The council still works from a 2004 guide
Ashford Borough Council decides extension applications under policy HOU8 of the Local Plan 2030, adopted in February 2019. Officers' reports still lean on an older document too: Supplementary Planning Guidance Note 10, Domestic Extensions in Urban and Rural Areas, published in June 2004. Read it before anyone draws a line. It's short, and it tells you how your neighbour's light will be judged.
Two tests do most of the work. For the 45 degree code, the planner draws a line from halfway across your neighbour's nearest habitable room window, and the extension shouldn't cross it. The 25 degree code looks at the same thing in three dimensions. A single-storey extension that stays under a 25 degree plane rising from that window is usually fine. A two-storey one that breaks it usually isn't. The guide calls both guidelines rather than fixed rules, and a secondary window, such as a small side light to a kitchen, doesn't count.
There's no fixed maximum depth for a rear addition in the guide. What it does insist on is that every extension stays subordinate to the house it's attached to. Two-storey additions should have pitched roofs. Flat roofs on two storeys, flat roofs in prominent spots and fake pitched roofs are normally refused. On materials it asks for clay tiles, slate and stock facing brick wherever possible.
Clay, rivers and what goes under the footings
The ground changes as you cross town. Kennington, on the north side, sits on Gault Clay, and the British Geological Survey rates most of the Gault outcrop in its very high category for shrink and swell. It also warns that the clay can carry sulphates that attack concrete. Down by the rivers in the south of town it's Weald Clay under alluvium, impermeable and slow to drain. Either way, expect building control to look hard at foundation depth, and tell your builder about any big trees near the line of the new wall.
Then there's water. Five main rivers meet at Ashford, the Great Stour and East Stour among them, and Kent County Council counts 1,571 properties in the town at some risk of river flooding, even with the Aldington and Hothfield reservoirs in place. If your house is in Flood Zone 2 or 3, an extension application needs a flood risk assessment. The Environment Agency's standing advice for minor extensions covers it, and it will push you towards a raised floor or flood-resilient finishes on the new part. Check the flood map for planning before you pay for drawings.
Which kind of extension suits which Ashford house
Here is how each type sits with local houses and local rules. The full guides go deeper.
Single-storey rear. The usual starting point on the semis and detached houses that make up nearly two thirds of the borough. Outside a conservation area you can go 3 metres from the original back wall on a semi or terrace, or 4 metres on a detached house, without applying. Going out to 6 or 8 metres needs prior approval, and the council asks the neighbours first.
Side return. Made for the narrow Victorian and Edwardian houses on streets like Kent Avenue and Sussex Avenue. Those sit in the Queens Road conservation area, though, where any side extension needs planning permission. Expect a party wall notice too.
Kitchen. On a north-facing garden the glazing decides whether the room works. Roof lights over the island bring in light without adding overlooking, which the 2004 guide is wary of.
Open plan. Knocking the old back wall out needs a steel beam, and on Gault Clay the pads that carry it need proper design. Ashford's building control team has its own structural engineer checking the calculations.
Wrap-around. An L-shape around the back and side always needs a planning application, because the side part takes it outside permitted development. It suits a semi with a wide side path and a deep garden.
Two-storey. This is where the 25 degree code bites. On a street of detached and semi-detached houses, the council will also look at the gap you leave to the boundary, because filling every gap turns a row of semis into a terrace. Keep the roof pitched.
Ground-floor bedroom. Plenty of families build one for a parent. Attach it to the house and HOU8 applies. Build it separately in the garden and policy HOU9 expects it to stay clearly ancillary and dependent on the main house, so it can't quietly become a second home.
Home office. Hybrid workers who take the high-speed train to St Pancras on office days still need a proper desk on the others. Attach the room to the house and it shares the heating and the broadband, with a door you can shut.
Planning. In any of the borough's 43 conservation areas, side extensions and rear extensions of more than one storey need permission, and cladding is out. Those same limits apply in the Kent Downs and High Weald National Landscapes. Some estate consents also remove permitted development, so read the conditions on the planning register first.
Cost and value. We don't publish prices. Foundations on shrinkable clay, flood-resilient floors and a steel for open plan can each move the figure a long way. Get builders round to look at the plot. Their quotes will tell you more than any average.
Where these facts come from
- Ashford Borough Council: SPG10 Domestic Extensions (2004)
- Ashford Borough Council: planning guidance and SPDs
- Ashford Local Plan 2030
- British Geological Survey: Gault Formation
- Kent County Council: flood risk to communities in Ashford
- Environment Agency: flood risk standing advice
- GOV.UK: householder permitted development technical guidance
- Natural England: Stodmarsh nutrient neutral methodology
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Questions people in Ashford ask
My neighbour's kitchen window faces my side wall. Will that stop my extension?
Not on its own. Ashford's 2004 guidance applies its 45 and 25 degree tests to the nearest habitable room window, and it says secondary windows aren't suitable for those tests. If that kitchen has a main window elsewhere, the side one carries less weight. A planning officer makes the final call.
Is my house too close to the Stour to extend?
Rarely. Being in Flood Zone 2 or 3 doesn't rule an extension out, but the application needs a flood risk assessment. For a householder job that usually follows the Environment Agency's standing advice, with the new floor raised above the estimated flood level or built with flood-resilient finishes.
Do I need to worry about Stodmarsh for a granny annexe?
The nutrient rule is aimed at a net increase in the population served by a sewage works, such as a new home. Ashford's annexe policy already expects an annexe to stay dependent on the main house. If yours would be lived in as a separate home, ask the council about Stodmarsh before you apply.
We live in Kennington. Does the clay mean deeper foundations?
Quite possibly. North Ashford sits on Gault Clay, which the British Geological Survey rates very high for shrink and swell. Your building control surveyor will check the foundation depth on site, and nearby trees can push it deeper.