering the existing building.

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

1. 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.
2. 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).  The cladding was specified as Iroko to minimise maintenance and increase longevity.
3. Timber by-products: such as orientated strand board (OSB (air tightness layer)) have 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.
4. External Joinery: High specification double glazed windows were specified to help reduce heat loss.  Powder coated aluminium was chosen for robustness and future recyclability.
5. Wood treatments: have been selected which limits 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.
6. 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 minimum maintenance 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.
7. Green roof membrane: 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.
8. OSB: Oriented Strand Board made from thinnings 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.
9. Glulam Beams: Small sections of timber from sustainable sources glue laminated to provide a larger structural grade timber.  Used for cantilever, around glass floor and over larger openings as lintels.
10. Earthwool: insulation to acoustic separating floor (where breathability is not required).  A+ Generic BRE Green Guide rating.  Made using recycled materials.  Made from rapidly renewable organic materials. No added formaldehyde binder.  No added dyes.  Up to 70% less embodied energy and recyclable.
11. Celotex Insulation A+ BRE Green Guide, CFC/HCFC free with zero ODP and low GWP. CE marking compliance to BS EN 13165:2001and manufactured in accordance with quality management systems with BS EN ISO 9001:2000 and Environmental ISO 14001.  The lightweight nature of the insulation means that less fuel is used when transporting from factory to building site.  Celotex claim that 100 times more energy is saved than that used for manufacture.

The extensions’ green roof provides 30 sq.m of biodiverse green roof with 16+ varieties of sedum.  Already birds, butterflies and bees have been taking advantage of the green roof.  Swallows have found a new home under the soffits of the green roof.   The garden has been designed to increase permeability and retain a rural feel with bee friendly species planted.  A new hedgerow also provides opportunities for insects, invertebrates, birds and other small mammals.

Whilst it was not a building regulation requirement to exceed U-values sustainability was a key decision in our clients commissioning ARCO₂.  The thermal performance greatly exceeds that of the Chapel and Sunday School.  Improvements to the existing building were also made to greatly improve performance including a new high efficiency Sedbuk A rated combi-heating system, insulating Sunday School walls, floor and roof, installing underfloor heating, new windows/doors.

U-Values:

Sunday School/Extension Floor: 0.17                        New Walls 0.13

Sunday School New Pitched Roof 0.10                      Dormer Roof: 0.11

Sun Room Extension Roof 0.11                                   Pyramid Roof Window 1.1

Windows/Doors 1.6

The main challenges relate to the unexpected partial demolition of the Sunday School,  specifically integrating a predominantly new structure within the old, developing new construction drawings and seeking building regulations approval while contractors are on site waiting for the information.  Cost was also a challenge and the additional works resulted in the contingency sum being exceeded.

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