🏘️ HMO Planning Permission Explained: C4 vs Sui Generis (Larger HMOs)

Converting a property into an HMO (House in Multiple Occupation) can be one of the most profitable strategies in UK property — but only if you understand the planning rules. Whether you’re creating a small shared house for young professionals or a large multi‑let for students, the planning system treats each type differently.

This guide breaks down C4 HMOs, Sui Generis HMOs, when planning permission is required, and the restrictions you must know before starting your project.

📌 What Is an HMO?

A property is classed as an HMO when:

• Three or more unrelated people live together,
• Forming more than one household,
• And share facilities such as a kitchen or bathroom.

This definition applies whether the property is a small shared house or a large multi‑let with ten bedrooms.

🏠 C4 HMO — Small HMOs (3–6 Occupants)

The C4 Use Class covers:

• Small HMOs
• 3–6 unrelated occupants
• Sharing basic amenities

✔️ When You Don’t Need Planning Permission

In many areas, converting a C3 dwelling (a normal house) into a C4 HMO is allowed under Permitted Development Rights.
This means no planning application is required — unless your council has removed this right.

⚠️ When Planning Permission Is Required

You must apply for planning permission if:

• Your area has an Article 4 Direction (common in university towns and cities)
• You are converting from C4 back to C3
• You are making external changes that require permission

🧭 Article 4 Areas

Councils use Article 4 to control HMO growth.
In these zones, any conversion to C4 requires full planning permission, even for 3–6 tenants.

🏢 Sui Generis HMO — Large HMOs (7+ Occupants)

Once an HMO has seven or more occupants, it automatically becomes Sui Generis — a unique planning category.

✔️ Always Requires Planning Permission

Unlike C4, there are no permitted development rights for Sui Generis HMOs.
You must submit a full planning application, including:

• Floor plans
• Elevations
• Fire safety layout
• Amenity space calculations
• Parking strategy
• Management plan

🔍 What Councils Assess

Local authorities will consider:

• Impact on neighbours
• Noise and disturbance
• Waste storage capacity
• Parking pressure
• Internal room sizes
• Over‑concentration of HMOs in the area

Many councils apply a “10% HMO saturation rule” — if more than 10% of homes within a radius are already HMOs, your application may be refused.

🧱 Key Differences: C4 vs Sui Generis

📝 Licensing vs Planning — Don’t Confuse Them

Even if planning permission is not required, you may still need:

• Mandatory HMO Licence (5+ occupants)
• Additional Licensing (varies by council)
• Selective Licensing (area‑based)

Planning permission and licensing are separate legal processes — you often need both.

🚫 Common Reasons HMO Applications Are Refused

• Over‑concentration of HMOs in the street
• Insufficient communal space
• Bedrooms below minimum size
• Poor sound insulation
• Lack of cycle or bin storage
• Parking pressure
• Poorly designed layouts

A strong planning statement and professional drawings significantly improve approval chances.

🧭 Should You Convert to an HMO?

HMOs can deliver:

• Higher rental yields
• Lower void periods
• Strong demand in university and city areas

But they also require:

• More management
• Higher compliance costs
• Careful planning strategy

If you’re in an Article 4 area or planning a large Sui Generis HMO, getting the planning route right is essential.

We have extensive experience with applications for C4, lawful development certificate, Sui Generis, change of use application and building regulations applications.

Contact us for a no obligation quotation today!