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Loft condensation: Explained..& practical actions to reduce or eliminate

The headlines

The previous articles described how to reduce damp problems inside the home.

This article explains:

  • Why loft condensation happens.

  • Why it is so important to stop it.

  • Practical actions you can take to deal with it, many of which are simple and easy.

Attic condensation caused by damp air from the home below
Attic condensation in winter

Most loft condensation is caused by moisture in the air rising from the home below.

If not stopped it leads to damage to the building, such as rotting roof timbers.

In serious cases it can lead to other issues, such as water dripping down onto ceilings and into rooms below.

There are three ways to fix this.

  1. Improving loft ventilation. There are simple ways to do this below.

  2. Reducing moisture levels in the air in the home below. This is important to do anyway to avoid damp issues indoors.

  3. Reducing the amount of moist or damp air leaking from the home up into the loft. Some of the common problems and solutions are shown below. Addressing these will help you save energy as well.

If you already have loft condensation issues, it might be that some action on all three of the above areas is needed.

Trivia: Did you know that traditional loft felt is no longer used? Roofers now use modern materials that help prevent condensation problems in lofts. These materials are what is called 'breathable' to help moist air get out. Even with these modern materials, condensation issues can still occur though.


Quick links to sections below


Why we get loft condensation

Loft condensation only happens when a loft is cold.

Damp air leaks up into it the loft from the home below. It lands on cold surfaces and dumps some of its water in the form of condensation.

It's the same as damp air in a home. When it hits a cold windowpane or a cold mirror it forms condensation.

The coldest surfaces in a loft that are the most affected, such as roof felt, roof timbers and brickwork.

If the loft stays very cold, the damp surfaces up there gradually get wetter as more and more damp air rises from the house below. These surfaces can become so damp that water starts dripping onto timbers and loft insulation below, or items being stored in the loft.

The problem has got worse over the years because:

  • Lofts are colder than they used to be because of better insulation.

  • Homes are generating and holding more damp inside air than they did historically. This is caused by changes in lifestyle, and homes generally having fewer draughts because of improvements in glazing and draught proofing.

  • The amount of loft ventilation in homes was probably adequate when they were originally built. Lofts would have been warmer then. As lofts are now cooler the amount of ventilation a home already has may not be adequate.

  • Poorly laid loft insulation can block up ventilation.


Why it is so important to fix it

The most important reason is because of how condensation affects wood timbers in a loft.

Most homes are built with roof timbers that are just natural wood. This means they aren't treated with anything to prevent them rotting.

This is absolutely fine as long as they stay dry. This is why there are many homes in the UK over a hundred years old with their original roof timbers.

If roof timbers get wet or moist persistently they start to rot.

Roof timbers suffering bad wet rot
Very badly rotted roof timbers

I'm sorry if all that looks very grim! The photo is a very bad case of rot.

The good news is that by taking actions such as those below problems can be avoided.

The good news is that many of these actions are easy. The simplest ones are also some of the most effective.


How to spot early signs of trouble

Condensation may only appear occasionally. Most of us don't visit lofts regularly though. When you DO visit the loft though, below are some tell-tale signs you can look.

These could all be indications of a condensation problem. Don't panic if you see them. Visual symptoms of damp don't automatically mean big bills.

White, black or even mould growing on the surface of timbers.

There is no certainty that these visible signs are because of condensation. They could be caused by:

  • A historical damp issue that has long been fixed

  • A problem with water ingress into the loft from a roof or gutter issue

Another easy thing to look for any moisture you might feel between the layers of roofing felt.

Condensation between roof felt laps
This should basically feel dry

Other signs are:

  • A musty smell of any sort in the loft.

  • Any degradation of loft 'stuff' that looks like it might be due to moisture.

The best time to go up in the loft and have a look is after a few days of really cold weather.

If you see something of concern, do seek professional advice. At the very least take a few photographs of any symptoms that worry you. They will allow you to see how if anything changes over time.


Actions you can take

As I said earlier, there are three actions that may all need to be looked at to solve this issue.

