The river comes first, then the drawings
Kent County Council's flood study for the borough, from 2017, says Dartford is mainly at risk from the tide, pushing up the Thames and Dartford Creek, with the Darent and the Ebbsfleet adding river risk inland. It counted 2,274 homes at tidal or river risk, 307 of them at medium to high risk. Most of the serious cases sit on the west side of town, where the Darent meets Crayford Creek near the A206. Greenhithe and Swanscombe have over 900 homes in the count, mostly behind the Thames defences at Ingress Park and Swanscombe, at risk only if those defences fail or are overtopped. Further south the Darent itself is the threat, through Sutton-at-Hone, Darenth and Hawley.
Why should a kitchen extension care? Dartford's own validation list asks for a flood risk assessment with any application in Flood Zone 2 or 3. For a householder job that's normally the Environment Agency's short standing advice form. It expects the new floor to sit at least 600 millimetres above the estimated flood level, or flood-resistant construction up to that height. A raised floor changes the step down into the garden, so check the flood map for planning before anyone draws a thing.
No design guide, so M10 does the work
Many councils publish a householder guide with a 45 degree line and set distances to the boundary. Dartford doesn't. None of its supplementary planning documents deals with house extensions. Planners fall back on Policy M10 of the Dartford Plan, adopted in 2024.
In plain terms M10 asks whether the addition respects the way the street was laid out, whether it looks bolted on, and whether the people next door lose light, privacy or outlook, or gain noise and cars parked outside. It also refuses schemes that eat an unacceptable amount of garden. That last test matters on the narrow plots of the town terraces, where a deep rear addition plus a garden room can leave very little lawn. A neighbour's kitchen window is what an officer will look at first. Draw the shadow before you draw the bifolds.
If your extension swallows a garage or a drive, expect the officer to ask where the cars go.
Estates where the rights have already gone
The council's householder page carries a warning many owners miss. Some properties built after 1990, and some in the Green Belt, had their permitted development rights taken away when they were approved. On those houses even a modest single-storey rear room needs an application. The council's planning admin team will check a property if you ask, and a lawful development certificate, drawn up with full plans, gives you something in writing for a future buyer.
Green Belt covers just over half the borough, including large stretches around Joyden's Wood and Longfield. Policy M12 allows an extension there if it stays proportionate and subservient to the original building. There's no percentage cap. It's a judgement against the original house, so earlier additions count against the next one.
Which type suits which Dartford house
Each type below links to a full guide.
Single-storey rear. The first choice for most owners. Outside the conservation areas a semi or terrace can go 3 metres past the original back wall without applying, or 4 metres on a detached house, and 6 or 8 metres through the council's prior approval scheme. Check first that your rights weren't removed when the estate was built.
Side return. Suits the older terraces around West Hill, where most houses went up after the railway arrived. Any guttering or footing that crosses onto the neighbour's side takes it out of permitted development, and a party wall notice is likely.
Kitchen. On the low ground near the Darent and the A206 the floor level may be set by the flood assessment rather than by the old house. Plan the glazing and the step around it.
Open plan. Removing the back wall needs a steel beam on new pads. Dartford ground ranges from chalk to Thanet Sand to soft river alluvium, so let the engineer see the trial holes before sizing them.
Wrap-around. Best on the semis that make up over 40% of homes in Wilmington and Joyden's Wood, where there's often room down the side. The side leg always means a planning application.
Two-storey. Always an application in a conservation area. Elsewhere M10's daylight and privacy tests decide it, and in the Green Belt the proportionate test bites hardest on this type.
Ground-floor bedroom. A good fit for the detached houses common in Longfield and Southfleet, where a parent can move in without stairs. In a flood zone, keep the bedroom on the raised floor.
Home office. Attached is warmer and easier to wire. A separate cabin on a small town garden can fall foul of M10's garden land test if it needs permission.
Planning. In the six conservation areas there are no permitted side extensions, no permitted rear extensions over one storey and no cladding. In the Ebbsfleet garden city area, applications go to the Development Corporation rather than the borough.
Cost and value. We don't print prices. A raised flood-zone floor, a denehole found in a trench or deep footings near trees can all move the figure. Get builders to see the site.
Old chalk pits under the gardens
North-west Kent was mined for chalk long before anyone built semis on it. Kent's historic environment record notes that Joyden's Wood alone may once have held over a hundred deneholes, and that many have since collapsed. It estimates about 200 across the wider Dartford area, most now blocked up.
An extension trench is exactly where one turns up. If the digger hits loose fill or a void, stop and call building control before pouring concrete. The fix is usually a deeper or bridged foundation, and it's far cheaper found early than after the walls are up.
Where these facts come from
- Flood risk to communities in Dartford, 2017 (Kent County Council)
- Local list of validation requirements, 2024 (Dartford Borough Council)
- Householder development (Dartford Borough Council)
- Supplementary planning documents (Dartford Borough Council)
- The Dartford Plan 2024 (Dartford Borough Council)
- Larger household extensions prior notification (Dartford Borough Council)
- Joyden's Wood deneholes, MKE975 (Kent Historic Environment Record)
- Flood risk assessment standing advice (GOV.UK)
- Permitted development for householders, technical guidance (GOV.UK)
- Ebbsfleet Development Corporation (GOV.UK)
How FirQuote works in Dartford: We connect you with local specialists who visit your property before giving you a price. You get up to 3 written quotes — no call centres, no estimates from photos, no obligation to accept any quote.
Questions people in Dartford ask
We're in Greenhithe near the river. Does the Thames barrier mean we can skip the flood assessment?
No. If the house is in Flood Zone 2 or 3 the council's validation list asks for one regardless of the defences. The county study says the risk there comes if the defences fail or are overtopped, which is why the floor level question still gets asked.
Our house was built in the 1990s. Can we just build a back extension?
Maybe not. The council says some post-1990 homes had permitted development rights removed when they were approved. Read the original permission or ask the planning admin team before you commission drawings.
We live in the Green Belt near Longfield. Is there a size limit?
There's no fixed percentage. Policy M12 asks that the extension is proportionate and subservient to the original building, so earlier additions count. Pre-application advice is worth paying for on a big scheme.
Is there a Dartford rule on how close to the neighbour I can build?
Not a published number. With no householder design guide, officers judge each scheme under Policy M10 on light, privacy and outlook for the neighbours. A shadow study on the drawings helps your case.