How to Damp Proof and Insulate a Garden Shed (Mega-Guide)

How do I damp proof my shed?

It’s a question that’s on every ‘sheddie’s’ lips. But the answers are scattered far and wide across the internet. So if you’ve got a garden shed or office that you want insulated and damp-proofed – you’re in the right place..

So what we’ve done to answer all your questions on how to keep damp out of sheds is bring an old guide back off the bench. We’ve updated our guide to damp-proofing a shed for 2021. And we’re going to do our best to quickly and succinctly answer every question on damp.

If you’re ready for sure-to-work tips and hacks for damp-proofing a shed, read on!  

Key Takeaways for Damp Proofing a Shed:

  • Damp can be caused by condensation, leaks, rising damp, and pooling groundwater
  • Damp can cause respiratory problems and irritate asthma
  • Not all wooden sheds need to be insulated
  • Damp items should be removed from storage sheds
  • Mould and mildew can be treated with sprays
  • Gaps in window and door frames should be sealed
  • Ventilation is key to preventing damp
  • Timber sheds need to be treated regularly to prevent dampness and rot

Key Terms for Damp Proofing a Shed:

wooden shed summerhouse at the end of a garden in front of a small table with drinks and lights on it with its door open and lit up inside
Opening doors and windows will help to circulate air and combat damp in sheds.

Part 1 – Shed Damp

To understand how to damp-proof a wooden shed, first, we have to understand what damp is. Let’s get a definition of damp down, then we’ll move on to protecting your shed against it.

Damp is the presence of moisture, mildew, and mould in buildings. Damp can occur in sheds due to external (e.g. rain) or internal (e.g. condensation) factors. If left untreated it can damage your wooden shed and cause health problems.

When you don’t air out your shed, it invites moisture build-up. This, in turn, creates mould spores.


Mould is a fungus and can cause ‘black mould’ in cellulose-rich building materials (i.e. wood). 


green and black mould growing from rising damp on floor up tiled wall
Credit: Unsplash

Mildew is a type of mould but not the other way around. 


It’s a living organism that grows where there is:


  • Warmth
  • Damp
  • Humidity
  • Organic matter


The term mildew is often used generically to refer to mould growth. However, it’s a bit different and as such, might require a different treatment than mould.

One of the main causes of damp in sheds is humidity. Now, air humidity of around 30-60% is ideal for humans. But below 30%, we can experience dry skins and lips, itchiness, and scratchy throats.


Above 60% can cause sweating for us or mould, mildew, and, damp in your shed. And, if you have damp and mould in your home you're more likely to have respiratory problems.


Remember, just breathing in your shed can create moisture that leads to damp.

Damp is caused by excess moisture. This moisture can come from:


    • A leaky roof
    • Rising damp
    • Damage to windows
    • Rain and groundwater ingress
    • Condensation


So what is condensation?


Condensation is when water in gas (vapour) reverts to a liquid state (as droplets). This occurs between a cold surface and hot air. This is because cold air has less moisture in it than warmer air.


This is why we often see condensation on a surface that divides two areas of different temperatures. For example, a window in your shed.


This process can be worse in seasons with more moisture in the air, like spring and winter. 


Damp can also be caused by decomposing grease and pests, and other organic materials like grass and seeds. Storage of damp furniture, equipment, and even bikes can also contribute to damp.


open shed with man inside putting upturned bike back on shelving
Make sure to wipe damp bikes before putting them back in storage.

One of the main causes of damp in garden sheds is interior condensation. 


Factors that can affect dampness in a shed are:


  • Single-glazed windows - With direct contact to the outside air
  • Rising damp - From water absorbed by groundwork in a concrete base
  • Leaks - From guttering and/or roofing
  • Treated air - Either heated or air-conditioned inside air that is different to the outside temperature 


We’ll explain in parts 2 and 3 how to insulate and damp-proof your shed to combat these problems. Just know that dampness in a wooden shed can be made worse in winter. This is due to colder air outside as well as less regular aeration - with windows closed against the cold.

Aside from being potentially dangerous to your health, damp is a problem for outdoor garden buildings. 


Wood, or timber, is one of the most susceptible materials to damage by moist conditions. These conditions can also be made worse by bouts of wet weather and poor airflow in sheds.


