/ Home & Energy

Don’t be a drip! Watch out for dodgy damp advice

Damp companies that offer ‘free surveys’ may seem appealing, but our latest undercover investigation found several companies recommending unnecessary treatment that could cost hundreds of pounds.

Everyone loves a freebie, but if you’re tempted by the ‘free surveys’ on offer from damp-proofing companies, you may end up spending more than you need.

In our snapshot damp investigation, we invited damp-proofing companies to carry out an assessment of our properties’ damp problems. In two thirds of cases they recommended unnecessary or inappropriate treatment, or missed the problem completely. But does that mean you have to pay to get good advice?

All we needed was a plumber

In one case, our property had a leaky toilet – and any damp specialist should have instructed us to get this fixed before the room could even be assessed for other potential damp problems.

There was no evidence here of rising damp, and yet four of the eleven companies told us that we needed to install a chemical damp-proofing course in the walls and re-plaster the room – at a cost of up to £1,440!

That’s not to say all the companies were bad. We did see some good practice, with just over half of the companies that visited this property giving us helpful advice.

How to get good damp advice

Deciding whether to take your chances with a free survey, or shell out hard cash for independent advice is a toughie. Even though I’ve seen these results first-hand I know I’d be tempted to try my luck with the free option first – although I’d make sure to get at least three companies to come round and quote for the work.

Then, if there were inconsistencies in the work recommended or I had any inkling that the work might be unnecessary, I’d definitely consider getting an independent damp specialist round.

If you think you might need to call on a damp company, check our damp advice guide first for info on the different types of damp that can affect your home (if it’s just suffering from condensation you won’t need a specialist).

[This Conversation has been closed and is not open for commenting.]

Carrie says:
30 September 2013


I have 2 problems as follows:-

1. condensation in winter in the loft which started after I’d had new plastic fascias fitted. The guy who did it was going to come back & fit some vents in the soffits but unfortunately passed away suddenly before he could do that. I’ve approached a damp specialist company who say that as condensation isn’t their specialist field they would charge £90 plus vat to come & survey the problem. Under the circs I’m a bit reluctant to pay that as I think I know what the problem is – I just need a solution.

2. Mould on my clothes in the wardrobes – on the outside wall of a bungalow – & a kind of fusty smell in drawers & aforesaid wardrobes. No evidence (so far as I can tell anyway) of any damp or mould on the actual walls. I think my neighbour has blocked off some or all of the air vents on that side of the house but when my partner investigated all seemed ok – suspect he’s moved stuff while my partner looked & then put it back. Anyway could that be the cause and/or what else could it be?

Would it be possible to get one company to do both jobs without having to pay the £90 survey charge mentioned by the company I did approach? NB this is a national company recommended by the PCA & Which & I didn’t find their response too helpful. They told me to approach the PCA to find out what kind of help I needed which I’ve done & they said that one damp company should be able to do both . . back to square one . . .:-(

Thank you for any advice you are able to give


Some caution is required, having not had sight of your building, but some initial comments:

1. Maintaining eaves-level ventilation is absolutely essential if condensation is to be avoided. It will get worse in winter, when the underside of the slates are colder, and you should get vents fitted as soon as possible. This should not be a problem for a competent joiner; round vents which can fit a drilled hole circa 50-75mm diameter are available. Do ensure that they have an integral insect mesh, or you’ll have wasps in the roof before you know it.

2. Try leaving the windows open when you’re in, assuming that you have a toplight or similar, and see if that makes a difference. If it does then ventilation (or lack thereof) is the problem and you could consider having a builder add more vents, if required.

Hope this helps.

A quick Google confirms that white 75mm dia pvc eaves vents are available for the grand sum of £2.790 plus P&P per pack of ten from a well-known online hardware and tool supplier. The joiner would use a hole cutter to form the opening in the soffit (i.e. underside) of the eaves then fit the vent.

Different fixings are required for face-fitted vents in order to prevent water ingress.

Gareth says:
30 September 2013

I own a 1920 mid terraced house. Since renovating the property and decorating I have had small damp patches show on a section of the downstairs wall which is shared with my neighbour. At first I thought it may be the filler and paints drying so I left a dehumidifier on for a few hours. These did go away so I thought job done. As soon as its switched off about 6 hours later they appear again. The patches are all about 300mm off the floor and randomly spaced. The floor is concrete. There is no sign of damp any where else in the house up or down. When I got the property it had been empty for a while and had bad condensation damp through out. The boiler did not work and the loft not insulated. I carried out the renovation then had the heating fixed and loft insulated. I also fitted trickle vents in the windows. My neighbours house is currently empty. Also the joining house is set forward from mine and not in line. I have been in the house 3 weeks now.

