Why HMOs Develop Persistent Smell
A House in Multiple Occupation (HMO) presents a uniquely challenging odour environment compared to a single-tenancy property. The combination of high occupancy density, shared cooking facilities, multiple people with different habits, and typically high tenant turnover means that smell compounds accumulate faster and more diversely than in any residential setting.
The kitchen is used by 4–8 people with different cooking habits, different cuisines and different standards of cleaning up. The bathroom is shared, creating a persistent damp environment. Individual tenants may smoke, keep pets or use strong-smelling products. Over a 12–24 month tenancy with no professional treatment, the accumulated smell in all surfaces of the property is typically significant.
The problem is compounded by the fact that each individual tenant is habituated to the smell — it develops gradually, and no one person is aware of how bad it has become. When new tenants arrive or the property is put back on the market, the smell is immediately obvious.
The Main Odour Sources in HMOs
- Kitchen cooking smell: The single biggest contributor in most HMOs. Multiple cuisines, high-frequency use, shared extractor fan that is rarely cleaned, grease accumulation on walls and ceiling. Cooking smell spreads from the kitchen throughout the property via shared corridors and ventilation.
- Cigarette and vape smoke: Even in no-smoking properties, smoking in gardens, on doorsteps and in rooms with windows open deposits compounds indoors. In properties where smoking is more widespread, wall and ceiling contamination can be significant.
- Damp and poor ventilation: Shared bathrooms with inadequate ventilation, drying clothes indoors, and the general moisture produced by multiple occupants creates conditions for mould and persistent damp smell. HMO rooms are often smaller and less well ventilated than rooms in single-tenancy properties.
- Pet odour: If pets are permitted (or tolerated), dander and urine compounds accumulate in carpets and soft furnishings over time.
- General habitation smell: The combined effect of multiple people’s body odour, sebaceous oils, food smells and microbial activity on all porous surfaces produces a background smell that is hard to identify but immediately noticeable to anyone entering the property fresh.
Communal Areas: The Biggest Challenge
In an HMO, the communal areas — kitchen, bathroom, hallways and shared living spaces — accumulate the highest concentration of mixed odour compounds. These are the spaces that every tenant uses and that no individual tenant takes responsibility for cleaning thoroughly.
The kitchen ceiling and upper walls are almost always heavily contaminated with cooking grease and associated volatile compounds. Hallway carpets absorb odour from every room as tenants move through. The bathroom develops persistent damp smell from inadequate ventilation and high moisture load.
Standard cleaning of these areas between tenancies — wiping surfaces, mopping floors — removes visible dirt but does not address the compounds embedded in the surfaces themselves. This is why a property can appear visually clean but still smell strongly to anyone entering it for the first time.
Individual Rooms
Individual rooms in an HMO develop their own specific odour profile depending on the occupant’s habits. Common issues by room:
- Bedroom: Body odour, sebaceous oils in the mattress, damp from drying clothes. UV inspection for pet urine if animals were present.
- Kitchen: Cooking grease on all upper surfaces, extraction unit, ceiling. The highest-priority area in most HMOs.
- Bathroom: Persistent damp and mould smell from high moisture and inadequate ventilation. Check for failed extractor fan.
- Hallways: Accumulated cooking and general habitation smell from high-traffic use. Carpet in hallways retains more odour than any other area.
Landlord Obligations and HMO Licensing
Licensed HMOs are subject to regular inspection by the local authority. While there is no specific legal standard for odour in residential properties, HMO licence conditions typically require that the property is maintained in a good condition and fit for habitation. A property with a severe odour problem may fail inspection on this basis.
More practically, persistent odour in an HMO affects the landlord’s ability to re-let rooms quickly at the desired rental level. London HMO rooms command a significant premium over rooms in non-licensed shared houses — a property with a reputation for poor smell affects occupancy rates and the quality of tenants it attracts.
Professional Treatment Between Tenancies
The most effective approach for HMO landlords is professional treatment as a standard part of the end-of-tenancy process, particularly after:
- A long tenancy (12+ months) with no previous professional treatment
- Confirmed or suspected smoking in rooms or communal areas
- Pet ownership by any tenant
- Feedback from prospective tenants about smell during viewings
- Recurring complaints from existing tenants about smell in communal areas
Professional treatment for an HMO typically involves:
- Specialist kitchen degreasing of all upper surfaces, extraction unit and ceiling
- UV inspection for pet urine in carpeted rooms
- Professional enzyme treatment of any urine deposits
- ULV cold fogging throughout all rooms and communal areas
- Monitored ozone treatment of the whole property
HMO Licensing Renewal and Odour Documentation
Some local authorities in London require evidence of professional cleaning or maintenance as part of the HMO licence renewal process. A written treatment report from a professional odour remediation company provides documentation of the treatment carried out, the date and the methods used. We provide this as standard with all HMO treatments.
Cost for HMO Treatment
HMO treatment is priced by property size and the number of rooms. As a guide:
- 4-bedroom HMO (Advanced treatment): from £895 + VAT
- 6-bedroom HMO (Advanced treatment): from £1,100 + VAT
- Complete treatment (with kitchen degreasing): from £1,500 + VAT
For landlords with multiple HMOs, we offer scheduled maintenance programmes at discounted rates. Full pricing guide →