Passivhaus Retrofit of 1940s Semi
The house upgrade was designed for owner Chris Copeman by architect Gil Shalom using the Passive House Planning Package (PHPP) produced by the Passivhaus Institut. This program calculates the energy the house will use for heating and shows how alterations in the design and materials impact on the overall performance.
To start ...
The floor was taken up, dug out and replaced with a concrete slab with 30cm of insulation below. The inner walls were underpinned with thermal blocks. Some walls and two internal chimneys were removed and brackets added to support the stack in the loft.
Next, the roof
The roof was stripped and insulation boards were fixed above the rafters, with counterbattens and breathable membrane on top, before the battens, tiles and solar panels were replaced.
Sheep’s wool insulation was fitted between and below the rafters. Extra glulam timbers and joists were added to the loft to make a new room in the roof with a small bathroom.
Airtightness
Possibly the hardest job. Plaster was removed from all the exterior walls and wiring was chased into the brickwork. Special airtightness tapes were used to seal round all rafters, pipes and windows before replastering to complete a continuous airtight layer around the whole house. Airtightness tests were performed at two stages showing that the building had been made 20 times more airtight than current Building Regulations.
Ventilation
Now airtight, controlled airflow could be added back to the building in the form of heat recovery ventilation. Ducting was run through the house to supply fresh air warmed by the heat recovered from air extracted from bathrooms and the kitchen. The Paul MVHR unit operates at 94% efficiency and uses only 20W.
Windows
Windows and doors were replaced with triple-glazed, tilt-and-turn, high performance units. These have argon-filled panels, double seals and coated glass to maximise solar gain whilst reducing heatloss. They were hung outside the masonry walls to reduce thermal bridging from the bricks.
Finally ...
External wall insulation was attached to the outside walls down to the foundations and up to meet the roof insulation boards. This was then rendered with a three-part cement-based render system. (kingsleypassivehouse.com)
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This is part of the Beginner's Guide to Renovation & Makovers from the November 2020 issue of SelfBuild & Design magazine.
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