In office rooms the air temperature must be at least 20 degrees Celsius under ASR A3.5 for light work while seated and should not exceed 26 degrees Celsius. Ventilation follows ASR A3.6: a carbon dioxide concentration below 1,000 ppm counts as hygienically unobjectionable, and above that ventilation measures have to be considered.
| Item | Value | Legal basis |
|---|---|---|
| Minimum air temperature, light work while seated | 20 degrees Celsius | ASR A3.5, table 1 |
| Minimum temperature for break, sanitary and first aid rooms | 21 degrees Celsius | ASR A3.5 |
| Target upper limit for air temperature | 26 degrees Celsius | ASR A3.5, point 4.2 |
| Carbon dioxide, hygienically unobjectionable | below 1,000 ppm | ASR A3.6, point 4.2 |
| Air volume per employee, seated activity | 12 cubic metres | ASR A1.2 |
What minimum temperature applies in an office
The minimum temperature in workrooms follows ASR A3.5 and depends on the physical demands of the work and on posture. For light work while seated, the normal case in an office business, an air temperature of at least 20 degrees Celsius applies. Break rooms, sanitary rooms, canteens and first aid rooms need at least 21 degrees Celsius while in use.
A Technical Rule for Workplaces (ASR) is a rule published by the Federal Ministry of Labour and Social Affairs that gives the broadly worded requirements of the Workplace Ordinance concrete values. Anyone who complies can rely on the presumption of conformity in section 3a paragraph 1 ArbStättV. Departing from it means justifying the departure in the risk assessment.
| Physical demand | Mainly seated | Mainly standing or walking |
|---|---|---|
| light work | 20 degrees Celsius | 19 degrees Celsius |
| medium work | 19 degrees Celsius | 17 degrees Celsius |
| heavy work | not provided for | 12 degrees Celsius |
Air temperature is the temperature of the room air measured with a thermometer, and the table above refers to it. Room temperature as ASR A3.5 uses the term is the temperature perceived at the workstation, which also takes in radiant heat from glazing and radiators. A desk at 20 degrees Celsius against a cold glass facade can therefore be criticised.
The minimum value applies throughout working hours, not as a daily average. Requirements at the individual desk are covered in the screen workstation article.
When heat in the office becomes a safety issue
The air temperature in workrooms should not exceed 26 degrees Celsius under ASR A3.5. Above that value ASR A3.5 sets out a three-stage model that turns from a duty to consider into a duty to act as the temperature rises. ASR A3.5 nowhere creates an entitlement to time off because of heat.
| Air temperature in the room | Employer duty | Typical office measures |
|---|---|---|
| above 26 up to 30 degrees Celsius | measures should be taken | use sun protection, night-time cooling, ventilate in the early morning, reduce internal heat sources |
| above 30 up to 35 degrees Celsius | effective measures are required | flexitime and shifted working hours, relaxed dress rules, provide drinks, move tasks to cooler rooms |
| above 35 degrees Celsius | room is not suitable as a workroom without special measures | relocate or interrupt the activity, technical cooling, measures as for hot work |
The hierarchy of controls comes from section 4 ArbSchG and is binding: structural and engineering measures before organisational ones, organisational before personal ones. On a summer day, working shading comes before the flexitime arrangement, and a fan does not cool the air, it only improves heat loss through the skin.
Under ASR A3.5 suitable sun protection has to be provided for windows, skylights and glass walls where solar radiation leads to increased heat load. A south-facing office with a large glazed area and no shading is an open item before the first hot day.
How often an office has to be ventilated
ASR A3.6 requires that healthy breathing air is available in sufficient quantity during working hours. The rule does not set a fixed ventilation interval in minutes but assesses the result through the carbon dioxide concentration of the room air. Below 1,000 ppm the air quality counts as hygienically unobjectionable.
