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London is looking hard at the space above its existing buildings. A pattern book for roof extensions and a new small sites design code could make the principle easier to agree. The detail will still come down to a good rooftop extension survey of the building you’re adding to.
London has been extending upwards for centuries. Mansards, loft conversions, an extra storey on a terrace: the city’s homes have never really stood still. What’s new, however, is the level of interest from City Hall.
Recently, the London Assembly’s Planning and Regeneration Committee wrote to the Mayor about it. As reported by the Architects’ Journal, it asked the GLA to produce a pattern book for upward extensions. The idea is simple: set out what an acceptable rooftop addition looks like, and let boroughs apply or adapt it. The committee pointed to estimates that London could add somewhere between 140,000 and half a million homes on top of existing residences. In fact, Tower Hamlets and Haringey already have borough codes that do something similar.
At the same time, the GLA has published a draft Small Sites Design Code, written with RCKa and open for consultation until 4 December. If an infill or small redevelopment scheme meets its criteria, planners treat its design as acceptable in principle. That clears the first planning hurdle. It covers conservation areas too, and applies wherever a borough doesn’t already have its own small sites framework.
A CODE BUILT ON DIMENSIONS
The small sites code works in three layers. First, the site type: twelve of them, grouped as infill, redevelopment and reconfiguration. Then the character context: suburban, terraced, high street or flatted. Finally, dimensional parameters for each combination, such as the number of storeys and a privacy zone between neighbouring homes.
For us, though, that last layer is the interesting one. When acceptability comes down to set distances and heights, the numbers on your drawings have to be right. A boundary in the wrong place or a neighbour’s window that isn’t shown can turn a compliant scheme into a non-compliant one.
For architects, that could mean less time arguing the principle of an extra floor and more time on the design itself.
WHY DELIVERY HAS STALLED
However, the committee was frank. Despite all the policy support, delivery has been low. It put that down to risk. Building regulations have tightened, especially with the post-Grenfell reforms. On top of that, building over something that’s already there, often with people living in it, brings real technical and financial uncertainty.
The architects quoted by the AJ added their own concerns. Some worried a looser regime could produce poor additions. Others pointed out that roof space quickly fills up with plant, ventilation and outdoor amenity once you take energy and comfort seriously. We also know existing residents rarely welcome building work above their heads.
A pattern book alone won’t solve those problems. However, every one of them gets easier when you properly understand the existing building from day one.
WHERE A ROOFTOP EXTENSION SURVEY EARNS ITS KEEP
A design code tells you what’s allowed. A measured survey tells you what you’ve actually got. On a rooftop scheme, the gap between the two is where projects go wrong.
- Roof and parapet levels – Codes are likely to set heights relative to the existing building and its neighbours. That needs accurate levels on Ordnance Survey grid and datum, not a guess from old drawings.
- The street, not just the building – Elevations of the neighbouring properties show how an extra storey sits in the streetscape, which is what a pattern book will judge it against.
- Boundaries and neighbours – On infill sites, a topographical survey picks up boundaries, levels, trees and the windows and heights of adjoining homes. So you can test a scheme against privacy distances and storey limits before it goes in.
- Hard-to-reach roofs – Our drone surveys capture flat roofs, mansards and chimneys safely, without scaffolding.
- Inside the building too – Floor-to-floor levels, stair cores and structure all shape what can go on top. A 3D Revit model at the right level of detail gives the whole team one version of the truth.
- Occupied buildings – Post-war, flat-roofed estates are an obvious candidate for adding homes. Surveying them means working around residents. Our teams regularly work in live hospitals, schools and occupied offices, so a block of flats with people at home is familiar ground.
Setting up a total station on a central London roof to capture precise measurement data
WHAT THIS MEANS FOR YOU
If you’re an architect looking at upward extensions or small infill sites in London, the planning picture may be about to get clearer. The building itself won’t. That’s why starting with reliable data on the existing structure, roof and street takes a lot of risk out of the job, even before the first sketch.
“Clearer rules on what can go on a roof or a small site are good news for architects and for tackling the housing crisis in London. But a code can only be applied to the building as it really is. Old drawings and assumed levels are where rooftop schemes come unstuck. Get an accurate picture of the building, the roof and the neighbours at the start, and the design conversation gets a lot simpler.”
Claire Fenwick
Managing Director, Spatial Dimensions, and President of The Survey Association
Our permanent in-house teams have been measuring London’s buildings since 2012, from our London office on Westminster Bridge Road and our head office in Sevenoaks. Our managing director, Claire Fenwick, is President of The Survey Association and a Fellow of CICES. Good survey practice matters to us well beyond our own jobs. If you’ve got a rooftop or infill scheme coming up, give the London team a call on 020 3409 1937 or email london@spatial-dimensions.co.uk.
Not sure what level of detail you need? Our guide to level of detail in 2D measured building surveys is a good place to start.