Please help!!!!


1. Have you checked the outside of the masonry for any defects which might be leading to either penetrating dampness (for example failure of mortar joints) or localised condensation/cold bridging?

2. Do you know if this is a cavity or solid wall structure?

3. How did you finish the internal walls when you renovated – plaster on the ahrd (type of plaster?), strapping and lining, insulation?

I would be tempted to seek the advice of an RICS building surveyor, if I were you.

Gareth, as I’ve suggested elsewhere why not have a look at the useful Historic Scotland guidance on dampness in historic buildings – I can’t imagine our more severe climate on this side of the border makes the information any less relevant:


If this link doesn’t work for you, use http://www.historic-scotland.gov.uk, click the “learning and resources” tab and in the menu is “free publications”. Click this for a list, and you’ll find “DAMP, Causes and Solutions” (and some other useful-looking guides).
If anyone has a damp problem it pays to do some common-sense investigation first. To help this I’d advise anyone to read both this publication and the earlier SPAB one.
At least you will have some understanding of the possible problem(s) when you involve “experts” and at best they might help you solve the problem yourself.

Samuel Semmens says:
1 October 2013

Is the method used by “Dr Damp putting their patented bricks at regular intervals the most effective method of dealing with rising damp? as my damp course is past it and high readings of 9 in the sitting room on the dampness meter. Can I have your opinion please

Never heard of it.

Heritage House says:
1 October 2013

Patented bricks – sounds like the schriver or holland methods – none of which work – research has proven so, and are a complete con.

[This comment has be edited due to breaking our guidelines. Thanks, mods.]

I live in a mid terrace, 2up/2down, Victorian house (1842).

There is damp showing on the inside of the wall behind the front living room radiator at low level and damp showing (paint falling off) at higher level 1.5m on the exterior front wall.
There is no sign of damp above this level outside.

The damp proof course was inserted in 1997, with a 30 year guarantee.

My question: is it possible to determine if this is rising damp through the damp course or due to another reason?
Should I get an independent surveyor to look and where can I find someone.

Thank you!


Rising damp, where it actually exists, is unlikely to extend significantly above ground level – about 200-300mm in my experience, and even that only in extreme cases. I would therefore look for other potential sources such as penetrating dampness from leaking rainwatergoods, open mortar joints, or defective masonry. Condensation is also a possibility.

As for independent advice, the RICS should be able to provide a list of qualified building surveyors in your area. Alternatively look for an architect accredited in conservation under the RIBA and/or AABC schemes (there is a similar system in place in Scotland).

Tess, there is also a useful and unbiased Historic Scotland Inform Guide on dampness in historic properties which might be of assistance to you:


Hi Peter, the link you posted returned a 404 error. I searched on their site but couldn’t see that particular guide.


Tess, if you look 7 posts up I’ve shown how to find the document, and another that is well worth looking at.

Heritage House says:
1 October 2013

The ‘guarantee isnt worth the paper its on.
No, its not rising damp,
Radiator – hot / cold – warm the fabric, cool it = condensation.


[Hi Pete, please do not advertise your services on Which? Conversations. Any more infringements may result in a ban. Thanks, mods.

Heritage House says:
1 October 2013

Mods – we dont advertsie anything – we try to steer people in the direction of intelligent and unbiased information that will help them make sensible decisions about not ruining their houses, or losing a lot of money on fraudulent cons.
Dont forget we make no money from our involvement with this forum – all we do is help – we sell nothing – we have an interest in old buildings… If you feel we stand to gain from anything we say or do on this site, please let me know… in the meantime, has the damp industry put pressure on you by any chance?



Hello Heritage House, we’re referring to you asking people to Google your company. That is a form of advertising, even if the service you provide is free-of-charge. We’re very happy for you to contribute comments as a member of the community and try to help others. Thanks.

“…asking people to Google your company. That is a form of advertising …”

That’s an entirely reasonable policy, which I support wholeheartedly in this specific case.

The Terms & Conditions for this website suggest that contributors choose a screen name (pseudonym). It could avoid accusations and work for our moderators if everyone with a commercial involvement was required to do this. Names and company names are far too easy to trace.

Meanwhile back on the topic of dampness, it is evident that condensation is a major problem or contributor to dampness problems in both old and new buildings. Everyone needs to know about condensation and the measures that can be taken to avoid or decrease the problem.

I am dismayed to read that Damp Proof guarantees are worthless.

How does a ‘normal’ householder know who to trust in these matters?


Tess, I’m afraid the answer is the same as it has always been. You do sufficient research to understand what questions should be asked and answered, and to let the experts know that you have a clue. Exactly the same is true for getting a car repaired or getting yourself/family repaired.

