Condensation in roofs has become more of a problem as we introduce more insulation and eliminate draughts in our homes. It is often linked to older style impermeable roofing felt which has been around since the 1930s although breathable membranes, which were introduced in the 1980s, are not immune in some circumstances.
Both of these materials perform a number of functions:
- To provide temporary weatherproofing to the building before the main roof covering is installed (membranes can normally provide a couple of months of protection to direct exposure to the elements)
- A secondary barrier to rain and snow which is driven under the roof covering by the wind
- Prevent potential pests like insects and birds from entering the roof through small gaps.
Despite its benefits, older style roofing felt can contribute to an unwanted side effect – condensation in the roof which can lead to the rotting of timbers and damp appearing on ceilings. Roofing felt is impermeable to water so it will not allow moisture to escape from the roof.
Breathable membrane does allow water vapour to escape from the roof space but if other circumstances are working against it then it may not be sufficient on its own to prevent condensation.
Nowadays condensation problems are well understood and most new homes are designed with suitable ventilation to prevent condensation occurring. This is covered for house designers by BS 5250:2011+A1:2016 (Code of practice for control of condensation in buildings). In the British Standard, reference is made to a well-sealed ceiling, which means tradesman installing plumbing and electrical services, as well as ceiling plasterboard, have worked in a way which prevents air from finding its way from the home into the roof space. For a normal ceiling (not a a well-sealed one) using a vapour permeable membrane then there should be a 7mm gap along the eaves in the roof space to allow adequate ventilation.
In properties 20 to 80 years old condensation can be a potential problem, particularly with the recent drive to insulate houses by putting thick layers of thermal insulation in lofts and to reduce air infiltration by stopping draughts. The loft insulation means the roof space is colder than before which encourages condensation in the roof. Installation of a wood burning stove has also been cited as a cause as the wood burner seems to provide a “thermal” in the house, helping all the moist air to rise faster.
What Causes Condensation In The Loft Or Roof Space?
Warm air can contain more moisture than colder air. Warm moist air enters the roof space through gaps in loft hatches or where bathroom plumbing or other services go through the roof space. When this warm moist air hits the cold air in the roof space, water droplets condense on the nearest cold surface – the roofing felt. It can be hard to identify the exact spot causing problems as once water condenses it can then run down the rafters and form damp spots away from the original source of the drip.
Condensation is most likely to be a problem during cold weather when the loft is at its coldest and doors and windows in the home are closed. It is less likely to be a problem in summer months unless there is a more serious problem.
The solution to condensation in roofs is straightforward. Prevent moist air from entering the roof space and ensure there is adequate ventilation and air flow in the roof space to carry any moisture laden air to outside the roof space.
Preventing warm moist air from entering the roof space:
- Consider how to reduce moisture in the house with improved extraction in the kitchen, bathroom and utility room
- Ensure that the loft hatch has a suitable seal to prevent air rising into the roof space and is well insulated.
- Avoid having gaps in bathroom ceilings and make sure that any shower extractor fan is not discharging into the roof space.
- If you have one, ensure the central heating cold water tank in the loft is covered with a lid, so no evaporation can occur.
- Consider how recessed lighting in ceilings and other light fittings can allow moist air into the roof space.
Cooking, boiling the kettle and bathing/showering are some of the biggest culprits for generating moist warm air (as well as people breathing!). Washing and drying clothes can also add to air humidity. It is important to have adequate air extraction in these areas so the moist air is cleared to the outside of the house quickly, rather than being allowed to cause condensation and mould problems.
Kitchen extractor hoods and wall or ceiling mounted bathroom/toilet extractors can play a part. If mould and condensation is a problem more generally then a Mechanical Ventilation Heat Recovery System (MVHR system) may be worth a thought if a full house refurbishment is being considered. The benefit of a MVHR system is that it recovers the heat from the extracted air and uses it to heat incoming fresh air from outside.
Adequate ventilation in the roof space
- Check that any recently installed thermal insulation has not covered any ventilation holes in the eaves.
- Consider if items stored in the loft are reducing air flow across the roof space and reducing ventilation.
- If you have enclosed soffits then consider adding eaves vents to improve air circulation (be aware that old roof soffits may contain asbestos though). These can be installed from the outside using a ladder or sometimes internally from the roof space.
- Consider adding some form of roof ventilation. Roof vents which replace tiles can be installed but due to cost this is much better done as part of a re-roof. To add eight vented tiles into a roof space would cost around £650-£700 (made up of 8 x vented tiles @£30 + access tower @£150-£200 + £260 labour ( 1 day for 2 people). To do this as part of a reroof would cost around £250.
On new houses you can often see roof vents installed in the roof. These are generally for extractor fan outlets rather than for ventilating the roof space.
