Archive Storage Conditions: Humidity, Temperature and Light, and the Record That Proves Them
TL;DR: Archive storage conditions come down to four agents of deterioration: relative humidity, temperature, light and pollutants. The Archives and Records Association advises a consistent relative humidity between 35% and 60%, cool conditions with gradual rather than sudden change, and notes that light damage is cumulative and cannot be reversed. The Canadian Conservation Institute measures light as a dose, lux multiplied by hours. Continuous wireless logging gives the record, but it only protects a collection if someone reviews it and acts.
Last updated: 14 September 2026
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Key takeaways
- Archive storage conditions are shaped by four agents of deterioration: relative humidity, temperature, light and pollutants.
- The Archives and Records Association advises a consistent relative humidity between 35% and 60%, and says gradual change in RH and temperature is acceptable.
- BS 4971:2017, as quoted by the ARA, puts the emphasis on keeping temperature low and relative humidity moderate.
- Light damage is cumulative and irreversible. The Canadian Conservation Institute measures exposure as lux multiplied by hours.
- A record protects nothing on its own. The ARA says monitoring data must be reviewed, interpreted and acted upon.
What damages archives in storage?
Archives are damaged by four things the Archives and Records Association calls agents of deterioration: relative humidity, temperature, light and pollutants. Its guide to environmental management for paper archives explains that, left uncontrolled or incorrect, each one causes damage and speeds up deterioration.
The effects are specific. High relative humidity can cause mould, more pest activity, cockling of paper, warping of boards and corrosion of metal fasteners. Low relative humidity can cause embrittlement, splits and tears, and chemical deterioration such as yellowing. Warmth speeds up decay, softens waxes and coatings and makes adhesives fail, while very low temperatures leave objects stiff and brittle.
Good archive storage conditions manage all four, but relative humidity and light are where continuous monitoring earns its keep, because both do damage slowly and out of sight.
What relative humidity should an archive store be kept at?
Good archive storage conditions start with a consistent relative humidity between 35% and 60%, according to the Archives and Records Association. It adds that gradual change in relative humidity and temperature is acceptable, and that microclimates suit material with specific needs.
In archive storage conditions, consistency matters as much as the range. The ARA notes that when warm air is cooled, relative humidity rises, and when cold air is heated it falls. A store where the heating runs by day and switches off at night can cycle through a wide humidity swing every 24 hours without the average ever looking wrong.
The sector has also moved away from one set of numbers for every collection. The ARA describes a context-based approach, where archive storage conditions reflect the conditions the material has historically been kept in, seasonal change and location, with risk taken into account.
What temperature is best for archive storage?
For temperature, the best archive storage conditions are cool and steady. The ARA says paper-based archive materials benefit from consistently cool conditions, and quotes BS 4971:2017: to slow the rate of decay of all archive material, there should be an emphasis on keeping the temperature low and the relative humidity moderate.
Temperature swings matter less in themselves. The ARA describes temperature fluctuation as a low threat to archive materials, but warns that it may cause a matching fluctuation in relative humidity, which is why the two are always logged together.
In practice, monitoring archive storage conditions means watching trends, not single readings. A store that creeps a few degrees warmer every summer, or a room above a boiler that runs warm all winter, shows up clearly in a continuous record.
How much light is too much for a collection?
Any light is too much for the most sensitive material, because light damage adds up. The ARA states that all light is damaging, that light high in blue and ultraviolet such as daylight is the most damaging, and that light damage is cumulative and cannot be reversed.
The Canadian Conservation Institute, in its guide to light, ultraviolet and infrared, describes the total exposure of a surface as the product of light intensity in lux and time in hours. It explains that conservation adopted 50 lux as a benchmark for sensitive objects because it keeps the human eye well within full colour vision, and that ultraviolet and infrared are not necessary for seeing, so they are simply damaging.
Dose is what makes a light record useful when judging archive storage conditions. An object lit at 50 lux for 8 hours a day over 300 days receives 120,000 lux hours; the same object at 200 lux for 2 hours a day over the same days receives exactly the same dose.
How should you monitor archive storage conditions?
Monitor archive storage conditions continuously, and review what you record. The ARA describes three approaches: spot readings with a handheld device, dataloggers that record at set intervals, and telemetric systems that send readings by radio. Continuous methods capture both short changes over minutes and long changes over months.
Four practices make a record of archive storage conditions worth having.
- Review and act. The ARA is blunt: it is not sufficient to measure, record and archive data; it must be reviewed, interpreted and acted upon.
- Measure inside enclosures too. Conditions inside boxes and storage furniture can be very different from the room, so the ARA suggests monitoring inside them.
- Calibrate. Maintain equipment and calibrate it periodically, so the data stays accurate.
- Place sensors thoughtfully. Mount room sensors on internal walls at object height, away from radiators, doors and direct sun, and give rooms under roofs or against external walls their own sensor.
Wireless monitoring removes the manual download that dataloggers need, but the building matters. The ARA notes that radio telemetry can struggle to transmit through the structure of historic buildings, so test the signal from the most enclosed store first.
What are the limits of wireless monitoring?
Wireless sensors record archive storage conditions; they do not replace conservation judgement. Four limits are worth knowing.
- No ultraviolet reading. A lux sensor measures visible light, not ultraviolet, which the ARA and CCI both identify as especially damaging.
- Not reference instruments. Monitoring sensors should be checked against a calibrated reference; we suggest doing it once a year.
- No pollutants. Dust and gases from paints, glues and air fresheners are agents of deterioration that temperature and humidity sensors do not see.
- No control. Sensors alert; they do not run humidifiers, dehumidifiers or heating.
What does an archive monitoring kit include?
Logging archive storage conditions needs a gateway, a humidity and temperature sensor per store and a light sensor for sensitive displays. Our archive and collections monitoring kit combines a UG63 gateway, four AM102L sensors and an EM500-LGT light sensor, with live prices and one click to the basket.
The AM102L reads temperature to ±0.2°C between 0°C and 60°C and relative humidity to ±2% at 25°C, and has no screen, so it stays discreet in a reading room or gallery. For more on measuring light, see our guide to lux levels, and for choosing between Milesight’s ambience sensors, the AM102 vs AM102L vs AM103 comparison.
Frequently asked questions
What humidity should archives be stored at?
For archive storage conditions, the Archives and Records Association advises a consistent relative humidity in the range of 35% to 60%, with gradual rather than sudden change.
What temperature should archives be stored at?
Cool and stable. The ARA quotes BS 4971:2017, which puts the emphasis on keeping temperature low and relative humidity moderate, and notes temperature swings matter mainly because they drive humidity swings.
How many lux is safe for sensitive archive material?
The Canadian Conservation Institute explains that 50 lux became the conservation benchmark for sensitive objects. Damage depends on dose, lux multiplied by hours, so exposure time matters as much as the level.
Do wireless sensors work in historic buildings?
Often, but thick walls can block radio. The ARA notes that telemetry can struggle through historic structures, so test the signal from the most enclosed store before installing.
How often should monitoring sensors be calibrated?
The ARA says to maintain equipment and calibrate it periodically. We suggest checking monitoring sensors against a calibrated reference instrument once a year.
Keep the record, and read it
Archive storage conditions are won slowly: a steady humidity band, cool rooms and a controlled light dose, proved by a continuous record that someone reviews.
See the archive monitoring kit with live prices, or send us the number of stores and displays and an engineer will plan the sensors within one working day.
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