OFFICE ODOUR
AFTER COVID OR
EXTENDED CLOSURE

What Causes Office Closure Smell

An office that has been closed for an extended period — whether for refurbishment, a public health event, a long bank holiday or any other reason — develops a distinctive smell that most people recognise immediately on re-entering. This smell is a combination of several factors that compound over the period of closure:

• HVAC recirculation without fresh air exchange: Most office HVAC systems, when set to a low or standby mode during closure, recirculate internal air rather than drawing in fresh air. Without occupants and their activities generating fresh air exchange, the same air is cycled repeatedly, accumulating dust, mould spores and VOC compounds.
• Mould growth in static HVAC conditions: When air movement slows and humidity is not actively managed, moisture accumulates in ductwork, on coils and in filter housings — creating conditions for mould growth that distributes MVOC smell throughout the office when the system resumes.
• VOC off-gassing from building materials: Carpets, MDF furniture, wall coverings and adhesives all continue to off-gas VOCs at low levels. Without ventilation and occupant activity, these compounds accumulate in the air.
• Food and organic matter decay: Items left in refrigerators, on desks or in bins during unplanned closure can decay, producing particularly unpleasant odour compounds that absorb into nearby surfaces.
• General dust and particulate settlement: Without air movement from occupancy and HVAC operation, dust settles on all horizontal surfaces. When disturbed on re-entry, it becomes airborne and contributes to the overall stale quality of the air.

HVAC: The Primary Culprit

In most London offices, the HVAC system is both the primary cause of closure smell and the primary route to resolving it quickly. During extended closure:

• Fresh air intake dampers are typically closed or minimised to reduce energy consumption
• Filters accumulate particulates and become a substrate for mould
• Cooling coils accumulate moisture and mould during low-use periods
• Ductwork, particularly horizontal sections, accumulates settled dust

The fastest first action when preparing an office for return: run the HVAC system with maximum fresh air intake for 24–48 hours before staff arrive. This flushes the accumulated stale air and significantly reduces the closure smell before anyone enters. Replace all filters before resuming normal operation.

Surface Accumulation During Closure

Without the air movement and maintenance activity of normal occupancy, surfaces throughout an office accumulate compounds that contribute to the closure smell:

• Desk surfaces, keyboards and equipment accumulate a fine film of dust and VOC deposits
• Carpets settle with accumulated particulates that become airborne when walked on
• Soft furnishings (meeting room chairs, reception sofas) absorb ambient VOC compounds during the closure period
• Walls and ceilings continue to off-gas whatever compounds were embedded before closure

Standard post-closure cleaning — vacuuming, surface wiping, mopping — addresses the visible dust and surface deposits. It does not address VOC compounds embedded in surfaces or accumulated in HVAC systems.

Kitchen and Break Room: Priority Area

The office kitchen or break room is almost always the worst-affected area after an extended closure. Items left in the refrigerator continue to decay; food particles in drains accumulate biofilm; spills and residue left on surfaces at the start of the closure have had months to absorb into surfaces and generate bacterial activity.

Priority actions for the kitchen before staff return:

• Fully empty and clean the refrigerator, including the drip tray and door seals
• Run an enzyme drain cleaner through all kitchen drains and leave to dwell
• Clean the dishwasher filter (a common odour source often overlooked)
• Wipe down all surfaces with a disinfectant cleaner, including the underside of shelves and cabinet interiors
• Empty and clean all bins including any that were not emptied before closure

Prevention During Future Closures

If you know an office will be closed for an extended period:

• Empty all refrigerators before closing and leave doors slightly open
• Empty all bins thoroughly
• Set HVAC to a maintenance mode with some fresh air exchange rather than full recirculation
• Replace HVAC filters immediately before closure
• Consider a dehumidifier in any areas prone to moisture accumulation
• Schedule a return visit midway through a long closure to ventilate and check for issues

Preparing the Office for Staff Return

The recommended sequence for preparing an office after extended closure:

Professional Treatment for Office Closure Smell

Professional odour treatment for offices uses the same staged approach as residential treatment, adapted for commercial spaces:

1. HVAC pre-treatment: Fogging agent introduced into the HVAC system to treat internal duct surfaces and distribute treatment solution throughout the office via the existing air system
2. ULV cold fogging: Specialist odour-neutralising solution fogged throughout all office areas, meeting rooms, reception, kitchen and storage
3. Monitored ozone treatment: Industrial ozone generators run throughout the office, neutralising residual VOC and MVOC compounds in the air and on all surfaces
4. Safe re-entry confirmation: Real-time O₃ monitoring before staff return. Treatment documentation provided for records

Office treatment is typically carried out outside working hours — evenings or weekends — with the office ready for normal occupation the following morning.

Cost

Office treatment is priced by floor area. As a guide:

• Small office up to 100 sq m: from £695 + VAT
• Medium office 100–300 sq m: from £1,100 + VAT
• Larger offices: quoted individually after assessment

Out-of-hours scheduling at no additional charge for standard evening and weekend slots. Full pricing guide →

Common Questions