The results of damp in a wooden shed can be:


  • Premature rot
  • Mould on walls and roof
  • Warping and sagging of timber


These results are not just bad for wooden garden sheds, they’re potentially dangerous too. Rot and sagging timber can make your outdoor shed structurally unsound!


shed frame without roof being constructed on a wet patio facing front on
Try to keep sheds raised off of moisture-rich ground where pooling can occur.


Check out our quick guide on how to prevent your shed from rotting for more info. 

Getting Rid of Mould in a Shed

So now that we’ve answered what damp is, let’s look at how to get rid of mould and mildew in your shed.

One of the first questions to ask when damp-proofing your shed is:


Are you in it regularly?


If it’s during winter, the answer is - probably not. And there’s your first problem. With no fresh air flow, stagnant air just sits in your shed. This air holds moisture and can condense on walls and windows. Boom - now you have mould and mildew in your shed.


So make sure you air out your shed.


Picture of a wet puppy on a sandy beach with the side out looking up to its owner
Avoid letting damp in your shed - no matter how tempting! Credit: @allaboutorla/instagram


It’s also smart to avoid storing damp items in your shed. This includes everything from rags to tools and bikes. Yep, even bikes! If you do have to store things in your outbuilding, make sure to dry them off before they go back in the shed. 


If you’ve bought a wooden shed with pressure-treated wood for extra protection, you shouldn’t need to treat the inside.


Although, if you want to prevent mould in your shed:


    • Keep it ventilated - Open doors and windows or install vents. If you regulate your shed’s temperature, moisture will be allowed to diffuse from high to low concentration (i.e. inside to out).
      Insulate it - Maintain your shed’s interior temp. And provide a layer to stop condensation from hitting surfaces
    • Seal gaps - Caulk your shed’s base. Use a draught excluder. Spray windows with expanding foam.
    • Guttering - Install adequate guttering for run-off and prevent moisture leaking in through the roof
    • Membrane - Think about installing a vapour membrane between your shed’s framing 
    • Get a hygrometer and dehumidifier - A hygrometer measures humidity and a dehumidifier will treat air and remove excess moisture.


Make sure you have an available plug socket for the last two items or buy battery-operated versions.


For suggestions on dehumidifiers, check out these reviews of the best dehumidifiers for 2021. For hygrometers, check out these reviews of the best hygrometers for 2021.  

The best way to treat mould in a damp shed is to stop it from ever forming. Still, to treat shed mould or stop your shed from going mouldy, follow these steps:


  1. Remove everything from your shed. You can use this stage to check furniture and tools for damp and mould.
  2. Check your shed’s base for spills and the roof/walls for leaks.
  3. Fill a spray bottle with a diluted bleach solution (1 parts bleach to 4-10 parts water). Wear gloves and old clothes. Open all shed doors and windows and treat mould with spray and a sponge. 
  4. Leave your shed to air out for a full day if possible.
  5. Apply shed treatment and pesticide to the outside timber of your shed.
  6. Leave the building to air.
  7. Respray affected areas with a diluted vinegar spray. You can add a fragrance to combat the smell of vinegar.
  8. (Optional) Leave open containers of baking soda or a dehumidifier in your shed.


White surface with hands wearing blue plastic rubber gloves cleaning with a Dettol spray bottle and wipe
Credit: Unsplash

To get rid of musty odours in storage sheds, you first need to combat the cause. This will probably be mould, mildew, and damp. Make sure to remove everything from your shed to check for structural damp and offending items (damp cloths and rags).


Then, clean your wooden shed’s walls and floors with a diluted bleach spray. Make sure to ventilate your shed whilst cleaning. Rinse the bleach off and dry thoroughly.


Check out this full guide on cleaning your shed with bleach to combat mould. 


Top tip: Immediately wash and dry the clothes and shoes you wore while cleaning. Try not to bring damp or mould back into your house!

Our first tip is - don’t let mould sit. Try to remove mould as soon as you see it. Also, make sure to protect yourself when tackling mould in your garden outbuilding. Make sure to wear a surgical mask or a ski mask. Also, wear gloves when cleaning.


You don’t want to inhale mould spores, leading to irritated asthma and respiratory problems.


And remember to try and protect your plants. If you’re removing mould from your wooden shed’s exterior, consider what damage you might cause to plants. 


Try to opt for a diluted cleaning solution. Make sure to water your plants beforehand to discourage chemicals from bonding with them. Read our post on tips for pruning your garden if you want to keep plants out of the way.  


