Climate action begins at home

PHT member Tate Harmer has delivered a newly certified project, Kintyre Passivhaus, in Hertfordshire. It was essential to the climate change activist client that the home have the smallest environment impact possible so it was a quick decision, when looking at the various options, to opt for Passivhaus. The resulting new home melds into its rural setting, uses natural materials and combines technology with a fabric-first approach to achieve the Passivhaus standard.

Kintyre

We wanted to do an eco-house, because we’re worried about the climate crisis. We wanted to make sure our family’s negative impact on the environment was as little as possible. We put out a board saying, ‘Yes, it’s a Passivhaus,’ and explained what it was.

Client, The Sunday Times: Building the future April 2019

Set in a conservation area it was important that the external design fit in with the surrounding area and properties. The 10-acre site had been home to a 1960s prefab bungalow when the client purchased it for £1.15m in 2014. In order to win planning for the new home, which was awarded on the first attempt, a traditional feel to the building was maintained. This is particularly evident in the shape of the pitched roof which echoes the style of other nearby buildings.

The new structure, which had a build time of 16 months, maximises the footprint of the previous bungalow to fit four bedrooms and two bathrooms in the vaulted roof. It was important to the client to have a low-energy home that did not compromise on open plan living. The daylight flooded contemporary interior accentuates this with a double-height void that was carefully designed to accommodate high levels of insulation to help maintain its Passivhaus credentials. The 20in-thick walls are filled with Warmcel recycled-paper insulation. A foam slab beneath the poured concrete floor ensures it feels ambient without any underfloor heating.

While the potential for heat loss was increased by the double height living area, the rectangular plan of the house is arranged around a north-south axis with triple glazing predominantly placed on the south side to optimise controlled solar gains and help mitigate any losses not solved by the extra insulation. Brise soleils to the south and deep window reveals provide shading & help to ensure summer comfort.

Kintyre

This project demonstrates how to design and build a Passivhaus as a contemporary English cottage. A simple rectangular form and pitched roof take inspiration from the surrounding cottages and open the ground floor to the beautiful southern views across the fields. Carefully selected timber cladding was adopted, not just to clad the walls but also pop-out windows and the roof. Various widths of cladding board wrap the building to create a seamless, crisp finish. This is quite an unusual design feature that we feel works really well, and we hope to carry forward in future designs. In particular the idea of hidden drainage that sits behind the cladding, thus creating a flush finish.

Tate Harmer

Key Stats

Treated Floor Area (TFA): 192.4m²

Form Factor: 2.98

No. Occupants: 4

Year of completion: 2018

Renewables: ASHP

Construction Type: Timber frame

Total project cost: £800,000

Energy Performance

	Airtightness (≤0.6ACH@50pascals)	0.44
	Thermal Energy Demand (≤15kWh/m².yr)	13.6
	Thermal Energy Load (≤10W/m²)	9.8
	Primary Energy Demand (≤120kWh/m².yr)	40

The family spend approximately £40/month on energy bills.

Mechanical ventilation with heat recovery (MVHR) coupled with an air source heat pump (ASHP) provide the main sources of heating alongside a wood burning stove and back boiler connected to a thermal store. Wiring has been installed so that PV panels can be installed in the near future.

The thermally broken, tripled glazed windows and doors (uninstalled) have U-values of 0.80 and 0.79 respectively while the timber wall comes out at 0.11, the timber roof 0.9 and concrete floor 0.9.

To prevent heat loss through the building fabric, a split timber frame separates the structural elements of the building from the larch cladding and a rubber membrane is sealed beneath the wooden roof.

Key

Larch cladding
Waterproof membrane
PPC aluminium capping
Glidevale eaves vent
Hidden gutter
100mm-thick rigid insulation
Tape to timber frame

Kintyre has recently won a 2019 RIBA East and RIBA East Sustainability Award which has given this beautiful Passivhaus home some very well deserved recognition.