Buying an existing HMO in Cardiff: your due-diligence checklist

Cardiff's resale HMO market can offer a faster route to a running income stream than converting a vacant property yourself, but buying a property that is already let and licensed involves a different set of risks. An existing HMO brings sitting contract-holders whose agreements pass to you on completion, a licence that does not transfer automatically, and potentially inherited compliance gaps that become your responsibility the moment you take title. Welsh property law applies rules at each stage of this process that differ from the position in England, and a buyer who researches a Cardiff HMO using general UK due-diligence guidance risks missing points that are specific to Wales.

This guide covers the main due-diligence areas for a Cardiff HMO purchase: planning and use class, the licensing position, the existing occupation contracts, financial verification, and the physical condition of the property. An interactive due-diligence tracker at the foot of the article lets you follow your progress across each area as you research a deal. For a broader view of what makes a Cardiff HMO a sound acquisition, see our 2026 HMO investment guide.

Planning permission and use class in Cardiff

The first step for any Cardiff HMO purchase is a planning check. In Wales, converting a single-family dwelling (Use Class C3) to an HMO of up to six people (Use Class C4) requires planning permission. This is not the position in England, where the C3 to C4 change was permitted development nationally and councils applied Article 4 Directions to withdraw that right in named wards. In Wales, no permitted development right for C3 to C4 has ever existed, so planning permission is required for every Cardiff HMO regardless of ward. Article 4 Directions are an English mechanism that does not determine the planning position in Cardiff. Our full article on Cardiff HMO planning covers the use class framework in detail.

When buying an existing HMO, ask the seller for the planning permission documentation and verify whether the recorded use class on the title matches the current use. Search Cardiff Council's planning register for outstanding enforcement notices. An HMO operating in C3 use without valid C4 permission is in breach of planning control, and that breach passes to the new owner on completion. For properties with seven or more occupants, the large HMO sui generis use class applies, with different planning implications still.

HMO licence status and the transfer question

Confirm the licensing position early. In Wales, mandatory HMO licensing applies where a property has three or more storeys, five or more occupants, and two or more households: all three conditions must be present. Cardiff also operates an additional licensing scheme in Cathays and Plasnewydd that requires smaller HMOs in those wards to hold a licence regardless of storey count. If the property falls within either scheme, the existing licence must be current and all its conditions complied with. An HMO licence in Cardiff is not transferred automatically to a new owner. The incoming owner must apply for a new licence in their own name before or immediately after completion. Cardiff Council recommends applying in advance to avoid a gap in licensed status. Operating an unlicensed HMO is an offence that can lead to prosecution and a rent repayment order of up to 12 months' rent under the Housing (Wales) Act 2014. For how licensing thresholds and the additional scheme work in Cardiff, see our guide to HMO licensing in Wales.

Reviewing the existing occupation contracts

When you buy a tenanted HMO, the existing occupation contracts pass to you as the new landlord on completion. Under the Renting Homes (Wales) Act 2016, the people living in the property are contract-holders, not tenants, and their rights run independently of the sale. Before exchange, ask for copies of all occupation contracts and check two things carefully. First, that written statements were issued to each contract-holder within 14 days of their occupation start date: a landlord who did not issue a statement in time cannot serve a valid section 173 no-fault notice until the deficiency has been remedied and a further six-month notice period has elapsed. Second, that each security deposit was protected in an approved scheme within 30 days of receipt and the required documents were issued at the start of the contract. These obligations transfer with the property, and inherited shortfalls become yours from the moment completion takes place.

Financial verification: what the numbers actually show

The headline rent in a property's marketing particulars often reflects full occupancy at current market rates. Verify this against actual rent receipts for the last 12 months and the passing rent written into each occupation contract. Rents that are below current market level because the landlord has not reviewed them pass with the property and bind the new owner. Check the void history: a property with persistent empty rooms points to a pricing, management or condition problem that will not resolve on its own at completion. Confirm also that the seller and any managing agent are currently registered with Rent Smart Wales: an unregistered landlord or unlicensed agent is in breach of the Housing (Wales) Act 2014, and understanding whether the current operation is compliant is part of forming an accurate picture of what the property is worth.

Physical inspection: room sizes and compliance

A standard building survey will assess the structure and condition of the property but is unlikely to cover HMO-specific elements. Commission a survey that includes a room-by-room floor area check against Cardiff Council's published minimum sizes, the electrical installation condition report (EICR), gas safety certificate, fire alarm system, and smoke and CO alarm provision. Cardiff's bedroom minimums depend on whether the property provides a separate living room: a single room requires at least 6.5 square metres where a living room is provided, or 10 square metres where none exists. Any room below the applicable minimum needs to be reflected in the purchase price or brought into compliance before the licence application, since Cardiff Council will not license a bedroom that falls short of its published standard. For the full Cardiff size table and amenity ratios, see our article on HMO room sizes and amenity standards in Wales.

EPC rating and the upgrade trajectory

All privately rented homes in Wales must currently achieve a minimum EPC rating of E. The Welsh Government has proposed requiring a minimum of C for the private rented sector from 2030, and the cost of reaching that standard varies considerably by property type and construction. When appraising a Cardiff HMO purchase, check the current EPC rating for the building and identify what the upgrade route to EPC C would involve. Where the current rating is D or below, factor the estimated cost of the required works into your offer. Our guide to EPC C by 2030 for Welsh landlords covers the improvement pathways and what typically moves a rating.