A local roofer will be able can advise on the best steps to take to improve the roof space ventilation and avoid condensation in roofs. Provided safe access to the roof space is available then most of these actions are fairly low cost (under a couple of hundred pounds).
Hi,
We have extended our ground floor by 60sqmts and added underfloor heating for the entire ground floor (about 135 sqmts). I have noticed that after the winter after the building works, the timber in the loft has been getting moist and showing signs of water dripping at places. Are these 2 things interconnected. We do have 2 bathrooms whose extractors pipe runs through the loft and connected to a vent into roof.
The insulation is decent and laid evenly. We do use the loft space for storage (does this effect the moist levels?)
Any suggestions to resolve the issue would be much appreciated.
thanks
Hi John. Six weeks ago, I added extra insulation to the loft and made the beginners error of running the insulation too close to the edges, thinking that as insulation is air tight it would still ventilate. Having gone up last week for the Christmas decorations, I found condensation dripping down from the lining and the insulation was now damp. The next day I scrambled around the loft pulling the insulation away from the sides until I had a clear view of the edges. Three days later I took another look and the condensation has mostly gone from the roof lining. However, areas of the insulation are still damp. The loft is also now much more breezy. Unfortunately a small damp patch has since appeared in the bedroom ceiling below the worst area of damp insulation. Will the attic begin to dry or should I put a dehumidifier up there and run it a few hours every day? If I did, should I put a temporary loft hatch sheet of wood with a small hole for the extension lead or won’t a small gap in the loft hatch matter (I don’t want to simply let more moisture go up there from the house). Would a dehumidifier work given I’ve now restored air flow around the loft? Cheers, Adrian
Isn’t air tight = typo!
Hi Jon, we have a 1970s semi, with concrete tiles, roof felt (which is original and brittle and damaged in areas, and vents in the soffits. The loft is well insulated and we have made sure the vents are clear. We do get condensation forming on the felt on a cold clear day and also a damp patch in the corner of a first floor bedroom, which is wet to the touch when it’s very cold, this is the North side of the house. We have no ridge vents. I’m thinking of buying the bullet and getting the roof resolved with a breather me mbrane, should I also get ridge vents at the same time? I’m also going to improve extraction from the bathroom and kitchen.
Does this seem the right approach or would just ridge vents work?
Thanks
Hi Jon,
I came across your informative piece whilst searching for an explanation of a weird moisture problem in my loft which hitherto roofing experts have been unable to explain.
My house, which I bought quite recently, is a 1970s semi with pitched, tiled roof with bitumen felt secondary barrier (likely to be the one originally fitted). The roof did have two obvious leaks which were down to a combination of eroded ridge mortar and torn felt underlay in places. Rain was coming into the ridge line and running down the felt, leaking into the loft where it found holes in the felt. To remedy this, I had a dry ridge system fitted (ie. rather than another mortar ridge) and have since been in the loft in the location of the previous leaks and can no longer see rainwater ingress. During this work, the roof was inspected and any broken tiles were replaced. The roofer who did this was confident that there’d be no leaks coming through the tiles, save perhaps for any hairline cracks concealed by the covering of moss on the roof.
During rainy conditions the (old) loft insulation becomes slightly moist in places, like a fine mist has been spray over areas of the loft. I have noticed a little moisture on the underside of the felt above several locations of the moist insulation but this is barely perceptible, amounting to a few tiny droplets on my hand. When I touch the felt in the affected areas a black residue/dust comes off on my hands and the insulation is blackened or grey in large areas of the loft. I’m not sure if this is mould or dirt/dust (both the felt and insulation are old) or, if it is mould, whether or not this was caused originally by an historical problem that has since been resolved. When I put my hand in between some of the felt laps in the roof, I can feel dampness, suggesting to me at least that rainwater is still getting under the tiles somehow, but could this be condensation?
The loft does not smell damp and there is no obvious decay of the visible wood roof structure, although there’s some chipboard flooring which is weakened and broken in places. There are also patches of damp on one of the chipboard floorboards like one might expect from a direct leak but the felt above it has no obvious perforations and both the rafters and felt above this floorboard are not obviously wet. It is conceivable I suppose that a leak is coming through the tiles and felt onto the floorboard but the felt dries by the time I observe it, leaving damp patches on the floorboard, apparently coming from nowhere. Alternatively, it could be condensation that gets so bad in that area such that it drips from the felt/rafters onto the floorboard then the felt dries. Without being in the loft to observe this happening, it is impossible to say.
Roofers will typically rule out leaks first, then assume condensation if a moisture problem persists. Given that moisture on insulation is spread over large areas in the loft, to varying extents, rather than concentrated in specific areas, this might suggest that this is down to condensation, rather than leaks. However, the house is being renovated and has not been heated for months, so there is no temperature differential to cause condensation. The remedy prescribed for condensation is normally more ventilation but I have soffit vents and I can actually feel a breeze in the loft.