Suitable questions are:
– how will you determine whether it is X or Y?
– what do you think is the most important question that we need to answer?
– if it is X, would you do Y or Z in this case?
– what leads you to the conclusion that it is X and we should do Y? Couldn’t it be Z?
– can I see a sample contract and guarantee? (And understand why the
exclusion clauses are there before bothering to read what’s covered!)
– do you do X?
And if they say “no” when “yes” would be to their advantage, then I’m more inclined to believe them when they say “yes” to other questions.

In my experience the professionals enjoy talking to someone that already knows a little about their subject and is also prepared to listen to their advice and understand it.

I hope that hasn’t patronised you!

Dry Rot says:
2 October 2013

Hi Which consumers,

If you look through the posts in this thread you will see many comments on the lines of: they are conning you – rising damp doesn’t exist – only rises 200mm if it does – visit my web site I am ace and… I am the only one who can help – nothing to sell but the truth – I know best….. Et al

Just what motivates these selfless paragons of consumer rights? Money? Fame? Bitter outrage? a desire to help consumers?

The truth is that nobody knows, but the likelihood is that it’s a combination of all of these.

Do your own careful work and don’t be misled that the majority of companies are out to con you… that is untruthful and if it were true than it would be a very sad world we live in. There are many independent surveyors who can help – there are many specialist damp companies with much more knowledge and experience than these evangelist’ hobbyists. Read what they say and think…. is that really knowledge or is it opinion?

Best wishes to all and I hope your wall remain forever dry.

Dyr Rot

Is the Property Care Association a reputable source of surveyors who can come and visit my house?


Dry Rot

We’ve had a number of posters in recent weeks advising that, despite previous injected dpc treatment, problems continue in their properties. Others have commented on conflicting advice, together with wildy varying prices. Clearly something is amiss.

There is no doubt that there are reasonable damp and rot specialists out there; I can name you a couple. I can, however, also name a vert many who in my experience will gild the lily. One of the problems is that the contractor has a vested interest in selling his product. He is not impartial on any fair reckoning. And the lay householder has no way of telling.

In previous replies, posters have been directed to publications by the likes of Historic Scotland and SPAB. It’s hard to see how you could claim that either body is an “envagelist hobbyist”, not least as the former is a government department with something more than a passing knowledge of heritage management issues. I would suggest that their opinion is to be preferred over a “specialist” who might have completed a couple of weeks’ training provided by a trade body.

If you want to discuss the technical aspects of damp, then come forward with a cogent and reasoned argument rather than an ad-hominen attack. If you want to discuss the BRE advice (much of which is glibly ignored by “specialist” damp firms), then I have a copy here. Do you want to review what the Massari publication or the University of Edinburgh paper really says, then come back with a balanced case? Shall I dig out my copy of Ashurst, or perhaps the joint EH/HS guide to the green treatment of rot? How about trying to explain to me how a dpc “cream” will work when injected into an impermeable granite or whinstone/greywhacke wall? Then we’ll find out who the “evangelical hobbyist ” really is.


If in doubt, speak to an RICS qualified (i.e. chartered) building surveyor with experience in the conservation and repair of traditional and/or historic buildings. They have nothing to sell, will invariably have been through a 3 or 4 year college/university course before completing several years of practical pre-qualification experience, and albeit that they charge a fee, it can save you money up front. Or likewise a conservation architect (RIBA/AABC/RIAS/RSUA, depending on where you are in the UK)

Mic_Fly says:
3 October 2013

Hi All,
I wonder if anyone can help. I’m a first time buyer and looking to buy an end terrace built around 1880. I had a full building survey done and its come back with some damp along the bottom of the kitchen (rear) and porch. Both along the outside wall.
My surveyor didn’t seem to bothered, said its expected in houses of this age and once the central heating is on it should be kept under control.
Does anyone have any knowledge or experience with houses of this age? Should I be worried?
Its been empty for 6 months, so I suppose having the doors & windows closed, along with the heating off wouldn’t help?

I don’t know if I should be concerned or not, Any ideas

Thanks all


You have before you a report by a qualified surveyor, who has undertaken a full building survey and advises that this is not something to be unduly concerned about. He’s not selling anything for or on behalf of a rot/treatment firm and will presumably be RICS qualified. Unless there’s something obviously amiss then I’d be tempted to take his advice at face value.

Take a look at the Historic Scotland or SPAB guidance referred to in previous posts. This gives you an idea of the kind of issues you should be watching out for.

