House Extension Forest Hill SE23 Above a Canal Nobody Remembers
Lewisham’s conservation area appraisal contains a sentence most people in SE23 have never read. Havelock Walk, it records, was built along the line of the former canal in the early 1860s, and provides an interesting example of former industrial warehouses converted into residential and workshop uses. The nineteenth century granite paving is still there. A canal ran through Forest Hill, was filled in, and a street was laid on its bed.
That is the kind of thing this area keeps quiet. On the surface it is a hilly Victorian suburb of substantial villas and terraces climbing towards the Horniman Museum, with later Edwardian and inter-war houses on the higher ground. The land reaches a hundred and six metres. Around fifteen thousand people live here across not quite two square kilometres, which makes it the least crowded ground in this part of south London. Owner occupation runs at just over forty-seven per cent, the average age is thirty-six, and a quarter of residents are under eighteen.
Underneath, it is one of the most heavily designated postcodes in Lewisham. Four separate conservation areas reach into SE23, the largest of them carrying an Article 4 direction across the whole of its forty-five hectares. There is a selective licensing scheme covering the ward. And there is a four hundred member amenity society that reads the applications and quotes national policy back at the council. Design And Build works throughout SE23, and every discipline the job calls for is on our own staff.
On a slope, not a plot: house extension Forest Hill
Havelock Walk and the canal it was built on
Start with Havelock Walk because it explains the rest. A canal bed is made ground: material tipped into a channel and levelled, rather than soil that has been sitting undisturbed since the last ice age.
It behaves differently from undisturbed soil under load, and its depth changes along the old channel rather than evenly across a site. The warehouses beside the walk were built for storage, converted later for living and working, and the appraisal notes modern materials used alongside the originals to produce idiosyncratic elevations. Anything touching foundations near that line wants a proper ground investigation rather than an assumption.
Level changes, overlooking and 106 metres
The hill is the defining constraint on almost every SE23 project. Gardens fall away behind houses, or rise steeply above them, and both cause the same argument at the council.
On falling ground an addition needs stepped footings and often a retaining structure along one flank, with considerably more spoil taken off site than a level plot would produce. On rising ground the problem inverts into overlooking: a raised floor level or a first floor window looks straight into the garden behind. Before any depth or finished floor level is fixed, our engineers take levels right across the plot — on a hillside those two numbers drive the price more than anything else.
Surface water where the water used to be
Water still finds the low ground. Parts of SE23 record meaningful surface water flood risk, and the streets near the old canal line are among them.
It affects where a soakaway can go, what the drainage strategy has to show, and occasionally whether a scheme needs a flood risk assessment with the application. Check your own address on the national flood risk map. It takes a minute, and being high up on a hill does not settle the question the way people assume.
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Builders Forest Hill and 45 hectares of designation
The whole area, not just part of it
The Forest Hill conservation area was designated in 1976 and extended in 1994 and again in 2010. At about forty-five hectares it is the fifth largest in the borough, and an Article 4 direction applies across the whole of it.
That is broader than most. Windows, doors, roof coverings and comparable external changes all need permission inside the boundary, where the same work a street away might need none. Lewisham publishes the boundary street by street, and the phrase to watch is parts of — Dartmouth Road, Devonshire Road, Ewelme Road, Taymount Rise, Thorpewood Avenue, Westwood Park and Waldram Crescent are all in it only partly. Benson Road, Clyde Vale, David’s Road, Havelock Walk, London Road, Manor Mount, Pearcefield Avenue and Waldenshaw Road are in entirely.
Cobbs Corner, ten properties in two terraces
SE23 holds the fifth largest conservation area in Lewisham and the smallest one in the borough at the same time.
Cobb’s Corner was designated in 1975 and comprises ten properties in two terraces. Ten. The controls that apply inside it are the same controls that apply inside a forty-five hectare designation, which is a useful thing to know if your house happens to be one of the ten and your neighbour’s, forty metres away, is not.
Mount Ash Road carries a separate one
The Sydenham Hill and Kirkdale conservation area was designated in 1976 and divides into three character areas: Mount Gardens, Mount Ash Road and Lammas Green. A separate Article 4 direction applies to Mount Ash Road alone.
Lewisham describes it as a unique example of Victorian byelaw housing designed as a set piece of identical three-storey terraces enclosing the road on both sides. Identical is the operative word. On a street built as one composition, an alteration that would pass unnoticed elsewhere reads as a break in the run.
