Two-storey extension plans and drawings in Hertfordshire

Hertfordshire at a glance

Nation: England
Price region: East of England
Postcode areas: AL, CM, EN, HP, SG, WD
Towns covered: 33 listed below, plus surrounding villages
Site visits: Free, no obligation

What a set of extension plans involves

Two-storey extension plans involve a measured survey of your house, design options, and a set of scaled drawings showing the existing and proposed floor plans, elevations, a site plan and a location plan. These are the drawings needed for a planning application or lawful development certificate. Building regulations drawings with construction details follow as a separate, more technical set.

Across Hertfordshire we cover Watford (WD1), Hemel Hempstead (HP1), Stevenage (SG1), St Albans (AL1), Welwyn Garden City (AL6) and Cheshunt (EN7), plus the smaller places around them.

Fees

Planning drawings (survey and design) are a guide of £2,000–£3,500 and building regulations drawings and specification £1,500–£4,000, with your design stage priced in writing before it starts.

Rules in England

In England, the plans support either a householder application, costing £548 (or £575 for applications made from 8 December 2026), or a lawful development certificate for permitted development, costing £274 (about £288 for applications from 8 December 2026). They must show the extension's relationship to the original house, the boundaries and neighbours, because two-storey rear permitted development depends on the 3 m and 7 m limits.

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.

Getting the design right

Planning drawings versus building regulations drawings

Planning drawings show what the extension looks like and how it affects neighbours. Building regulations drawings show how it is built: foundations, structure, insulation, fire safety, ventilation and drainage. Most two-storey extensions need both, prepared at different stages.

Compare options early

Sketching two or three layouts, such as rear, side or part two-storey, is the cheapest point to make big decisions. Each option comes with a guide cost and a view on the approval route, so you choose with the full picture rather than discovering limits later.

How we work in Hertfordshire

Look at the house
We start in Hertfordshire with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Get it approved
Once you're happy with the design we submit it to the council for Hertfordshire and deal with any questions from the planning officer.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build and sign-off
Vetted teams working under S&K build the extension, and we arrange the building control completion certificate at the end.

Towns we cover in Hertfordshire

Two-storey extension plans and drawings in Hertfordshire: questions

Do the plans include structural calculations?

Not at planning stage. Structural calculations and beam design are prepared by a structural engineer once the design is agreed, and they form part of the building regulations package. We coordinate the engineer's work with the drawings so steel sizes and floor depths match.

Do I own the plans once they are drawn?

You receive copies of the drawings to use for your project, including your planning application and building regulations approval. Copyright in drawings normally stays with whoever prepares them unless agreed otherwise. Your written design stage price sets out how the drawings can be used.

Can I use plans from a previous owner's planning permission?

Sometimes. If the permission is still valid, usually within three years of the decision in England, you can build to it. The drawings may still need updating for building regulations, and the design may not suit your needs. We check old plans and permissions at the free site visit.

Neighbouring areas

All extension services in Hertfordshire · About two-storey extension plans and drawings