Natural ventilation is ventilation through windows, doors or shafts without a technical system, and the standard case in office buildings. A mechanical system replaces it but must then secure that air quality permanently. Cross ventilation works faster than burst ventilation through a single window; a permanently tilted window is not a suitable measure under ASR A3.6.
| Carbon dioxide concentration | Assessment | Consequence |
|---|---|---|
| below 1,000 ppm | hygienically unobjectionable | no further measures required |
| 1,000 to 2,000 ppm | hygienically noticeable | ventilate more often or reduce occupancy |
| above 2,000 ppm | hygienically unacceptable | further measures required |
For the duration of burst ventilation ASR A3.6 names about 3 minutes in winter, about 5 minutes in spring and autumn and about 10 minutes in summer. The critical room is almost never the single office but the fully occupied meeting room, and a simple carbon dioxide meter there is the cheapest robust measure on this topic.
Air volume and room size: why open-plan offices are noticed first
The air volume per employee should be at least 12 cubic metres under ASR A1.2 for mainly seated activity and at least 15 cubic metres for mainly non-seated activity. As reference values for floor area, ASR A1.2 names about 8 to 10 square metres in a single office and 12 to 15 square metres per workstation in multi-person and open-plan offices.
Three worked examples:
- Single office, 12 square metres, height 2.50 metres. Air volume 30 cubic metres for one person, well above both ASR A1.2 values.
- Two-person office, 20 square metres, height 2.50 metres. Air volume 25 cubic metres per person, floor area 10 square metres per workstation. The area is below the reference value and needs a justification.
- Converted open-plan room, 60 square metres, height 2.75 metres, 12 workstations. Air volume 13.75 cubic metres per person, just above the minimum, floor area 5 square metres per workstation and far below it.
Densifying workstations worsens air volume, floor area and carbon dioxide concentration at once. The duties quick-check shows which duties depend on headcount.
Documenting room climate in the risk assessment
Room climate is not a separate assessment procedure but a chapter of the risk assessment under section 5 ArbSchG and section 3 ArbStättV. What is required is not continuous measurement but a traceable assessment per room type with date, readings, measures derived and a check of effectiveness. Five steps are enough.
- Record measurements. Measure the air temperature at head height of a seated person and near the window, plus the carbon dioxide concentration in the busiest room.
- Compare against the ASR values. Hold the readings against ASR A3.5 and the carbon dioxide thresholds of ASR A3.6, noting deviations with room, date and time.
- Narrow down the causes. Establish whether the deviation comes from solar radiation, missing sun protection, occupancy density, a faulty heating system or blocked ventilation openings.
- Decide on measures and implement them. Work down the hierarchy of controls in section 4 ArbSchG and assign a responsible person and a deadline.
- Document and check effectiveness. Add readings and measures to the documentation and re-measure after the next heating or heat period.
Who ventilates the meeting room and when belongs in the safety training. The office safety checklist turns temperature, ventilation and sun protection into separate check items, and the article on the risk assessment in the office shows where the chapter belongs.
What gets criticised at an inspection is usually the absence of any assessment, not the temperature itself. Breaches of the ArbStättV are administrative offences under section 9 ArbStättV, with a fine range up to 25,000 euros.
What applies at home and for mobile work
The annex requirements on room temperature and ventilation do not apply to teleworking places in the home. Under section 1 paragraph 3 ArbStättV only the risk assessment, the safety training and the requirements for screen workstations apply to teleworking places. For mobile work without a permanently installed workstation the ArbStättV does not apply at all.
The difference in one sentence: in the office on site the employer owes concrete values under ASR A3.5 and ASR A3.6, at a teleworking place only the assessment and the safety training, but no minimum temperature. The general obligation from section 3 ArbSchG remains, and the burden from poor conditions at home belongs in the assessment of mental stress. The line between telework and mobile work is drawn in working from home and telework.
In practice: assess and document the arrangements on site, and cover working from home in the safety training. Both together need an occupational safety specialist on site plus digital, audit-proof documentation. We are happy to clarify open points in an initial conversation.
This article is general guidance and does not replace legal advice on your individual case. What governs is the current version of the ArbStättV and ArbSchG and the current Technical Rules for Workplaces, together with how the supervisory authority for your location interprets them.
