Ventilation & damp — Dulwich SE21, SE22
Ventilation in Dulwich, where the outside of the building is the hard part
The airflow is the easy half. In Dulwich the question that decides the job is where a terminal is allowed to go — because a great many properties here need consent from two separate bodies before anything appears on an elevation, and one of them is not the council.
Most ventilation work needs a hole in an outside wall, a soffit or a roof. In much of Dulwich that is not a question you can answer on the day, because a large part of the area sits under The Dulwich Estate’s Scheme of Management as well as inside a conservation area.
The Scheme of Management — the current version dates from November 1999 — requires freeholders to get prior written consent for alterations to the external appearance of a property. A louvre on a front elevation is an alteration to the external appearance. That consent is separate from, and in addition to, whatever the council requires, and the council here is not one council: Dulwich runs across Southwark, Lambeth and Lewisham, so the planning half depends on which side of a boundary the house sits.
On top of that, several of the conservation areas carry an Article 4 direction, which removes permitted development rights that would otherwise let minor external work go ahead without permission.
None of that makes the work impossible and none of it is a reason to live with mould. It makes the duct route a design decision taken before anyone quotes, rather than a discovery made with a core drill already in the wall.
How we route it so it does not become a planning problem
In order of how often it solves it. The aim is always the shortest run that meets the rate and lands somewhere nobody objects to.
Out of the rear elevation
The obvious answer and the right one more often than people expect. A rear elevation not visible from the street is a very different proposition from a front one, and a longer duct run to reach it is usually a far smaller problem than a consent application. It costs pressure, which is why the fan is chosen for the run rather than for the room.
Through the soffit rather than the face
A soffit terminal sits under the eaves overhang, looking down rather than out, and on most elevations it is close to invisible from the pavement. It needs the duct taken over the wall plate and down into a plenum in the eaves void — more work in the loft, nothing on the brickwork.
Reusing an opening that already exists
A redundant airbrick, a capped flue, an old extract hole from a kitchen that has since been moved. Working back to an opening already in the fabric avoids a new one entirely, which is the cleanest answer there is when consent is the constraint.
Matching the terminal to the elevation
Where a terminal genuinely has to be visible, the finish and the position are chosen for how they sit on the building as well as for what they move. We say up front where one will be seen from, with a photograph of the spot, before anything is agreed — because that is the thing that gets objected to later.
What we do not do is guess. We are a ventilation contractor, not your planning consultant, and we will not tell you what the Estate or the council will approve. What we will do is put the options in writing with the airflow consequence of each, so you or your architect can take the right one to them — and we design assuming the discreet route, because that is the one most likely to be agreed.
The buildings themselves
Dulwich stock is largely period and largely generous: Georgian and Victorian villas, later Victorian and Edwardian terraces and semis, and a good deal of substantial twentieth-century infill. Three things about it come up on nearly every survey here.
- Solid walls run cold. One brick thick with no cavity means the inside face sits below room temperature all winter, so it is the first surface moisture lands on — behind furniture, in corners, down window reveals. It is a surface temperature problem being fed by a moisture problem, and ventilation is the half of it that can be fixed without touching the fabric.
- The original ventilation has usually been removed. Chimneys capped, sash windows replaced or draught-sealed, floor voids blocked. Each was sensible on its own; together they took away the air change the house was designed around.
- Period features are in the duct route. Cornice, picture rails, deep skirtings, panelled doors and plaster ceilings that nobody wants opened. That is a real constraint on where a run can go and it is worked out on the survey, not on the morning.
Where a property has already been converted to flats — common on the larger villas — the wet rooms very often ended up in the middle of the plan with no external wall behind them. That single fact decides more of the cost than anything else, and it is the first thing we check.
Questions we get asked in Dulwich
Quite possibly, and there are two different permissions to think about rather than one. Being in a conservation area can mean an Article 4 direction applies, which removes permitted development rights that would otherwise let minor external alterations go ahead without planning permission. Separately, if the property is subject to The Dulwich Estate's Scheme of Management, that requires the Estate's own prior written consent for alterations to the external appearance — and a new louvre on an elevation is exactly that. The two are independent: the Estate's approval is in addition to whatever the council requires, not instead of it. We are not planning consultants and will not tell you what either body will approve. What we will do is design the route that needs the least, and set out the alternatives in writing so you can take the right one to them.
It is a scheme covering a large part of Dulwich under which freeholders must obtain the Estate's prior written consent before altering the external appearance of a property, changing its use, or carrying out works to trees. The current version dates from November 1999. Whether it applies to your particular property is a question for the Estate's Scheme of Management office rather than for us — it depends on the title, and it is one of the first things a conveyancer flags on a purchase, so it may well already be in your paperwork. The practical point for ventilation is simply this: if it does apply, budget for a consent step before anything is cut, and design the route on the assumption that the least visible option is the one that will get agreed.
In the large majority of cases, yes, and that is how we design here by default. The usual answers, in order of how often they work: out through the rear elevation, which is not visible from the street; through the soffit under the eaves, where the terminal looks downward and is close to invisible from the pavement; or back to an opening that already exists in the fabric, such as a redundant airbrick or a capped flue. Each costs something in duct length and therefore in pressure, which is why the fan is specified for the run rather than for the room. It is a design decision taken before anyone quotes, not a discovery made with a drill already in the wall.
It depends which part of Dulwich you are in, because the area spans three London boroughs — Southwark, Lambeth and Lewisham. That catches people out, particularly on roads near a boundary, and it matters because conservation area boundaries, Article 4 directions and local planning guidance are set by each borough separately. If you are unsure, the borough is the one that collects your council tax. Where the Scheme of Management also applies you are dealing with the Estate as well, whichever borough it turns out to be.
Yes, and listed buildings need it more than most — they are usually solid-walled, usually cold-surfaced, and have usually lost their chimneys and their draughts. What changes is that listed building consent is likely to be needed for work affecting the character of the building, inside as well as out, and that internal routing matters as much as the terminal. In practice that means favouring routes through voids, cupboards and service risers over anything that touches cornice, panelling or original plaster, and being willing to accept a longer run to avoid them. Bring us in early, alongside whoever is advising you on the consent, rather than after a specification has been written that cannot be built.
Yes, and that is exactly why it has to be designed rather than assumed. Every metre of duct, every bend, every grille and every insect screen takes something off what a fan can deliver — a unit rated 15 l/s on the box can be moving half that on a long run with two tight bends. The answer is not to give up on the discreet route, it is to specify for it: rigid or semi-rigid duct instead of concertina flexible, the shortest path the building allows, gentle bends rather than tight ones, and a fan chosen for the resistance it actually has to work against. Then we measure it at the grille when it is in and give you the figure in writing, so the compromise is proved rather than hoped for.
Not sure where to start?
Send us a message with what you have noticed at home. We will tell you honestly whether you need a survey, a system, or neither.
Or see what it costs — unlike most in this trade, we publish our prices.
Trained on the systems we install
Certificated — and here they are
Most trade sites show you a row of logos. These are the actual certificates, both sat in August 2026. Tap either one to read it, or download the PDF.
- 12-month workmanship guarantee On top of the manufacturer’s warranty, which we register in your name. If anything we installed fails because of the way we installed it, we come back and put it right. What it covers.
- Company no. 12092552 Registered in England & Wales. Trading as Cavalli Ventilation since July 2019, and in ventilation since 2003.
- Airflow measured on every install A calibrated anemometer at the grille, recorded and handed over. The only figure that counts is the one measured in your room.