Planning a retrofit for a London period property

London has a very old housing stock. In Kensington and Chelsea around 65% of properties were built before 1919 – the highest proportion of any local authority in England and Wales – and several other inner boroughs, including Hammersmith and Fulham and Haringey, exceed 50%. Improving these homes is possible, but the approach needs to suit how they were built.

How period homes differ

• Solid walls. Most pre-1919 houses have solid brick walls rather than cavity walls. These walls take up and release moisture, and insulation must allow for that.
• Suspended timber floors. Ground floors are often timber over a ventilated void. They can be very draughty, but the void ventilation must be kept working.
• Timber in walls. Floor joists often bear into external walls. Insulating internally can make those joist ends colder and wetter if the detail is not designed.
• Sash windows and chimneys. These provide character and, often, unplanned ventilation. Changing them affects both heat loss and air quality.

Start with the right order

1. Fix repairs first – roofs, gutters, pointing and leaks. Insulating a wet wall makes problems worse.
2. Understand the building through an assessment.
3. Reduce uncontrolled draughts while planning adequate ventilation.
4. Insulate where it is lowest-risk and most effective – often lofts and floors before walls.
5. Design wall insulation carefully, with junctions checked.
6. Size the heating system once fabric improvements are known.

Planning, conservation and consent

Rules depend on the property and the borough. For example, Islington Council’s checklist explains that external wall insulation on a house can sometimes be permitted development, but that flats and maisonettes need planning permission, and that conservation areas and Article 4 directions can remove those rights. Listed buildings need listed building consent for works affecting their character, including many internal changes.

Some areas also have private estate controls in addition to planning, such as the Dulwich Estate Scheme of Management (Southwark) and the Hampstead Garden Suburb Trust (Barnet).

Leasehold flats

Many period houses are divided into flats. The lease usually decides who owns the external walls, roof and structure. Insulating walls or replacing windows may need the freeholder’s consent, and some measures work best when the whole building is treated together.

Choosing wall insulation

Where external insulation is not acceptable on a street elevation, internal insulation may be considered. Materials that manage moisture – often described as vapour-open or capillary-active – are commonly used on solid walls, but suitability depends on the wall’s exposure and condition. Junctions with floors, party walls and windows should be checked; temperature-factor (fRsi) modelling is one way to do that.

Ventilation is part of the plan

As draughts are reduced, deliberate ventilation becomes more important. A ventilation strategy should be in place before or alongside airtightness improvements, so that moisture from cooking, bathing and breathing is removed.

Sources and further reading