Clearly the person describing himself as as a destructive fungus i.e Dry Rot, has little or no understanding of just how many inappropriate and unnecessary damp proofing treatments are sold by the large national companies who employ salesmen on commission. The Which report highlighted just how serious and widespread this problem is.

All of the professionals in the industry including many architects and surveyors who campaign against this outrage do so because like myself they are sick and disgusted by this blatant scam.

Every week we come across examples of a chemical DPC having been injected into walls which were affected by condensation with calcium carbide on site testing confirming no evidence of rising dampness. The sickening thing is that in many cases young couples trying to buy their first property have been forced to borrow thousands of pounds they cannot afford to pay for these completely unnecessary treatments.

In need of advice! says:
3 October 2013

We lived in our home for 2 years and had to relocate due to work so rented our property out. While we lived there we had small amounts of mould around our back door which was in the bedroom and behind a very large wardrobe (on same wall as the back door) so we were advised to sort out the air bricks as the property was built in 1910, so we had this done. The only other issue we came across was that due to their being no window in the bathroom there was nowhere for the hot air to go so we purchased a dehumidifier. We would leave this on all day in the bathroom with the door closed and had no problems since,
Now the tenants have moved into the property they have continuously complained about issues the main one being damp. They had admitted they dry clothes in the house, leave the bathroom door open and only put the dehumidifier on for an hour a day but have moved it in the bedroom! (we left it for them to use). Their bed and mattress have mould on as well as some of their clothes. We have kept explaining that leaving the bathroom door open without the dehumidifier is causing the issues as we didn’t have any in 2 years and they have only been there for summer. Now they are asking us to replace all their furniture and get surveys done and fix the damp problem. Can anyone advise me what is the best thing to do? Thank you!

In Need of Advice:

Based on your description, it sounds like the first objective should be to provide “user-proof” ventilation. There are a number of ways to do this including permanent ventilators (“strip vents”) in windows, although these are often expensive to retrofit, air bricks into the rooms, or the installation of mains-powered extract fans with humidistat controllers in the bathroom & kitchen areas.

I wonder, however, where the damp could be coming from? Obviously the kitchen and bathroom (especially the latter) can introduce significant quantities, but bedrooms aren’t usually so much of a problem. Have a look at the Historic Scotland Inform Guide on dampness to get some pointers.

Hi All,

I’ve been reading this thread for over a year. We have significant damp/condensation problems in our house – we approached a company via this website who identified most of our issues as condensation related (which we agree with). We have made significant changes to our house, including:

1) Replacing all our windows (26!) with new ones with trickle vents – most of which left open
2) Installing extraction fans in all 3 bathrooms connected via humidistats
3) Installation a whole house ventillation system upstairs
4) Installing 2 high powered heat exchange system downstairs in the basement and 1 unit in a room with issues on ground floor – all connected to humidistat
5) Ripping out entire kitchen so we could move cooker to external wall for extraction straight through wall via powerful cooker hood.

There are no water leaks – everything has been checked, yet despite all the ventillation (nearly every unit run all day) we still have humidity in the house of 80-95% in all rooms (although since whole house ventillation we have no water running down the walls!). We live in a Valley and we think that we just live in an area with moist air and there is nothing we can do.

Not very helpful I guess but thought I’d share our situation for the benefit of the thread – ventillation helps but is not always a cure – we are still scratching our heads on what to try next.

In need of advice! says:
3 October 2013

Sorry forgot to mention the bathroom comes off the bedroom-more of an ensuite

Have you measured the outside humidity to see whether you are in a perpetually moist environment. Sounds unlikely though.

Interesting situation, ggg. Do you have any near neighbours? If the problem really is your location, then they should be suffering the same problems. If they aren’t, then what’s different?

Outside is around 10% lower than inside circa 75% RH – if there is anything else we can try/investigate please let me know. Its a detached house (original bit around 1890) with walls which are solid and around 3 foot thick – its also built into a hillside with the basement being underground (previously a cellar which someone thought they would tank and make a gamesroom – not a great idea).

All our neighbours have problems but all are different due to different types of property, we also all suffer from Valley cough from time to time! My point is that achieving the perfect 40-50% RH might not actually be possible?

For some context here’s a picture of our house from last year.


Quite a typical morning picture with the mist above the Valley.

Dry Rot says:
3 October 2013

Hi 999,

I carry out surveys weekly where mould and humidity have caused problem. Although PIV’s and such are great tools, it is always essential to get good information before specifying, particularly when such a lot of work and expense is involved, as in your case.

It is not always just a case of poor ventilation; air temperature is key also. To get the true picture and compare the condition outside with those in, you need temperature as well as RH. RH alone tells you very little, simply because a small decrease in air temp will drive RH up and conversely a small increse will drive the RH down – all without reducing or increasing the water vapour in the air. This point is crucial. There are cases where installing a PIV will make matters worse (though this is uncommon).

