Condensation is water vapour in the air turning back into liquid water when the air cools to its dew point, the temperature at which it can hold no more moisture. It shows up as droplets or a damp film on the coldest surfaces nearby: a window, a metal wall, a concrete floor, or the side of a box.
At Wigwam
Our units aren't climate-controlled. They're clean, dry and secure, but the temperature and humidity inside aren't regulated, and you can't change that yourself: our terms don't allow portable heaters in a unit at any time (clause 19), and you can't connect any utilities or services to a unit unless we've authorised it (clause 22(e)), so there's no power for a dehumidifier.
The outdoor steel containers at Chipping Norton, Shipston-on-Stour and Warminster are watertight, which keeps rain out but doesn't stop condensation forming inside. Our booking system lists the Chipping Norton containers as insulated against condensation; ask us about the others before you book. For our indoor units, we don't publish the conditions inside or how each building is insulated, so if condensation is a worry for what you're storing, ask us about your site.
Why it matters
Warm air holds more water vapour than cool air, so the same air can be dry by day and wet by night. The Canadian Conservation Institute gives the numbers: air at 50% relative humidity cooled by 10°C reaches 100%, and any further cooling puts water on objects. Much of that water can come in with damp items, so pack them clean and completely dry, on a dry day if you can, keep them off the floor, and leave a gap at the walls.
It also matters if something is damaged. Our Contents Protection (an RSA Self Storage Customers' Goods policy) lists burst pipes and water leakage among the risks it covers, but the same policy excludes atmospheric or climatic damage, so condensation is something to prevent rather than insure.
Related terms: Relative humidity · Damp · Temperature fluctuation · Container unit
Related questions: Do storage units get cold in winter or hot in summer? · Are storage units waterproof?