Retrofit in Lewisham: transforming the borough's Victorian terraces

Most of Lewisham was built between 1880 and 1930. Those Victorian and Edwardian terraces, the long streets of Forest Hill, Brockley, Catford and Hither Green, are some of the most robust buildings in London, structurally solid and full of character. They are also, by modern energy standards, significant carbon emitters, with solid walls, single-glazed windows and uninsulated floors that leak heat throughout the colder months.

Retrofit is the process of improving those buildings to perform better. Done well, it reduces energy bills, improves comfort and dramatically cuts carbon emissions over the lifetime of the building. Done poorly, it can cause moisture problems, damage historic fabric and leave a building worse off than before. The difference is almost entirely in the quality of the thinking that goes into it.

Why Lewisham's housing stock is ideal for retrofit

Solid brick construction is actually one of the better starting points for retrofit, because the walls have a degree of thermal mass that helps regulate internal temperatures. The challenge is that solid walls cannot be insulated in the conventional way, by filling a cavity, because there is no cavity. The options are either internal wall insulation, which reduces floor area slightly but is highly effective, or external wall insulation, which changes the external appearance and requires planning permission in conservation areas.

New Makers Bureau's preferred approach in Lewisham's conservation areas is internal wall insulation using breathable materials, wood fibre boards or hemp, that allow moisture to move through the wall rather than being trapped. Combined with floor insulation beneath existing boards and careful attention to draughts and cold bridges, this can make a very significant difference to how a Victorian terrace performs.

The carbon case for improving rather than replacing

A Victorian terrace in Lewisham contains a large quantity of embodied carbon in its brickwork, its timber structure and its foundations. Demolishing it and replacing it with a new building, however energy-efficient, releases all that carbon immediately and then spends more carbon building the replacement. The carbon debt can take decades of operational savings to pay back, if it ever does.

Retrofit conserves that existing carbon investment and improves the building's operational performance. For most Lewisham terraces, whole-house retrofit is the option that makes the most sense on carbon, on cost and on planning grounds.

What a retrofit project looks like in a Lewisham terrace

A typical whole-house retrofit in a Lewisham Victorian terrace involves several overlapping interventions: internal wall insulation to the main elevations, insulation below the ground floor boards, loft insulation or a new insulated roof if there is a loft conversion planned, high-performance secondary or replacement glazing, and draught-proofing throughout. These are combined with improved ventilation, either through mechanical heat recovery or carefully designed passive ventilation, to ensure that the improved airtightness does not lead to condensation or air quality problems.

New Makers Bureau approaches retrofit projects as a whole, designing the complete strategy before starting any part of it. Piecemeal improvements that have not been thought through together often create problems that cost more to fix than they saved.

Planning for retrofit in Lewisham's conservation areas

Most internal retrofit work does not require planning permission. Where external changes are proposed, such as external insulation, new windows or roof works, the conservation area rules apply. Lewisham's conservation officers are generally supportive of energy performance improvements, provided the external appearance of the building is not compromised. Secondary glazing, which sits behind existing sash windows without replacing them, is usually acceptable and performs very well thermally.

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