For example I visited a small flat, last week where mould is a problem and the local authority installed a PIV as a kneejerk reaction. The mould carried on being a problem and I was called in.

After the compulsory cup of tea and chat with the tenants it became clear that the electric storage heating was far too expensive for them to run, as was the electric emersion heater. Thus the flat was often kept at only 15 degrees C with the use of oil based radiators for quick delivery of localised heat, combined with a hot water bottle filled from the kettle when watching TV (yes fuel poverty drives some people to that).

More time chatting and it became clear that the kettle was also used to boil water for the sink (to wash up pots), and of course fill the hot water bottle.

Thus the high RH was due to lack of adequate heating combined with excessive moisture production vie the very frequent kettle boiling. Add a cold (if dryer), air supply through a PIV and the benefit of the new air ‘dryness’, is lost with the depressed air temp. Using data loggers over at least a couple of weeks period, prior to specifying would have helped identify these issues and maybe that would have been a good idea in your case.

I am not saying that is the cause in your case, I’d have to survey the house to do that, but it is an illustration, as your question implies – it is not just about ventilation.

The above also illustrates how important it is to talk to home owners/tenants and get as much information as possible.

Dry Rot.

I totally agree and I am very aware of the importance of correctly heating a property and not drying clothes etc – this is one reason why we are re-doing our kitchen as we want to ensure that in future all steam from cooking is ducted outside – what we found intersting is that we have not been able to cook for the last two months (apart from microwaving in the porch) so we have not generated any moisture and the kitchen has remained at a very high RH.

The problem of damp and condensation is actually very complicated with many subtle factors but also it also takes a long time to see if any particular remedy is working!

Our ventillation system is not purely PIV we have extraction as well and has been a success up to a point – the problem we have now is how to proceed to make it better.

In your situation I would do some long-term “surveys” myself to attempt to rule certain possibilities in/out. What I suggest below presumes there is no penetrating and no rising damp (no comments from heritage house, please).

Get one or more humidity+temperature sensors; typically they are called weather stations and are surprisingly cheap nowadays. Best if they measure 0-100%; some only do 20-80%. The first one I saw, from maplin, costs £30.

Get a handheld non-contact thermometer – the first one I saw was £30 from maplin.

Measure the temperature and humidity of the air in the room. Use the non-contact thermometer to measure the temperature of the surface of each wall and window etc. Keep a log of the measurements over the day and over the year.

From the standard graphs of temperature vs dew point
(e.g. http://en.wikipedia.org/wiki/Dew_point#Calculating_the_dew_point)
and the above measurements you will be able to see just how close/far from the dew point each surface is. Obviously the higher the margin the better!

If you find some surfaces are below the dew point then you have two choices: (1) raise the surface’s temperature or (2) reduce humidity by removing water from the air.

If there is a large temperature gradient across the wall it is possible for water to condense inside the wall, so if the other side of the wall is cold and the wall is porous to water vapour, that should also be considered.

Obviously if there is a lot of water vapour in the external air then frequent air changes will (without de-humidification at the point of entry) bring lots of water vapour into the house.

This advice is worth what you paid for it.

Hi – yes I think I will start to have a go at data logging. I did buy some humidity sensors from Amazon (£5 each) which I positioned around the house which has been useful to detect we have an issue but being able to capture and graph the data will be a step forward.

Hopefully people reading this will see that there is not always a simple fix – I wish we just had a water leak somewhere (perhaps we do!)


IMHO humidity in the middle of a room is not directly of interest w.r.t. condensation. Humidity is, of course indirectly interesting, but what is directly interesting is the dew point. Having a non-contact thermometer is a good way of assessing the dew point on various surfaces around the room.

Besided, non-contact thermometers are cheap and fun to play with, and are even useful for other things, e.g. calibrating ovens and radiators etc!

Your comments about what you’ve tried and what has/hasn’t worked are very interesting. I suspect/hope many in the industry already know all these things, but I/we don’t. Thanks.

Ah – just realized that we have one of these already for the baby (well now toddler) – I shall commandeer for my investigations!



1. Is there any insulation at all, and if so then what kind?

2. What’s the central heating regime?

Hi Peter,

The walls are all solid so no cavity insulation, only insulation is in loft which up to current standards.

Heating is oil fired rad system, as part of our attempts to control problem we installed new stat so house is controlled to never go below 12c – that seems to have improved things but combined with increased ventilation means we are burning almost 4000 litres a year which frankly is costing us too much – I am considering putting up insulated false walls in the really cold areas as a last resort.


