Retrofit for living

In this Retrofit, we have considered the living conditions of the residents as well as their energy use and bills. Before doing any design work, we met with them and asked their views of the existing house – what was good, what wasn’t good and how it could be improved. We also studied how they lived there and used energy. The changes we have made are predicted to achieve the target 80% cut in CO₂ emissions. They have hopefully also made it a much better place to live in. Early feedback from the residents – who have carried on living there throughout the work – is encouraging.

One of the major changes has been the creation of a solar ventilating lightwell and mezzanine above the existing stairs. This insertion has brought natural light and amenity space into the centre of the house – previously a dark, window-less place. The house feels bigger and loftier as a result, surprisingly so. Alongside this lightwell is the residual space of the existing loft, which has been brought within the thermal envelope of the building. Warmer in winter and cooler in summer, this has become the prime storage space for the house – a new facility which has been well received by the residents.

House and terrace

The house is a mid-terrace three bedroom house on the Windsor Park Estate in London Docklands, built in 1992. This house and many others on the estate is tenanted under the ownership of the East Thames Group.

The terrace has an east-west orientation, with the front facing east. This orientation was chosen as posing a harder challenge to capture solar energy compared with a more favourable south-north orientation.

Ventilation strategy

The pre-retrofit occupant feedback survey identified higher than average consumption of electricity, including higher usage from the washing and drying of clothes. It also revealed frequent opening of windows and doors to provide rooms with fresh air.

From this feedback, it became apparent that a natural ventilation strategy allowing the opening of windows to provide higher levels of ventilation would be more suitable than a mechanical ventilation strategy providing lower levels of ventilation. The strategy which has been developed uses openable windows for incoming air and a high-level opening rooflight in a newly-created lightwell above the internal stairs for exhaust air. The lightwell also serves as a clothes drying space to allow the residents dry their clothes naturally, instead of using a powered tumble drier.

Insulation strategy

Four different whole house insulation schemes were developed and analysed for energy performance and affordability. With only a small difference between the best and worst performing schemes, other issues have been considered in selecting the final insulation strategy, notably planning impact on the external appearance of the terrace and long term benefit to the tenants.

In the final selected scheme, the external appearance from the street is retained by installing insulated dry lining to the interior of the front wall. With less constraint at the rear, rigid insulation with self-coloured render finish is being installed to the exterior of the rear wall. The suspended precast concrete ground floor is being insulated with thin high-performance vacuum insulation panels, protected from puncture by thin steel sheets. Much design development and analysis has been carried out to arrive at the solution for the roof. This is a hybrid solution with the outer parts of the roof insulated at loft level, and the central part insulated at rafter level. This creates excellent storage space within the thermal envelope of the building, which is warm in winter and cool in summer. For the insulation at rafter level, existing roof tiles have been taken up to allow the fitting of insulation on top of the rafters, as well as between and below them. Natural insulation materials of rigid wood fibre and flexible hemp-flax quilt have been used. These have low embodied energy, good sequestration of CO2, relatively high thermal mass and good moisture vapour permeability – an important consideration given the provision for drying wet clothes.

Existing double glazed windows are replaced with high performance triple glazed windows with thermally-broken wooden frames. These incorporate an openable side panel with fixed louvers to provide a secure means of ventilation at night and during the day, when the house may be unoccupied. Average U value of the windows is 0.84 W/m2K.

Other alterations

A short mezzanine is provided within the lightwell adjacent to the clothes drying space which provides access to a small plant room containing solar power equipment and to the loft storage spaces. The mezzanine is accessed from a fixed space-saver stairs from the first floor landing. The space under the stairs can provide for a small home office space with desk and computer.

The creation of the solar ventilating lightwell above the stairs has brought a transformation to the centre of the house, using space and daylight.

The upper raised part of the front roof supports an array of six solar photovoltaic panels. The upper raised part of the rear roof supports two large solar thermal panels. This leaves the lower retained parts of the roof intact and free from solar panels.

Other energy saving measures

Other measures include flue gas heat recovery, single point mechanical ventilation with heat recovery to the kitchen and bathroom, low energy lamps and light fittings, low energy appliances and standby energy savers. A proposed waste water heat recovery system has been omitted due to insufficient mains water pressure.

Energy targets

The overall project is predicted to achieve the target 80% cut in CO₂ emissions compared with the average for a standardised house in 1990.

Total primary energy use (predicted by SAP 2009) = 84 kWh/m2.yr

Total CO2 emissions (predicted by SAP 2009) = 16.6 kg/m2.yr

Week 11 - December 2010. The house is a mid-terrace three bedroom house on the Windsor Park Estate in the Docklands area of London, built in 1992. Scaffolding is required to replace the windows externally and carry out works to the roof, installing roof insulation and solar panels.

Week 1 - October 2010. Commencement of retrofit works. The front wall will be insulated internally, to respect the external appearance of the house and character of the estate.

Week 3 - October 2010. Installation of thin high-performance insulation to the suspended concrete ground floor, using ‘Nanopore’ vacuum insulation panels overlaid with cellular foam sheeting and steel sheets for puncture protection.

Week 4 - November 2010. Injection of cavity wall insulation into the un-filled cavities of the party walls, through an array of small holes drilled into the walls.

Pre-Retrofit - Spring 2010. Ceiling and loft hatch above stairs. The stairs are in the centre of the house in a dark, window-less space.

Week 11 - December 2010. Equivalent view above stairs after removing ceiling and forming solar ventilating lightwell with large rooflight in the centre of the house. A transformation with space and daylight.

Week 8 - November 2010. Existing roof tiles have been removed to allow installation of rigid wood fibre insulation on top of the existing rafters.

Week 9 - December 2010. Step in roof level resulting from adding insulation on top of the existing rafters.

Week 11 - December 2010. Inside the loft waiting for delivery of the hemp roof insulation. Hanging metal brackets will support the insulation quilts installed below the rafters.

Week 33 - May 2011. The Retrofitted house in the terrace. The alterations are deliberately unobtrusive.

Week 15 - January 2011 - The new triple glazed windows are finally delivered and fitted. The windows have an openable side panel for extra ventilation in the summer months. Fixed metal louvers will maintain security when they are left open.

Week 17 - February 2011. Photovoltaic solar panels on the front roof pitch, facing east. Photo shows linear ventilator for the ‘breathing roof’.

Week 19 - February 2011. More work required to the kitchen! The residents have been living in the house throughout the Retrofit!

Week 20 - March 2011. Solar thermal panels to the rear roof pitch, facing west. Photo shows rooflight with automatically opening vents.

Week 26 - April 2011. The mechanical ventilation unit with heat recovery has been fitted above the cooker in the kitchen. Photo shows unit and ducts with boxing-out removed.

Week 27 - April 2011. Rear wall of house showing new insulated render and triple glazed windows, now with secure ventilation grilles fitted.

Week 27 - April 2011. Fixed security grilles have finally been fitted over the ventilator panels next to the windows. These grilles provide for secure ventilation day and night. Resident very pleased to have these in time for the April heatwave.