Your Home Climate
Air Quality · The problem library

Why is the humidity in my home so high, and what brings it down sustainably?

Recently reviewed·Reviewed June 2026, next review December 2026

Sustained high humidity is the result of more moisture being produced than the home can remove. The sources are predictable: cooking, washing, drying clothes, showering, breathing, and a building that is sealed more tightly than the ventilation strategy assumes. The lasting fix is usually a better path for moist air to leave, rather than a dehumidifier running constantly.

Editorial confidence
High confidence. Multiple regulator, government or academic sources agree.
Evidence status
Recently reviewed · reviewed June 2026 · next review December 2026
Monitoring
Every six months, plus whenever Approved Document F whole-dwelling ventilation rates are revised.
Evidence drawn fromBuilding standards: ADF, CIBSEProfessional bodies: EST

You may not need to read the rest of this page

You probably already have enough to act if:

  • Multiple rooms read above 60% RH on a hygrometer
  • Condensation appears on more than one window each morning
  • You have not yet checked existing extractors and trickle vents
Open the ventilation hub

This is probably the wrong page for you if:

  • Damp is confined to a single wall or floor (likely rising or penetrating damp)
  • Indoor RH is already inside the 40-60% band

Healthy indoor relative humidity range

40-60% RH

Source: Chartered Institution of Building Services Engineers · CIBSE Guide A treats this band as the comfort and health target for occupied dwellings; sustained excursions above it promote mould growth.

Whole-dwelling ventilation rate (existing housing)

0.3 l/s per m² of internal floor area

Source: Building Regulations; Approved Document F · Approved Document F sets the minimum continuous whole-dwelling ventilation rate.

Who this advice is for

Applies to

  • Sustained indoor relative humidity above 60% across multiple rooms
  • Houses with ineffective extractors or trickle vents that have been closed
  • Properties with retrofit airtightness work but no ventilation upgrade

Not intended for

  • Localised condensation on a single cold surface (handled under condensation-windows)
  • Rising or penetrating damp from external water ingress

What it usually looks like

These are the symptoms readers describe most often. None of them alone is diagnostic, but together they build a picture.

  • Hygrometer reading consistently above sixty per cent
  • Damp washing taking days to dry indoors
  • Window condensation in every room
  • Furniture feels cold and slightly damp to touch

Most common in: New-build flat · Loft conversion · Victorian terrace · Edwardian semi-detached

Before you buy anything

Watch the house respond as you scroll.

These checks are listed in the order we would work through them. The illustration on the left changes with each one, so you can see what each check is actually addressing before deciding whether it is worth doing.

Warm wet air settles on the coldest surface and stays there. The window streams; mould follows.

01

Identify the largest moisture sources

A tumble dryer that vents indoors can add several litres of water to the air per cycle. Knowing the worst sources lets you cut them off first.

02

Audit the extractors

Bathroom and kitchen extractors that do not vent properly to outside are the most common cause of high humidity in modern homes. Test them with a piece of tissue.

03

Open trickle vents and check window seals

Closing trickle vents to save heat is one of the most common causes of damp. The energy cost of leaving them open is far smaller than people assume.

04

Use a dehumidifier as a diagnostic, not a permanent fix

Running a dehumidifier for two weeks tells you how much moisture the house is producing. If it fills the tank daily, ventilation is the answer rather than a permanent machine.

05

Consider whole-house ventilation if the problem is house-wide

A continuous low-rate ventilation system designed for the house's volume is the right answer for a permanently damp building, not point extraction.

Before you spend money

The cheapest answer is usually the one nobody sold you.

  1. 01

    Put a digital hygrometer in the worst-affected room for two weeks and log the morning and evening reading.

    Indoor humidity is invisible. £15 of measurement decides between ventilation, fabric and behaviour, and routinely saves four-figure spend on the wrong system.

    £10 to £20
  2. 02

    Open every trickle vent in the house and confirm they are not painted shut.