  1. Improving loft ventilation.

  2. Reducing moisture levels in the air in the home below.

  3. Reducing the amount of air leaking from the home up into the loft.

The sections below cover each of these. I also have a section at the bottom of what I call 'Poor solutions'.


1. Improving loft ventilation

There are some very quick easy things to check and do:

Tweaking loft insulation

Ensure loft insulation is not blocking ventilation at the edges of the roof. Pull it back to create a gap of at least 50mm. It is usually possible to do while still fully covering the ceiling below.

Simple loft felt vents

These are called 'lap vents'.

They ensure there are gaps between different layers of roofing felt. They cost under £3 to buy and take seconds to fit.

This YouTube video is excellent at telling you more about how they work and a step by step guide to fitting them.

Alternatively you can use short lengths of pipe insulation

Too much stuff (aka JUNK!)

A loft that is stuffed full of 'stuff' can reduce air flow.

Simple roof modifications requiring professional help

There are further relatively simple modifications that can be made to the roof. These either improve the ventilation around the edges or on the roof itself. These obviously need professional help to install.


2. Reducing moisture levels in the air in the home below

Please see here for my series of articles that help you do this.


3. Reducing the amount of moist air leaking from the house up into the loft

Loft hatch

This is probably one of the biggest and most common culprits. See my article here giving you information on how to draught proof a loft hatch.

Built in cupboards and wardrobes

The biggest culprits are airing cupboards or cupboards that were used as airing cupboards in the past.

These frequently have holes in the ceiling where pipes go through to the loft (or USED to go through).

This can also be the case though for any cupboard with pipes or cables going into the loft. See my article on how to fix these problems.

Air loss into loft through airing cupboard pipes
This is typical but I have seen MUCH worse!

Recessed ceiling spotlights

Older ceiling light fittings can be very leaky. Switching to a modern ceiling spotlight would reduce this heat and air loss, and usually uses the same sized hole in the ceiling.

Access doors into loft spaces

As well as being an obvious heat loss, a poorly sealed door will leak damp air into a loft space.

Bathroom extractors

These should never be allowed extract their air straight into the loft.

Loft boarding

There should be at least 50mm gap between the underside of loft boarding and the insulation below.

This ventilation is to help any damp air that finds its way into spaces under loft boarding to get away as quickly as possible.


Solutions I believe are poor

The following solutions are poor in my opinion. They are like using sledgehammers to crack nuts.

Leaving loft hatch open

This is something that is really an emergency solution. Hot air rises naturally in a home. An open loft hatch (even partially) wastes a significant amount of energy. It effectively 'chimneys' heat out of the house.

Dehumidifiers in loft

Dehumidifiers only work efficiently if they are in enclosed spaces (such as a room with a door shut). A dehumidifier in a loft will have to work very hard as it will be continually sucking in moisture from outside.

Spray foam insulation of roof rafters

On the face of it, these spray foam systems look very attractive, as they may make lofts warmer. But there are downsides.

  • These products can make loft damp situations worse unless loft ventilation is increased.

  • Installation is expensive with a long payback period.


Quick links to the other main articles on this subject.

Other supporting articles on damp:


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Mark Thompson

Get Energy Savvy - simple practical home energy efficiency information

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2 comentários

29 de dez. de 2022

Some good advice here. I too have a long association with damp and mould issues, both as someone who has worked in the industry and as a landlord and tenant having to deal with these problems. The main thing I have found is that very few people are knowledgable about damp and mould; either they don’t want to know or are genuinely ignorant of the seriousness of the subject. Mould spores can be extremely hazardous to your health and can compromise the very structure of your roof and the ceilings and joists below. Common misinformation imparted by landlords and contractors is to improve ventilation within the home by leaving windows open and to avoid drying clothes indoors. Whilst it i…


21 de dez. de 2022

Another excellent article, Mark. Got me wonderI got if my “leaky roof” problem may (at least in part) be associated with poor loft ventilation. In my eagerness to effectively lag the loft space, I’ve pushed the lagging up against the roof in the eaves. Will check and make sure ventilated.

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