A new roof would undoubtedly fix my problem (how could it not?) but to feel confident in this solution, I first need to understand the problem I’m fixing. Some of the explanations I’ve had so far from experts do not seem plausible to me and therefore I cannot feel confident in the solutions proposed by these experts. At the moment, I can’t rule leaks or condensation in or out. I’d be grateful for any suggestions that you may have as to what could be causing this problem because trying to work this out scientifically is driving me round the twist!
Hi Jon,
very informative Q&A on here, thanks for that. I and some of my neighbours all have the same problem of excessive condensation in the loft. Some of them are getting mold in the top floor room. All homes are 2013 built. Ventilation is good and air movement obviously apparent. I am wondering if the problem could be the sarking material installed right up to the inside of the ridge tiles with no gap at the apex of the pitched roof internally. Can this allow warmer air to gather high up in the loft and cause condensation?
Shoud there be a gap in the sarking along the ridge tile internally to allow air to go up through the ridge tile?
I have checked the soffits, insulation gap, inlet pipe and all are clear and we have the wafer gaps instaleld so the insulation does not cover the edges.
Sadly the developer and NHBC are not interested in helping.
Great website and hope you can help a bunch of us.
Kind regards
Haydn
Hi Jon
What a useful article – thank you.
I have an issue in a top floor flat. The loft is not insulated on the loft floor, and is plasterboarded to the ceiling and walls in the loft (I have no idea why!). It’s an old Victorian converted building. We are experiencing damp patches on the walls inside the flat. Our roofer has confirmed that the roof tiles are not natural slate, and the felt is not a breathable type. The roof is sound .We’ve had roof vents put in but the damp keeps on appearing.
I’m wondering if there is condensation on the roof membrane which is causing moisture to run down and enter our flat at the front of the property. The loft itself is dry.
Reading your article it looks like we ought to insulate the floor of our loft space to try to prevent warm moisture laden air from entering the loft space. Is this the right way forwards?
Thanks for your help on this very frustrating matter.
Hi Jon,
Thank you for a very informative website but I am wondering if you can give me some advice concerning my specific problem.
We seem to be suffering from a condensation problem in the loft. We have noticed white patches (which we presume is white mould) on the bitumen 1f roofing felt in the loft.
But this problem has only become an issue since having new Upvc soffits and Fascias fitted recently. The Upvc soffit has prevented soffit holes in it. Prior to this we had the original wooden soffits and fascias and the wooden soffits had large rectangular vents in them with a wire mesh -I counted 13 of these rectangular holes in the previous wooden soffit! 13 at the front and the same number at the back. And we suffered no condensation problem with the original wooden soffits!
It seems to me that there is not enough ventilation going into the loft compared to the previous wooden variety and my question is what is the best way to go about rectifying the situation?
I have thought about having installed 10 circular soffit vents both front and back. into the Upvc soffit boards which is in addition to the Upvc prevented slots which to be honest are not very wide-is this likely to cure the problem or should I also consider having some roof vent tiles fitted as well (if this is a good idea how many front and back and where would you position them?)-I am not too keen on having ridge vent tiles fitted.
I have read that you can have too much ventilation and that too much ventilation can be a bad thing as well-is this true?
Also on the subject of the white mould do I need to think about having it treated in some way.
People have mentioned to me to use a mild bleach solution but is that a good idea bearing in mind our home is from 1991 so our roofing felt is 30 years old! Could the bleach damage the felt in some way-if so what could you recommend instead. And if a very mild bleach solution is suitable , by spraying it onto the felt , some bleach might be sprayed on the timber frame either side of the felt so is that a good thing as well or do we just wipe off the bleach from any wood with a cloth?
I thought about treating the white mould to see if it comes back otherwise how would I know if the extra ventilation has helped?
Any advice you can offer me would be greatly appreciated.
Kind Regards
Raymond L
Hi Raymond,
If the condensation problem started when the soffits were replaced then this does seem to indicate that ventilation is your problem. NHBC guidance for a normal pitched roof would be to have the equivalent of a 10mm gap running around the eaves. A 10mm air gap is the equivalent of 10,000 mm² per metre of eaves. The soffit vents you purchase will tell you how much of an air gap they deliver. 70mm circular vents usually have an air gap of around 2,150 mm². These can supplement any existing soffit ventilation you have. If you were using 70mm circular vents alone for your soffit ventilation then you would need approx. 5 per metre (based on 2,150 mm² each) if you used these to deliver the required overall area. For NHBC guidance on this, which would also meet Building Regulations, see https://nhbc-standards.co.uk/7-roofs/7-2-pitched-roofs/7-2-15-ventilation-vapour-control-and-insulation/
I would expect the soffit vents to solve the condensation problem, provided that they are installed to the manufacturers instructions and that air flow through the eaves into the loft is not blocked with stored items or been boarded over. Usually you would only need to add 5mm ridge vents on a larger roof (10 metre span) or a pitch over 35 degrees. On a cold roof there is no particular problem of too much ventilation but there should be no need to add roof vent tiles if the eaves ventilation is working effectively.
