Short answer
Store papers in acid-free boxes, on shelves off the floor, in a unit kept below 75°F and below 65% humidity. A climate-controlled unit does this best. Keep originals you can't replace, like birth certificates and passports, at home in a locked, safe place instead.
Paper holds up well if it stays cool, dry and steady. It fails quickly when it gets damp. Most document damage in storage is mold and water, not age.
The conditions paper needs
The National Archives gives simple limits for family papers: keep the temperature below 75°F and humidity below 65% to prevent mold and reduce insects. It also warns that humidity below 15% can make paper brittle.
The Library of Congress aims lower still, recommending a cool, relatively dry environment at about 35% relative humidity that stays stable. A climate-controlled unit gets you much closer to that than a regular one.
Pick the right boxes
Ordinary cardboard is acidic and can stain papers over time. The National Archives recommends boxes and folders made of stock that is lignin-free and acid-free or buffered, and says, “Don’t overstuff the box.”
Some extra tips:
- Keep acidic paper, like newspaper clippings, apart from other documents. The Library of Congress recommends storing acidic papers separately so the acid doesn’t spread.
- Remove rubber bands and metal clips, which can rust and stain.
- Use file boxes with lids, labeled on the outside.
Where to put them in the unit
The National Archives advice applies directly:
- Store items on a shelf so they don’t get wet.
- Keep them away from leaks, such as the roof line or the door.
- Keep food out of the unit, since it attracts insects and rodents.
- Avoid spaces like damp basements, garages and hot attics, which a regular unit closely resembles.
A simple metal shelf unit lifts boxes clear of any water that gets in under the door.
What not to keep in a storage unit
Some papers are too important to leave in a place you visit rarely. The FTC lists documents to keep forever and lock up, including:
- Birth certificates and adoption papers
- Social Security cards
- Passports and citizenship or residency papers
- Wills, powers of attorney, and pension and retirement plans
Keep the originals at home, in a fire-resistant safe or a bank deposit box. If you store copies or older records in a unit, shred anything with account numbers you no longer need.
Business and tax records
Many small businesses use storage for files. The same rules apply: acid-free boxes, shelves, a controlled unit. Keep a list of what’s in each box so you can find a single file without opening every one.
If you store files in a city with damp summers, compare verified options such as climate-controlled storage in Charlotte, and ask how each facility manages humidity.