House extension plans in Brookmans Park cost £895 with us, fixed, for the laser measured survey, the drawings, the forms, submission and replies to the case officer until the decision; Welwyn Hatfield Borough Council's householder fee of £548 is paid to the council untouched. Welwyn Hatfield's Local Plan names Brookmans Park as a large excluded village: the village itself is outside the Green Belt, and the fields and lanes around it are inside. Which side of that line your house sits on decides how far it can grow, so it is the first thing we check.
On this page
- Is my Brookmans Park house in the Green Belt?
- How far can a detached Brookmans Park house extend with no application?
- When is prior approval the better route for a Brookmans Park house?
- Can a crown roof go on a Brookmans Park house without planning permission?
- When does a Brookmans Park extension need Welwyn Hatfield's permission?
- Is Brookmans Park in a conservation area or under an Article 4 direction?
- What do house extension plans in Brookmans Park cost for a rear, deeper rear or side extension?
- Frequently asked questions
Is my Brookmans Park house in the Green Belt?
A house inside the village is not in the Green Belt. Policy SP 3 of the Welwyn Hatfield Local Plan 2016-2036 lists Welwyn, Welham Green, Brookmans Park and Cuffley as "large excluded villages", which it defines as "villages excluded from (not in) the Green Belt".
The Green Belt boundary is drawn round the village, so a house on a lane beyond it is in the Green Belt and one a few doors inside is not. Which side your lane is on shows on Welwyn Hatfield's policies map, and we look your house up there ahead of surveying.
In the Green Belt, a national test comes first. An extension is not inappropriate development only if it does not result in a disproportionate increase in size over the original building, meaning the house as it stood on 1 July 1948 or as first built after that (NPPF, August 2026, policy GB7(1)(b) and footnote 40). Earlier extensions count against it. Welwyn Hatfield adds a size guide in paragraph 24.10 of its Local Plan, which our post on extension plans in Hatfield sets out. Where a house is in the Green Belt, we work out the original size from the planning history and put the sums on the drawings.
The Green Belt does not remove permitted development rights. A house on a Green Belt lane can still extend within the national limits below with no application.
How far can a detached Brookmans Park house extend with no application?
A detached Brookmans Park house with its rights intact can extend 4 metres at the back with no application, or up to 8 metres through prior approval. Paragraph 21.1 of the Local Plan describes Brookmans Park as "relatively formal, regular street layouts with predominately large detached housing at low densities". That matters, because the national rules allow a detached house more than a semi or terrace. With its permitted development rights intact, a Brookmans Park house can do the following under Class A and Class B of the General Permitted Development Order 2015:
| Work | Detached house | Semi or terrace | GPDO paragraph |
|---|---|---|---|
| Single-storey rear extension, no application | Up to 4 m deep, 4 m high | Up to 3 m deep, 4 m high | A.1(f) |
| Single-storey rear extension through prior approval | Up to 8 m deep | Up to 6 m deep | A.1(g) |
| Rear extension of two storeys | Up to 3 m deep and at least 7 m from the rear boundary | The same | A.1(h) |
| Any extension within 2 m of a boundary | Eaves no higher than 3 m | The same | A.1(i) |
| Side extension | Single storey, up to 4 m high, no wider than half the original house | The same | A.1(j) |
| Roof addition | Up to 50 cubic metres | 40 cubic metres on a terrace, 50 on a semi | B.1(d) |
With no application, the drawings you need are for building control: our building regulations and structural package is from £1,195, and a certificate of lawfulness is optional proof, from £795. An estate built under one planning permission can have had its rights removed by a condition, so we read the planning history first.
When is prior approval the better route for a Brookmans Park house?
Prior approval is the route for a single-storey rear extension deeper than the no-application limit, up to 8 metres on a detached house. Welwyn Hatfield notifies the adjoining neighbours and judges only the effect on their amenity, under paragraph A.4 of Class A. Our larger home extension prior approval service is from £625, Welwyn Hatfield's fee is £249, and after approval building regulations drawings are £795 and structural calculations from £425. The route is open in the Green Belt too, because the Green Belt is not article 2(3) land.
For example (illustrative, not a real job), consider a detached Brookmans Park house that wants a 6 metre kitchen extension across the back. At 4 metres it needs no application; at 6 metres it goes through prior approval, and the neighbours' windows are what the council weighs. A two-storey version of the same room would need a full householder application instead.
Can a crown roof go on a Brookmans Park house without planning permission?
