Passivhaus

New

Build

The Client’s Vision

When the clients first walked through the gate of an overgrown plot in Nailsea, they saw past the seriously dilapidated bungalow and knee-deep brambles to recognise something special—a generous garden carpeted with snowdrops and dominated by four magnificent mature oak trees. Having spent forty years in Victorian housing with enormous heating bills and a substantial carbon footprint, they approached retirement wanting something different: a highly sustainable, easy-to-live-in home with minimal running costs that would serve them for the rest of their lives.

After approaching four architectural practices to explore both refurbishment and new-build options, the clients selected MJW Architects based on our proven Passivhaus expertise—still relatively rare in the UK—and the comprehensive 70-page specification we provided, which included six design options tailored to their specific requirements. Their brief was clear: demolish the redundant bungalow, retain all four oak trees, maximise the garden potential, and create an energy-efficient home for life.

Design Concept and Approach

The architectural response centres on achieving certified Passivhaus performance—a rigorous German standard that delivers exceptional thermal comfort with minimal energy consumption. This required high levels of insulation throughout the building envelope, airtight construction achieving no more than 0.6 air changes per hour at 50 Pascals pressure, and triple-glazed windows to eliminate heat loss. Timber frame construction achieves thermal values of at least 0.12 W/m²K across walls and roof, whilst Mechanical Ventilation with Heat Recovery (MVHR) provides constant fresh air and climate control.

The form of the house responds carefully to its context. Positioned tight against the northern boundary to maximise southern garden space, the building steps up to two storeys on the garden side, creating a dramatic glazed elevation that floods the interior with natural light. This south-facing glass wall incorporates an innovative feature: large solar shutter doors that slide vertically in front of the glazing. These can be opened to maximise beneficial solar gain during cooler months or closed to prevent overheating in summer, providing user control over the home’s thermal performance.

Material selection reinforces the environmental credentials. External vertical timber cladding echoes the mature oak trunks and will weather naturally to blend with the garden setting, whilst the zinc roof offers longevity and recyclability. Triple glazing throughout maximises thermal performance. Internally, timber flooring provides a durable, contemporary surface that contributes to the home’s natural material palette. The design framework ensures these materials work together to create an envelope so thermally efficient that conventional heating systems—radiators or underfloor heating—are unnecessary.

Responding to Site Challenges

The most significant challenge arose from neighbouring concerns about replacing a single-storey bungalow with a larger two-storey house. Issues of overlooking and overshadowing required careful negotiation. Through direct dialogue with neighbours and design refinements that addressed their concerns, an acceptable solution was reached. The final design mitigates overlooking through strategic window placement and the building’s positioning tight against the northern boundary, whilst the contemporary architectural language makes a positive contribution to the streetscape.

Restricted site access during construction added complexity, particularly given the exacting standards required for Passivhaus certification. Achieving the necessary level of airtightness demands meticulous attention to detail at every construction stage—there is no margin for error. Every junction, penetration, and interface must be perfectly sealed and tested. This rigorous construction approach was managed successfully through close site supervision and specialist contractor expertise.

The Completed Home

Four Oaks delivers on its environmental promise with remarkable efficiency. The open-plan living spaces remain light-filled throughout the day thanks to the south-facing glazing, with the solar shutters providing control when needed. The MVHR system and high insulation levels create remarkably even temperatures throughout, maintaining comfortable warmth of 20°C or above through winter with minimal additional heat input. When desired, a small log burner in the corner provides a cosy focal point, though it functions more as atmospheric feature than necessity.

The house creates multiple cherished spaces for the clients. The mezzanine gallery overlooks the garden and frames views to the oak trees, whilst bedroom doors open onto a balcony with views across neighbouring fields. The kitchen window frames one of the original oaks at full height, bringing the garden into daily life. Whether facing summer heatwaves or harsh winter weather, the house provides calm, comfortable living with running costs that genuinely average well below £5 per week for heating and hot water.

Key Features

• First certified Passivhaus in North Somerset
• Timber frame construction with thermal values of 0.12 W/m²K
• Airtightness of 0.6 air changes/hour maximum
• Triple glazing throughout
• Innovative vertical solar shutter doors for thermal control
• MVHR system providing fresh air and climate control
• PV solar panels generating electricity
• No conventional heating system required
• Two-storey glazed elevation maximising natural light
• External vertical timber cladding and zinc roof
• All four mature oak trees retained and integrated
• Annual heating and hot water costs below £5 per week
• Zero carbon in operation
• Contemporary open-plan living with mezzanine gallery
• Regional Finalist, Building Excellence Design Award
• Featured by Passivhaus Trust and Build It Magazine