Buying a dehumidifier often feels like the obvious solution when your home starts feeling damp. You switch it on, empty the water tank, and expect the musty smell and mould patches to disappear. Sometimes it helps—but many homeowners are surprised to find their home still feels clammy, walls still look stained, and mould still returns even after weeks of running the machine.
So, why is your home still damp even after using a dehumidifier?
The answer is usually simple: a dehumidifier can remove moisture from the air, but it cannot fix the source of the damp. If moisture is entering through walls, rising from the ground, or being created faster than the unit can handle, the dampness will continue.
This guide explains what a dehumidifier can and can’t do, the most common reasons damp persists, and what you should do next for a long-term fix.
What A Dehumidifier Can Actually Do
A dehumidifier is designed to reduce airborne moisture. That’s useful because high humidity contributes to:
- Condensation on windows and cold walls
- Musty smells
- Damp-feeling air
- Mould growth in corners and behind furniture
In many homes, lowering humidity improves comfort quickly. It can also help dry out minor moisture after cooking, showering, or drying laundry indoors.
A dehumidifier is especially helpful for:
- Condensation-prone bedrooms
- Bathrooms with poor ventilation
- Utility rooms where laundry dries indoors
- Basements that feel humid year-round
However, a dehumidifier is not a full damp-proofing solution.
What Can a Dehumidifier Not Fix?
This is where most people get caught out. A dehumidifier cannot:
- Stop rainwater from soaking into external walls
- Repair broken gutters, downpipes, or roof leaks
- Stop rising damp travelling up from the ground
- Remove salts from plaster caused by long-term dampness
- Fix poor ventilation or airflow patterns in the building
- Correct cold bridging or missing insulation
It may reduce symptoms temporarily, but if moisture is still entering or trapped in the structure, the dampness will return.
You Might Have Rising Damp (And A Dehumidifier Won’t Stop It)
If damp is coming up from the ground, you’re dealing with rising damp — and a dehumidifier won’t solve it because the moisture source is continuous.
Common signs of rising damp include:
- Damp patches low down on ground-floor walls
- Tide marks up to around 1 metre
- White powdery salts on plaster
- Crumbling skirting boards
- Blown plaster that feels soft and flaky
A dehumidifier might make the air feel drier, but the wall can still stay damp because moisture is travelling through the masonry itself.
If you suspect rising damp, you’ll need a proper damp-proofing treatment plan, not just humidity control.
You Might Have Penetrating Damp From Outside
Penetrating damp is moisture entering through walls due to external defects. This often becomes obvious after heavy rain, but it can still be present during dry spells if the wall stays saturated.
Typical causes include:
- Leaking or overflowing gutters
- Cracked render or damaged brickwork
- Missing pointing or gaps in mortar
- Faulty window seals
- Roof tile damage or flashing issues
Signs include:
- Damp patches on external-facing walls
- Staining that gets worse after rainfall
- Peeling paint and bubbling plaster in one area
- A cold, wet feel to the wall surface
In these cases, a dehumidifier is only treating the indoor air, while water continues entering the wall from outside.
Condensation Might Still Be Happening In The Same Places
Even if a dehumidifier lowers overall humidity, condensation can still form in cold “problem zones” such as corners, window reveals, and behind furniture.
This is usually linked to:
- Cold bridging (thermal bridging)
- Poor insulation
- Limited airflow in certain rooms
- Furniture pushed tight to the external walls
You might notice:
- Mould is returning in one corner only
- A cold patch that feels damp even when the room is warm
- Condensation behind wardrobes or sofas
In these cases, the home may need insulation improvements, better ventilation, or targeted cold-bridge fixes alongside the dehumidifier.
Your Dehumidifier Might Be Too Small For The Space
Not all dehumidifiers are equal. If the unit is undersized, it may not be able to keep up — especially in winter or in a large, moisture-heavy household.
Common signs your dehumidifier isn’t powerful enough:
- The tank fills constantly, but the damp never improves
- Humidity readings stay high (often above 60%)
- You still see condensation daily
- The machine runs nonstop without reaching target levels
Larger properties, open-plan spaces, and homes with multiple damp rooms often need higher-capacity units or multiple dehumidifiers to make a noticeable difference.
The Dehumidifier Might Be In The Wrong Place
Placement matters more than most people realise. If the unit is in a hallway while the damp is in a closed bedroom, it won’t be as effective.
For best results:
- Place it in the room with the highest humidity
- Keep internal doors open (if safe to do so)
- Close windows while it’s running
- Keep the unit away from walls and furniture
- Ensure airflow isn’t blocked by curtains or clutter
If damp is mainly in a bathroom or kitchen, extraction fans and ventilation upgrades may work better than trying to dehumidify the whole home.