A crown roof, a flat top built between the slopes of a hipped roof, can go on a detached Brookmans Park house without planning permission within the Class B limits, because it raises the usable loft without raising the ridge. On a detached house it can be permitted development under Class B if the roof space it adds, with any earlier roof additions, stays within 50 cubic metres (B.1(d)), no part goes above the highest part of the existing roof (B.1(b)), nothing extends beyond a roof slope that forms the front of the house and faces a road (B.1(c)), and the materials are similar in appearance to the house (B.2). Side-facing windows must be obscure-glazed and fixed below 1.7 metres.
A crown roof that raises the ridge, or a hip-to-gable change combined with one that takes the volume over 50 cubic metres, needs a householder application. Then Welwyn Hatfield judges the bulk against the street, and we draw a street elevation with the houses either side so the officer sees the real comparison. If a neighbour's light becomes the question, a daylight assessment is a separate specialist report, not part of our fee.
When does a Brookmans Park extension need Welwyn Hatfield's permission?
A Brookmans Park extension needs a householder application once it passes any limit in the table above. The usual cases on a detached house are:
- A two-storey side extension. Class A.1(j) allows a side extension only on one storey, so a second floor at the side always needs an application. Welwyn Hatfield's 2005 Supplementary Design Guidance, which paragraph 26.11 of the Local Plan keeps in use, asks for at least 1 metre between a two-storey side extension and the flank boundary; our Hatfield post walks through how that gap sets the width.
- A two-storey rear extension deeper than 3 metres or within 7 metres of the rear boundary.
- A roof that rises above the ridge or exceeds 50 cubic metres.
Each is our planning drawings service at £895 plus Welwyn Hatfield's £548. With consent granted, a Brookmans Park job moves on to £795 for building regulations drawings and from £425 for calculations. If you book all three at the outset, the planning, building regulations and structural package, from £1,495, takes the place of the planning service. Building control's own charges are separate.
Is Brookmans Park in a conservation area or under an Article 4 direction?
Welwyn Hatfield lists 10 conservation areas, from Welwyn Garden City and Old Hatfield to Northaw, Essendon and Lemsford, and none is named for Brookmans Park (Welwyn Hatfield conservation areas). The council's current Article 4 directions cover employment sites, land west of Vineyards Road in Northaw, land at Digswell Park Road, and additional storeys and HMOs in Hatfield; none names Brookmans Park (Welwyn Hatfield Article 4 directions). So a Brookmans Park house keeps the national rights in the table unless a planning condition on the house has removed them, which the planning history shows. We still check the council's map for your address.
What do house extension plans in Brookmans Park cost for a rear, deeper rear or side extension?
For a detached Brookmans Park house, a 4 metre rear extension with no application needs only our building regulations and structural package, from £1,195; a two-storey side extension needs planning drawings at £895 first, with the building regulations drawings and calculations after permission.
| Plan | Route | Paid to us | Paid to Welwyn Hatfield |
|---|---|---|---|
| A 4 metre single-storey rear extension | No application | From £1,195 | None |
| A 6 to 8 metre single-storey rear extension | Prior approval | From £625, then £795 and from £425 | £249 |
| A two-storey side extension | Householder application | £895, then £795 and from £425, or the package from £1,495 | £548 |
Where a mature tree stands near the new footings, a tree survey may be needed with an application; ours, by a partner arboriculturist, is on the tree survey page, from £445. For the rest of the borough, see our Welwyn Hatfield page, and for the next town south, loft drawings in Potters Bar.
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
Is Brookmans Park in the Green Belt? The village is not: Welwyn Hatfield's Local Plan names it a large excluded village, outside the Green Belt. The fields and lanes around it are Green Belt, so a house beyond the village boundary is judged on whether its extension is disproportionate to the original building.
How deep can I extend a detached house in Brookmans Park without planning permission? Up to 4 metres for a single-storey rear extension with no application, if the house keeps its permitted development rights. Up to 8 metres goes through the larger home extension prior approval, where the council consults the neighbours.
Can I add a crown roof to my Brookmans Park house without an application? On a detached house, yes if it stays below the existing ridge, within 50 cubic metres of added roof space, off the front slope facing the road, and in matching materials. Otherwise it is a householder application.
Do Green Belt houses lose their permitted development rights? No. Green Belt is not article 2(3) land, so the national limits still apply; the Green Belt test only bites when an application is needed.
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.
