Extension plans for a Hatfield house cost £645 drawings + £150 survey (£795 total) with us, a fixed fee covering the laser measured survey, existing and proposed drawings, the application pack, submission and the case officer's queries. Welwyn Hatfield Borough Council's householder fee of £548 is paid to the council on top. In Hatfield the design is usually shaped by one number in the council's own guidance: a 1 metre gap between a two-storey side extension and the boundary.
On this page
- Does Hatfield have the same extra consent as Welwyn Garden City?
- What does the council's design guidance ask of an extension?
- Why does the 1 metre gap matter so much in Hatfield?
- Do the newer houses on the old aerodrome site have the same rights?
- How does the HMO direction affect an extension?
- What if the house is in Old Hatfield or the Green Belt?
- What will the council check before it validates?
- How long does a decision take?
- Frequently asked questions
Does Hatfield have the same extra consent as Welwyn Garden City?
No. Welwyn Garden City's Estate Management Scheme, a second consent with its own design guide, covers most of that town; the council's scheme page does not extend it to Hatfield. Our Welwyn Garden City post covers that scheme. A Hatfield home needs planning permission only where the work goes beyond permitted development, and the controls that add to that are different ones:
- Old Hatfield historic core is one of the borough's 10 conservation areas, and the only one in Hatfield.
- An Article 4 direction for houses in multiple occupation, confirmed in April 2011, covers Hatfield.
- The Green Belt wraps round the town, so houses beyond its edge face a size test.
What does the council's design guidance ask of an extension?
Welwyn Hatfield adopted a new Local Plan in October 2023, but it says, at paragraph 26.11, that the council's 2005 Supplementary Design Guidance will continue to inform decisions until it is reviewed. Paragraph 5.2 of that guidance sets the householder rules:
- Subordinate scale, matching materials, and no loss of light or dominance through the length, height or closeness of the extension.
- A 1 metre side gap. Any two-storey, multi-storey or first-floor side extension must keep at least 1m from the flank boundary, and more where the street's spacing calls for it. The aim is to stop a terracing effect and to leave the neighbour room to extend too.
- Dormers within the roof slope, below the ridge, in proportion with the windows below, with their cheeks at least 1m from the flank wall or the party wall.
Why does the 1 metre gap matter so much in Hatfield?
Because of how the town was built. Hatfield was designated a post-war New Town in 1948, and in the 1950s whole neighbourhoods were laid out between the railway line and the A1. The council's design guidance describes it as built to a relatively high density, characterised by terraced housing and cul-de-sac groupings with open frontages.
On an end-of-terrace house or a semi, the side plot is often narrow. A two-storey side extension built to the boundary would fail the guidance; one set 1m in may leave a room too narrow to use. We measure the plot width on the survey and test three options before you choose:
- Two storeys, set 1m in, where the plot is wide enough for a useful room.
- A single-storey side extension to the boundary, which the 1m rule does not cover, with a first floor over the back instead.
- A rear extension only, which on many terraces is permitted development up to 3 metres deep, or 6 metres through prior approval.
Open frontages are part of the town's character, so a front extension or porch is judged against the street, not just the house.
Do the newer houses on the old aerodrome site have the same rights?
Not always. After the aircraft industry closed in the early 1990s, the former Hatfield Aerodrome was redeveloped in the 2000s for housing, a university campus and a business park, adding around 2,000 homes. Newer estates are sometimes granted with conditions that remove permitted development rights. We read the planning history of every address before relying on permitted development, and if the rights have gone, the work needs a householder application, which is the service priced above.
How does the HMO direction affect an extension?
If you plan to let rooms rather than live in the house, the April 2011 direction means turning a family house into a small house in multiple occupation needs planning permission in Hatfield, judged against the council's HMO guidance. An extension that adds bedrooms for letting is read with that in mind, so tell us at the start. Our HMO drawings service covers the change of use; a separate June 2022 direction removes the right to add storeys to blocks of flats in Hatfield, which does not affect houses.
What if the house is in Old Hatfield or the Green Belt?
Old Hatfield. In a conservation area, side extensions, cladding and roof additions need planning permission, and the design has to preserve or enhance the area's character. If the council asks for a heritage statement, our heritage statement service is from £565; we tell you at the quote stage whether your work needs one.
The Green Belt. Policy SADM 34 of the Local Plan allows an extension only where it is not disproportionate to the original building, meaning the house as it stood on 1 July 1948 or as first built after that. Paragraph 24.10 adds a figure: an extension taking the footprint, volume, or height and width 50% beyond the original would generally be refused, though each case is judged on its merits and a smaller one can still fail. Earlier extensions count. For those houses we work out the original size from the planning history and set the sums out on the drawings.
What will the council check before it validates?
The council's householder list asks for floor plans and elevations at 1:50 or 1:100, every elevation shown including blank ones, and no "Do Not Scale" note on any drawing. Where an extension takes over a garage or a parking space, it wants a parking plan showing that the garage still fits a car and how hardstanding drains. Our drawings follow those rules as standard. If you want the council's view before applying, written householder pre-application advice is £223, or £383 with a meeting, from 1 April 2026.
How long does a decision take?
In the year to 30 June 2026, Welwyn Hatfield decided 225 of 240 householder applications (prior approvals excluded) within 8 weeks, according to the government's PS2 statistics. Most are decided by officers rather than the committee.
Frequently asked questions
Do I need Estate Management consent in Hatfield? Not on the council's published description: the scheme covers most of Welwyn Garden City, and its page does not extend it to Hatfield. We check the map for any address near the boundary between the towns.
Can I build a two-storey side extension right up to my boundary? Usually not. The council's guidance asks for at least 1m to the flank boundary for two-storey and first-floor side extensions. A single-storey side extension is not caught by that rule.
Does the 1 metre dormer rule apply to a permitted development loft? No. It applies when the dormer needs planning permission, for example in Old Hatfield or where rights have been removed. Permitted development has its own national limits.
What else will the job cost? Building regulations drawings are £545 drawings + £150 survey (£695 total), or take our planning, building regs and structural package. See the house extensions page, our Welwyn Hatfield page and the Hertfordshire page. In neighbouring Hertsmere, see extension plans in Borehamwood.
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.