Top tip: For a natural mould and mildew treatment, diluted white vinegar in a spray bottle. Use with a sponge soaked in hot water and baking soda.


And always make sure to ventilate your wooden shed whilst cleaning.


Glass window with condensation and water steaking down it
Condensation and single-glazing can cause real problems for timber sheds.
older man in a blue shirt and cap helping a young blonde child build a timber shed wall in the garden
Tongue and groove wooden sheds provide excellent insulation and a weather-resistant seal.

Part 2 – Insulating a Shed

Disclaimer: Insulating your shed is not necessarily something you will need to do. 

For example, if you have a tight-sealing tongue and groove shed made from high-quality timber, this need decreases. 

Additionally, you may find it hard to install insulation batts in, say, a metal shed. This is due to their single-skin and rail construction. Basically, there’s nowhere to put batts!

That being said, having insulation means you can regulate your shed’s temperature more consistently. This means that you can keep warm air in and keep cold air out.

Key Takeaways for Insulating a Shed:

  1. Make sure your shed is dry, waterproof and in good condition (or new) before insulating
  2. Combat draughts by sealing gaps around window and door frames
  3. Choose the appropriate insulation (and membrane) material
  4. Secure insulation batts with board or plasterboard panels

So, why do wooden sheds need insulation?

The reason you might think about insulating your wooden garden shed is because of the dew point.

According to Google, this is:

‘The atmospheric temperature below which water droplets begin to condense and dew can form’.

Basically, this is where all that moisture-rich, humid air in your shed can settle and cause condensation.

Granted, condensation can be worse in metal sheds due to metal conducting heat better. But areas like windows and door frames are still at risk from condensation. 

By insulating your shed, you can trap heat inside and regulate that temperature versus outside. Wooden prefab sheds are often the best solution to this as they offer a tight seal and good insulation.

However, your needs will also depend on what sort of climate you live in. And, by storing your tools in a climate-controlled shed, you’ll extend their usage-life in the long-run.

There are a lot of different options for insulating a wooden garden shed, including:

Bubble wrap

Yes, you could really use bubble wrap to insulate your shed. We’d suggest you at least go for the foil-backed kind, though. Easily affix bubble wrap to walls and ceilings with an adhesive or staples.

However, its heat and sound insulation properties are fairly minimal. Only use this option if it’s the only thing going.

Fibreglass insulation

Fibreglass is especially good at blocking sound and comes in insulation batts. These can be fitted in your wooden shed’s frame.

Remember to always wear:

  • Glasses 
  • Gloves
  • A face mask

When working with insulation. Small pieces of fibreglass can cause irritation if inhaled and also to eyes and skin.

Top tip: After installing your insulation, take a cold shower first. This will help to close your pores and wash off any microfibres. Then you can finish with a hot shower.

Fibreglass insulation can also be useful if you’re looking at soundproofing your shed. 

Cross profile of pink fibreglass insulation batts in a wall cavity
Insulation can help regulate the temperature inside your shed.

PIR insulation boards

PIR is a type of rigid insulation board that’s popular for walls and even flooring. It’s also fibre free!

PIR comes in foil-backed boards of varying thicknesses. Its popularity means that you should be able to fit suitable sizes to fit your wall cavity. Simply cut boards to size and slide them in.


If you want the insulation offered by fibreglass without the itchiness - simply go for thermal wool. This is also a more environmentally-friendly solution.

Plus, wool offers stellar insulation and is safe to handle.

You can also consider changing, or adding additional cladding to better insulate your shed.


Plasterboard will offer effective wall covering. The problem is, it’s quite flimsy and won’t offer that much resistance against water and damp.


Hardboard sheets are a step up from plasterboard in terms of strength. But they still won’t offer much in the way of water resistance.


The good thing about plywood is that it comes in varying thicknesses. Plywood will prove sufficient for wall-boarding. Plus, it’s tough and durable.

Tongue and groove

Tongue and groove wooden sheds equal a robust build with a sleek design. It’s also a lot easier to paint and treat timber due to there being no overlap. A tongue and groove design also means that sheds are weather-resistant and well-insulated.

Pallet board

By de-nailing and sanding down old pallet boards, you can clad the outside of your shed and be on-trend. Re-purposing and pallet boards are all the rage at the moment. Simply stain and treat the boards and affix them to your shed’s vertical struts.