Your Home Might Still Have Poor Ventilation
A dehumidifier can remove moisture, but if your home traps humid air, moisture builds up again quickly. This is common in properties with:
- Sealed windows and no trickle vents
- Weak extractor fans
- Blocked air bricks
- Closed chimneys and reduced airflow
- High moisture production (large households, frequent cooking, indoor drying)
If ventilation is poor, humidity rises again as soon as the dehumidifier switches off.
A long-term fix may include:
- Better extractor fans (humidity-controlled models are excellent)
- Positive Input Ventilation (PIV) systems
- Improving airflow behind furniture and in cupboards
- More consistent daily ventilation routines
Your Walls May Be Salt-Contaminated (Even If The Air Is Dry)
This is a big reason homeowners feel “stuck”. If damp has been present for a long time, salts can build up in plaster. Even after moisture levels improve, salts can continue to:
- attract moisture from the air
- create staining
- damage paint finishes
- cause repeated bubbling or peeling
So you may think the wall is still damp when actually the structure is drying, but the plaster is contaminated and needs replacing.
In these cases, the correct repair often includes:
- removing damaged plaster
- using salt-resistant replastering systems
- allowing proper drying time
- redecorating with suitable finishes
You May Be Dealing With Multiple Damp Causes At Once
Many homes have more than one damp issue. For example:
- Condensation in bedrooms due to poor airflow
- Penetrating damp in one corner due to a gutter leak
- Rising damp low down on the ground floor
A dehumidifier might improve one symptom but won’t fix the rest. That’s why damp problems often feel “random” unless a proper survey is done.
A professional inspection helps identify whether you’re dealing with:
- condensation damp
- penetrating damp
- rising damp
- cold bridging
- hidden leaks
Once you know the cause, you can choose the right solution instead of relying on trial and error.
What To Do Next If Your Home Still Feels Damp
If your dehumidifier hasn’t solved the problem, here’s the most practical next-step plan:
1. Check Humidity Levels
Use a hygrometer and track readings:
- Under 60% is generally a safer range for reducing mould risk
- Persistent readings above 60% suggest moisture is still building up
2. Inspect External Maintenance
Look for:
- leaking gutters
- cracks in the walls
- damaged pointing
- roof issues
3. Look For Damp Patterns
Ask:
- Is it worse after rain?
- Is it always low down?
- Is it in corners and behind furniture?
4. Improve Ventilation
Even with a dehumidifier, you may need:
- better extraction
- airflow changes
- heating consistency
5. Get A Professional Damp Survey
If damp persists, a survey gives you clarity and prevents wasted spending.
Get A Proper Damp Diagnosis With WeatherDry
A dehumidifier can be a helpful tool, but it’s not a cure-all. If your home is still damp, it’s usually because moisture is entering from outside, rising through the walls, or being trapped by poor ventilation and cold surfaces. Until the root cause is treated, the damp will keep returning — no matter how often you empty the water tank.
WeatherDry can help you find the real reason your home feels damp and recommend the right long-term solution. Whether you’re dealing with condensation, rising damp, penetrating damp, or cold bridging, our specialists provide expert surveys and tailored treatments that stop damp at the source. Contact WeatherDry today for peace of mind and a healthier, drier home.
FAQs related to Dehumidifier
1) Shouldn’t A Dehumidifier Fix Damp Completely?
Not always. A dehumidifier removes moisture from the air, but it won’t stop water from entering through walls, rising from the ground, or leaking from outside defects.
2) How Do I Know If I Have Rising Damp Instead Of Condensation?
Rising damp usually affects the bottom of walls and may cause tide marks and salts. Condensation tends to show as mould in corners, on cold surfaces, and around windows.
3) Why Does My Dehumidifier Fill Up But The Wall Still Looks Damp?
The air may be dry, but moisture could still be in the wall fabric, or salts in the plaster may be attracting moisture and causing staining.
4) Where Should I Place My Dehumidifier For Best Results?
Place it in the most affected room, keep doors open if possible, and close windows while it’s running. Avoid blocking airflow around the unit.
5) When Should I Call WeatherDry?
If damp keeps returning, worsens after rain, appears low down, or causes repeated mould and peeling paint, a professional damp survey is the best next step.
References
- https://energysavingtrust.org.uk/dealing-damp-home/
- https://www.cse.org.uk/advice/condensation-damp-and-mould/
- https://www.property-care.org/homeowners/advice/condensation/
- https://www.property-care.org/homeowners/advice/rising-damp/
- https://www.property-care.org/homeowners/advice/penetrating-damp/
- https://www.gov.uk/government/publications/damp-and-mould-understanding-and-addressing-the-health-risks-for-rented-housing-providers/understanding-and-addressing-the-health-risks-of-damp-and-mould-in-the-home–2
- https://www.nhsinform.scot/healthy-living/indoor-health/damp-and-mould-indoors/