Many landlords assume that increasing the number of rooms in their HMO is simply a case of notifying the council and updating their HMO license. Wrong. If you’re converting a C4 HMO (6 occupants or fewer) into a Sui Generis HMO (7 or more occupants), you need full planning permission. Failing to do so could lead to enforcement action, fines, and a refusal to grant an HMO license altogether.

If you’re considering this conversion, read on to understand the planning process, common mistakes, and how to avoid being the landlord who gets it wrong.

Step 1: Understanding the Change from C4 to Sui Generis

In planning terms, small HMOs (up to six people) fall under Use Class C4, which means you don’t need planning permission in most areas unless the property is in an Article 4 area.

However, the moment you go beyond six occupants, your property moves into the Sui Generis use class, which means it no longer falls within the same permitted use. This is a material change of use, and you need planning permission.

This is where many landlords trip up. They assume that because they already have an HMO license, they can just apply for a HMO licence variation. No. The licensing department and the planning department are two completely separate entities within the council. One does not override the other.

Even if the HMO officer tells you to apply for planning permission, that doesn’t mean the planning department will approve it. The HMO officer’s opinion is irrelevant when it comes to planning decisions.

Step 2: Do You Need Planning Permission? (Yes, You Do.)

If you’re in an area covered by an Article 4 Direction, then you already know planning permission is required for any new HMO, even a C3 to C4 conversion. However, even in non-Article 4 areas, you still need planning permission when moving from C4 to Sui Generis because you are increasing the intensity of use.

This is the part many landlords overlook:
✅ Adding a 7th occupant = A MATERIAL CHANGE OF USE
✅ You must submit a planning application for this change
✅ You cannot just ‘amend’ yourHMO  license and hope the council ignores planning requirements

Step 3: The Planning Application Process

Pre-Application Advice (Optional but Recommended)

Most councils offer a pre-application advice service, where they review your proposal and give feedback before you submit a full application. This can help you anticipate objections and tailor your application to increase your chances of approval.

👉 Cost: £500 – £1,000 depending on the council
👉 Timeframe: 4-8 weeks

We typically recommend doing this unless you are confident your property meets all requirements and there are no local objections to HMO expansion.

Full Planning Application

If you proceed with a full planning application, you will need to submit:

• Existing and proposed floor plans
• Site location plan
• Design and access statement (explaining how the conversion meets planning requirements)
• Parking and waste management plans
• Fire safety strategy

👉 Application Fee: £462 (England)
👉 Timeframe: 8-12 weeks for a decision

What the Council Will Consider

When assessing your application, the council will look at:
✔️ Room sizes & amenity space – Are the rooms big enough? Is there enough communal space?
✔️ Parking provision – Will the additional tenant create parking issues?
✔️ Waste management – Can the property handle extra waste storage?
✔️ Impact on neighbours – Will more tenants cause noise or over-occupation complaints?

If there are strong objections from local residents or if the council believes the area is already oversaturated with HMOs, your application may be refused.

Step 4: HMO Licensing

Only after securing planning permission should you apply to vary your HMO license to reflect the additional tenant. If you apply for the license before getting planning, you risk having the application rejected because the property does not have the correct use class.

Steps to update your license:
1️⃣ Submit proof of planning approval
2️⃣ Provide updated floor plans
3️⃣ Ensure compliance with minimum room sizes and amenity requirements
4️⃣ Upgrade fire safety measures if necessary (e.g., additional fire doors, escape routes)

👉 Cost: Varies by council (£500-£1,500)
👉 Timeframe: 4-12 weeks

Step 5: Avoiding Common Mistakes

🚫 Mistake #1: “I already have an HMO license, I don’t need planning permission.”
❌ Reality: Moving from C4 to Sui Generis requires planning approval. The licensing team cannot override planning rules.

🚫 Mistake #2: “I’ll just add an extra tenant without telling the council.”
❌ Reality: If the council finds out (and they will, via inspections, tenant complaints, or council tax records), you can face enforcement action, fines, and even prosecution.

🚫 Mistake #3: “My HMO officer said I should apply for planning, so it’ll be fine.”
❌ Reality: HMO officers and planning officers do not work together. The planning department makes the final decision, not the HMO team.

🚫 Mistake #4: “I’ll just apply for planning later if I get caught.”
❌ Reality: Retrospective planning applications are far harder to get approved. If your application is refused, you may be forced to evict a tenant and revert back to a 6-bed HMO.

Final Thoughts: Is It Worth Expanding?

Converting a 6-bed HMO into a 7-bed can be a great way to increase rental income and maximize property use, but only if done legally.

✅ DO apply for planning permission before making changes
✅ DO get professional advice to improve approval chances
✅ DO ensure compliance with all space, fire, and amenity standards

❌ DON’T assume your existing HMO license is enough
❌ DON’T add an extra tenant without approval
❌ DON’T rely on HMO officers for planning advice

If you’re considering this conversion and need help with the planning process, feel free to get in touch. Better to do it right the first time than risk costly enforcement action later.

If you’re ready to move forward with converting your 6-bed HMO into a 7-bed, we can handle the HMO planning permission process for you. Get in touch today to discuss the next steps.