I do not have any expertise in cleaning of roofing membranes so can’t really add much here. It should dry out with adequate ventilation but if you can identify the specific membrane material you have then that may help you find an appropriate cleaner if you feel it is needed. As an example, DuPont Tyvek Supro Breather Membrane is made of a composite of high density polyethylene and polypropylene but others membrane materials include three layer polyolefin composite sheet. Membrane data sheets don’t mention any specific maintenance activity regarding cleaning. Durability is certainly affected by exposure to light but I cant comment on the impact of mild bleach. This is more a cosmetic / visual appearance issue as it shouldn’t affect performance. To check out whether you do have a roofspace humidity problem (and whether you have solved it when you make changes) you could use a moisture meter in the area. You can get a cheap digital hygrometer for around £10.
Hope this helps
Kind regards
Jon
Hi Jon,
Hoping you can advise? We are in the process of converting our single garage into a habitable space. We are almost at the end. We have noticed that there appears to be condensation spots on the ceiling and walls. These are darker brown areas on the p[asterboard. The room was plastered about 4-5 weeks ago.
A week ago we had a liquid screed floor poured in and this appears to be mostly dry.
We are just not sure if there is a problem here or not. Could the spots we are seeing disappear in time given the floor potentially is not fully dry (it looks dry)?
My fear is that our building contractor (who is also a roofing contractor) has not build the roof properly. The conversion has a flat room which has to be build up as part of the conversion. The original roof was removed and the new roof was laid a block or two higher. The garage is joined to our house with the outside wall of the garage being a boundary wall with the neighbour.
I am not sure if a vapour barrier was put in place. It may be have been but I did not witness this going in. Also, I don’t think the space above the ceiling is adequate. There is no overhang on the front or rear of the conversion. The fascia’s are flush with the outside walls. On the boundary wall, the same is true.
The builder is aware and recently installed 7-8 3″ circular vents which were installed into the fascia along this wall. I don’t think it has made a difference.
One time last week, there was actually water dropping out of the spot light socket in the ceiling.
The job is not yet complete and the builder is aware but I don’t want to get fobbed of by him.
We do have building control on this but all communication is between them and the builder remotely. Building control have not been to the property because of Covid.
Any thoughts here will be really appreciated. I have some pics if this will help?
Many thanks,
Ed.
Hi Ed,
Sorry to hear of your problems. It’s hard to understand the precise roof construction from your description but picking up that there are vents in the fascia, my general comments assumes this is a cold flat roof.
In a cold flat roof the insulation sits flush immediately above the plasterboard ceiling, with a 50mm air gap above that and then a timber deck and waterproofing. Cold roofs are notorious for condensation, especially in near freezing weather conditions. You don’t mention where you are in the UK but there are many cold flat roofs in homes in England & Wales. The key to making them work is good cross ventilation with an adequate (50mm) air gap to allow air to blow in one side of the roof and out the other, constrained on each side by the joists. They are not permitted under Scottish Building Regulations, which allow only warm flat roof construction, due to condensation issues in a cooler climate.
From your description you probably need to discuss with your roofer whether the ventilation is sufficient. He may have accounted for this elsewhere but if there are air vents on one side only and the other side is a house wall there is little scope for effective cross ventilation through the 50mm air gap. Not a huge problem with a draughty garage but a bigger issue with an air tight heated living area. There is inevitably a fair amount of drying out as the plaster and floors dry out, so moisture levels are excessively high compared to normal living conditions but it would be best to raise your concerns with the roofer and ask how he has achieved adequate air flow across the roof. The damp spots on the walls are just likely to be part of the wall drying out at a slightly different rate.
Hope this helps
Kind regards
Jon
Hi Jon,
I have had issues with condensation, mold and damp patches on my attic roof for the last 4 years. I had is converted 5 years ago. It has an open stairs and their is also an open stairs from the ground floor. We installed a stove just after the attic. The roof has old felt which is impermeable and the eaves have no insulation on the roof section its just under the flooring. The attic space has 75mm king span insulation in the roof and walls.
The mold got so bad 2 years ago, it destroyed everything I had stored in the eaves.
I have installed 3 roof tile vents at the front and back of the roof, they are level with the top of the eaves. I have boxes of silica in the attic space and both eaves but they are not making a difference. The roof tiles made a slight difference but the mold is coming back. I have pictures of the attic and watermarks if it would help.
Thank you so much for reading my email. I would really appreciate any advice you can give me to help solve this problem.