If you can’t, or don’t want to add cladding or insulation to your shed, you could always heat it.

Keeping your shed warm at a low ambient level can help to regulate the difference in indoor and outdoor temperature.

Consider using an electric radiator on a low setting. This will be cheap to run and energy-efficient. Or, you could invest in a tubular heater for constant, low-level heat. 

These compact and tubular-shaped heaters are particularly suited for prolonged heating of an area due to their very low running costs.

We’ve written a quick guide here to learn more about how to insulate your shed.

But it’s fair to say you might be wondering how you can insulate your shed cheaply.

  • Cheapest way - Foil-backed bubble wrap (available at DIY/hardware stores. As cheap as £14.99 on eBay for 8.4m roll)
  • Medium-cost way - Fibreglass, wool, or PIR insulation
  • More expensive way - Insulation batts and a vapour membrane. And/or installing double-glazing

Barring these options, some quick fixes to cheaply insulate your shed are:

  • Sealing window and door frames with a silicone gun set
  • Buying a draught excluder
  • Laying down carpet 

With timber and wooden garden sheds, you shouldn’t need to seal the base. 

However, make sure that timber and flooring is treated. Also, a timber-frame subfloor or base can help to raise your shed off the ground. A gravel base can then provide adequate ventilation and drainage. 

If you’re building a concrete, brick shed, or metal shed you will need to seal the base. Then, the following will apply for all sheds (including sealing your wooden shed, if you decide to).

  • Using silicone or a mastic sealant, seal around your shed’s base on the outside
  • Repeat the step for the base on the inside if need be
  • (Optional) Do the same for any exposed bolt holes
  • Alternatively, use a liquid damp seal and paint on

Sealing the base of your shed in this manner can help with water resistance and ingress.

metal shed built on paving stones with a step ladder and a pallet with coffee mug and drill on top
Caulking your base and bolt holes is essential for metal sheds built on concrete bases.

Most sheds are built with waterproof roofing materials. However, even felt and bitumen shingles can become water-damaged over time.

For a metal shed, you might even consider anti-condensation roofing panels.

Making sure that you seal around joins in your wooden shed and that your felt is fitted accurately will provide you with the best roofing. For an upgrade from felt shingles, you could also consider using weather-resistant EPDM.

This is a synthetic rubber for shed roofs that provides waterproofing. You can find EPDM as an optional add-on for many of our wooden sheds.

pent roof wooden timber shed with felt shingle roof

timber shed interior with walls and roof visible
Check your shed walls and roof for any signs of leaks, damps, and holes.

Part 3 – Damp-proofing a Shed

By this stage in our ultimate guide, we’ve run through what damp is and how to insulate your shed. Now, let’s move on to damp-proofing your wooden shed.

To damp proof a wooden shed, open doors and windows or install shed vents to circulate air. Reduce moisture levels in your garden shed by circulating air to combat damp. You can also use a dehumidifier in your outdoor shed to stop moisture buildup which causes damp.

So if you’re asking yourself, ‘how do you damp proof an outbuilding?’, there are three main areas you need to consider.


To damp proof your shed, you need to protect it from moisture up high as well as down low.

Check your roof for any gaps, holes, and leaks. Are these being caused by insufficient drainage? If so, you might want to think about upgrading your shed guttering system

A guttering and water butt system can ensure that runoff is further directed away from your shed’s base. This, in turn, can combat water pooling and even rising damp. 

felt roof shed with black gutters
Good guttering can help direct run off water.

Felt roof shingles, on the other hand, offer good value for money. But like any roof material, they will deteriorate over time. Lucky for you, you can repair a felt roof with silicone gutter sealant. Simply secure loose patches and rips and tears.

If you need to replace your wooden shed’s roof, though, consider doing so with EPDM.

Windows and doors

Windows and doors can be particular pain points for damp-proofing wooden sheds.

Wood can rot, crack, and shrink over time. The resultant gaps can cause rainwater to easily ingress. So, start by regularly treating and maintaining your wooden frame.

If need be, apply wood filler or expanding foam to seal up gaps in window frames. Then, simply cut off the excess. You can repeat this process with your door frame. Alternatively, you can buy a draught excluder to tuck at the bottom of your shed door.

Single-glazed windows will also have more direct contact with outside air.