Perry Vale, Christmas Estate and the fourth designation
A fourth conservation area, Perry Vale and Christmas Estate, reaches into SE23 as well. Applications on Sunderland Road and Gaynesford Road are determined under it.
So four designations touch one postcode, each with its own boundary and its own emphasis, and none of them is announced on the pavement. Establishing which reaches a specific address is the first thing we do, and it takes minutes rather than meetings.
Design and build Forest Hill, and the statement that comes first
Setting counts, even when your house does not
Lewisham’s requirement is worth quoting because of how far it reaches. A heritage statement is required for all planning applications affecting buildings in conservation areas and listed buildings, both nationally listed and locally listed, including applications affecting the setting of a building.
Setting. Your own house need not be listed, and need not even be inside a conservation area, for the requirement to bite. If the work affects how a designated building is seen, the statement is required. Applications on Devonshire Road have been published under the heading adjacent to conservation area for exactly that reason. Our architects prepare the heritage material alongside the drawings rather than bolting it on afterwards.
A society that checks the HMO register
The Forest Hill Society covers SE23 and has around four hundred members, and its objections are not the usual complaints. They are written in policy language.
On one Dartmouth Road application the society argued the proposals would result in harm to the significance of the conservation area through the loss of features which contribute positively, that this harm would be considered less than substantial, and that it should be weighed against public benefits. That is the national policy test, applied correctly. On another they noted there was no record of a previous application for the change of use, and that the property was not registered with Lewisham as a house in multiple occupation. They check the register. A scheme that anticipates that scrutiny rarely has trouble with it.
House renovation Forest Hill where one house became four
Converted flats that never met the regulations
Most of the big villas here were carved up decades ago, and one particular kind of conversion carries a licensing consequence buyers rarely hear about.
Lewisham’s additional licensing catches buildings converted into self-contained flats where fewer than two thirds are owner occupied and the conversion did not comply with the building regulations in force at the time and still does not. That is a description of a great deal of 1970s and 1980s work. If you are buying into a converted Forest Hill villa, whether the original conversion was done properly is a question with a licensing answer as well as a structural one.
Offices becoming flats on Dartmouth Road
The conversions happening now run the other way round. On the commercial spine the pattern is offices and shops becoming homes rather than houses being subdivided.
Recent applications cover an office at first, second and roof level on London Road becoming two flats with a new shopfront below, a Class MA prior approval turning offices on Clyde Terrace into two flats, and a roof-level addition on Dartmouth Road creating a flat above a retained one. One went further and converted a garage and two floors into a single dwellinghouse with a courtyard. Interior design belongs in that conversation early, because a commercial shell has none of the things a home needs.
Construction company Forest Hill, and the licence nobody mentions
Selective licensing since July 2024 [H3]
This one surprises people. Forest Hill sits in Lewisham’s selective licensing designation three, alongside Bellingham, Downham, Grove Park and Whitefoot. The scheme began on 1 July 2024 and runs for five years.
Selective licensing is not about houses in multiple occupation. It applies to a privately rented property occupied by a single household or by two unrelated sharers, which is to say an ordinary let. If you are renovating to let, or converting and letting on, the licence is part of the job rather than an afterthought, and the standards attached to it shape the specification.
Every trade we need is already employed [H3]
Add it up and an SE23 project can involve one of four conservation areas, an Article 4 across the whole of the largest, a heritage statement reaching to setting, a hillside site, made ground near an old canal, a licensing regime and an attentive amenity society.
Those are not seven separate appointments. The survey, the drawings, the heritage material, the engineering and the build sit inside one construction company. Surveyors on our own staff handle the Party Wall etc. Act 1996, we lodge with Lewisham ourselves, and where a scheme turns out to need no permission a lawful development certificate records it.
Area We Cover
Which SE23 street, and which designation?
Those two answers do most of the work. The street decides which of the four conservation areas reaches you, whether the Article 4 applies, and how far the ground falls. Everything else follows from them.
Send the address and back comes the position on all of it: which designation applies, what the direction removes, whether a heritage statement is needed, what the slope and the ground will demand, and whether permitted development is still available. We cover Forest Hill and SE23 — Dartmouth Road, Devonshire Road, Havelock Walk, Taymount Rise, Waldram Crescent, Wood Vale, Honor Oak and Perry Vale — along with Sydenham, Catford, Brockley, East Dulwich and the surrounding SE districts.
The survey costs nothing. On this hill it begins with the levels and the boundary map.
