The Deerings

Location: Harpenden, Hertfordshire
Completion Status: Completed October 2017	Occupancy: Occupied May 2017
Architect: Gresford Architects & Tye Architects	Consultant: Green Building Store, Certifier: WARM
Contractor: MBC Timber Frame	Client: Private
Certification: May 2017	Certifier: WARM
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The Deerings is a detached Passivhaus that replaces a former bungalow, and is a contemporary addition to a traditional suburban street scene in Harpenden, Hertfordshire. This simple two storey rectangular form and design optimises its performance by adopting a ‘fabric first approach’ while also meeting the client’s space and lifestyle aspirations. Passivhaus formed part of the client's original brief.

Completed in October 2017, this was a joint project by Tye Architects, who prepared initial plans and secured planning consent, and Gresford Architects, who developed the scheme through the detailed design and construction phases.

An open plan ground floor allows views of the garden through large sliding doors to the rear of the house across the living area flooding the interiors with natural light. A minimalist timber and steel staircase also allows light to pass through into the depth of the plan. The 5-bedroom home includes a cosy snug and a spacious home office tucked away behind a wall clad in ash battens. The ash cladding continues onto the ceiling of the living room creating a warm and cosy feel in contrast to the more open and light dining and kitchen areas.

The Deerings - all images Gresford Architects ©Quintin Lake

Energy Performance

The home was occupied in May 2017, and by the beginning of the following November, the heating had still not been turned on. A specialist Passivhaus certified wood burner was occasionally used and although a back-up gas boiler was supplied, the house performed so well during winter that it was never turned on. Even on the coldest days, without the heating, the house maintained its ambient temperature of around 21 degrees.

All south facing windows have external blinds and an openable rooflight in the stairwell can aid night purge ventilation.

Thermal Energy Demand: (≤15kWh/m².yr)	12 kWh/m²/yr
Thermal Energy Load: (≤10W/m²)	09 W/m²
Airtightness n50 ACH@50pascals (≤0.6ach@50pascals)	0.5ach
Primary Energy Renewable Demand (PER)	37 kWh/m²/yr
Primary Energy Renewable Generation (PER) (in relation to projected building footprint area)	25 kWh/m²/yr
Frequency of overheating (> 25 °C):	2%

The Deerings

Construction

A south facing first floor rear terrace and an integrated ground floor garage made the thermal envelope design quite challenging to meet Passivhaus Standard. The house was built from a super-insulated timber frame, which was constructed off-site by MBC Timber Frame. The frame was supplied with insulation and airtight membrane, and erected on a passive slab, also provided by MBC. The frame was erected in 3 weeks, significantly speeding up the overall programme, and minimising wastage and disturbance to neighbours.

Recycled paper insulation and timber cladding was chosen to reduce the carbon footprint of the building, minimising the use of concrete and steel to less than 10% of the total volume of the building. Another challenge was working closely with the superstructure engineer to minimize the use, size and positioning of the steel to reduce thermal bridges.

English Chestnut has been used to clad the front and rear facades. The sleek, horizontal cladding is punctuated by a series of carefully placed windows, with smaller windows located on the side elevations to reduce heat loss and to avoid overlooking adjacent houses.

The Deerings