Heritage House says:
3 October 2013

Everyone seems to be missing one vital point. Are the buildings concerned ‘solid walled, and built with breathable materials’ or cavity walled.?

If we are talking solid walled – then problems will continue until breathability is established – lime plaster, porous walls, etc – will prevent excessive build up of condensation and wick it away. Such a structure with gypsum plaster or cement render will trap water into the structure and make it even colder and better able to conduct heat – thus increasing condensation. ‘Old’ buildings, solid walled – need to be allowed to breathe.

I surveyed one today – in which the RICS surveyor had insisted needed to be tanked, and injected by a property care association member. The walls were lime plaster, limewash, over limestone and lime mortar – in superb condition. There was NO damp anywhere – a carbide test showed totally dry. Interestingly the thermo hygrometer showed 80% RH internally. This is an unusual property in being beautifully original, and lovingly restored with traditional materials. It was in perfect condition – no moisture, no condensation, nothing.

The surveyor is now being reported to the RICS professional standards committee and a negligence claim lodged by the owners.

Fortunately, more and more people are asking questions, and becoming informed.

[This comment has been edited for breaking our guidelines. Thanks, mods.]

Well I’m not blaming anyone for our situation nor are we using any chemicals. We bought our house 4 years ago we are working with what we have – ripping the plaster from all the walls might well solve it but that’s not really an option I can consider unless I come into some money or can guarantee it will solve the problem (though I am doing that in the cellar with the intention of lime mortaring – that’s a wip) – if a higher than normal RH is nothing to worry about then that’s interesting given that everything I’ve read says that anything above 70 is too high. We do accept that we live in the country and it’s not like living in a timed frame built modern house but that doesn’t mean we should accept towels that never dry, mould forming and damp smells.

Heritage House says:
3 October 2013

Hmm.. silly question I know – but are the walls dry? Have you drilled and checked to see there isnt moisture in them? Heat loss in solid walls is quite low, if they are dry, but increases a lot if damp. Windows – double glazed? EH and others recommend things like roman blinds – good insulators at night. What feed temp on rads? Keep it down to about 40 – rmemeber – rate of loss of heat is proportional to excess over room temp.. Hard to comment more without knowing a lot more – Ventilation on its own isnt really a good idea – as you observe – you just chuck warm air away – best to try and attack any moisture sources, and recognise that RH can go up if weather is damp – you cant win all the time, unless you have a whole house system that controls heat, RH and air quality – which isnt cheap, and frankly, generates horrible air – a lot of people dont like passivhous for that reason. Keep feeding info at us – your comments are interesting and all of us would be interested in seeing your problems solved !

For your whole house ventilation system to work properly your house needs to be as tight as possible. Having trickle vents and external extraction comprises this. It’s a bit like trying to fill a leaking bucket or blowing up a balloon with holes in it. I think you would be better having one system or the other. Other posts seem to bear out that a whole house MVHR system will serve your particular problems best.

Ok, but the ventillation system essentially replaces the inside air with outside air only passing it through a HRU to save energy costs – so really what is the difference of having the trickle vents open – its the same air? I can understand not having the trickle vents open in the rooms where the air is being extracted (which we don’t).

Please note that I’m posting here for the purpose of letting people know the issues we have had and the results we have seen thus far from the work we have undertaken – what this forum lacks are real case studies and updates from people who have received advice, followed it and have hopefully solved their problem – I guess if they do they move on and don’t read this forum anymore!

Dry Rot says:
3 October 2013

hi 999,

You can find good such groups on linkedin such as the building pathology group and diagnosis of damp defects…

You are spot on about happy clients not being bothered to engage. That is just life. We get 100’s of good feedback forms from happy clients but the ones we really value are the critical ones, which lead us to make improvements.

Good luck with the project. Maybe someone to put some data logging in for you inside and outside so you can get the differential vapour pressures and use BS5250 to delve a bit deeper. It would be fun and it’s easy.

I could, but I am remaining anonymous as I don’t want to commercialise the discussion, (and get the outraged luddites wailing on at me), there are lots who could do this via a postal service, just place them as per the instructions and then send them back for analisys, or you can buy some yourself – they are peanuts in comparison to the money you’ve spent.



Thanks for that – I will check out linkedin, I should really do data logging – the company I work for does telemetry including devices which measure RH and temperature – I’ve just not installed them because the rooms in question are out of reach of my wifi signal (stupid thick walls) – I will have to get that sorted. I’ve downloaded the bs5250 so will have a read in my spare time.


