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Huddersfield radical retrofit

Sara Darwin of PHI Architects has undertaken a sensitive low energy renovation of a 1960s house in Huddersfield, designing the improvements using Passivhaus Planning Package (PHPP) software.  The house was originally designed by architect Arthur Quarmby, two years before he started work on his own subterranean house at Underhill, for which he would become known in the 1970s, as the first earth shelter dwelling.

The low energy retrofit involved the extensive addition of roof, floor and internal wall insulation, alongside a comprehensive airtightness strategy using Pro Clima airtightness membranes and tapes  and PERFORMANCE triple glazed timber windows and doors supplied by Green Building Store.

Arthur Quarmby’s original design

The house appears to be single storey from the street, but inside it opens up with living accommodation in the upper floor, level with the canopy of the trees in the wood below. Arthur Quarmby used stone from Huddersfield’s recently demolished Packhorse Hotel to construct the house. The design has clear influences of Frank Lloyd Wright, with pyramidal roof around a central chimney, deep overhanging eaves and an extending ‘fin’ wall to shelter the upper terrace and divide public and private space. Mr Quarmby demonstrated his environmental design skills using passive solar principles; the kitchen and bathroom are situated to the north and living spaces to the south for winter sun, but shaded by the deep roof overhangs to prevent overheating in summer.

The retrofit

In 2015 Phi Architects had been working with clients looking to build their own eco-home but not able to find a site. This property was in the perfect location with great potential but the challenge was to bring the fabric up to modern comfort standards, whilst respecting the original design and outlook.

The thermal insulation standards of the 1970s meant the cavity walls were uninsulated and there were extensive areas of single glazing, resulting in a house that demanded high levels of heat input. Any passive solar gain was quickly lost through the fabric. The ‘form factor’ was poor due to the large surface area of the thermal envelope in relation to the floor area. The suspended timber floor structure to the single storey section sat above an unheated void/ basement area, which drained the heat from the house.


Sara Darwin used the PHPP software to inform the thermal design for the house. A number of thermal improvements were proposed including: triple glazed windows, internal Pavadry wood fibre insulation, new roof insulation, insulation to suspended timber floors, lower ground floor insulation with VIPs (vacuum insulation panels) to the concrete slab and a demand ventilation system. A full MVHR was investigated but low ceilings to the lower ground floor meant it was difficult to accommodate supply ducts to the bedrooms without restricting head height. The demand-controlled ventilation system comprises sensors in bathroom, kitchen, utility room. In the living rooms and bedrooms the windows have moisture-sensitive trickle vents. The PHPP was used to quantify the thermal upgrades in terms of cost and reduction in kWh/m2/ year.


Considerable efforts were made to improve the overall airtightness of the house. A full parge coat to the walls and taping/sealing the joist ends into this coat was essential for the inclusion of internal insulation to the walls, as this is sensitive to moisture movement. The main roof was fully refurbished with a new breather membrane, insulation and Pro Clima Intello airtightness membrane to the inside. A new wood burning stove was installed,  with dedicated external air supply to help with airtightness.

Triple glazed timber windows & doors

Changing the windows from single to triple glazing had a significant effect as part of the retrofit strategy. Green Building Store’s PERFORMANCE range of triple glazed timber windows and doors (including entrance and tilt and slide doors) offering a whole window U value of 0.85 W/ m2K were chosen for the project. The windows were outward opening casement windows, finished in RAL 7038 on the exterior and a clear finish internally.

The existing glazing pattern of large panes of glass without smaller openings was ideal for Passivhaus-inspired design, where frame lengths are minimised (being the weakest link in the window component). Only a few alterations to the design were made, such as re-configuring top lights into a more practical side opening casement. We chose the PERFORMANCE range from Green Building Store because the clients wanted windows made from natural materials and the PERFORMANCE range offered good value for money for triple glazed windows. Green Building Store were very helpful with details and specification and were very thorough in putting together a comprehensive quote for the client and made ordering very efficient.

Sara Darwin from PHI Architects

The quotation for the PERFORMANCE windows was highly competitive in relation to the others received, and it was good to do business with a local supplier, especially as the company’s energy efficiency objectives seemed to be aligned with ours. We found Green Building Store to be friendly, efficient, and trustworthy. We got to know Abi, Luke, and Jason in particular and they lent an ear when we were under stress in different stages of the project! Having a single point of contact worked well, and we always felt that Luke (Gilman) was on our side! We’re delighted with the windows and doors. We had the outside frames factory spray-painted to our specified RAL colour but retained a more natural finish on the inside frames revealing the detail of the engineered wood. With 12 windows and 2 external doors, the project’s success depended heavily on the quality of these products and Green Building Store responded brilliantly to their varied specifications, production, and delivery. We were very pleased with the advice given throughout the project and continue to be very happy with the airtightness and performance of all the doors and windows.


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