If the inside of your garden storage box is damp, start by emptying it and checking where the moisture appears. Widespread droplets beneath the lid can point to condensation; a wet trail from one corner after rain suggests a leak. Both can happen together, so I would check the box before buying sealant or replacing it.
My Keter Marvel+ has kept its contents protected in heavy rain. Even so, I would never put wet cushions inside and expect the closed box to dry them. Keeping rain out and getting moisture out of stored items are separate jobs.
Is it condensation or rain getting in?
Condensation forms when moist air meets a surface cold enough for water vapour to become liquid. An outdoor lid can cool while the air and contents inside still hold moisture. You may find droplets without an obvious hole in the box.
Empty the box on a dry day, wipe it out and let it dry with the lid open while you are nearby. Inspect the empty interior again after the next spell of rain and during a dry, cold period. This is a practical way to look for a pattern; it is not a waterproofness test.
| What you find | What I would check first |
|---|---|
| Fine droplets across the underside of the lid | Wet contents, blocked vents and moisture trapped overnight |
| A wet line beneath one joint after rain | Lid alignment, panel connections, cracks and seals fitted to that model |
| Water mainly at floor level | Standing water outside, base support and water brought in on equipment |
| Damp fabric but little visible water on the box | Whether the fabric was fully dry before packing and whether air can circulate around it |
Do not force a hose into the joints to recreate rainfall. Pressure can drive water through places that would behave differently outdoors, and a flooded box will not help you identify the original problem.
Remove the moisture source first
Take out wet gloves, covers, cushions and tools. Brush soil and grass off equipment before storing it, following its cleaning instructions. A pile of damp clippings or a soaked cover can keep adding moisture long after the weather improves.
Dry fabric somewhere suitable for the material before returning it. If you find mould, follow the item’s care instructions and check whether it can still be cleaned effectively. Putting a dry outer cover around a damp cushion only hides the problem.
For the winter routine and decisions about bringing cushions indoors, see my garden cushion storage guide. Here, the priority is finding why the storage unit itself stays wet.
Restore airflow around the box
Find the ventilation openings shown in the instructions. Clear leaves and dirt from them without damaging any mesh or covers. Inside, move bags and fabric away from the openings. Outside, check whether a hedge has grown over the back or whether the unit has been pushed hard against a fence.
I would leave enough access to inspect the back and sides as well as the lid. It is easy to keep the visible front tidy while leaves collect behind the unit. Follow the specified clearances rather than assuming a universal gap suits every design.
Ventilation is a deliberate part of many stores. IKEA’s outdoor-box guidance describes openings that let condensation dry out. Asgard’s shed-care advice similarly calls for airflow around its units. Sealing every opening can work against that design.
Check the lid and base before adding sealant
Remove anything pressing against the lid and check that it closes evenly. Look for a missed panel connection, loose fitting or visible damage. Compare the assembly with the instructions, especially at corners where several parts meet.
An uneven base can twist the structure and alter the way the lid meets the sides. Check for rocking, unsupported areas and water collecting around the floor. My base and paving checks explain what to look for.
If you find damage, ask the maker about the correct replacement part or repair. Do not drill extra holes or smear sealant over unknown gaps as a first step. Some gaps are intended for ventilation or drainage, and alterations may affect the warranty.
Will a moisture absorber help?
A moisture absorber can be a useful extra after you have dried the box and dealt with leaks and wet contents. Asgard suggests one for persistent condensation in its metal sheds. It will need checking and emptying or replacing according to its instructions.
I would not expect a small absorber to compensate for a soaked cushion pile or a damaged lid. Keep any liquid collection container upright and away from stored fabric, and follow the product’s handling directions. Do not add a heater or charging equipment to a damp box to try to dry it.
When a different storage arrangement makes sense
If the same contents keep getting damp despite sound assembly and clear ventilation, move those items to a drier location. An outdoor box may be convenient for weather-tolerant garden accessories without being suitable for everything you own.
For a replacement, prioritise accessible ventilation, a lid that closes cleanly and enough room to pack without compression. Compare suitable formats in my garden storage box guide. Changing boxes while keeping the same wet contents and cramped position is unlikely to solve the cause.
