TL;DR
Empty the shed completely before cleaning anything -- a shed cleaned around its contents gets cleaned once and stays dirty. Check for nests and pests before you start, wash the interior dry-first and wet-second, keep pressure off any wood, and get everything bone dry before it goes back in. Plan on most of a day.
Empty it first, and sort as you go
There is no shortcut here. Cleaning around stacked contents means the floor never really gets done and the walls never get seen.
Carry everything out onto a tarp and sort into four piles: keep, relocate, donate or sell, and dispose. Deciding while items are in your hands is faster than deciding twice.
Two categories deserve attention as they come out. Anything soft or absorbent -- cardboard boxes, old cushions, fabric, bags of soil -- is where pests nest and moisture collects, and most of it should not go back in. Anything chemical needs checking for leaks, swelling, or unreadable labels.
If the volume is beyond what a car trip can handle, a junk removal run is usually cheaper than several weekends of hauling.
Check for pests before you touch anything
Sheds are attractive to wasps, mice, rats, spiders, and occasionally larger animals. Look before you disturb.
Wasp and hornet nests in the eaves or roof peak are a genuine hazard and are pest control work, not cleaning work. Do not spray one with water.
Rodent droppings are the other one to take seriously. Dry sweeping droppings and nesting material sends dust into the air. The safer sequence is to ventilate the shed, dampen the material with a disinfectant solution first, then pick it up with gloves rather than sweeping, and bag it.
Pest control is a separate trade. If there is an active infestation, a structural nest, or evidence of something larger living in there, cleaning does not solve it and the pest work comes first.
Clean the interior
1. Ventilate. Doors and windows open, and keep them open through the whole job.
2. Dry first. Sweep or vacuum ceiling, walls, shelves, then floor, in that order. Get cobwebs off the rafters before anything is wet, because wet cobwebs smear.
3. Wash top down. A bucket of mild detergent and a brush or sponge. Walls, then shelving, then floor. Use as little water as the job allows -- a shed does not dry quickly.
4. Treat any mildew. A diluted bleach solution handles surface mildew on non-porous interior surfaces, with the doors open and gloves on. Never combine it with an ammonia-based cleaner or any acid.
5. Deal with the floor last. Wood floors get a damp mop, never a flood. Concrete floors can take more water, and oil staining is a degreaser job -- the method is in degreasing a garage floor with years of buildup.
6. Dry completely. Doors open, a fan if you have power out there, and as many hours as it takes. Putting contents back into a damp shed guarantees mildew.
Widespread black growth on the framing, or a musty smell that does not clear with ventilation, is a moisture problem in the structure rather than a cleaning problem, and mold remediation is a separate trade.
Clean the exterior by material
The exterior method depends entirely on what the shed is made of.
Vinyl or resin sheds are the easiest. Mild detergent, soft brush, garden hose rinse. Do not use abrasives, which scratch resin permanently.
Metal sheds wash the same way. Watch for rust at the base panels and along fasteners; rust holes at ground level usually mean the panel is at the end of its life.
Wood sheds need the gentlest treatment. Apply a wood cleaner or a mild detergent, let it dwell, brush along the grain with a soft brush, and rinse with a garden hose. Do not pressure wash a wood shed -- the soft growth between the grain lines erodes first and leaves a raised, splintery surface that will not take stain evenly, as explained in what high pressure does to a wood deck.
Painted or stained sheds get the paint tested first. Press masking tape onto the surface and pull it off; flakes coming away mean the coating is not bonded and washing will strip it.
For heavy green growth on a shaded shed, a diluted bleach-based exterior wash with dwell time works far better than scrubbing, which is the argument in soft washing and when it applies.
Check the structure while it is empty
An empty shed is the only time you can see it properly.
Look at the roof from inside for daylight, dark staining, or soft spots in the sheathing. Check the floor for soft or springy areas, especially near the door and the corners.
Check the base. Sheds on skids or blocks settle, and a shed sitting directly on damp soil rots from the bottom. Look for a clear gap and drainage away from the structure.
Check the door for square, the hinges for rust, and any vents for blockage. A shed with no ventilation traps humidity and will grow mildew no matter how well you clean it. Note anything that needs fixing before the contents go back.
Put it back better
Nothing absorbent on the floor. Cardboard wicks moisture and houses insects. Use plastic bins with lids.
Everything off the floor, on shelves or pallets, so air moves underneath.
Label the bins. Unlabeled bins are how a shed fills with things nobody opens.
Store chemicals correctly. Fuel, solvents, pesticides, and pool chemicals belong in original labeled containers, out of reach of children, away from anything that sparks, and never stacked where one leaking container drips into another. Never store an acid product next to a bleach product.
Do not store anything that must stay temperature-stable, paint that will freeze, or documents and textiles you care about. A shed swings from freezing to very hot and back. Garden furniture that overwinters should go in clean and dry -- see cleaning patio furniture by material.
FAQ
How do you clean a storage shed?
Empty it completely, check for nests and pests, sweep from ceiling down to floor while dry, then wash top down with a mild detergent using minimal water. Treat any surface mildew, dry the shed fully with the doors open, and put contents back in sealed bins rather than cardboard.
Can you pressure wash a shed?
Vinyl, resin, and metal sheds tolerate low pressure with a wide tip. Wood sheds should not be pressure washed, because the soft grain erodes first and leaves a permanently raised, splintery surface. Use a cleaner, a soft brush, and a garden hose on wood instead.
How do I get rid of the musty smell in my shed?
Ventilate thoroughly, remove everything absorbent, clean the surfaces, and dry the shed completely with the doors open. If the smell returns after all that, moisture is entering the structure -- from the roof, the base, or poor ventilation -- and that is a repair issue rather than a cleaning one.
What should you not store in a shed?
Anything that must stay temperature-stable, paint that can freeze, documents, textiles you care about, and food. Sheds swing between freezing and very hot. Chemicals may be stored but only in original labeled containers, out of children's reach, and never with acids beside bleach products.
How do I clean mouse droppings safely from a shed?
Ventilate first, then dampen the droppings and nesting material with a disinfectant solution rather than sweeping them dry, which sends dust into the air. Pick the material up with gloves, bag it, and wash the surfaces afterward. An active infestation is pest control work.
A shed cleanout is mostly a sorting job with a wash at the end, and the material of the shed decides how gentle the wash has to be. If the volume coming out is more than you want to haul, get a quote and we will size the removal with you.