Dry Rot says:
3 October 2013

Hi ggg (you can see I am old and half blind as I have addessed you as 999 in the past),

The data loggers are only about £50 each – I use LASCAR ones. The data is taken at whatever intervals you fancy – I use half hour or hour as any shorter gives too much info. Either use a psychrometric chart to convert to Vp in kPa or the Vaisala calculator and you can see what the balances are between moisture and temperature. The graphs the software supplies can help you get a better understanding as they include RH, air temp and display a dew point set too. Of course what you like to see (amongst other things), is a nice big gap between the air temp and the dew point temp (especially in poorly insulated dwellings)… playing with these will expand your understanding.

The ‘scurrilous’ damp proofing industry, which is routinely slagged off on mass here, do great courses on this, including condensation workshops and master classes – these are short but crammed with gold dust knowledge and they’re cheap too. Of course only the really good damp proofing firms, who are dedicated to improvement, attend these courses, but they are open to all.


I drilled into one wall in a damp room and it appeared dry inside, however when having the ventilation fitted through the walls the installer said some of the walls were damp. The house is part old, part extended and rebuilt in the 80 ‘s so some bits have dpc some don’t and it’s hard to figure which do and don’t.We are having new hole drilled soon for cooker hood so I can check that one.

Dry Rot says:
4 October 2013

Good morning GGG,

I understood that the only issue was high RH? Is this just because of a hygrometer reading, or have you some symptoms which are visible; mould; damp patches and such? Persistent RH’s of 80% plus can lead to mould on surfaces and even on clothing, leather and such, so if this is not happening it is unlikely that the RH is at that level for much of the time. This is where data logging is so useful – it enables all the peaks and troughs to be seen and ironed out. It can also take account of surface temperatures via ibuttons.

If the walls look dry, then don’t bother drilling holes in them, you are only causing damage for no gain – if they were wet they’d be cold and at high RH’s you’d have condensate forming on them.

Forget about breathability – walls as thick as yours don’t ‘breathe’ in that sense, the amount of water vapour passing through the decoration, plaster, inner leaf, rubble, outer leaf over a 24 hour period is but a tiny fraction of what leaves by the door, window of extractor fan each and every second.

Breathability only matters in the outer zone of the walls – ie the face of the stones or the face of render – ie lime pointing/render = good – cement render/pointing = bad.

Keep focused; what is ruining your enjoyment of the dwelling? Address that, but avoid digging for technical problems which don’t really matter.

Finally, you say you keep the house at 12C.. that is on the cold side and will tend to increase RH so with cold solid walls the dew point may be reached. Whilst BS5250 says that the walls may have a temp 10% below the room temperature, this can mislead, as the bit of wall behind furniture, where the effects of the heating are reduced, can be orders below this. I have blogged on this with good detail but I cannot point you to my blog as this thread is toxic in some quarters and I’d be attacked by the cabal.

Good luck with it ggg


Hi Dryrot,

I should say that the minimum we keep the house is 12C, normally we are around 17.5-18C when actually in the house and not in bed. We have eliminated most of the mould forming behind cupboards with the whole house ventillation and by not having furniture too close to the walls, we do still suffer from mould forming round windows where it gets wet and in corners of certain rooms (the cellar is a different story that has pink mould growing on the very clammy walls – the one wall I ripped off the plaster and is now just stone feels much better). I will start my logging this weekend as I’ve been given some kit from work.

I am interested in reading your blog (and any others) – not sure how you can communicate it to me though without posting my email address.

Rose says:
5 October 2013

Hi! I hope you can help. Over the past 2 days a damp patch has suddenly appeared behind a radiator on an internal wall on the ground floor of our house. The patch covers an area to the left of the radiator and extends higher than the radiator. Would you have any idea what the cause might be please?


I’m afraid that it’s impossible to give a definitive answer without seeing more information. As a general rule, however, you need to rule out any possible sources of dampness in the area focussing on leaking pipes. Bear in mind that dampness can travel a surprising distance from a leak so check both sides AND the rooms above the patch.

Notsure says:
5 October 2013

Live in a 1900 semi and recently had an issue with the flooring rotting because of damp, so wet could put screw driver through it without any effort.

The ground level outside has been raised to lay a path/drive and garage attached to side of house. The airbricks have been left exposed in little wells in the flooring of the garage (2 brick) with a further brick outside the garage (3 bricks down side of house) and 1 brick at the front under a bay window. We have a damp proof course injected a couple of inches above the top of the air bricks (can see 2 holes with green resin type stuff coming out of 1 of the holes spaces evenly down wall). at the front and front and round the corner to the start of the garage (6ft). the front and side of the house have been rendered and at the front and side up to garage this has been hacked off so it does not reach the ground (damp proof added through render so presume done after at some point). however the render has not been hacked back in the garage so meets the floor level. Also the injections do not continue into this section however i have found a tag which say ‘rentokil damp proof course) embedded in the render, not sure if this was done at same time as render or before, did have some render over it but not completely covered.