Hi Jennifer, sorry to read of your condensation problems. It does sound as if the roof area is not getting adequate ventilation. This can happen when lofts are converted, especially when insulation is added too close to the membrane. The impermeable membrane will not help the situation. I would have expected this to have been replaced with a breathable membrane when the loft was converted. You need a 50mm gap between the membrane and the insulation to allow cross ventilation of the air in the roof. That would be worth checking first to see whether you have this gap. The (horizontal) soffit boards should also have ventilation holes in them (or a gap between the soffit and the outside wall) to allow cold air in to ventilate the roof and blow across the membrane. The outside air should ideally blow through one set of eaves vents and out those on the other side of the house, or out through ridge vents at the top if you have those. Additional vent tiles would probably help if the 50mm gap mentioned above was in place.
Hope this helps.
Kind regards
Jon
My roof has a new breathable membrane and the original concrete tiles replaced. It has a new dry ridge and wet verge system. The joists were saturated with rainwater before the roof was repaired and now condensation is dripping from the membrane on the lower half of one side. Should I hire a de-humidifier to get ride of the saturated water? Should I put low energy heaters in the loft (I have 2 panel heaters) for a limited time to warm it up to clear the condensation, so the water vapour can escape through the memberane? Thank you
Hi Lin,
If you think that there is sufficient ventilation and this is just a temporary problem then a dehumidifier may be a solution. You need to get the timber to a dry state (below 20% moisture content). Bear in mind that some dehumidifiers don’t operate at low or freezing temperatures so do look at the operating specification. If using one do check and empty it regularly.
If this isn’t drying out the timbers then do look at whether the ventilation through the soffit and ridge tiles is sufficient.
Hope this helps.
Jon
Hi Jon,
We boarded out our loft last summer, giving us the opportunity to spread out some of our boxes that are kept up there and just generally increasing the storage capacity. During a recent cold snap we’ve noticed that the felt on the north facing side of the roof space has started getting what appears to be condensation and is dripping on to the boxes and boarded flooring below. We’ve since moved the boxes that were getting dripped on but wonder if a) the condensation has been caused by us increasing the boarded area of the loft and b) what would be the best option to remedy the problem? We don’t recall there being condensation previously but then we probably wouldn’t have noticed before due to the access not being there. On a side note, there are two bathrooms with ventilation piping running to the outside of the roof, one of which has had water staining near the exit vent in the bathroom ceiling. We’ve also not noticed any obvious looking vents in the loft while being up there.
Many thanks for any advice you can give,
I’m having exactly the same issues in my attic. Extra insulation and half floored so far. Felt is wet and dripping enough to wet the plywood. Only noticed after I went up to get the decorations. In checking the outside vents I saw the previous house owner had replaced the facia boards but didn’t add vents. Feck all air flow, I’ll be talking that first. Love to know if you find a solution
Hi Paul & Katie,
Thanks for the feedback. Boarding the loft could have slightly reduced the amount of warm air rising from inside the house into the roofspace, especially if you have holes in ceilings from recessed lighting. And the boarded loft, will also have a small insulation benefit. Both these mean the air in the roofspace is slightly colder than it was, and hence less able to hold as much moisture. So condensation is more likely. It may be coincidence that the condensation is on the north side of the roof but it does tend to form at the coldest point it can find.
It could also be that you have boarded too close to the walls, and over any soffit ventilation. The soffit is the horizontal board you can see when looking up at the roof from the ground. There should be a 7mm gap between the horizontal soffit and the outside wall, or alternatively the soffit should have holes drilled in it to allow adequate ventilation into the roofspace from outside.
Best remedies are to reduce the potential for moisture to get into the loft and to improve the ventilation within the roofspace.
See below in the comments for previous advice on reducing moisture ingress.
On improving the ventilation I would first check that the soffit ventilation is clear and not blocked (sometimes soffit boards are replaced as a DIY activity without any consideration for the ventilation requirement). Also that you haven’t placed stored possessions over the soffit. The ridge ventilation (at the apex of the roof) should also be checked as should any ventilation bricks in the gable ends as these tend to get filled with debris and cobwebs.
If this doesn’t remedy the problem then you may need to consult a roofer about adding ventilation tiles if you don’t already have them . You haven’t mentioned the age of the home but if the roof has an impermeable bitumen based felt then this reduces roofspace ventilation. Adding a number of ventilation tiles will help address this as part of the installation process involves cutting the roofing felt/membrane which will increase air flow.
It wasn’t quite clear to me how the bathroom extractor pipes run, but generally they should run horizontally in the roofspace to the outside. If they run vertically then there is a danger that water from moist air condenses and then drips back onto the extractor.
Hope this helps.
Kind regards
Jon
Hi,
Great website and article.
