Plans for a two-storey extension to a Chorleywood house cost £645 drawings + £150 survey (£795 total) with us, fixed. That covers the survey, the existing and proposed drawings, the checklists, submission to Three Rivers District Council and the case officer's questions. The council's householder fee is £548 on top. A two-storey extension almost always needs an application. Three Rivers judges it against two measurements, and in Chorleywood also against two conservation areas that cover some of the village's most extended streets.
On this page
What are the two measurements?
Both come from Appendix 2, the Design Criteria in Three Rivers' Development Management Policies document of 2013 (DM Policies LDD).
At the side: 1.2 metres. A first-floor extension, over a garage or an earlier single-storey extension, should be at least 1.2 metres from the flank boundary. A two-storey side extension may sit on the boundary at ground floor if its first floor steps in by 1.2 metres. The criteria say the gap "must be increased in low density areas". That matters in Chorleywood, where many houses stand in wide plots with generous gaps between them. Only in high-density areas will the council consider an absolute minimum of 1 metre.
At the rear: 45 degrees. A two-storey rear extension should not cross a 45-degree splay line drawn across the garden from a point on the shared boundary, level with the rear wall of the house next door. The council also weighs the spacing between the houses, land levels and the position of the neighbour's windows and extensions. On sloping Chorleywood plots, levels can tighten the splay further.
What does that look like on a real plot?
An illustrative example, not a real job: a detached 1930s house, 8 metres wide, with 3 metres between its flank wall and the side boundary. The neighbour's rear wall lines up with yours. A two-storey side extension with its first floor set in 1.2 metres leaves 1.8 metres of width upstairs. That is too narrow for a double bedroom, so the extension would have to step forward or back, and the council could ask for more than 1.2 metres if the street has wide gaps. At the rear, the 45-degree line starts at the boundary level with the neighbour's wall. A first-floor extension 3 metres deep would need to start about 3 metres in from that boundary to stay behind the line.
We draw both lines on the survey before any design, so you see the space you can realistically build.
Is my house on the Station Estate?
The Chorleywood Station Estate Conservation Area covers late Victorian and Edwardian houses built after James Beckley bought the land in 1894, divided it into plots and sold them to local builders (Station Estate appraisal, 2005). The estate grew around the station on the Metropolitan Railway. The appraisal counts 203 houses, only 40 of them added later, and calls it an excellent example of early surviving Hertfordshire Metroland. C.F.A. Voysey lived nearby at Orchard House (1899), and the appraisal notes the influence of his Arts and Crafts work on the estate. It describes the area road by road, including Shire Lane, Haddon Road, Hillside Road, South Road and Quickley Lane, with Lower Road along its northern edge.
A 2006 Article 4 direction removes some permitted development rights on the estate. For a two-storey extension the bigger effect is design: the council will expect the extension to keep the estate's roof forms, materials and detail, and the application needs a heritage statement, from £565 with us. Because the estate is a conservation area, the validation checklist also asks for a tree survey where trees are affected.
And around Chorleywood Common?
Chorleywood Common is a separate conservation area, divided in its appraisal into Character Zones A to E. An Article 4(2) direction there means alterations to windows, chimneys and front boundaries, and new hardstanding, even permeable hardstanding, need planning permission (council page). A two-storey extension needs permission anyway, but new windows on the front of the house and a widened drive in the same project are part of the application too. We draw them in one set so nothing is missed.
Do the Chilterns or the Green Belt affect me?
Three Rivers includes 546 hectares of the Chilterns Area of Outstanding Natural Beauty, now the Chilterns National Landscape. Most of it is chalk stream, river valley and the hillsides and woods beside them. Whether your house is inside is shown on the council's Proposals Map. Inside the boundary, development should conserve or enhance the landscape, and the council points to the Chilterns Buildings Design Guide and the technical notes on flint, brick and roofing materials.
Houses on the edges of Chorleywood can also be in the Green Belt. There, Policy DM2 refuses extensions that are disproportionate to the original building, individually or together with earlier ones. National policy dates the original building to 1 July 1948 (NPPF Chapter 13, GB7). A two-storey addition is the kind of extension that uses up that allowance fastest, so we read the planning history first.
Chorleywood also has its own neighbourhood plan, which is part of the development plan alongside Three Rivers' policies. We read its policies for your street as part of the check.
How long and how much in total?
In the year to 30 June 2026 Three Rivers decided 494 of 503 householder applications within eight weeks, prior approvals excluded (MHCLG live table PS2). Every application needs the council's Local Biodiversity Checklist, and an extension that raises the ridge needs a street scene elevation. Both are part of our set.
- Our planning drawings and submission: £645 drawings + £150 survey (£795 total).
- Three Rivers' householder fee: £548.
- In a conservation area, a heritage statement: from £565.
- After approval, a two-storey extension needs building regulations drawings and structural calculations. Our planning, building regulations and structural package is from £1,245 drawings + £150 survey (£1,395 total) for one extension.
Our Three Rivers page lists the council's validation rules, and the Hertfordshire page covers the county. For single-storey depth limits and the Rickmansworth conservation area review, see extension plans in Rickmansworth. Across the county boundary, Buckinghamshire asks for a 1 metre set-in instead: see two-storey extension plans in Chesham.
Frequently asked questions
Is 1.2 metres from the boundary always enough in Chorleywood? It is the minimum. Appendix 2 says the gap must be increased in low-density areas, and many Chorleywood streets have wide gaps, so the council may ask for more.
Where does the 45-degree line start? At a point on the shared boundary level with the neighbour's rear wall, drawn across your garden. Levels and the neighbour's windows can tighten it.
Do I need a heritage statement on the Station Estate? Yes. The estate is a conservation area, so a two-storey extension application needs one.
Does the Chorleywood Common Article 4 direction stop extensions? No. It brings windows, chimneys, front boundaries and hardstanding under planning control. An extension still needs its own planning permission.
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.
