What is Sui Generis? Planning Rules and Requirements For HMO Landlords

Six tenants can keep an HMO within Class C4. Add one more, and the planning position changes completely. Now it’s a sui generis HMO accommodating more than six people from different households. In England, a 7+ person HMO always needs planning permission whether Article 4 applies in that area or not. Planning to add more occupants and move to Sui Generis use? Real Estate Agents London can manage the property for you.

What is a Sui Generis HMO?

A Latin phrase “Sui Generis” means “in a class of its own” or “of its own kind”. Basically something that has its own separate category. In UK planning law, if a property use does not fit neatly into any of the standard Use Classes as set out in the Town and Country Planning (Use Classes) Order 1987. So it has its own planning classification that’s called Sui Generis. 

Generally, a normal HMO with 3-6 unrelated people who live together and share facilities falls under Use Class C4.  But once the number of unrelated residents exceeds six, it will be classed as a sui generis HMO for planning purposes. So basically:

Smaller HMO (3 to 6 people) → C4 Class

Larger HMO (7+ people) → Sui Generis

Well, it can change a property’s planning requirements. Just because planning rights are available to a C4 HMO doesn’t mean the same permitted rights automatically apply to a Sui Generis HMO as well. And that’s where this distinction becomes important. 

HMO Use Classes: C3 vs C4 vs Sui Generis

To understand why Sui Generis HMOs need a different planning approach, let’s compare the three use classes and see what changes as more people occupy the property. 

Quick Self-Check: Is My HMO Sui Generis?

The first thing to check is how many people from different households are living in your property. As a general planning rule: If it’s 3 to 6 occupants, it is Use Class C4 but it’s Sui Generis if more than 6 people occupy the property. However, if you’re already close to the six-person limit and plan to add more occupants, check the planning position before increasing occupancy. 

Secondly, check how the property is currently being used, rather than relying only on the number of bedrooms. For example, does the property have self-contained flats, bedsits or an annex? 

Note:  Before making changes to the property, confirm any planning or legal position with your local planning authority. These are only quick-check steps, not a legal determination. 

Do You Need Planning Permission for a Sui Generis HMO?

Yes, always. If you are creating a large HMO that falls under sui generis use, you need planning permission. Because the permitted development rights that can allow certain C3 to C4 HMO conversions do not cover the creation of a larger sui generis HMO. This specifically applies if you’re planning to: 

• Convert a single dwelling (C3) into a large HMO
• Increase an existing C4 HMO from 6 to more than 6 unrelated occupants
• Change another type of property or use into a sui generis HMO

So, if an agent or property listing says a 7+ person HMO needs “no planning”, check the property’s existing planning history and lawful use before proceeding.

Changing Occupancy or Use of an Existing Sui Generis HMO

Already have a sui generis HMO and want to add more bedrooms or occupants? Don’t assume that your existing planning permission automatically can cover this change. Let’s say you have planning permission for a 10-person HMO and want to convert the loft into two additional bedrooms. You may need further planning approval, depending on what your original permission allows and whether the proposed changes affect the approved use or development.

Sometimes, through an amendment to the existing planning permission, you can deal with smaller changes. However, a new planning application is required in case of substantial changes.

Apply for a Certificate of Lawfulness if the use has continued unchallenged for a long time (generally 10 years for most uses, 4 years for a single dwelling). It: 

• confirms that an existing use is already lawful
• does not grant new planning permission
• does not apply to new conversions or increased occupancy

Planning Permission vs HMO Licensing: Are They the Same Thing? 

Planning permission and HMO licensing are two different legal requirements. Having one doesn’t mean you have the other, too; they are not the same.

A property can have a valid HMO licence but still have a planning issue, and vice versa. For a complaint property, you need to meet both requirements separately. Running a smaller property? See do I need a HMO licence for 3 tenants as licensing rules can still apply below the mandatory 5-person threshold depending on your council.

Why Councils Assess Sui Generis HMOs So Closely

Because they are more closer to commercial-scale use than a standard family home, councils assess Sui Generis HMO applications more carefully than C4 conversions.