I have a property that was built in 1936. It has had a new roof installed at some point in it’s lifetime. The new roof consists of concrete tiles over thick bitumen based roofing felt. Having installed 100mm insulation and turned the heating on the felt is now dripping with condensation. The loft hatch is uninsulated and there appears to be no venting tiles. What would you recommend you rectify the issue?
Hi Lee,
Thanks for the feedback. Adding the 100mm insulation helps retain heat in your home, which is great for the occupants! However it has consequently reduced the air temperature in the roofspace. The lower the air temperature the less moisture it can hold, which is why you are now seeing condensation on the felt. Water will condense on the coldest surface.
There are a number of potential solutions for you depending on the level of problem and the budget you have. There are two basic things that need to be achieved.
1. Moisture Prevention: Preventing moist air from getting into the roofspace.
2. Adequate Ventilation: Ensuring there is adequate ventilation within the roofspace.
Moisture Prevention
To achieve 1 ensure that any moisture sources are kept well away from the roof. The loft hatch should have a seal (just like a window or door) to prevent warm moist air from rising into the roof space. Check that any bathrooms/kitchens have adequate air extraction; recessed halogen lighting in bathrooms is one potential source of moisture rising into lofts as is existing bathroom extraction that has pipes that run through the loft that leak extracted air into the roofspace.
Adequate Ventilation Of Roofspace
Depending on the build approach, there will be different features built into a roof to ensure adequate ventilation and these should first be checked to see if they have been blocked in any way.
A. Generally outside air is brought in to the roofspace by the horizontal soffits (the bits you see when looking up at the roof from the ground) which either have a gap between them and the wall or have holes drilled in them. Check that these gaps have not been blocked by items stored in the loft or by spiders webs and debris.
B. Any warmer moister air would generally be released through the ridge vents (at the apex of the roof) and these should also be checked.
C. Cross circulation of the air is achieved using brick vents in the gable ends of the roof.
Assuming all these are clear and you still have problems then other actions will have to be taken. The next step is probably to install a number of roof tile vents. These replace roof tiles and as part of the installation process the roofing felt will be cut which will allow better ventilation. They can also be an outlet for any mechanical extraction from bathrooms if required.
If these actions don’t address the condensation then the most expensive solution is to replace the building felt with a modern vapour permeable membrane. However if the roof functions well then this is should be the last resort.
Hope this helps
Kind regards
Jon
I have really bad condensation in half of my loft space. It’s a 1900-1920s house, which has red roof tiles and white roof membrane, insulation fitted in 2017 and partly boarded. I have 6 roof vents in the front part of loft where you can stand, 8 in the rear smaller part where you cannot stand. I have items in the loft, boxes and crates mostly. The loft opening and ladder is one unit. Earlier this year I fitted 10 vent flaps, that seemed to make a difference it went from wet to completely dry. But subsequently I have had External Wall insulation on one side of my house and since winter has arrived the condensation has returned to previous level, in fact it may be worse.
I’m at a loss of what to do.
Any other suggested remedies would be welcomed.
Thank you
Hi Heather,
Sorry to read of the problems you have had with condensation. As you are aware, condensation is caused when moist warm air hits colder surfaces. The external wall insulation will potentially increase the air temperature internally, with the rising warmer air able to hold more moisture and carry it higher. If that gets into the loft, with cooler temperature then it will condense on cold surfaces.
It sounds as if you have already tried to improve the ventilation within the loft area. So looking at ways to stop warm moist air from getting into the loft would be the next step. Rising moist air from kitchens and cooking or bathrooms and showers are possible sources – if these is suspected then improving extraction in the specific room could help. The loft hatch needs a seal to prevent air from below from entering the loft and watch out for other gaps in ceilings, such as holes cut for recessed halogen lighting in bedrooms and especially bathrooms. Also check that any bathroom shower ceiling extractor fans do not have pipes that are leaking moist air into the loft.
If the moisture is not coming from inside the house then consider external sources, potentially wet brickwork from damaged gutters / downpipes or from gaps in roof tiles or missing mortar from ridge tiles.
Hope this helps.
Kind regards
Jon
Hi
I have major condensation at back of kingspan on a vaulted roof .4 inch gap between kingspan and breathable felt so bad it drips onto floor when it gets cold outside.any ideas for me thanks
Hi Trevor,
Hard to be specific without knowing the context of the type of room and roof construction but to resolve condensation either the air humidity needs to be reduced, the surface needs to be warmer or the ventilation needs improving. Or a combination of all three. So as an example, a vaulted ceiling in a kitchen would generally need better air extraction to reduce the level of moisture hitting the surface. If the air circulation can be improved at the roof level that could also help. It sounds as if moisture is condensing on the felt – stopping any moisture laden air from hitting the cold felt would probably be a start.
Sorry I can’t be more specific but hope its given you some ideas on where to start.
