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Metal shed condensation

Updated: 22 October 2026

You open the door on a dry morning and the underside of the roof is beaded, though the grass is dry and the night brought no rain. Metal shed condensation is the usual cause: steel cools overnight, indoor moisture hits dew point, and water forms on the skin the way it does on single glazing. A wet line that appears only in rain, at a screw or where the doors meet, is a separate fault. The [metal garden shed comparison](/hub/garden-supplies/garden-shed-metal) holds these listings and their amazon.co.uk prices, checked by the Products Compared editorial team on 19 October 2026, with no lab test of any shed. Our links can earn a commission.

You open the door on a dry morning and the underside of the roof is beaded, though the grass is dry and the night brought no rain.

Our top picks

COZYBRITE COZYBRITE 6 x 4 metal shed

Best overall

COZYBRITE COZYBRITE 6 x 4 metal shed
6.2/10about £149.99
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COZYBRITE COZYBRITE 8 x 6 metal shed

Best value

COZYBRITE COZYBRITE 8 x 6 metal shed
5.4/10about £239.99
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Garden Universe Garden Universe 6 x 4 pent

Alternative

Garden Universe Garden Universe 6 x 4 pent
4.0/10about £169.99
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On this page
  1. 1.Dew or a leak
  2. 2.The base and the wet things you store
  3. 3.Vents these sheds actually list
  4. 4.What still counts as a leak

Dew or a leak

If the whole underside is damp after a cold, dry night and the outside of the roof is dry, that is dew. GardenSite's leak and condensation note describes the roof cooling overnight, like single glazing. Charles Bentley says metal conducts heat, so the skin reaches dew point. A leak shows while rain is falling, or just after, and it sits on one line: a screw, a cracked roof light, the doors, or the eaves where wind drives rain under the lap. GardenSite also lists missing washers, screws driven at an angle, and a base that is not level. One review of the COZYBRITE 8 x 6 describes a wet floor where the doors meet. Treat that as a joint, so one local drip is not automatically condensation.

The base and the wet things you store

The roof is where the water shows. Charles Bentley names a bare concrete base and wet kit, such as a mower brought in off the grass. Trimetals and Charles Bentley both say let new concrete dry, on the maker's timetable, because they do not share one waiting time. A damp proof membrane belongs with the slab. Trimetals' basing sheet describes thick polythene under the concrete or on top of it, with about 100 mm of concrete on gravel and the base kept flat. Polythene on the slab needs a floor over it, because you should not walk on the sheet. Leave the mower outside until the deck stops shedding water, then bring it in. Whether you get a deck or only a frame is on the metal garden shed buying guide.
COZYBRITE COZYBRITE 6 x 4 metal shed

Testsieger

COZYBRITE COZYBRITE 6 x 4 metal shed
6.2/10about £149.99
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Vents these sheds actually list

Charles Bentley's layout is a low inlet and a high outlet on opposite walls, left open. Two holes at one height move less air than that path, and neither layout warms the steel on a hard frost. These listings do not share one vent pattern. The COZYBRITE 6 x 4 claims a vent on the front, Garden Universe lists two above the door, and the COZYBRITE 8 x 6 and the Switdo list four. YODOLLA does not state a count, so check the diagram before you assume an opposite-wall pair. Blocking them to keep heat in keeps the water in. GardenSite suggests 20–25 mm of flame-retardant foam and says to ask building control. That figure is theirs, not a test on these amazon.co.uk sheds, and this page does not specify a lining. If the cold skin is why you hesitate over steel, see metal shed vs wooden shed.

What still counts as a leak

When the base is drier and the vents are clear, rain should not draw a new line at one fixing. GardenSite's checks are missing or split washers, screws at an angle, a cracked roof light, wind under the eaves, and a base rail that is not level so a lap gapes. Packing or recasting that rail belongs with assembly, on how to assemble a metal shed. Photograph the COZYBRITE 8 x 6 door joint in the rain and again on a dry morning. If it is wet only in rain, write to the seller about the doors and the threshold. Dew on sound steel is not by itself a fault under the Consumer Rights Act 2015.

Common questions

Why is the roof wet when it has not rained?
Steel cools faster than the air in the shed, and moisture condenses on the inside face. Which? notes that the inside temperature tracks the weather, so a clear cold night often leaves more dew than a mild one. Wet tools and a damp slab add vapour. Water spread across the roof, before any rain, is dew rather than a failed joint.
Will vents stop metal shed condensation?
Vents shorten how long damp air sits on the steel. They do not warm the sheet, so a frost can still leave beads. Charles Bentley wants a low inlet and a high outlet on opposite walls, left open. Holes at one height move less air than that layout, and covering them to hold warmth holds the moisture as well.
Does a concrete base make a metal shed damper?
A bare new slab can. It gives off mixing water while it cures, and it can draw damp from the soil. Charles Bentley and Trimetals both say let the concrete dry, on the maker's timetable rather than one shared number of days. Thick polythene under the slab, or on it under a floor, is the retailer pattern. A wet mower still adds vapour the membrane does not stop.
Should I line the roof to stop drips?
A liner can move the cold surface, and it can hide a leak until the board is wet. GardenSite suggests 20–25 mm of flame-retardant foam and says to ask building control. That thickness is their suggestion, not a figure measured on these listings. Dry the base and clear the vents before you buy a lining.
Is condensation a fault I can reject the shed for?
Ordinary dew on sound steel is not, by itself, proof the shed is faulty. Charles Bentley would not class it as a fault, and that policy is theirs alone, not an automatic finding under the Consumer Rights Act 2015. A cracked roof light, missing washers, or a door that weeps in the rain is a point to raise with the seller, with photos from rain and from a dry morning.

Related pages

Best metal garden shed

Metal garden shed

Metal garden shed buying guide: size, door and floor

How to assemble a metal shed: people, gloves and holes

Metal shed vs wooden shed: heat, treatment and use

Sources

Sources from the research digest. Listing prices and stars are amazon.co.uk figures from 19 October 2026.

  1. Planning Portal, outbuildings (retrieved 19.10.2026)
  2. Class E, GPDO 2015 (retrieved 19.10.2026)
  3. GOV.UK permitted development technical guidance (retrieved 19.10.2026)
  4. Building Regulations 2010, Schedule 2 (retrieved 19.10.2026)
  5. GOV.WALES, planning permission for outbuildings (retrieved 19.10.2026)
  6. mygov.scot, shed or garage (retrieved 19.10.2026)
  7. Which?, how to buy the best shed (retrieved 19.10.2026)
  8. GardenSite metal shed guide (retrieved 19.10.2026)