Museums · Guide

Museum and storage climate: keeping temperature, humidity and light in view.

By Frigo · Updated: October 2026

Wood, paper, textiles and canvas react to humidity and temperature, light-sensitive objects to every hour of light. This guide shows which guide values international guidelines and museum associations give, where manual checks reach their limits and what continuous measurement adds. Pick your country and you also see what the museum associations there recommend.

In short

Stability matters: mechanical damage to organic materials is caused mainly by changes in humidity. Slow, seasonal changes are considered less risky than rapid jumps.
Guide values: the Bizot Green Protocol gives, for many objects containing hygroscopic material, a stable 40–60% relative humidity and 16–25 °C, with fluctuations of no more than ±10% RH in 24 hours. Sensitive objects need tighter values.
Light: for very light-sensitive objects, specialist bodies give a maximum of 50 lux. What counts is the total of illuminance and time.
Germany: since 2022 the German Museums Association has recommended a climate corridor of 40–60% relative humidity and 18–26 °C in exhibitions, with gentle changes.
Austria: Museumsbund Österreich, ÖRV and ARC have endorsed this recommendation of the German Museums Association.
Switzerland: since 2024 ICOM Switzerland has recommended climate monitoring close to the objects and gives a corridor of 40–60% relative humidity and 16–25 °C.
The same everywhere: these values are recommendations, not laws. What applies to your objects is assessed by conservators and, for loans, also set by the loan agreement.

Who this guide is for

small and medium-sized museums
collections, archives and libraries
galleries, and churches and castles with exhibitions
people responsible for stores, including off-site stores

The values in this guide are orientation. Individual materials, objects and loans often come with tighter requirements.

Why fluctuations often do more harm than a single value

Wood, paper, parchment, leather, textiles and canvas are hygroscopic: they take up moisture from the air and release it again, swelling and shrinking as they do. The Canadian Conservation Institute (CCI) describes mechanical damage as a result of such changes in humidity. Where parts of an object cannot move freely, they are crushed as they swell and may crack as they shrink. Large fluctuations do more damage than small ones, many repeated cycles more than a few.

A constant value is not automatically good, though. Mould, corrosion and chemical decay depend on how high or low humidity and temperature are over time. The Baden-Württemberg State Office for Museum Support also points out that relative humidity rises when the temperature falls. If you lower the temperature in a store, keep an eye on the humidity.

The CCI also describes that an object which has already experienced a certain fluctuation should suffer hardly any further mechanical damage from another one of the same size, unless it has been weakened for other reasons. The standard EN 15757 builds on the same idea.

Guide values: what international guidelines say

In September 2014 the International Institute for Conservation (IIC) and the ICOM Committee for Conservation (ICOM-CC) agreed a joint declaration on environmental guidelines. It states that collections care should not assume air conditioning and that guidelines for permanent display and storage should be achievable for the local climate. The appendix lists existing guidelines, and the declaration notes that these are intended for international loan exhibitions. In 2023 the Bizot Group carried its guideline over with essentially the same content into the refreshed Bizot Green Protocol.

Guideline	Temperature	Relative humidity
Bizot (appendix 2014, protocol 2023)	stable, 16–25 °C	stable, 40–60%, no more than ±10% per 24 hours within this range
AIC (USA, appendix 2014)	15–25 °C	set point 45–55% with ±5% drift, 40–60% over the year, fluctuations minimised
AICCM (Australia, appendix 2014)	15–25 °C, ±4 °C per 24 hours	45–55%, ±5% per 24 hours, seasonal drift managed gradually up to 40–60%

According to the texts, these values apply to many or most objects, not to all. Bizot states that more sensitive objects need specific and tighter humidity control depending on material, condition and history. For loans, a conservator's evaluation is essential.

EN 15757: the past climate as the benchmark

The European standard EN 15757:2010 contains specifications for temperature and relative humidity to limit climate-induced mechanical damage in organic hygroscopic materials. DIN Media lists it as current. The text of the standard is not freely available, so we rely on a scientific paper describing the method. According to it, the climate to which an object has adapted over a long period serves as the reference. The seasonal pattern is derived from the measured data as a 30-day moving average, and short-term fluctuations around it are compared with limits derived from past fluctuations. The paper states at least one reading per hour. The method therefore requires a long and, as far as possible, unbroken series of measurements.

Light: illuminance and annual exposure

Light damage adds up. The CCI describes exposure as the product of illuminance in lux and time in hours, in other words lux hours. According to the CCI, 50 lux was adopted as the museum benchmark about 60 years ago because the eye still perceives colour well at that level. It is a value for seeing, not a limit below which no damage occurs.