Kind regards
Jon
I have noticed condensation on the north side of my pitched roof on a recent visit up in the loft
We don’t use the loft for storage
Only got my inverter in there from solar panels (which are fitted on south side of pitch)
3 years ago added 2no shower extractors to bathrooms to help ventilate them however they are covered with insulation and all connected ok 1 goes through gable and the other out into soffit (may be getting back into roof through vents?)
2 years ago added wood burner with a twin lined flue and vented fire plate going into loft
(Thought this could be a big contribution to warm air getting in loft so insulated around with A1 rated Rockwool)
House has cold roof construction trickle vents to soffits .solid roofing felt like you get on your shed roof
200mm of insulation over ceiling (away from eaves )
Since noticing this condensation I’ve used Rockwool A1 fire rated around wood burner flue 100mm thick
Ordered felt lap vents to help ventilation in roof space (yet to be fitted)
Ordered eave trays to go between rafters (yet to be fitted) as some areas of eaves you can see plaster board ceiling from below (plan to insulate tight to eave trays once they arrive) try to prevent warm air getting up into loft
Is there any thing else I could do if this doesn’t work or would you suggest not doing any of the above
Would lifting insulation up and putting tin foil on top plasterboard ceiling between ceiling rafters .then replace insulation on top help reflect heat back in rooms below .or would that cause more issues ?
Looking not to spend a fortune but know it needs to be fixed
Any advice would be good
Many thanks
Hi Ricky,
Thanks for your comments. Just to be clear the problem is created when warm moist air entering the loft is cooled and the moisture it contains condenses out as water droplets. Cooler air can not contain as much moisture. As houses with cold roofs get better ceiling insulation then the loft gets colder so the condensation problem gets worse as the energy performance improves. Insulating the shower extractor pipes and the wood burner flue will also result in a cooler loft, making the condensation issue slightly worse rather than better; that said it is absolutely the right thing to do as it will help improve the draw on the wood burner as the exhaust fumes will stay hotter and hence rise faster in the flue.
So warm (dry) air is not a problem in itself, although it obviously is less energy efficient if it is coming from the house itself. It is the moisture from cooking and bathrooms that hits the cold loft and condenses which is the problem. The wood burner is one contributor to transporting moist air upwards in the warm air it generates.
Reducing the opportunity for moisture to be carried by the warm air into the loft would be the starting point. So putting an air seal on the loft hatch could be part of the solution, as would be looking to see other places where moist air can get into the loft through light fittings and other pipes. Also if you have a cold water tank in the loft ensure you have a lid on it to prevent moisture from evaporation. It sounds from your description that you have a non-permeable roofing felt which does not help (that was typically used in homes older than 20-30 years old).
Once the loft is better sealed from the warm house then improving the ventilation with the vents etc will help vent any moist air faster giving it less opportunity to condense. The idea of putting tin foil on top of plasterboard would not help – it is effectively adding more insulation which will make the loft slightly colder and hence encourage condensation. It would maybe help the energy performance but that would better be done by adding extra insulation.
Hope this helps.
Kind regards
Jon
Dear jon davies
I’m facing similar problem in a ct scan room(20ft by 15ft) where square gypsum board false ceiling is provided(2ft by 2ft panels).It is seen that water droplet is accumulating on the gypsum board at a height of 8 ft of 10 ft room height.Now,what can i do to prevent this water droplet.There is no ventilation on the above space of the false ceiling.The room is consisted of 1 outer wall and 3 inner wall of the building.The ct scan room located at ground floor of a 6 storied building and outer wall situated on east side.
Hi,
I seem to have the same problem in that I insulated the attic two years ago and now it appears all the felt is damp with water droplets forming on the underside. I inserted two roof vents (both sides)but they do not appear to be working… It is an attic conversion. I was thinking I might install a fan into the attic space to try and get some air movement…Would this help??
TIA…
First can I say thank you for the great website. I’ve picked up some good tips.
I have recently had my loft insulation redone, and one third of the loft boarded over. Earlier in the year I also had my fascia and soffits capped over with plastic. I was informed that I did not need vents as there was a gap left between the fascia and soffits to allow the air to circulate.
I’ve just gone into my loft and I have noticed beads of water on the felt membrane, and some water marks on the boarding. I have now added Felt lap vents to help air circulation.
None of my double glazed window have trickle vents should I consider adding them or do you believe the flap vents will be enough?
Hi James,
Thanks for your comments. The amount of ventilation you will need depends on how much moisture is getting into the roofspace (I have read somewhere that 80% of the moisture in a roofspace comes through gaps in the ceilings below) and how effective the existing ventilation is already. You don’t say if the felt itself is a breathable membrane (better as it allows a level of ventilation) or impermeable (which doesn’t allow any air to pass through).
