## What sui generis means in practice
In England, larger HMOs can sit outside ordinary residential use classes and may require planning consent. The use-class framework comes from legislation such as the [Use Classes Order](https://www.legislation.gov.uk/uksi/1987/764/schedule/made), and local Article 4 directions can make the position stricter. Use the official [planning permission overview](https://www.gov.uk/planning-permission-england-wales) as a starting point, then check the council.
Licensing is separate from planning. The official [HMO licence guidance](https://www.gov.uk/house-in-multiple-occupation-licence) explains the national baseline, but local schemes can add extra requirements.
## The underwriting stack
Check five items before you model upside:
1. Planning use and whether the current or proposed occupation is lawful.
2. Licence status, room sizes, amenity standards, and fire safety costs.
3. Rent evidence by room type, not just total advertised rent.
4. HMO mortgage lender appetite for the exact size and use.
5. Exit market, including whether buyers need specialist finance.
The offer should be based on the weakest credible version of those five checks, not the best version.
## Finance and valuation
Sui generis HMOs can be valued on investment income, bricks-and-mortar comparables, or a hybrid depending on lender, valuer, location, and configuration. That uncertainty matters. If your refinance assumes an investment valuation but the valuer uses bricks-and-mortar evidence, your cash-left-in story can change sharply.
Example: annual net operating income of 42,000 at a 7 percent yield implies a value of 600,000. If the valuer instead anchors to local houses at 500,000, a 75 percent refinance is 375,000 rather than 450,000. That 75,000 gap belongs in your risk case.
## Operating costs
Large HMOs need more active management. Model utilities, council tax where applicable, broadband, cleaning, repairs, compliance inspections, licence renewal, and higher void churn. A rent roll without operating costs is not an underwriting model.
## Better buying discipline
Ask the council, solicitor, broker, and insurance provider specific questions before offer. Then put their answers into one linked model. If a seller's pack says "high yield" but cannot evidence planning, licence, rent, and refinance, the yield is not yet bankable.
## What to save in the model
For this sui generis hmo underwriting checks check, save the source links, date checked, calculator inputs, base case, downside case, professional question, and final pass or proceed decision in the deal notes. Also save who verified each assumption: broker, solicitor, council, insurer, accountant, or your own viewing notes. The article should not be the evidence itself. It is the checklist that tells you which evidence to collect, where to link it, and which calculator result changed the decision. For live deals, rerun the model whenever one assumption changes. If the answer changes, update the offer price before sharing the pack. Keep rejected assumptions visible too.