Local Impact Factors Councils Assess

• Parking and highways to see how extra cars and parking demand could affect the area.
• Character and appearance to assess if the property fits in with nearby homes.
• Residential amenity to assess the risk of noise, disturbance or anti-social behaviour.
• Living standards to ensure there is enough space and good living conditions for all occupants.

Article 4 Directions and HMO Density Policy

To remove permitted development rights, mainly for C3-to-C4 conversions, an Article 4 Direction is used. Changes that would normally be allowed may now need a planning permission in an article 4 area. Since Sui Generis HMOs already need full planning permission, this direction doesn’t change the planning route. Instead show that the council is trying to control the number of HMOs in the area, so your application may face more scrutiny.

Article 4 Directions can be:

1. Non-immediate – gives around 12 months’ notice.
2. Immediate – takes effect straight away to prevent a rush of conversions.

Many councils also have HMO density or saturation policies, that set the rules councils use to control and manage HMOs in their area. They assess how many HMOs already exist and set a limit to prevent a high concentration of shared housing in one street or neighbourhood. But the limits vary by authority. For example, 

• Brighton and Hove: 10% within a 50-metre radius
• Plymouth: around 25%.
• York: The council is thinking to reduce the limit to as low as 5%

Documents You Need for a Sui Generis Planning Application

Sui Generis HMO application requirements can vary from one council to another, and you may need more supporting documents than for a standard C4 conversion. Here’s a list of common documents. But checking your local council’s validation checklist before submitting an application is advised. 

How Long Does a Sui Generis Application Take and What Does It Cost?

Depending on property, council, and your proposal complexity, cost and time varies. Here’s a breakdown of costs and timeframes you can expect in a Sui Generis planning application.

Sui Generis Planning Tips to Improve Your Chances of Approval

• Check Article 4 and HMO density rules before buying a property or finalising your plans.
• Meet minimum room size requirements from the outset to not fix the cramped layouts later. 
• Book a pre-application meeting with the council; not compulsory but can flag problems while they are still cheap to fix. 
• Review both recently approved and refused applications to see what your council is willing to accept or grant.
• Think about common objections early; especially noise, parking, and waste and their impact on neighbours. 
• Strengthen your proposal by showing council how your HMO supports sustainability (feature EPC Cor above rating, heat pumps, or solar PV) 
• Use similar approvals as evidence. For example, if the council recently approved a similar 8-bedroom HMO nearby, mention it in your Planning Statement.

Is Sui Generis HMO a Good Investment? Investment Risks, Returns and Financing

A Sui Generis HMO can provide higher rental income than a smaller HMO. But you have to deal with more planning, compliance and financing risks. Thinking about moving from a C4 HMO to a larger property? Weigh both the potential returns and the risks of Sui Generis given below:

Financing is another important deciding factor. Sui Generis HMOs can be treated differently from standard buy-to-let properties and smaller C4 HMOs. Some specialist lenders may want planning permission approved before considering the loan, while interest rates may be higher and loan-to-value limits lower. So, speak to a broker who understands large HMO finance.

Thinking about investing in an HMO but not sure where to begin? Our HMO investment guide explains the basics you need to know.

Other Types of Sui Generis Use (Beyond HMOs)

Large HMOs are just one example of Sui Generis use. This category also includes different types of properties and businesses that do not fit into the standard use classes, such as:

• Nightclubs and drinking establishments
• Theatres and casinos
• Betting shops and payday loan shops
• Amusement arcades and petrol stations
• Hot food takeaways
• Scrapyards and tattoo parlours

These all follow the same core principle as Sui Generis HMOs: no permitted development rights, and a full planning application required for any change of use, either in or out.

Own a Sui Generis HMO? Real Estate Agents London Will Manage It For You.

Planning permission is just the start. The real work is running a large HMO well. From tenant management to maintenance and inspections, there is a lot to manage. 

Not Sure How to Run a 7+ Bed HMO Smoothly? Talk To Our HMO Management Team

We handle referencing, compliance, and day-to-day management for HMO landlords across London. Let our team manage your Sui Generis HMO from day one; keeping it fully let, compliant, and profitable.

Frequently Asked Questions