The Permitted Development Right to Add Another Storey: Your 2025 Guide
Adding an extra floor can be a game-changer for space and value. Since 2020, certain houses in England can add one or two additional storeys using Permitted Development rights (Class AA, Part 1 GPDO)—with prior approval from the local authority (so it isn’t a free-for-all, but it’s not full planning permission either).
Applies to England only. Rules can change—there’s an ongoing government consultation to tweak these rights—so always check the current position before you proceed.
1) Are you eligible?
Your project can use Class AA PD if the current house:
• Is a dwellinghouse (C3) and not a flat, nor within a building that contains flats.
• Was built between 1 July 1948 and 28 October 2018.
• Has not already had extra storeys added above the “original” house.
• Is not on Article 2(3) land (conservation area, AONB, National Park, the Broads, World Heritage Site) and not on a Site of Special Scientific Interest.
• Wasn’t created via PD change-of-use (e.g., Classes M/MA, N, O, P/PA, Q, etc.).
2) How many storeys can you add—and how high?
• If your house has one storey (e.g., a bungalow): add 1 additional storey.
• If your house has two or more storeys: add up to 2 additional storeys.
Key height limits:
• Overall building height after works must not exceed 18m.
• Each new storey must not add more than 3.5m to the building’s height (measured externally).
• Terrace or semi-detached? Your new height can’t be more than 3.5m taller than the next highest building in the row/attached pair.
There are internal height rules too: the floor-to-ceiling height of each new storey must be no more than 3.0m or no more than the height of any existing storey in the principal part—whichever is lower.
3) Design rules you must meet
Class AA has some non-negotiables that shape the design:
• Principal part only: Extra storeys must sit on the main (principal) part of the house, not over lower front/side/rear projections.
• Roof pitch: After completion, the roof pitch of the principal part must match the pre-development roof pitch.
• Materials: External materials must be of a similar appearance to the existing house.
• Side windows: No windows in any wall or roof slope forming a side elevation. Plan your layout accordingly.
• Structural works: Only within the curtilage to strengthen existing walls/foundations; no visible support structures on completion.
4) Prior approval: what the council actually checks
You must apply for prior approval (this is still PD). The local planning authority (LPA) considers:
• Amenity of adjoining premises (not just immediate neighbours): overlooking, privacy, loss of light and broader amenity impacts.
• External appearance of the house (not limited to the bits seen from the street).
• Impact on air traffic/defence assets and, in London, protected vistas (the LPA will consult bodies like Historic England or the CAA if relevant).
LPAs also notify adjoining owners/occupiers and allow 21 days for comments.
Timing: Expect a decision in about 8 weeks (56 days)—and extensions of time can be agreed in writing. If an eligible prior approval isn’t decided in time, there’s a “deemed consent” concept in the GPDO (with caveats: your scheme must fully comply).
What to submit: scaled plans and elevations, a location plan, and enough detail for the LPA to judge compliance. (They can refuse prior approval if insufficient info is provided.)
5) The three extra Class AA conditions people miss
Once prior approval is granted:
1. Construction Management: Before starting, you must submit a construction management/report (hours, dust/noise/vibration/traffic mitigation).
2. 3-year completion deadline: You must finish the development within 3 years of the prior approval date.
3. Completion notice: Notify the LPA in writing when works are complete (name, site address, completion date).
6) Building Regulations: what changes when you add a storey
PD is only about planning. You still need Building Regulations approval for structure, fire safety, sound insulation, thermal performance, drainage and stairs. Typical implications include:
• Structure: New loads = new design. Our affiliated structural engineer designs all structural steelwork layouts, foundation strengthening and any lateral stability upgrades.
• Fire safety & escape: More storeys usually tighten rules for protected stairs, alarms, escape windows/doors, and lining/compartmentation strategy (check Approved Document B).
• Acoustics & energy: Upgraded floor/ceiling acoustic separation and insulation to current standards (Approved Documents E & L).
• Stairs, headroom, guarding: Must comply with Approved Document K and related parts.
(Your LABC or Approved Inspector will advise case-by-case.)
7) What Class AA does not allow
• It doesn’t turn a house into flats (that’s a different set of rights under Part 20).
• It doesn’t apply to flats or houses created through PD change-of-use.
• It doesn’t apply on Article 2(3) land (conservation areas etc.).
• You can’t use it twice to stack more storeys later—the house can’t have had storeys previously added above the original.
8) Worked example (typical terrace/semi)
• Existing: Two-storey mid-terrace built in 1965 on ordinary (non-Article 2(3)) land.
• Aim: Add one extra floor of bedrooms plus new roof.
• Key checks:
• New overall height ≤ 3.5m higher than the next highest in the terrace + ≤ 18m total.
• New floor-to-ceiling height ≤ 3.0m (or ≤ tallest existing storey).
• No side-elevation windows; materials similar; roof pitch matches.
• Prior approval covers amenity/external appearance; neighbour notice served.
9) Timeline & paperwork (what we handle)
1. Feasibility & eligibility (build date, designations, previous additions).
2. Measured survey & outline design to Class AA constraints.
3. Prior approval pack: plans/elevations, design notes, compliance matrix; we coordinate neighbour/technical consultations via the LPA.
4. Construction management report (pre-start).
5. Building Regs drawings + structural steelwork layouts by our affiliated structural engineer.
6. Notify completion to the LPA; archive documentation for the client.
10) Common pitfalls (and easy wins)
• Building before approval: Don’t. Wait for prior approval or a formal “not required” confirmation.
• Over-height by a few centimetres: The 3.5m/18m caps are hard limits—design in tolerance.
• Side windows sneaking in: Not allowed under Class AA—use rooflights to side slopes or re-plan the layout.
• Article 4 Directions: Even outside conservation areas, councils can remove some PD rights—check local constraints early.
Key references (plain-English starting points)
• Planning Portal overview for additional storeys/extending upwards (limits, heights, definitions).
• Legislation: GPDO 2015 (as amended) introducing Class AA (the legal framework).
• Procedure & case law on prior approval (amenity/external appearance scope; timings).
• Neighbour notification & 21-day period; 3-year completion; construction management requirements.
Final word
Used correctly, Class AA can deliver serious space fast—without a full planning application. The trade-off is precision: tight height limits, design constraints, and a prior-approval test on amenity and appearance. That’s where a robust pack (and a solid structural strategy) pay for themselves.
Thinking about adding a storey? We’ll check eligibility, prepare your prior-approval submission, and coordinate structural steelwork layouts via our affiliated structural engineer—end-to-end, from feasibility to completion notice.
Disclaimer: This article is for general informational purposes only and does not constitute legal or professional advice. Always consult relevant professionals and local authorities before undertaking any development or change of use.