The Scottish museum body Museums Galleries Scotland gives the following maximum values. It assumes 2,184 display hours a year, i.e. seven hours a day, six days a week, over 52 weeks:

Sensitivity	Illuminance	Per year
Very sensitive, e.g. textiles, costumes, prints, watercolours, manuscripts	max. 50 lux	max. 100,000 lux hours
Moderately sensitive, e.g. oil and tempera paintings, wood, furniture, plastics	max. 200 lux	max. 450,000 lux hours
Insensitive, e.g. stone, ceramic, metal, glass	max. 300 lux	not stated

Museums Galleries Scotland refers to CIE 157:2004 of the International Commission on Illumination as the international basis. Assumptions about display hours vary by source, the CCI uses 3,000 hours a year in its examples. What counts is the assessment for your objects.

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Germany: German Museums Association

Climate corridor for collections (September 2022)

Exhibitions: 18 °C (under the workplace regulations) to 26 °C, relative humidity 40–60%. For exhibitions closed to the public for longer periods without permanent workplaces, 15 °C is also possible in winter.
Stores: lower limit 15 °C where the workplace regulations do not apply, upper limit and humidity as in exhibitions.
Fluctuations: guide value ±5% relative humidity and ±2 K within 24 hours. The limits should not be pushed permanently.
Monitoring: any change to existing climate parameters should be accompanied and evaluated with adequate monitoring.

The association issued the recommendation as an emergency measure during the energy crisis. Individual holdings may need adapted conditions, which specialists assess.

Standards for museums, checklist “Preserving permanently”

Minimum standard: relative humidity and temperature are kept as constant as possible, temperatures above 26 °C and below 4 °C are not reached. Humidity is observed. Particularly light-sensitive objects are identified and their lighting is limited in time and quantity of light.
Higher standard: temperature and humidity are measured in the immediate vicinity of climate-sensitive objects, recorded, regularly evaluated and archived. Art transports are monitored with data loggers. Light protection is checked with lux and UV meters or dosimeters.

Both are recommendations and quality criteria of the association, not legal obligations.

Austria: Museumsbund and museum quality seal

What the organisations say

Museumsbund Österreich, ÖRV and ARC: the Austrian Museums Association, the Austrian professional association of conservators (ÖRV) and the Austrian Registrars Committee (ARC) have endorsed the recommendation of the German Museums Association and recommend implementing it within institutions and in lending. In summary they give 15–26 °C and 40–60% relative humidity, with ±5% humidity and ±2 K within 24 hours.
Monitoring: they stress that changes to existing climate parameters must be accompanied and evaluated with adequate monitoring. The type and extent of implementation are up to each museum.
Museum quality seal: the criteria catalogue (2021) lists humidity, temperature and light among the most common causes of damage. The collections care plan should list conservation measures, measurements and checks, and the security plan should cover the control of light, humidity and temperature. The catalogue gives no specific figures.

Switzerland: ICOM Switzerland and VMS

Recommendations for climate monitoring (December 2024)

Corridor: 40–60% relative humidity and 16–25 °C over the year, with no more than 10% humidity and 4 K fluctuation within 24 hours. Seasonal, gradual changes are considered harmless, and the corridor should not be pushed to its limits at short intervals.
Where to measure: close to the objects, not in the supply or exhaust air of air-conditioning and not near entrances and exits, ideally out of visitors' reach. In showcases, measure at the object. An outdoor measurement helps with interpretation.
Evaluation: a log of special events, such as maintenance, events or closing days, helps with interpretation. Measures should only be planned once comparable data are available for at least one year with two seasonal changes.
Equipment: humidity sensors are not stable over the long term, and their calibration should be checked every year. Networked devices should only be installed where quick intervention in the event of network faults is ensured.
Loans: the borrower's climate data should be actual values, not set points, cover the same months as the loan request and show short fluctuations, for example with readings every 10 minutes.

The recommendations are published on the museum climate platform of ICOM Switzerland and the Swiss Museums Association (VMS). They are professional recommendations, not regulations.

Where a manual check leaves gaps

Stores. Hardly anyone spends long there. According to the Baden-Württemberg State Office, climate damage often goes unnoticed at first, and the first fine cracks cannot be seen with the naked eye.
Weekends, public holidays, closing days. If heating or a dehumidifier fails on Friday evening, without an alert it is only seen on the next round.
Showcases. The climate in a showcase can differ from the room. ICOM Switzerland points to possible higher pollutant levels in tightly sealed showcases and, for actively conditioned showcases, to the risk that a device fault changes the showcase climate in an uncontrolled way.
Loans. In lending, actual values are needed, not set points. According to the Baden-Württemberg State Office, objects from a markedly different climate, such as an unheated church, need to adapt slowly. Ask the lender about previous conditions.
Spot checks. A handheld meter shows a single moment. Fluctuations within 24 hours, which the guide values refer to, only show up in a continuous record.

