The Ultimate Guide to Curing Loft Condensation

Loft condensation is a common problem and usually affects homes in the winter when the loft is so cold that condensation forms as water droplets on the underside of the roofing felt. Folks then go into their lofts to retrieve Christmas decorations and realise the problem. In fact, the page you’re reading now gets thousands of visitors in December and January but virtually none throughout the rest of the year. If you’re seeing moisture and condensation in your loft, this guide is for you.

[Update 2022] If you’re in a hurry and are looking for the best product to solve common loft condensation problems, look no further than felt lap vents:

loft vent to ease condensation

Lap vent, can be purchased from Amazon

Loft lap vents are cheap and are ridiculously easy for anyone to install in minutes. They vent the roof so moisture escapes and can be installed internally so no scaffold or external work is needed. If you’re not in a hurry, then read the rest of my guide to loft condensation, its causes and how to prevent it.

This page is all about loft condensation, when you shouldn’t worry about it and some examples of when you should be concerned enough to take action.

If you’re suffering from condensation on your internal walls and windows, you’ve come to the wrong page and you should read this guide instead.

On this page we’ll cover:

  • Causes of loft condensation (read this first).
  • Examples of normal condensation and problematic condensation.
  • Products that a professional roofer can install from the outside of the roof to help alleviate the problem.
  • Products you can buy yourself and fit from inside the loft to help (DIY solutions).
  • Steps you can take to reduce moisture generally which should ease loft condensation.
  • Things you should never do – these will make the situation worse.

Causes of Loft Condensation

While there are many different causes of this type of condensation, the following are by far the most common as they increase the amount of moisture in the home, which may only become an issue in the winter when it condensates on cold surfaces:

  1. Changes have been made to the property such as extra loft insulation, boarding out the loft floor, wall insulation or new double glazing windows.
  2. The existing roof vents have been blocked by insulation, storage boxes and possessions etc.
  3. Loft water tanks and in particular, hot water tanks that don’t have lids to prevent steam from entering the loft space.
  4. An excessive amount of moisture being created by the house occupants.
  5. A general lack of ventilation in the house.
Condensation in the loft space

Water droplets on the underside of roofing felt. Tell tale signs of condensation issues. Note the rot to the top edge of the timber.

When diagnosing a loft condensation problem one must first understand how condensation works:

The loft spaces above most homes in the UK are designed to be cold, insulation is placed above the ceiling and this keeps the home below warm and the loft above cold.

But, as you are probably aware, when moisture comes into contact with a cold surface, it forms water droplets (condensation).

This is exactly what happens with the moisture in the house, it rises into the loft and during cold weather (typically near or below freezing external temperature) it condensates.

Changes to Loft Insulation

Any extra insulation you add to the ceiling will reduce the temperature in the loft, so condensation may worsen although this is rarely the sole cause.

The same applies to loft boards, these also keep the warmth out of the loft, making it colder and more susceptible to condensation.

This explains why most cases of problematic condensation affect either new well-insulated houses or older houses that have just had their insulation upgraded.

Boxes, Possessions and Incorrect Installation of Insulation in the Loft

The loft space should have adequate ventilation to prevent the build-up of moisture to an unacceptable level.

These vents are usually located at the eaves (the lowest part of the roof).

Unfortunately, placing boxes and possessions in the loft can disrupt the airflow and render the vents useless.

Pro tip:

Here is what the UK’s NFRC (National Federation of Roofing Contractors)  has to say about using a loft for storage:

The roof space is not intended to be a storage area, so if you do put items up there, you could restrict the air flow. The stored items may also become damaged by the condensation.

Pushing the loft insulation into the eaves can also block the airflow, this is a common mistake made by inexperienced DIYers:

Loft insulation

Loft insulation pushed into the roof eaves blocking the vents

Hot Water Tanks in the Loft

Some homes have a hot water tank placed in the loft, if you have one of these, it’s worth double checking that steam isn’t being released into the loft.

We have seen one case where a faulty thermostat was causing the water to boil constantly and the steam was condensing on the underside of the felt. Although rare, this could cause a lot of condensation, even in summer.

Pro tip:

First check for any obvious signs of water ingress that could be increasing the moisture levels in the loft. Broken roof tiles, leaking pipes and cracked roof leadwork are common culprits.

Other Things to Check in the Loft

Check that any ducting from extractor fans haven’t come loose.

Have the roof checked for leaks and repair them as required.

Inspect any plumbing pipework in the loft for leaks.

Ceiling downlighters and pipework passing through the loft and into the rooms below can also allow moisture to pass through, so these should be sealed appropriately.

Seal/insulate loft hatches if they aren’t already.

Excessive Moisture Being Created by the House Occupants

As already stated, moisture will condensate when it comes into contact with a cold surface, so if there’s more moisture in the home, there may be more condensation in the loft space.

