Innovative Islington Passivhaus: A Hidden Gem

Tucked away in North London, a remarkable two-storey Passivhaus-certified home has emerged in the space of a former single-storey garage. In response to conservation area restrictions, the urban infill design ingeniously incorporates a basement to maintain the building’s original height.

This project was crafted alongside a sensitive side extension to a neighboring Grade II-listed property, demonstrating seamless integration of modern efficiency and historical charm.

PHT member Dominic O'Riordan, the Architect and Passivhaus Designer, recommended the Passivhaus standard to the clients after his success with an EnerPHit retrofit. Certification was provided by PHT Patron Etude, and the project marked an exciting milestone as the building contractor's first-ever Passivhaus endeavour.

Key stats

Construction: Hybrid - cavity wall & timber frame
TFA: 111.5 m²
Form factor: 2.7
Build start date: 2021
Completed: 2023
Certified: Passivhaus, 2023

Garage replacement. Image credit: Dominic ORiordan

Construction

Islington Passivhaus Image credit: Dominic O'Riordan

The project is located in a conservation area, surrounded by neighbouring listed buildings. One of the planning conditions was that the new house needed to be built in brick and that brick slips were not permissible. Based on those constraints, cavity wall construction was chosen, with an external brick leaf.

The project was originally designed as a single detached dwelling to replace the existing garage and was to be built next to the neighbouring unheated garage. It is quite hard to design a small detached dwelling (110m² TFA) to the Passivhaus standard. The proposal was discussed with the neighbours who owned the remaining garage, raising the possibility of building a side extension to their house too. This meant that most of the east wall would be a shared party wall with the neighbouring house and therefore more efficient. The planning application was extended to a combined application for a new two storey dwelling, attached to a single storey side extension to the listed house.

Basement at Islington Passivhaus Image Dominic O'Riordan.

Cavity wall construction at Islington Passivhaus Image credit Dominic O'Riordan

The initial phase of the project involved the excavation and construction of the retaining walls and raft slab on insulation, which was undertaken by a basement contractor. The second phase involved construction of the first floor, using timber frame construction. A trusted contactor, who had never worked on a Passivhaus before, undertook the work, confident that that they could build the house if provided with the architect's detailed specification.

An example of how thermal bridging was minimised in the design is illustrated by the care taken that external bridge and railings were designed to be outside the thermal envelope and supported on the outer skin of the brickwork and did not penetrate the insulation layer.

External bridge structure over lightwell outside thermal envelope. Islington Passivhaus. Image credit: Dominic O'Riordan

U-values

Roof: 0.09 W/m²K

GRP membrane

Islington Passivhaus. Image credit: Dominic O'Riordan

Wall: 0.09 - 0.15 W/m²K

Insulated cavity wall, with facing brick.

Floor: 0.11 W/m²K

Insulated concrete raft

Further information can be found at the International Passivhaus Database listing

Building performance

Designed energy performance

Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)

0.5 @ 50 Pa

Space Heating Demand (≤ 15 kWh/m².a)

13 kWh/m².a

Heating Load (≤ 10 W/m²)

7 W/m²

Primary Energy Demand (≤ 120 kWh/m².a)

67 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Islington Passivhaus. Image credit: Dominic O'Riordan

Services

The house is heated with an air source heat pump and has a MVHR system. The site is oriented north-south. There are four mature trees that provide effective summer shading to the front elevation. The conservation planning officer would not allow any external shading devices in the conservation area. In order to improve the summer shading on the south facing elevation, the south-facing windows required deep reveals for shading. Parts of the outer skin of brickwork were built in full brick (215mm) rather than standard half (100mm), which increases the shading from the high summer sun.

Challenges & lessons learned

Minimising concrete use: The single storey planning height restrictions necessitated a basement. This meant that the clients and design team had to accept the additional embodied carbon of the required concrete retaining walls. The project team worked hard to minimise the use of concrete as far as was possible. The structural engineers' original design for 8 metre deep contiguous piling was adapted to L-shaped retaining walls in sections to reduce the amount of concrete used. Combining the project with the neighbour's extension also reduced the length of the retaining wall required along the boundary wall. The front lightwell is stepped and so the height of the concrete retaining wall along that length of wall was reduced. The ground floor is a timber frame construction to reduce further use of concrete.
Varied wall construction types: As the property is semi-detached with a part basement, there were a number of different types of wall construction. Consequently the airtightness and insulation detailing needed to change to suit the different wall types and these all had to be closely monitored to check that they were detailed and built correctly.
Contractor new to Passivhaus: The project demonstrates that the contractor does not need to have built a Passivhaus before, but they do need to be committed to the aim to achieve certification and be diligent in their work.
Sequencing: The hardest detail of the project for the project team was the need for the external brickwork to be built at the same time as the external insulation was being installed. The team of bricklayers were keen to make progress and did not want to be delayed. Basalt wall ties were used to minimise thermal bridging but also meant insulation needed to be installed simultaneously with the brickwork. This process left the design team very little time to inspect the external wall insulation. In hindsight, the team has reflected that it would have been better to work out a way to be able to insulate and install all the windows, have a preliminary airtightness test and build the external leaf of brickwork at a later stage.

Islington Passivhaus. Image credit: Dominic O'Riordan

Architect’s view

I had previously worked on a four storey house in Muswell Hill, certified to the EnerPHit standard and had thought that a new build would be more straightforward. However, the planning constraints and tight site meant that this was also a complex project. Aiming for the Passivhaus standards gave both projects extra commitment/ energy and encouraged me to fully engage in critical aspects of architecture such as the site, detailing, clients and contractor from start to finish. I am very proud of the finished house.

The owner grew up on the west coast of Ireland and tells stories of laying out her clothes at night so that she could get dressed straightaway in the morning. She is amazed and delighted that she now has a house where the internal temperature is so comfortable throughout the day and night and yet hardly needs any heat input.

The house has now been occupied for a year and we are undertaking a post-occupancy evaluation with the certifiers and hope to be able to share the results soon.

Dominic O'Riordan, Architect

Key team

Architect & Passivhaus Designer: Dominic O'Riordan
Contractor: Tico Contractors
Structural engineer: MHA Structural Design
Passivhaus Certifier: Etude

Passivhaus projects can fit into the tightest of spaces and can work around a range of planning constraints. Get some further Passivhaus selfbuild inspiration from the links below and from our Passivhaus goes Personal campaign.