Climate-controlled storage is storage in a building that holds temperature and relative humidity in a steady range all year, instead of letting the air inside follow the weather. It protects belongings that react to the air, such as wood furniture, pianos, leather, photographs, paper, art, electronics and wine, from the damp, heat and fast swings that cause cracking, warping, mold and corrosion.
What temperature and humidity control means
Relative humidity (RH) is how damp the air is, as a percentage, and it moves with temperature: when air cools, its RH rises, and when it warms, its RH falls. The Canadian Conservation Institute (CCI) gives an example of each extreme. A temperature drop of more than 10°C (18°F) can take the air to 100% RH, where water condenses on surfaces, and summer sun on a poorly ventilated attic drives the temperature very high and the RH very low.
That matters because wood, leather, paper and fabric take moisture from the air and give it back, swelling and shrinking as they do. Where a part is held tight, such as veneer glued across a joint, the stress builds, and that is where cracks, splits and lifting start. A climate-controlled building keeps temperature and humidity steady so those materials move as little as possible.
Why steady conditions matter more than one number
Look up the ideal storage humidity and you will find a different figure for each material. The Library of Congress recommends 30% to 50% RH and 70°F or below for photographs, with daily swings under 5%, and about 35% RH at room temperature or below for paper. The National Park Service warns that upholstery fabric can grow mold above about 65% RH and that textile fibers turn brittle below about 40%. The CCI says a perfectly correct RH value may not exist, and that the range doing the least harm is much wider than museums once assumed.
Where the sources agree is on what to avoid. The first is damp. The CCI puts the practical boundary at 75% RH, notes that the time before visible mold appears shortens sharply between 70% and 90%, and explains that the film of water on metal surfaces grows rapidly above 75%, which speeds corrosion. The second is large, fast swings in humidity, which crack and distort wood and make paint crack and flake. The CCI adds that a stable RH is no help if it sits inside the mold danger zone. What protects most household goods is a range that stays out of the extremes and changes slowly.
Household items that react to heat and humidity
| Item | What can go wrong | Conditions to avoid |
|---|---|---|
| Solid wood and veneered furniture | Cracks, splits and permanent warping; veneer that buckles as it swells and the glue softens | Large humidity swings; damp |
| Pianos and wooden instruments | Cracking and distortion in wooden parts | Humidity swings; high humidity |
| Leather | Mold that discolors or breaks down the surface | Damp |
| Upholstered furniture | Mold on fabric; rusting tacks and springs that stain the fabric and stuffing; brittle fibers | Above about 65% RH; below about 40% RH |
| Photographs | Faster deterioration, driven mainly by humidity for prints and by temperature for color photos and negatives | Damp, heat and daily swings |
| Paper, books and documents | Mold, especially on dirty or starched paper | Damp; heat; attics and basements |
| Paintings and framed art | Paint that cracks, flakes or separates | Humidity swings, especially toward dry air |
| Electronics and media | Corroded metal parts; condensation; tapes and discs that distort in heat | Damp; sudden cooling; heat |
| Wine | Fast, uneven aging; air getting past the cork; natural corks drying out | Temperatures above 75°F; day and night swings; very dry air |
Climate-controlled storage for furniture and pianos
Damage to wood from humidity swings is often permanent: the CCI lists cracks, splits, delamination and lasting distortion. It places veneer over corner joints (common on wardrobe doors and secretary desks) among the more vulnerable constructions, along with many musical instruments, which it calls often very sensitive to humidity swings and high humidity. If a piano is going into storage between homes, our guide to moving a piano safely covers the move itself.
Photographs, paper and art
For most photographic prints, the Library of Congress names humidity as the single most important factor. For color photographs and film negatives, temperature controls stability, and the Library recommends storage at 40°F or below. Clean paper resists mold until the air reaches about 80% to 85% RH, according to the CCI, while dirty or starched paper is more vulnerable. The CCI also notes that a swing toward drier air is a much higher risk for paintings than a swing toward damper air.
Electronics and wine
For electronics, damp air and condensation are the main concerns, since metal parts corrode. The CCI calls a temperature drop of more than 10°C the most dangerous kind of fluctuation, because it brings condensation. Heat is the other risk: the base of audio, video and data tapes deforms permanently, and discs distort quickly in direct sun.