    A significant share of UK humidity complaints disappear within two weeks of using ventilation that was already installed; free, and often diagnostic on its own.

    Free
  3. 03

    Vent the tumble dryer outside or switch to a condenser model that has actually been emptied.

    A vented dryer running into the room releases the moisture of half a load of washing into the air every cycle; eliminating that one source frequently moves whole-house humidity by five percentage points.

    Free

What we recommend, and why

Every recommendation explains why it comes first, the evidence behind it, how confident we are, and when it would not apply.

01

Identify the largest moisture sources before buying equipment

Why this comes first

Drying laundry indoors, unvented tumble dryers and long showers can each add several litres of water to the air per day. Removing or relocating the worst source is almost always cheaper than running mechanical equipment to compensate.

Evidence

EST guidance and Part F both treat source reduction as the first stage of any damp-air strategy before increasing ventilation capacity.

EST · ADF

Confidence

High confidence. Multiple independent sources agree on the direction and the order.

Exceptions
  • Homes where occupant activity cannot reasonably be changed (large family, no garden)
Next step
See the ventilation hub
02

Audit the ventilation system you already have

Why this comes first

Most damp homes already have extractors and trickle vents that are either disconnected, blocked or switched off. Restoring designed operation often returns humidity to the comfort range without any new equipment.

Evidence

Part F requires a working ventilation strategy; FETA commissioning guidance shows extractors commonly under-perform their nameplate due to duct routing and missing make-up air.

ADF · FETA

Confidence

High confidence.

Exceptions
  • Homes with no installed ventilation strategy at all
Next step
Plan it on the Home Planner

The trade-offs

Every choice gives you something and asks for something back.

  • PIV (positive input ventilation) from the loft

    You get

    Whole-house dilution of moist air for around £600 to £1,000 fitted; very low maintenance.

    You give up

    A faint slow-moving draught some occupants notice; less effective in airtight homes where there is nowhere for displaced air to go.

  • Continuous low-rate extract (CEV) in wet rooms

    You get

    Removes moisture at the source quietly and cheaply; meets Approved Document F as an alternative to boost extract.

    You give up

    Targeted rather than whole-house treatment; needs the wet rooms to be the actual problem.

  • Full MVHR

    You get

    Balanced supply and extract with heat recovery; the most controlled indoor environment available.

    You give up

    £6,000 to £9,000 fitted, and worth doing only where airtightness is at or under 3 m³/h·m² at 50 Pa; otherwise the heat exchanger is bypassed by infiltration.

Real homes that faced this

Publicly documented UK projects that ran into the same problem and reported what happened.

We did not run these projects. Each links back to the original publisher so you can read the figures in context and judge for yourself what carries over to your home.

How we'd approach this

Measure for a fortnight before any system gets a quote.

We would treat humidity as a measurement problem first and a kit problem second. A £15 hygrometer in three rooms for two weeks gives a clear pattern: morning peaks suggest bedrooms, evening peaks suggest cooking and bathing, all-day high readings suggest the fabric. Each pattern points to a different and much cheaper answer than whole-house ventilation.

We would also look for the obvious moisture sources before adding anything. Vented dryers, gas hobs without an extractor running, drying clothes on radiators and pots without lids release several litres of water into the air per day between them; turning those off solves a surprising share of complaints.

MVHR is only honest in a properly airtight envelope. In a leaky retrofit it tends to be theatre, and PIV or CEV is usually the more credible recommendation; we would not let the prestige of the kit drive the decision in a house it does not suit.

Evidence behind this page

Every recommendation on this page is traceable to its source. Click a publication to read the original.

Products that may help

Only consider these once the checks above have been ruled out. A product fitted into the wrong cause is rarely satisfying.

House Summary

The cheapest answer to high humidity throughout the house is usually the one that addresses the cause rather than the symptom. The list above is in the order we would work through it, because the checks at the top tend to rule out the most expensive mistakes further down.

Related decisions
Next Best Step

Ventilation; what your home actually needs

Take the next step