House
extensions
in Holborn, WC1

Holborn has few houses. Camden's Kingsway statement describes its area as predominantly commercial with little residential use, and in the Great James Street and Bedford Row sub-area offices dominate the main streets, although some homes remain, particularly in Millman Street. An extension here is usually to a house in one of those surviving groups.

The appraisal traces a progression in scale and grandeur from Millman Street, through Great James Street, to Bedford Row. Nos 3 to 16 Great James Street are listed Grade II* with their railings, so a rear addition there needs listed building consent, which is separate from planning permission.

These streets are covered by the Bloomsbury appraisal, which says rear extensions will not be acceptable where they would compromise the original pattern of rear elevations. Small, low additions that leave the back wall readable stand a better chance than full-width ones.

Ely Place forms a quiet enclave of 18th-century terrace houses, mostly Grade II, where the original plot widths and building heights are mostly intact. Keeping them intact is the starting point for any change at the back.

Millman Street mixes later 20th-century housing with late 19th-century terraces of the Rugby Estate, the appraisal notes, so what can be added at the back depends on which kind of house you own and what its neighbours are.

Conservation area designation also gives Camden greater control over the removal of trees. In the small yards and gardens behind Holborn's terraces, a tree can decide the footprint of an extension, so its position and roots are surveyed before the design starts.

Camden's Kingsway statement asks for careful consideration of the impact of schemes on residential amenity where homes sit close by, as on Newton Street. The windows, roof and plant of a rear addition are placed with the outlook of neighbouring homes in mind.

In the Hatton Garden area the characteristic materials are red brick, London stock brick and Portland stone, with slate for roofs, and a rear addition there is detailed in those materials so it belongs to its building.

On the most intact Georgian streets, such as Doughty Street, an addition at the back is judged most closely against its group.

In Holborn's Georgian streets the back walls may have been altered by earlier office uses, with fire escapes, plant and pipes; an extension is a chance to clear those and return the rear elevation to something closer to its original form.

Around Lamb's Conduit Street, small independent shops and a pedestrianised stretch make for a lively townscape, Camden's appraisal says. For a house nearby, we check the depth of the yard and the light reaching neighbouring windows before suggesting any rear addition, because the plots are tightly packed.

For related work outside Holborn, see Belsize Park Gardens, NW3: a whole-house project in Belsize Park, NW3, whose scope included the loft, the basement and an extension. We point to it because the work is comparable; the project itself is outside Holborn.

Party walls in a Georgian terrace are old and sometimes thin. Before an extension is drawn, the engineer checks how its foundations and roof will bear on them and what the neighbours' side of each wall needs.

Access is the practical constraint: deliveries and spoil go through the house or a rear yard, so we plan both, and serve party wall notices on both neighbours, before work starts.

Sources: Camden Council: Kingsway conservation area statement (December 2001) ; Camden Council: Bloomsbury conservation area appraisal and management strategy (adopted 18 April 2011) ; Historic England: Nos 3 to 16 Great James Street and attached railings, list entry 1113197, Grade II* ; Camden Council: listed buildings ; Camden Council: Hatton Garden conservation area appraisal and management strategy (August 2017).