When you're planning a home improvement, the first question is often: "Do I need planning permission?" The second question should be: "If I don't need it, is that actually the better route?"
Permitted development can seem like a blessing - build faster, cheaper, without the council's approval. But there are real trade-offs that deserve a closer look.
What's the Difference?
Permitted Development (PD): The government has pre-approved certain minor works that don't need planning permission. You just notify Building Control and proceed.
Planning Permission: You apply to the local authority, they assess your design against planning policy, and they approve or refuse before you start.
On the surface, PD looks better. But let's dig deeper.
The Case for Permitted Development
Speed
PD is fast. Building Control approval typically takes 4-6 weeks. Planning permission? Typically 8-13 weeks for a straightforward application, potentially months if there are objections.
If you're racing against a school holiday deadline or need the space urgently, PD wins.
Cost
PD is cheaper. You pay Building Control fees (typically £400-800) and perhaps a structural engineer (£500-1,500).
Planning permission adds architect fees (£1,500-3,500), planning application fee (£200-500), and potentially agent fees if you hire a planning consultant.
For a straightforward extension, PD might cost £2,000 total. Planning could be £4,000-6,000.
No Refusal Risk
You cannot be refused PD. If your extension meets the rules, it's approved. Planning permission can be refused, forcing you back to the drawing board.
Privacy
You don't have to publish your plans publicly. With planning applications, your designs are searchable online and neighbours can object.
The Case for Planning Permission
Design Freedom
PD has strict rules: rear extensions are limited to 4m deep (3m for semi-detached), roofs must match existing angles, windows go in certain places. These aren't suggestions - they're hard limits.
Planning permission has no such limits. You can propose a 6m extension, a bold modern design with unusual materials, or something that breaks PD rules entirely. The council assesses on planning policy - not arbitrary size limits.
If your vision doesn't fit PD constraints, planning permission is the only option.
Future Resale Value
This is where it gets interesting. A planning-approved extension is transparently legitimate. A buyer's solicitor sees the planning file, knows the design was publicly assessed, and there's zero ambiguity.
PD projects are safe if done properly. But PD doesn't create a paper trail. If you did a PD extension 10 years ago and it's now slightly non-compliant (e.g., the roof materials have faded, or Building Regulations were updated), a surveyor might flag it as "unauthorised work." This doesn't mean you've broken the law - it means there's no clear documentation.
When selling, a surveyor's concern about "unauthorised PD extension" can weaken your negotiating position, even if the work is legal.
Flexibility with Future Changes
Say you do a PD rear extension now. Five years later, you want to add a side extension. If you've already used your PD allowance, the side extension needs planning permission anyway.
With planning permission, you can modify or expand a design more easily because it's already subject to planning policy rather than PD rules.
Conservation Areas and Listed Buildings
In conservation areas, many PD rights are removed. You often need planning permission anyway. In this case, there's no trade-off - permission is the only option.
The Hidden Costs of Permitted Development
Design Constraints
You might be paying less in fees, but you're constrained to a generic box design. If you wanted large windows or a sloped roof, that's not PD-compliant. Your architect has to redesign around the rules.
This cost isn't in fees - it's in compromise. You get a cheaper, blander extension.
Disputes with Neighbours
PD doesn't mean your neighbour can't complain. If they believe the work breaches PD rules (e.g., it's too deep, or the materials aren't matching), they can lodge a complaint with the council within four years.
Planning permission, by contrast, is final once granted. Neighbours had their chance to object during the application period. Once approved, they can't reopen it.
Resale Complications
As mentioned, a PD extension without clear Building Regulations sign-off (or a non-compliant PD) can cause friction when selling. A planning-approved extension is transparent.
Timeline Comparison
Permitted Development (typical):
Building Control application: 1-2 weeks
Building Control approval: 4-6 weeks
Construction can start immediately after approval
Total pre-start time: 5-8 weeks
Planning Permission (typical):
Preparation and submission: 2-4 weeks (if using architect)
Council assessment: 8-13 weeks
If approved, Building Regulations: 4-6 weeks (in parallel)
Total pre-start time: 12-18 weeks
Planning takes longer, but you're not paying architect fees during council assessment - that's done upfront.
Cost Comparison (Rear Extension Example)
Permitted Development:
Structural engineer survey: £500
Building Control approval: £600
Total: ~£1,100-1,500
Planning Permission:
Architect design: £2,000
Planning application fee: £400
Structural engineer: £500
Building Control approval: £600
Total: ~£3,500-4,000
The difference is real, but only if you don't need an architect anyway. If you're using an architect for the design (because you want something custom), the extra cost to add planning is just the application fee and slightly more design time.
Honest Recommendation
Use Permitted Development If:
You're happy with a standard design (rectangular box, pitched roof, standard windows)
You want to move fast
You're in a straightforward location (not conservation area, not listed)
Budget is tight and you're willing to sacrifice design flexibility
You plan to stay in the property long-term (no resale concerns)
Use Planning Permission If:
You have a specific design vision that doesn't fit PD rules
You're in a conservation area or listed building (you may need it anyway)
You want absolute clarity for future resale
You have time and the extra cost is acceptable
Your neighbours might object - it's better to get it resolved during the application rather than after
The Middle Ground:
Many people do both. They design to PD compliance (saving on design complexity), get Building Regulations approval, but also submit a planning application to get full transparency and avoid future ambiguity. This costs the extra application fee (£200-500) but buys complete legal certainty.
One More Thing: Building Regulations Apply Either Way
Whether you choose PD or planning permission, you need Building Regulations approval. This is where the actual safety checks happen. Don't skip it.
The choice between PD and planning permission is about paperwork, design constraints, and future resale clarity. The choice to get Building Regulations approval is not optional - it's the law.
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