No. Don't plan on running a dehumidifier: our terms don't let you connect any utilities or services to a unit unless we've authorised it, so ask us first if you think you need power. What keeps a container dry is dry packing, moisture absorbers that need no power, breathable covers, and a look in through the winter. Our booking pages for Chipping Norton and Shipston-on-Stour say "We also insulate our containers to stop condensation"; for any other container, including Warminster's, ask when you book.
Why containers get condensation
Condensation forms when moist air cools against a colder surface. In a steel container that surface is the steel. As our guide to self storage versus a shipping container puts it, "When the outside temperature drops overnight, the internal surfaces of the container cool down fast." The same guide says the moisture comes from two sources: "the air itself and the goods you bring in".
Insulation works on the first source, the cold steel. It can't take out moisture that arrives with your goods, which is why packing matters even in an insulated container.
What to use instead of a dehumidifier
Clause 22(e) of our storage agreement says you mustn't "connect or provide any utilities or services to the Unit unless authorised by Us", and clause 19 says "You must not use portable heaters in the Unit at any time." Passive kit does the job without power:
| What | What it does | Where it goes |
|---|---|---|
| Tub-style moisture absorbers (supermarkets and hardware shops sell them) | Pull moisture out of the air without power | Standing level and clear of your things; replace them when they're full |
| Rechargeable desiccant packs (the kind you dry out at home) | The same job, with no power needed in the unit | Take them home to recharge, and swap in a dry set while they do |
| Silica gel sachets | Absorb moisture at item level | Inside sealed tubs of small metal parts, electronics, books, documents and photos |
| Pallets or off-floor racking | Keep things off the cold floor | Under everything that isn't on its own legs. Bring your own pallets. |
| Breathable covers (blankets, dust sheets, old cotton sheets or duvet covers) | Keep dust off without trapping damp | Over furniture, mattresses and leather |
| A small battery hygrometer | Shows the relative humidity when you visit, and so whether your absorbers are enough (there's no set number) | Somewhere you'll see it as you open the door |
Plastic for the move, breathable covers in the unit
Use plastic for the move, breathable in the unit: take off any plastic wrap the removal company put on, because plastic sealed around furniture for months traps moisture against it. A mattress can stay in a mattress bag once it's completely dry, but don't seal a mattress bag airtight: leave the open end open, or use a breathable cover (see mattress bag).
Packing a container so condensation has little to work on
- Dry everything first, including defrosted fridges, freezers and washing machines, left with the door ajar. Our container guide is plain about damp goods: "you will seal the problem in and make it worse", so anything already damp or showing mould stays out.
- On a very cold day, let items from a freezing van warm up before you seal them into tubs or boxes: cold metal can take a film of moisture as it warms.
- Lift everything off the floor on pallets or racking.
- Leave gaps around and between stacks, and away from the walls, so air can move.
- Put the absorbers in last, where you can reach them without unstacking.
Clothes and leather furniture
Clothes go in a rigid lidded container, bone dry, with the lid on but not sealed. Vacuum bags trap any moisture left in the fabric, so keep them for short stays; our guide to stopping clothes going musty in storage covers clothes in detail.
Leather: damp can mould and discolour it, as the Canadian Conservation Institute notes. Clean and dry it (condition it if you normally do), cover it with breathable fabric, stand it on pallets or blocks, and keep it off the walls.
Tools, metal parts and business stock
Bare metal and machine tools can rust from condensation. Clean and dry each part, give bare metal a light protective wipe at home, and leave the tin or spray at home: clause 18(c) bars "combustible or flammable substances including but not limited to gas, paint, petrol, oil, cleaning solvents or compressed gases". Then pack small parts in sealed tubs with silica gel sachets, and keep power tools in closed cases with silica gel.
Aerosols, including spray lubricants and spray paint, can't be stored whether or not the can shows the flame symbol: an aerosol is a pressurised can of gas. A petrol engine can go in once it's been run completely dry (tank emptied, carburettor run until the engine stops, oil drained). If it still smells of fuel, leave it out (clause 18(f) bars "any item that emits fumes, or odours"), and keep the fuel itself somewhere else. Fuel cans can't go in, even empty.
For fabric rolls and soft stock on a long stay, swap sealed polythene sleeves for breathable wrap.
Already storing? What to do if you find condensation
A hygrometer tells you when to act, and it reads relative humidity (RH). The Canadian Conservation Institute's guidance reads: "At 60% RH visible mould growth just possible on some surfaces", and "any intermittent period at less than 55% will stop growth". It counts "Damp, over 75% RH", and says "above 75% RH all corrosion speeds up a lot". So:
- Under 60%: carry on, and don't worry about a brief rise.
- Staying above 60%: add absorbers, empty full ones, and check that nothing is touching the walls or sitting on the floor.
- Above 75%, or water on the walls or metal: act on that visit. Wipe metal dry, take anything damp home to dry, and ask us on 0800 2545585 about moving to an indoor unit at the same site. Can I switch from an indoor unit to a container? compares the two.
Clause 26 advises you "to inspect the Unit before storing Goods and periodically during the Storage Period". Through the winter, look in monthly; if you can't get there yourself, agree who will look in monthly and change the absorbers. Access is normally 6am to 10pm; check your site's page and confirm your hours when you book.
Will insurance pay for condensation damage?
Don't count on it. Our guide to climate-controlled storage says the contents-protection policy "specifically does not cover atmospheric or climatic damage"; the Summary of Insurance, provided to you when you take the cover, has the exact wording. Does contents protection cover damp and mould? explains where the line sits.
What to ask us before you book
- Whether the Warminster container is insulated.
- Whether the container you're offered has any vents.
- Whether a container or an indoor unit at the same site suits your things for the length of your stay (clause 26 says "You must ensure the Unit is suitable for the storage of the Goods intended to be stored in it"), especially upholstery, a piano, oil paintings or valuable solid-wood pieces.
- Whether you can have power authorised, if you think you need it.
Call us on 0800 2545585 and we'll talk it through for your site, or get a price online for a container or an indoor unit.
Related questions