Guidance note on environmental management for collections and climate sustainability 

24 Nov 2023

This short guidance note was prepared by a group of committed Icon accredited conservators and conservation scientists in response for the need for cultural heritage institutions to operate in a more sustainable manner in response to the global climate crisis, rising energy costs and local and national carbon reduction policies.

Since the 1970s a set of narrow parameters for relative humidity (RH) and temperature have come to be accepted as the ‘gold standard’ for preventive conservation. However, achieving and maintaining these narrow parameters has proven difficult and costly, both financially and in terms of greenhouse gas emissions. And, for the vast majority of historic materials there has been no need for storage or display within these narrow parameters.

As a result, conservation professionals are moving away from the idea of a one-size-fits-all set of parameters to a context based approach. This means providing environmental conditions which mirror the historic conditions the materials have been kept in for decades, and often centuries, the historic annual relative humidity (RH) averages, local climate, seasonal changes and geographical location which take into account risk.1

The greatest risk to materials in daily practice is poor handling, often referred to as physical force followed by fire, water and pests. Other risks you might like to consider are theft, vandalism, neglect, chemical deterioration, temperature and light.

What does this mean for you?

  • As experienced conservation professionals, we can offer the reassurance that maintaining RH in the range of 35% to 65% is proven to be safe and sustainable for materials housed in a well maintained building - in the UK.2
  • Keeping rooms cooler over winter will help to maintain RH above 35% and reduce your energy bill.3
  • For storage areas and display spaces that are closed for extended periods over the winter, such as show rooms in historic houses, temperature levels can be lowered even further to above 5ºC. It is important to maintain at least 5ºC to minimise the risk of water freezing in pipes and causing a leak. Cold temperatures represent a low risk to most historic materials and actually increase preservation lifespans of objects.4

So why does relative humidity matter so much?

Relative humidity mainly affects organic materials such as wood, paper, and textiles made of natural fibres. It influences the rate of damaging chemical reactions, mould growth, and insect activity. Fluctuations outside of 35% to 65% can cause cracking, warping, and other forms of irreversible damage to the organic objects in your collection. However, it’s useful to note that many organic objects will safely and slowly acclimatise to the environment they are kept in over time, even when it is less than ideal. In this case moving the objects or changing the average RH levels may pose a greater risk of causing damage.5,6

Remember that maintaining a consistent relative humidity around 35% to 65% is the key to preserving your collections. Drift within these parameters is OK. Large variations are not. By focusing on maintaining consistent levels to those achieved in previous years, perhaps a bit cooler over winter, you will be able to save on energy costs and reduce your climate impact without compromising the preservation of your collections. It's a win-win situation!

It is recommended that you seek preventive conservation advice for the small number of materials including, for example; archaeological iron and copper, panel paintings and parchment, which require specific conditions and RH control measures. A preventive conservator can help you evaluate sustainable options for humidity control as well as offering advice on other risks facing your collections. Icon Accredited preventive conservators can be found by searching the Conservation Register using “preventive conservation” or “collections care.”


Dr Christian Baars ACR, National Museums Liverpool
Michelle Stoddart, Science Museum Group
Dr Nigel Blades ACR, National Trust
Kathryn Hallett ACR, Historic Royal Palaces
Amber Xavier-Rowe ACR, English Heritage Trust
Pedro Gaspar, V&A
Prof Sarah Brown, The York Glaziers Trust
Linda Ramsay ACR, National Records of Scotland
Saya Honda Miles, Historic England Archive
Jane Henderson ACR, Cardiff University

(Supporters updated 08/01/2024)

To note: There are exceptions to any general guidance. Please ensure that you consult with a fully trained/ qualified conservator restorer prior to implementing any changes.


Why is this being published this now?

The climate emergency is exponentially increasing whilst practice around environmental control continues to follow guidance based on temperature and relative humidity bands. There have been several discussions during 2023 at UK and international levels about the relevance and appropriateness of older environmental guidance. Arts Council England are in the process of updating the Government Indemnity Scheme Guidance to reflect an approach based on risk management rather than temperature or humidity values Government Indemnity Scheme | Arts Council England; the Bizot Group have been discussing an update to their Green Protocol which follows the same path; the National Museum Directors’ Council advocate a risk management approach to lending collections items Principles For Lending And Borrowing - National Museum Directors' Council Website (  As we are moving away from recommending set ranges for material and following a risk management approach, Icon is also conscious that there are a number of organisations that will not have the conservation expertise to aid is such decisions therefore we felt it appropriate to publish this guidance.

What is its purpose?

To support institutions which do not have conservators on their staff and to advocate for a risk-based approach to decision making around temperature and relative humidity levels to reduce energy use.

Who drafted this guidance?

It was drafted by Lorraine Finch ACR and Dr David Thickett. This was also discussed with members of Icon's Policy Forum. 

If you have any specific feedback please send this through to [email protected] so that it can be shared with the authors. 

All members are invited to join the Icon Policy Forum. If you wish to take part, please email [email protected] 

When was it written?

November 2023.

Who are the supporters so far?

In 2023 the Supporting institutions are:

Dr Christian Baars ACR, National Museums Liverpool
Michelle Stoddart, Science Museum Group
Dr Nigel Blades ACR, National Trust
Kathryn Hallett ACR, Historic Royal Palaces
Amber Xavier-Rowe ACR, English Heritage Trust
Pedro Gaspar, V&A
Prof Sarah Brown, The York Glaziers Trust

Can I add my institution to list of supporters?

Yes! Please contact Geanina Beres, Communications Manager at Icon to do so by emailing [email protected]


  1. Environmental Statement from Heads of Conservation in the UK.
  2. Comparison of Environmental Control Strategies for Historic Buildings. David Thickett
    p314-320, Studies in Conservation. Volume 65, 2020 - Issue sup1: Special issue: IIC 2020 Edinburgh Congress preprints.
  3. Conservation Heating 24 Years On. Nigel Blades, Katy Lithgow, Sarah Staniforth & Bob Hayes. p15-21, Studies in Conservation. Volume 63, 2018 - Issue sup1: IIC 2018 Turin Congress preprints.
  4. Principles for developing low-cost, sustainable stores. Xavier-Rowe, A., P. Lankester, and D. Thickett. Transcending Boundaries: Integrated Approaches to Conservation. ICOM-CC 19th Triennial Conference Preprints, Beijing, 17–21 May 2021, ed. J. Bridgland. Paris: International Council of Museums.
  5. BS EN 15757: Specifications for temperature and relative humidity to limit climate-induced mechanical damage in organic hygroscopic materials.
  6. The Ideal Climate, Risk Management, the ASHRAE Chapter, Proofed
    Fluctuations, and Toward a Full Risk Analysis Model. Stefan Michalski. Contribution to the Experts’ Roundtable on Sustainable Climate Management. April 2007.