Every home is different and we all live different lifestyles, every home will have a different humidity level and dew point, but here are some common household tasks that can produce excessive amounts of moisture:

  • Showering and bathing without opening the window or not using an extractor fan or having an inefficient fan.
  • Cooking, boiling water and washing up without opening windows or using extractor fans.
  • Drying clothes on radiators without considering where the moisture is going.

Moisture from the clothes on radiators must go somewhere

It is also worth noting that homes with young children/babies often suffer from excessive moisture, this is because newborn babies need to be kept in a warm home so windows are rarely opened and clothes washed frequently and bottles and equipment boiled often.

Pro tip:

Hanging wet clothes indoors has caused damp and condensation in so many homes that many landlords often create tenancy agreement clauses stating that tenants must not dry clothes indoors.

General Lack of Ventilation in the Home

Loft condensation is made worse by a lack of ventilation in the home.

It goes without saying that during the winter months, most homeowners keep their windows shut.

It’s therefore important that window trickle vents (or another type of window vent)  are installed and opened during the cold months.

Wall vents should not be blocked and kitchen and bathroom extractor fans should be suitable for the size of the room and used where possible.

Windows in unoccupied rooms can be partially opened to allow the room to breathe.

Double glazing and wall insulation all help to keep the house warm but can prevent moisture from escaping, so more of it rises to the loft and condensates.

Window vents, trickle vents

Window trickle air vent

What’s the Difference Between “Normal” and “Excessive” Condensation?

It’s perfectly normal for the loft to generate some condensation during a cold snap.

This could be made worse by a lack of wind, as this reduces the airflow through the loft vents.

It should however clear when the temperature rises and the wind increases.

Excessive condensation would be where it forms during warmer weather or doesn’t clear at all during the winter.

If the loft feels damp, mouldy and stale with visible signs of fungal growth to the timbers then this could be as a result of excessive and problematic condensation forming.

Pro tip:

It’s normal for lofts to experience some condensation, especially during periods of cold weather, but it should be adequately vented so the moisture soon clears.

Products That Can Be Professionally Installed

The following types of loft ventilation can be installed from outside of the roof, so should be fitted by a roofing professional.

Don’t forget; these products don’t work so well during calm weather when there’s no wind or draft.

Ridge Vents

How to vent a loft

Ridge vents are placed at the very top of the roof and should be used in conjunction with ventilation lower down the roof.

These ridge vents act as an exhaust, moisture is pushed out of the loft via the ridge vent.

Tile Vents

Tile specific vent

Universal tile vent

Vents can also be placed midway up the roof, these are fairly cheap to purchase and any roofing contractor should have the skills to install them.

Eaves Vents

Eaves vent

Eaves vent nailed to fascia board

Pre drilled soffit vents

The eaves is the lowest part of the roof and most houses should have an eaves vent system fitted, either to the fascia or the soffits. These are installed in new houses and also when new roofline fascias and soffits are fitted. They should ideally be used in conjunction with vents further up the roof.

Products That Can be Fitted “DIY”

The products we have mentioned so far need to be installed from the outside of the house, which means ladders, possibly an access tower scaffold and/or walking onto the roof.

There is, however, one product that you can buy online from Amazon and install from within the loft.

The product is a lap vent and is designed to open up the overlapping felt so an airway is created.

This product significantly increases the airflow through the loft, is cheap, easy to install and can be purchased from Amazon. Go check out the reviews on Amazon, to date is has a 5/5 star rating and glowing reviews.

Pro tip:

Lap vents are the easiest, quickest and cheapest way to add extra vents to a loft that is experiencing condensation.

Steps You Can Take to Reduce Moisture in the Home

We have already provided details of products that can be fitted to your roof to release moisture and reduce condensation but the next step is to try and reduce the amount of moisture being generated in the first place.

If you are experiencing high levels of condensation in the loft, then you really should start by asking yourself where this moisture is coming from and how you can reduce it before it rises into the loft.

Some of the suggestions may seem obvious are worth exploring:

  • Avoid drying clothes on radiators during cold snaps and when you do, try to keep a couple of windows at least slightly open. An article by the Daily Mail newspaper suggests that moisture levels in the home increase by up to 30% when washing is dried on radiators.
  • Showering and bathing should be done with the door closed and a window opened afterwards. Make use of the extractor fan if you have one and if it’s not working efficiently, upgrade it to a better one.
  • When cooking and boiling water in the kitchen, keep windows at least slightly open and again make use of extractor fans.
  • Be mindful that any moisture you create in the house must go somewhere and if you don’t make an allowance for this, it will rise into the loft and during the cold winter months will condensate on the first cold surface it comes into contact with, which will be the felt.

Pro tip:

By drying clothes on radiators you are increasing the moisture levels in the property by up to 30%.

