Energy efficient makeover of 1960s bungalow

Architect Gil Schalom has undertaken an extension and radical retrofit of a 1960s dormer bungalow in Southwell Nottinghamshire, transforming it into an energy-efficient two storey 3 bedroom house, optimising the light and views at the rear of the property.  21°s PERFORMANCE triple glazed timber windows and doors, including several French Doors, were chosen for the project.

Design issues

The original bungalow was in a poor state of repair and so lent itself to full retrofit treatment, with a project budget of £200K. The owners wanted to make the house suitable for whole life use with a downstairs bedroom as potential space for elderly relatives. The retrofit involved extending the footprint of the house at the rear of the house and addition of two bedrooms upstairs. The upstairs bedrooms were designed so that both rooms were able to access a balcony area, benefiting from stunning views over to nearby Southwell Minster. Although most of the project was finished with crisp white render, at  the rear of the house, Cedral cladding, made from fibre/ cement, offered a cost-effective and low maintenance alternative to timber cladding. An additional cost for the project was the need for the specification of pilings for the foundations as the project was located in a marshy area. 

Insulation and airtightness strategies

The insulation and airtightness strategies included:

• Roof: Full replacement of the roof, with thermal bridge-free detailing. 100 mm sarking insulation above rafters and 150 mm Rafter Roll 32 enhanced performance glass mineral wool insulation between rafters and service void below rafters.  Warm flat roof with 150 mm PIR insulation over deck, finished with EPDM membrane.
• Walls: Use of 200mm EPS(180 below DPC) external wall insulation throughout. Extension walls have Marmox Thermoblock thermal break below DPC. Windows & doors mounted in plywood box frames to project them outwards into the EWI zone.  EWI wraps around frames 60 mm.  Compacfoam breaks supporting the door cills.  Splayed reveals to outward opening French doors, all others inward opening.
• Floor: Insulation of the suspended timber floor at groundfloor level from below and all masonry walls received down stand insulation both sides below DPC; Intello membrane laid over entire existing floor boards with wall upstands plastered over.
• New extension floor:  constructed with Jetfloor concrete beams and profiled silver EPS insulation infill, with additional 150 mm Platinum EPS above and self-levelling screed above that.
• Use of wet plaster and Pro Clima tapes/ membranes for airtightness

Triple glazed timber windows & doors

PERFORMANCE triple glazed timber windows, doors and French doors were chosen for the project, in timber finish colour RAL 7015

Juliet balcony

Upstairs the three ‘doors’ leading into the balcony are actually large Tilt and turn windows, offering a cost-effective solution for the project.

Installation detailing

The installation detailing for the windows and doors was carefully undertaken so that the window and door frames are wrapped within the external insulation, to help minimise thermal bridging. Plywood frames were used to position the frames within the insulation and help overlap the EWI insulation onto the frames. This explains why the windows and doors are slightly recessed into the walls and also why only a part of the frames are visible.