For wine, Purdue University's enology extension names high temperatures and temperature swings as the greatest storage hazards. It puts long-term storage at 50°F to 60°F (10°C to 16°C), allows up to 75°F for one to four weeks, and says wine should never see 86°F (30°C) or above. Swings can let air in past the cork, and the Australian Wine Research Institute adds that natural corks can dry out and leak in very dry air. Our guide to packing a wine collection covers getting bottles ready to move or store.
Why a garage, shed or attic is a poor place for a long stay
The Library of Congress tells readers to keep photographs and paper out of attics and basements, and to keep photographs away from vents, radiators, exterior walls and anywhere at high risk of condensation, leaks or extreme swings. According to the CCI, attics overheat in summer sun, which drives the humidity very low. Basements, and ground floors in buildings without one, are associated with damp, either rising through the structure or condensing on cold surfaces.
Garages and sheds are not named in these guides, but most share the problem. They are rarely heated, cooled or insulated the way a house is, so the air inside follows the weather: warm afternoons, cool nights and damp spells. When a warm, humid afternoon gives way to a night more than 10°C (18°F) cooler, that is enough for condensation. The longer the stay, the more of those cycles a dresser, a box of photographs or a case of wine goes through.
Questions to ask a storage provider
- Is the whole building climate-controlled all year, or only some units?
- Do you control humidity as well as temperature, and how do you keep it steady?
- If something I own needs a specific range, such as wine, can you tell me before I book whether your building suits it?
- Who loads and unloads, and are my things wrapped and inventoried first?
- Are my belongings sealed in a space of their own, apart from other customers' goods?
- How is the building secured, cleaned and kept free of pests?
- How is storage billed, and is there a minimum term?
- What liability applies to my goods while they are in storage?
Here is how we answer most of them. At Silicon Valley Moving & Storage, our own crew inventories, wraps and loads your belongings at your home. The truck goes to our warehouse at 186 Barnard Ave in San Jose, where the crew unloads everything into sealed, labeled vaults that never leave the building. The warehouse and vaults are climate-controlled with stable humidity, and the building has 24/7 security monitoring, controlled access and on-site security. It is built to fire and military code, with daily cleaning and pest control. Storage is billed per vault, per month, month to month with no minimum, and labor is quoted separately. Our page on climate-controlled storage in San Jose covers the process, and specialty storage covers wine, art, antiques, instruments and electronics.
Quick answers
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Do I need climate-controlled storage?
Probably, if you are storing wood or veneered furniture, a piano, leather, upholstery, photographs, papers, paintings, electronics or wine for months. Those materials crack, warp, grow mold or corrode when the air turns damp, gets very hot or swings quickly.
What is the difference between climate-controlled and regular storage?
Storage without climate control has no heating, cooling or humidity control, so the air inside follows the weather outside. A climate-controlled building holds temperature and relative humidity in a steady range all year, which helps protect wood, leather, fabric, paper and metal from cracking, warping, mold and corrosion.
What humidity is best for storing furniture?
There is no single correct number. The Canadian Conservation Institute puts the practical limit for damp at 75% relative humidity and says the least harmful range is wider than museums once assumed. For upholstery, the National Park Service warns of mold above about 65% and brittle fibers below about 40%. For wood, large and fast swings are what cause cracking and warping.
Can I store photographs and papers in an attic or basement?
The Library of Congress advises against both. Attics overheat in summer, which drives humidity very low, and basements tend toward damp. It recommends a cool, dry and stable space instead.
Putting furniture, a piano or a collection into storage while you move or renovate? Tell us what you are storing and request a free storage quote or call us at (408) 941-0600. If something you own needs a specific temperature or humidity range, ask us before you book.
Sources: Canadian Conservation Institute, Agent of Deterioration: Incorrect Relative Humidity and Agent of Deterioration: Incorrect Temperature (Stefan Michalski), and Musical instruments; Library of Congress, Care, Handling and Storage of Photographs and Care, Handling, and Storage of Works on Paper; National Park Service, Conserve O Gram 7/4, Upholstered Furniture: Agents of Deterioration; Purdue Extension, Wine Storage Guidelines (FS-58-W, Christian Butzke); Australian Wine Research Institute, Transport and storage. The right conditions differ by material; for a valuable piece, ask a conservator about its specific needs.