Extension plans for a Sarratt house cost £645 drawings + £250 survey (£895 total) with us, fixed, from the measured survey to submission and the case officer's questions. Three Rivers District Council's householder fee of £548 is paid on top. What makes Sarratt different from almost anywhere else we work is that every house in the parish is in the Green Belt. So the first question is not how deep the extension can go, but how much the house has grown since 1948.
On this page
Is my Sarratt house in the Green Belt?
Yes. The Sarratt Neighbourhood Plan states that 100% of the parish is currently in the Green Belt (Sarratt Neighbourhood Plan). That covers the village around the Green, Church End, and the hamlets of Belsize, Chandlers Cross, Commonwood and part of Bucks Hill, about 2,600 people in all.
The council's revised Local Plan may change Green Belt boundaries in future, as the neighbourhood plan notes. Until a new plan is adopted, the current boundary applies.
How big can a Green Belt extension in Sarratt be?
National policy allows the extension of an existing building in the Green Belt provided it does not result in a disproportionate increase in size over the original building (NPPF Chapter 13, GB7(1)(b)). The original building is the house as it stood on 1 July 1948, or as first built if later.
Three Rivers' Policy DM2 says the same thing in local terms: extensions that are disproportionate, individually or cumulatively, will not be permitted. It adds three things the officer weighs: how close the house is to other buildings, whether it is or would become prominent, and whether the extension keeps the Green Belt open (DM Policies LDD). Neither document puts a percentage on "disproportionate". The council's older Green Belt guidance on floorspace, which DM2 refers to, is not something we have read, so we judge each case from the planning history and the numbers.
In practice that means:
- Earlier extensions count. A cottage enlarged in the 1970s and again in the 1990s may have little left to add. We separate the original house from every later addition on the survey.
- Outbuildings are judged separately. DM2 supports garden buildings only if clearly subordinate, not prominent, and without features of a dwelling such as dormer windows.
- The garden cannot grow into a field. Extending the residential curtilage into the countryside will not be supported.
- Replacement houses. A replacement must not be materially larger than the house it replaces; where the original is under 110 square metres, measured externally, it may be up to 110 square metres, excluding a garage.
We give the officer a floorspace table of the original house, the earlier additions and the proposal. It turns a judgement into a set of figures.
What does the Sarratt Neighbourhood Plan add?
The plan was made after a referendum in November 2025, and Full Council resolved on 9 December 2025 that it forms part of the development plan (Three Rivers, Sarratt Neighbourhood Plan). Three policy areas reach a householder extension:
- Policy 2, Design Principles. Proposals must take account of the Sarratt Design Code (January 2020), and a proportionate statement should go with any application showing how the code has been taken into account. For an extension that can be a page, but it needs to be there.
- Policy 3, Historic Character. Work in or affecting the Green and Church End conservation areas should conserve or enhance them, taking account of the 1994 appraisals, and keep the Green's open space.
- Policy 7, Landscape. Map 7 identifies important views of the Chess valley and of the open fields round the village and hamlets, and new development should not harm their key features. Inside the Chilterns National Landscape, or in its setting, a proposal must conserve and enhance its special qualities.
The plan describes what local character looks like: domestic-scale buildings from the 16th century to now, warm brick beside flint and timber framing, and brick and flint boundary walls. A rear extension in matching brick with a clay-tiled pitched roof starts on the right side of that test.
Is my house in a conservation area or listed?
Possibly both. Sarratt has two conservation areas, The Green and Church End, both established in 1969, and 93 listed buildings across the parish, most of them Grade II. The plan notes 25 Grade II listed buildings on the Green alone, including the pump, and the Grade II* Church of the Holy Cross at Church End. A listed house needs listed building consent for most extensions as well as planning permission, and any house in a conservation area needs a heritage statement with its application, from £565 with us.
In a conservation area, a single-storey rear extension within the national limits can still be permitted development. Side extensions, two-storey rear extensions, cladding and roof enlargements cannot.
What about the Chilterns National Landscape?
Part of the parish, mostly to the west and south-west, lies in the Chilterns National Landscape, formerly the Chilterns AONB. A National Landscape is "article 2(3) land", which removes the same permitted development rights as a conservation area: no side extensions, no rear extension of more than one storey, no cladding and no loft enlargement under Class B without an application. The right to add storeys under Class AA does not apply there either. We check which side of the boundary your house is on before the survey.
How long and how much in total?
Three Rivers decided 494 of 503 householder applications within eight weeks in the year to 30 June 2026, without an agreed extension of time (MHCLG live table PS2). Every application needs the council's Local Biodiversity Checklist (validation checklist). For a Green Belt scheme, the council's householder pre-application advice at £115 can be worth it before the drawings are final.
- Our planning drawings and submission: £645 drawings + £250 survey (£895 total).
- A heritage statement, if needed: from £565.
- Three Rivers' householder fee: £548.
Our Three Rivers page sets out the council's rules, and the Hertfordshire page covers the county. For the next parish south-west, see two-storey extension plans in Chorleywood; for another Three Rivers village with a new neighbourhood plan, see extension plans in Abbots Langley. Our house extensions service explains each drawing.
Work out your fee
FFP-01 · Rev AHouseholder application fee, paid to your council at submission.
Prices include one measured survey of a house of up to two storeys (£250). A flat or maisonette is £50 less; a house of three storeys or more is £50 more. One survey covers every service on the same job.
Plus the Planning Portal's own charge if the application goes through the Portal: up to £149 including VAT, depending on the application type, and some types have none (source).
Get this fee in writingor email hello@fixedfeeplans.co.uk
No obligation. Nothing is sent until you ask; your enquiry comes to us and nowhere else.
Frequently asked questions
How much can I extend a house in the Green Belt in Sarratt? There is no fixed percentage. National policy and Three Rivers' Policy DM2 refuse extensions that are disproportionate to the house as it stood in 1948, or as first built, counting all earlier extensions together.
Do I need to write anything for the neighbourhood plan? Yes. Policy 2 expects a proportionate statement showing how the Sarratt Design Code has been taken into account. We write it with the drawings.
Can I build a garden room in Sarratt without permission? Sometimes, under permitted development, but not in front of the house and with tighter limits in a conservation area or the National Landscape. Where an application is needed, DM2 asks for a clearly subordinate building with no dormers.
Is the council fee included? No. The £548 householder fee is paid to Three Rivers at submission.
If the application goes through the Planning Portal, the Portal adds its own service charge: nothing, £99 or £149 including VAT, depending on the application type and complexity, paid to the Portal at submission and not normally refunded with a council fee (Ashford Borough Council, Planning Portal service charges, 11 September 2026). It is not ours and not the council's. Other submission routes exist; where your council accepts one without a charge, we can use it.