Think about installing double-glazed windows to provide further insulation and protection against damp. The compressed air between double glazed glass creates a vacuum. This means that the transfer of heat is greatly reduced.


Make sure to regularly treat wooden sheds with wood treatment and wood stain to protect against rot.

Combatting rot before it occurs is your best defence against damp. Once rot sets in, it can compromise your wooden shed. It’ll also create moist conditions that can lead to further dampness in your wooden shed.

Another line of defence to prevent moisture in a shed is simple storage.

Try to dry tools and equipment off before returning them to your storage shed. You can also use storage boxes and drawers to create tight seals around tools. This can help prevent rust, corrosion, and dampness. 

Top tip: Go one further and put silica sachets in your tool drawers to absorb moisture.

Also, make sure not to leave damp cloths or open liquid containers in your wooden shed which can contribute to damp.

Expanding foam and silicone can be useful for sealing gaps in your wooden shed’s frame. Any opening through which wind might blow like door and window frames are prone to water ingress. 

To combat this, use an expanding foam spray in visible gaps and shave off the excess. Or, use a silicone sealant around your frames and joins to provide a water-tight seal.

apex shed roof with white vents installed to shed eaves
Installing vents will help with airflow and heat regulation.
  • Install vents in your shed’s eaves, windows, and skylights
  • Install a whirligig to your shed’s roof or an electric fan in your shed’s eaves
  • Also, heat your wooden shed or use a dehumidifier and monitor humidity with a hygrometer

To ventilate a small wooden shed, you’ll need some form of passive ventilation. This can be achieved by installing vents in your shed’s eaves or even just drilling some holes. Make sure to do this at both ends of your shed in the direction of steady airflow.

Circulating airflow in your shed means that moisture-rich air won’t hang around. It can also help to regulate your shed’s indoor temperature versus outdoors.

Think about what you need to use your shed for.

If you’re utilising your garden building as a wooden office or workshop, ventilation is key. You don’t want tools and even electronics suffering from damp conditions. Installing a whirligig to sit on your shed’s roof, or an electric fan, if you have utilities hooked up, can help to regulate air.

To read more about installing utilities in your wooden shed, check out this helpful guide. 

Building a concrete shed base for your shed floor can lead to issues like rising damp. This is because concrete is porous and can absorb moisture from the surrounding ground. 

Rising damp is when this water from the ground is absorbed through floor bearers into your shed’s floor.

To build a damp-proof concrete shed base - make sure to put a damp-proof membrane under your shed. Also allow your base to dry sufficiently, and don’t build it much larger than your shed’s actual base.

On top of this, simple measures like considering the lay of the land will help to stop any issues. Try to build your shed base in an area that:

  • Has adequate drainage
  • Isn’t on boggy or marshy land
  • Is higher than the surrounding area
  • Isn’t close to overhanging or dense shrubbery

To damp proof a shed’s base you need to make sure to build a barrier between your shed’s floor and the ground. You can do this by constructing a simple timber substructure. This space will allow for ventilation and provide a barrier to the moisture-rich ground.

You could also look at constructing a gravel base for your wooden shed. Creating a garden shed base from gravel also allows for proper drainage. This way, you won’t get water pooling around your wooden shed base.

And, to get the best of both worlds, you could use a grid system foundation base. This provides ground clearance and can be filled with gravel to allow for drainage. 

Then, you can use laminate, plywood, vinyl, or even carpet to keep any chill off your wooden shed base.

You can also prevent damp in your wooden shed by treating timber with waterproof paint. Timber will need to be treated regularly anyway to prevent rot and cracking. But using a shed treatment with a mould and fungal inhibitor can help in preventing dampness from occurring.

wall filled with various tools hung from it including axes and spanners
Try to store tools in boxes and drawers with silica packets to avoid corrosion.

Part 4 – Vapour Membranes for Damp-proofing a Shed

One of the most common questions we hear when talking about damp proofing a wooden shed is – do I need a membrane?

So, to finish off our guide on all things sheds and damp, we’re going to cover shed membranes once and for all!

If you’ve read this guide then (firstly, well done!) you should have figured out how to damp proof a shed floor. We’ve also covered insulating and damp-proofing your shed’s roof


But when do you need a membrane? Let's start small:


What is a shed membrane?


A breather membrane is a plastic sheet layer that goes between your shed’s walls and insulation to help with moisture. Properly defined, a vapour barrier alone does not control air movement; it controls the movement of moisture.


