Last week Footprint visited Anne Thorne Architects‘ recently completed PassivTerrace retrofit in Hawthorn Road, LB Haringey for client Metropolitan Housing Partnership. This mid-terrace, solid-wall Edwardian house is part of the Technology Strategy Board’s Retrofit for the Future programme which is funding the retrofit of 86 different low rise affordable homes with the aim of 80% reduction in CO²emissions.
Front of house: internal insulation
Rear of house: external insulation
The approach for the retrofit was ‘Fabric First’ so high levels of insulation (250mm) and airtightness were key parameters of the project. Consistent with what is proving to be the norm with terraced house retrofits, insulation is external at the rear of the house and internal at the front of the house driven largely by external appearance and its location in Campsbourne Cottages Conservation Area.
Photos showing the depth of insulation required
Triple-glazed windows from the Green Building Store
The house is approached as a whole circular system: the heat recovery ventilation system is 90% efficient. Additional heat requirements come from solar and internal gains, although these are unlikely to be as high as with a new build Passivhaus. Although many Passivhaus projects have no central heating system, the project team opted for a small boiler with strategically placed radiators to alleviate extreme weather conditions. A gas boiler supplies hot water, approximately 60% of which is predicted to be powered by solar thermal panels on the roof.
Small radiators are used for extreme weather conditions
Natural insulation has been used throughout the interior: sheeps wool for the front of house and wood fibre on the party wall, to prevent heat being lost to neighbours. Chimney stacks were also filled with insulation. Due to financial constraints rendered polystyrene insulated panels were used for the rear wall; it was deemed more important for the internal walls to have natural insulation than the external walls due to breathability. Moisture and humidity are a concern with internal insulation in retrofits, and alongside the standard post occupancy evaluation that will take place over a two year period, UCL’s Ben Croxford and his students will also undertake additional evaluation to monitor moisture in the internally insulated walls. See UCL student Elisa Prestia’s informative blog which documents the construction process from June 2010 to completion and includes the house plans and interviews with the project team.
A draught-free layerof continuous internal plaster links the building membranes within the walls, ceilings and floors, whilst a new triple-glazed internal lobby allows the existing Edwardian front door to remain.
According to Anne Thorne Architects, PHPP was used to model existing and potential heating needs and energy use, and to understand the effect of small adjustments to the design of insulation, quality of windows, air-tightness , cold bridging, ventilation strategies and heating & hot water systems.
Final Passivhaus testing for certification will take place shortly. The total budget for the project was £200,000, which included refurbishing the fire-damaged property, converting what was previously two flats into one home, and the energy retrofit which was funded by £80,000 from the Technology Strategy Board.
Primary energy target: 90 kWh/m2/yr
Annual carbon emissions: 15 kg/m2
Front Wall: 0.21 W/m2K
Party Wall: 0.31 W/m2K
Rear Wall: 0.15 W/m2K
Ground Floor: 0.18 W/m2K
Loft and Roof: 0.11 W/m2K
Windows: 0.75 W/m2K
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Filed under: Eco-projects