To prevent moisture I would look to ensure your loft hatch is sealed and that there are no lighting fixtures or extractor fan pipes which are adding to the moisture in the loft and that any cold water tank has a lid. For a typical home with a breathable membrane then a 7mm gap at the eaves is recommended. To some extent, whatever products you use, it will depend on the prevailing winds around your home and whether this air flow is blocked by other houses. Also make sure that you are not totally blocking air flow in the roof with stored possessions.
It is cold at this time of year, so is the worst time for condensation. It may be the felt lap vents do make sufficient difference. If not and depending on any condensation problems in the Iiving spaces, I would probably be looking to improve bathroom/shower/cooker extraction. The challenge with trickle vents for windows is they do also let out all that expensively heated warm air. As homes get more and more airtight to reduce heat losses (which also means they keep in moisture) then MVHR systems (Mechanical Ventilation & Heat Recovery) start to make more sense. I am not suggesting this for your home but if condensation is an issue then an extractor fan with heat recovery could be one possibility.
Hope this helps.
Kind regards
Jon
Hi Jon,
I have recently done my loft up with non itch insulation under floor boarding and ybs foil with 25mm eve clips then plasterboard on top of that. I am getting moisture running into the soffit are, beads of water of the roof felt, and i can’t board up under the purling to complete the roof space until i can find a solution to the moisture problem. This is only happening on 1 side of the loft (front of house north facing side) other side which is south facing is bone dry. i have silicon sealed the old loft hatch in loft & on landing and fitted a staircase for access which is near the troubled side but have 2 windows front & back and will leave both slightly open to see if it changes the outcome as we have a cold snap at the moment, Hope you can help.
Kind Regards,
Pete b.
Hi Pete,
Thanks for the comment. Moisture running into the soffit off the roof felt is an indication that warm moist air is hitting something cold, especially as you say this is occurring on the north side and after you have insulated the loft floor (which will have made the loft cooler than before). The basic approach is to either stop the warm moist air from getting to the loft or improve the ventilation of the roof space.
From your description I am not quite clear on the changes you have made (is the loft still separated from the house and is the loft still an unheated space or is something you are looking to use regularly? Also are you planning to insulate the roof itself?) so apologies if the comments below are off track.
The basic approach would be to stop the moist air (maybe from a bathroom or kitchen?) from finding its way into the loft. If I am right in assuming that, with the new access staircase, the loft is still separated from the house with a hatch then improving the sealing on the hatch would be the place to start. Also check that any vent pipes going through the roof space (shower extractor?) are intact and not pushing warm moist air into the roof space. There is also the possibility this is wind driven rain – see if you can find the highest point of condensation and look around there for maybe ingress through a ridge tile. If none of the above work then improving the ventilation would be the next consideration – one option would be roof vents which would reduce the condensation problem but make the loft space cooler. If you were wanting to use the loft space regularly then making it a “warm roof” with insulation will increase the air temperature in the loft and as a result reduce the condensation problem.
Hope this helps
Kind regards
Jon
9 December 2019: Just to clarify the problem is created when warm moist air is cooled and the moisture it contains condenses out as water droplets. As houses with cold roofs get better ceiling insulation then the loft gets colder so the problem gets worse.
Hi Jon
Thanks for a great article.
I have a dilemma and need some advice on how best to tackle the problem.
We have a loft which has been I dilated with celotex and there was sufficient spacing between the room to allow air circulation.
I’ve notice under the ever section there is condensation on the old style felt and as a result it’s rolling down the celotex and onto the floor of the storage area under the eve.
I’ve had 8 vent tiles fitted by a roofer on the lower part of the roof near the front of the house. This has made no difference.
The roofer suggested if the vent tiles didn’t clear the issue then we may need to consider putting ridge vent tiles along the whole of the roof.. we’vealreadyspent near enough £800 already.
Could you give some suggestions to a struggling man like me who is trying to make a home for his family
Can ceilings be porous? If so would it be beneficial to put tin foil between joists to act as a moisture barrier?
I get very isolated droplets of condensation on the roofing felt next to a few rafters. I have plenty of soffit vents but wondered if a vent on the apex would help?
Thanks
Invaluable info. Thank you Jon. Searched alot before getting to you and i now know the reason for the condensation along the inside of the roofing felt. It occurs directly above my bathroom extractor and watertank area where i have not got a proper lid for.
The use of extractor fans in key areas; namely bathrooms and kitchens can also pose a useful tool. Typically these are the dampest rooms in the house, so providing a mechanism whereby the moisture in the air can be drawn outside can be beneficial for reducing the humidity inside, and hence the amount that can make its way into the loft.
Cassie you are absolutely right. Removal of the moist air is a key element of avoiding condensation more generally. I have added a little more detail to the article regarding extractors. Thanks for your feedback.
Kind regards
Jon
Update: Also added information on whole house extractors known as Mechanical Ventilation Heat Recovery systems.