If you have the windows closed during the winter, the moisture will remain in the home and condensate on cold surfaces such as window panes, cold taps and the felt in the loft.

Why Some Homes Experience Loft Condensation and Some Don’t

Every home is different and some are more drafty and less well insulated than others, this has a two-fold effect on condensation:

  1. Heat escapes into the loft, a warmer loft is less likely to produce condensation
  2. Moisture escapes via old windows, uninsulated walls and drafty front doors, so less moisture rises into the loft, thus less condensation forms.

Excessive loft condensation is often (but not exclusively) the result of an imbalance between insulation and ventilation.

Many houses constructed before the 1980’s don’t have any, or very little loft ventilation because the house is so poorly insulated and it’s just not needed.

Upgrading the insulation to these houses can lead to condensation in the loft, and as such, ventilation should be installed or upgraded along with the insulation.

Unfortunately, insulation installers rarely have enough knowledge or expertise to calculate the required ventilation when upgrading the insulation.

It should be noted that in some homes, it may be impossible to completely eradicate loft condensation but your goal should be to reduce to an acceptable level i.e when it only forms mildly, clears quickly after cold weather and doesn’t lead to mould or rot to the roof rafters.

Pro tip:

Every property is different and some well-ventilated buildings never experience condensation.

Things You Should Avoid Doing


One of the first things many DIYers do when they see condensation up in the loft is to add extra layers of insulation above the ceiling.

While this insulation is great at keeping warmth in the home, it’s not a water barrier, so moisture will still pass through it into the now even colder loft space and condensate.

Excessive amounts of insulation can actually make the problem in the loft worse.

Boxes and Possessions

We have already discussed this but it’s worth mentioning again, the loft isn’t designed to be a storage space and too many boxes and possessions in the loft can disrupt the airflow.

Living in a Sealed Airtight House

Too much insulation and too little ventilation can lead to high moisture levels in the home.

This isn’t ideal at any time of the year but during the cold winter months, it will lead to condensation somewhere.

Avoid blocking air vents, open up window trickle vents, don’t cook/bath/shower without thinking about ventilation.

Don’t dry clothes on radiators during cold weather spells, if possible use a tumble dryer and if not, keep a window at least partially open to vent the moisture.

Removing Loft Insulation

As previously stated, insulation placed above the ceiling reduces the loft temperature and can make condensation worse, but removing the insulation isn’t the best course of action, it would be more appropriate to increase the ventilation in the loft and allow the excess moisture to escape.

Additional Steps You Can Take

The following steps could reduce or eliminate loft condensation but only at a considerable cost.

We suggest you first have your property inspected by an independent surveyor before you proceed with any of these options:

  1. If the roofing felt isn’t breathable then have it removed and replaced with one that is. This will involve removing all the roof tiles, replacing the felt and retiling, so scaffold will be required.
  2. Have the ceiling removed and a waterproof barrier fitted to the ceiling joists, then install a new ceiling.
  3. Have the roof converted from a “cold roof” to a “warm roof”. This involves the removal of all insulation above the ceiling and new insulation placed directly underneath the roof tiles. You are effectively converting the loft space to a warm environment where moisture will not condensate.
Loft foam

Sprayed insulation under the roof tiles. The loft is now warm and no condensation will form. Image from Permaseal

Further Reading

Jeff Howell writes for the Telegraph newspaper and has written several no-nonsense articles about soggy wet lofts and condensation problems:

Why is there condensation in my loft?

DIY advice – wet roof spaces

Phil Parnham offers an opposing viewpoint with his article about the myths and realities of loft condensation:

Condensation in Loft Spaces: myths and realities

The National Federation of Roofing Contractors also has a PDF help sheet that was updated in 2020:

NFRC help sheet

Our website also has an in-depth guide to damp issues along with several case studies and some relevant helpful tips for those suffering from damp problems:

Cost to damp proof a house – examples

Get a Quote

We hope you found our guide to solving loft condensation helpful.

If you want a second opinion from a rated and reviewed tradesperson, hit the link below to see how we can help you:

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Quick FAQs:

Loft condensation in winter is perfectly normal and with adequate ventilation, the moisture should clear in a short time. Persistent condensation or high levels of moisture in the summer should be investigated further.
For loft condensation, we recommend felt lap vents, which are very easy to install DIY and improve the ventilation in the loft space.
Provided you have adequate insulation on the floor of the loft, the temperature of the property below the loft should not be affected should you wish to install loft vents.
You can add extractor fans to shower/bathrooms if they don't have them, use a tumble dryer instead of radiators to dry clothes, install window trickle vents and other types of vents to improve the overall ventilation in the home. Passive extractor fans are also an option for problematic condensation problems.

This guide was written by and was last updated in April 2022.

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Author - Danny Woodley
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