What a sensor adds

A sensor measures temperature and relative humidity around the clock. Light can also be activated where it makes sense. Every reading goes into a continuous, time-stamped record. For each sensor you set an upper and a lower limit. If a value leaves that range, all named people receive an alert by app and email, with SMS as an option.

A monthly PDF report is created automatically for each sensor, and the data can be exported at any time. Frigo AI sums up each week, per sensor and in plain language, what stood out, with a severity level. If a sensor or the connectivity unit stops sending data, Frigo alerts the named people, so gaps in the record become visible at once.

The sensors are wireless and stick on, with no drilling and no cables. Installation takes under five minutes per sensor, which can help in churches, castles and other historic buildings. One connectivity unit per site usually suffices: it plugs into a socket and has its own mobile connection, so no Wi-Fi is needed. Larger buildings may need several units. Museum and off-site store can be managed in one workspace. Whether a sensor makes sense in a particular showcase depends on the showcase and the radio connection, which we clarify case by case.

Important: Frigo measures the air at the sensor's location, not inside the object. It controls neither heating nor humidification or dehumidification and replaces neither the assessment by conservators nor the terms of a loan agreement. Please check with us before use whether measurement accuracy and calibration are sufficient for your purpose, for example for a facility report.

If power fails, the connectivity unit keeps running on its built-in battery for about four hours and sends alerts as long as the mobile network is available. Once the battery is empty, Frigo reports that the connectivity unit has stopped sending data. The sensors do not store readings, so there is no data for that period. New readings arrive once the connectivity unit has power again.

How the system is built is explained under How does Frigo work?.

Four things to set per room

the range for temperature and relative humidity, agreed with your specialists and, for loans, with the loan agreement
the measuring point: close to the objects, not in the airflow of heating or ventilation and not right by doors
who is notified, including at weekends and on closing days
who checks on site, what to do then and where special events are noted

Frequently asked questions

What temperature and humidity apply in a museum?

There is no single legal value. The Bizot Green Protocol gives, for many objects containing hygroscopic material, a stable 40–60% relative humidity and 16–25 °C, with fluctuations of no more than ±10% RH in 24 hours. The German Museums Association recommends 40–60% relative humidity and 18–26 °C in exhibitions, ICOM Switzerland 40–60% and 16–25 °C. Tighter values apply to sensitive objects.

Why are fluctuations a problem?

Organic materials swell and shrink with humidity. According to the Canadian Conservation Institute, mechanical damage such as cracks is caused by these changes, and larger and more frequent fluctuations do more damage. ICOM Switzerland considers slow, seasonal changes within a corridor harmless.

How much light can light-sensitive objects take?

For very light-sensitive objects such as textiles, watercolours, prints and manuscripts, Museums Galleries Scotland gives a maximum of 50 lux and 100,000 lux hours a year. The Canadian Conservation Institute stresses that exposure is illuminance multiplied by time and that 50 lux is a value for seeing, not a damage limit.

What does the standard EN 15757 require?

The standard aims to limit climate-induced mechanical damage in organic hygroscopic materials. According to a scientific paper, the climate to which objects have adapted over a long period serves as the reference. The seasonal pattern and short-term fluctuations are derived from data with at least one reading per hour. The exact text of the standard is available from the standards bodies.

Where should a measuring device be placed in a room?

ICOM Switzerland recommends measuring points close to the objects, not in the supply or exhaust air and not near entrances and exits, ideally out of visitors' reach. In showcases, measurements should be taken at the object. An additional outdoor measurement helps with interpretation.

Does Frigo replace conservation climate monitoring?

No, Frigo supports it. Frigo measures the air at the sensor's location, keeps a continuous record and alerts you to deviations. Assessment, limits and measures remain with your specialists and the loan agreements. Please check with us beforehand whether the measurement accuracy is sufficient for your purpose.

Sources

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This article is guidance, not legal advice and not conservation advice. It reproduces recommendations from professional associations and specialist bodies, which can differ. What counts is the assessment of your conservators, loan agreements and lenders' requirements, and the manufacturers' information. Frigo measures at the sensor's location, not inside the object, and does not control anything. Alerts require a working connection. During a power cut the connectivity unit keeps running on its built-in battery for about four hours, after that Frigo reports that the connectivity unit has stopped sending data. Sources as of: October 2026.