This is general guidance based on standard permitted development rights in England. Rules differ for listed buildings, conservation areas, and properties with Article 4 directions. Always confirm with your local planning authority before starting work.
Do I Need Planning Permission for a Two-Storey Rear Extension in Welwyn Hatfield?
A two-storey extension to the rear of your property, adding significant living space on both the ground and first floor. Subject to stricter conditions than single-storey extensions.
Planning in Welwyn Hatfield
88%
of planning applications granted
95%
decided within the statutory or agreed time
54%
of householder applications decided within 8 weeks
In the year to December 2025, Welwyn Hatfield decided 630 planning applications. 424 of these were householder projects such as extensions, loft conversions and outbuildings, of which 87% were granted.
Planning statistics: MHCLG planning application statistics, the year to December 2025. Conservation area and Article 4 data: planning.data.gov.uk, © Historic England / Crown copyright. Open Government Licence v3.0.
Important: Additional Restrictions May Apply in Welwyn Hatfield
Welwyn Hatfield has 9 conservation areas. These include Ayot Green, Ayot St Lawrence, Beehive, Essendon, Northaw Village, Old Hatfield. If your property is in a conservation area, some or all permitted development rights may be restricted. For example, you may need planning permission for changes that would normally be permitted, including alterations to the roof, cladding, or extensions visible from a public highway.
Check with Welwyn Hatfield planning department before starting work to confirm whether your property is affected by any special designations.
Permitted Development Rules for a Two-Storey Rear Extension
Generally permitted under Part 1, Class A of the GPDO, but with stricter conditions than single-storey extensions. The maximum depth is 3m from the original rear wall, and the extension must be at least 7m from the rear boundary.
Conditions
- 1Maximum projection of 3m from the original rear wall
- 2Must be at least 7m from the rear boundary
- 3Must not exceed the height of the existing roof ridge
- 4Roof pitch must match the existing dwelling as far as practicable
- 5Side-facing upper-floor windows must be obscure glazed and non-opening below 1.7m from the floor
Size and Dimension Limits
- Maximum depth: 3m from the original rear wall
- Must not exceed the height of the highest part of the existing roof
- Eaves height must not exceed the eaves of the existing dwelling
When Permitted Development Does Not Apply
- Must not cover more than half the curtilage
- Must be at least 7m from the rear boundary
- Does not apply to flats or maisonettes
- PD rights may be restricted in designated areas
- The Larger Home Extension scheme does not apply to two-storey extensions
What About Building Regulations?
Building regulations approval is likely required
Full Building Regulations approval required covering structural design, foundations, thermal performance (Part L), fire escape routes, sound insulation between floors, ventilation, and drainage.
Building regulations are separate from planning permission. Even if your project is permitted development, you may still need building regulations approval. Contact Welwyn Hatfield building control or use an approved inspector.
How to Apply in Welwyn Hatfield
If you need planning permission for your two-storey rear extension, you can apply through Welwyn Hatfield's planning department or via the national Planning Portal.
If your project is permitted development and you want written confirmation, you can apply for a Lawful Development Certificate (LDC) from Welwyn Hatfield. This provides proof that your project does not need planning permission, which can be helpful when selling your property.
What Happens If I Build Without Permission?
Enforcement action can require partial or full demolition. Two-storey extensions built without proper permission are particularly problematic when selling, as mortgage lenders and solicitors will flag the issue during conveyancing.
Frequently Asked Questions
Do I need planning permission for a two-storey rear extension in Welwyn Hatfield?
Does a two-storey rear extension in Welwyn Hatfield need building regulations?
How do I apply for planning permission in Welwyn Hatfield?
How long does planning permission take in Welwyn Hatfield?
What percentage of planning applications does Welwyn Hatfield approve?
Find a Builder in Welwyn Hatfield
Browse local builders on Tradesfolk. Read reviews, compare quotes, and hire with confidence. 100% free for homeowners, always.