In cold weather, a shed membrane can prevent moisture from inside soaking into your insulation. In hot weather, a vapour barrier can stop hot, humid air ingress into your shed. Either way, it can help prevent rot, mould, and even damp insulation.


However, putting a vapour barrier on the outside of framing runs the risk of condensation forming. But it will further protect your shed from rain and water ingress. 


When using a shed membrane and insulation, check the guidelines first!

To break shed membranes and damp-proofing down for you, we’ve come up with a comprehensive comparison.

Shed and Climate Comparison for Vapour Membranes 

Do you live in a hot and humid climate and you insulate your shed or use an air-conditioner?


If so, put your vapour barrier on the outside of your wooden shed’s walls. 

This will stop moisture from entering your timber shed. That’s because moisture ingress will be absorbed by cool, dry air inside your shed.

Do you live in a cold climate and use your outdoor shed year-round? If so, you’ll need to insulate and heat it anyway to prevent damp.


If you add a vapour membrane to your wooden shed, place it on the inside of your framing. 


This will protect your insulation and frame from moisture-rich air inside your shed. Any moisture ingress to your wooden frame should be absorbed by outside air at night when it's colder.

If you don’t heat your shed or use air-conditioning then you don’t need a vapour barrier.


Otherwise, it’ll just cause condensation and damp. If you’re building a concrete shed base, however, you still need to sink a moisture membrane under your slab. This will help against rising damp.

Like an unheated shed, a shed with no insulation doesn’t need a vapour barrier.


This is because any moisture-build up (even in hot weather) should be removed by colder air at night. It’s important that you still properly ventilate your shed for this to happen, though!

If you insulate your shed but don’t heat or air-condition it, don’t use a vapour barrier.


Insulation slows heat transfer but a further vapour barrier will just trap moisture in hot weather. 

Do you still have questions about using a moisture membrane in your shed? If so, read this quick guide as to if you need a vapour barrier in your shed or not. 

Does my shed need a vapour barrier Garden Buildings Direct infographic with three tiles for different sheds and climates with icons and arrows regarding air flow, insulation, and vapour barriers
Use this infographic to decide if your wooden shed needs a vapour barrier.

How To Damp Proof a Wooden Shed

There you have it – our updated mega-guide to damp-proofing a wooden shed.

We’ve searched and scoured the internet and racked our brains to come up with all the best answers to your questions. Refer back to this guide if you ever have questions about damp-proofing or insulating your wooden shed.

And tell your friends! The next time someone asks you how to damp proof their shed, send them our way. We’ll answer every question they’ve got.

But just to recap, if you want to damp proof a wooden shed:

  • Make sure to ventilate your wooden shed by opening doors and windows to allow airflow
  • Install double-glazing in your shed to regulate temperature
  • Make sure to seal any gaps in your wooden shed’s frame with expanding foam or silicone
  • Patch felt roof shingles or replace them with EPDM
  • Direct excess water away from your shed’s roof and base with roof guttering
  • Treat wood regularly
  • Remove damp items and spills and lock up tools 
  • Clean any mildew and mould with bleach or vinegar spray
  • Insulate and use a vapour membrane where necessary
  • Heat or air-condition your shed and use a dehumidifier 

And if you’re undecided between damp-proofing a timber or metal shed, then check out our guide to stopping condensation in metal sheds.  

Shop The Master Apex Shed


Treating the timber of your wooden shed can provide it with a weather-resistant exterior. Further insulation and vapour membranes can be used in a wooden shed’s walls to prevent moisture ingress. Any gaps around your shed’s windows, roof, and door should be sealed.

To keep a shed-damp free make sure to store tools in tightly-sealed containers with silica packets. Don’t store damp items or open liquid containers in your storage shed. Make sure to ventilate or regularly aerate your shed to keep it damp-free.

For concrete shed bases and metal sheds, sealing the base is essential. You might also decide to seal the base of your timber shed, though. Work around the outside first, following the line of your shed’s base with a silicone gun. Repeat on the inside. 


Then, make sure to use a draught excluder for gaps that you can’t seal, like the base of your shed’s door.

A dehumidifier works by drawing in moisture-rich, humid air and running it over refrigerated coils. As the water in the air condenses, the moisture is removed and collected in the dehumidifier. Cold, moisture-free air is then filtered back into the room.