Anyway had floor taken up and mold/fungus was found growing all way through underfloor space from front to back of house. This was treated/sprayed to prevent return, cause was identified that the injected damp proof course at front was above the level of the internal floor, a couple of the floorboards actually touched the wall so soaked up moisture and rotted. Damp proof person said the fungus actually attracted moisture so will have drawn moisture into house more, when floor taken up smell of damp was overpowering. All removed and treated new sections of floor replaced where needed, rest of floor relayed as wood was sound.

Anyway thought it was sorted so had new solid wood floor installed over top, this lasted 2 months then suddenly popped up in middle where it had expanded due to absorbing moisture, got the installer to come out and refit but am worried will happen again without fixing problem. Is 4 air bricks enough for underfloor space 7mx4m unfortunately a conservatory/kitchen has been installed at back so no air brick at back of house only side and front, 2 of the bricks are in the garage as well. Damp company seemed to think it was fine. Have invested in a dehumidifier RH in house was 70% similar to outside levels it is drifting down slowly now (had it on for 3 days constant got about 7L of water from it so far) current level 63%. Any advice please

Hi, I live in a terraced house and I have an issue with one wall in the kitchen. After moving in and removing the tiles on the walls (which were hanging off) the old plater was removed back to the brick and replastered/painted etc. 2 years later I have bubbles in the wall as well as brown patches in the white paint. This is happening in the centre of the wall only, the celing and floor are dry based on the damp/moisture meter and the middle is reading 50+% moisture. My neighbour has no pipework on that side so I am at a loss as to where the damp is coming from. I have removed the plaster back to the brick to investigate and the damp smell is growing as is the mold on the bricks surface. Where is the moisture coming from if the top, bottom and other side are all dry???

Any ideas?


What kind of plaster is it? Modern gypsum-based plasters (the brown coloured Thistle and Carlite types) are typically poor where there are dampes and/or salts present.

That said, the key is to try and work out where the moisture is coming from. What age and type of construction is the terrace?

1905 property. Apologies it was not plastered it was renedered using sand and cement. I have just had a surveyor from Kenwood who advises it may be from lack of an effective damp proof course and suggested a new chemical damp proof course and then replaster the walls with a waterproof rendering system.

I have another company looking tomorrow so will let you know their verdict!


Rising damp, where it does exist, would be typically found at the base of the wall. I’m thus a bit intrigued as to why the PCA surveyor has diagnosed it as appearing half way up whilst the floor level is dry. Have I misunderstood?

Hi Peter, No you have not misundestood. The floor level is giving a very low reading for moisture and in some areas as low as 5% once you check about a metre up the wall the ready is 30% to 50% moisture detected.

If it is rising damp I am baffled as to why the reading is so high in the middle of the wall and also where the mold is appearing on the exposed bricks.

Will let you know what the 2nd company suggest.

Heritage House says:
9 October 2013

Simple – its already been damp proofed once and very typically water is being forced up behind the first lot of waterproofing plaster and coming out in the middle where it can get out – this is a very common problem. Get rid of all the tanking plaster down below and get the wall breathing, and you’ll not have any more problems!

Dry Rot says:
9 October 2013

Hi Den,

Rising damp will when active give higher readings at low level than higher up. However, if it is controlled by a DPC (chemical or otherwise), there will be a residual ‘salt band’ higher up the wall, where the threshold of evaporation used to be. This will remain damp due to the hygroscopic nature of the salts. Merely plastering in cement render or dry lining will remove the surface salts, leaving the deeper salts in the brickwork forever.

This is why damp proofing companies always remove and replace the plaster at low level – to remove the salts which are concentrated there by years of damp rising and evaporating.

Of course, I or anyone else cannot diagnose damp over the internet so get good advice and do your research. There are very good independent damp specialist surveyors out there (try the PCA website) and some RICS chaps too – but if using RICS you should stress that you wants detailed advice on damp as many do not provide this service, but those that do are usually very good.

Some contractors also can be honest and very helpful – you can always tell when they are bulling you… listen and think; did they take time; look inside and out; give broad or detailed advice and do they justify their recommendations with sound methodology or just spout opinion and rush to a ‘treatment’.

Good luck with it.


Heritage House says:
9 October 2013

You always know when someone is talking rubbish – rising damp – has never been proven. Anyone recommending the pca has a vested interest. I refer you to previous discussions about dry rot..

We aren’t allowed to give out references on this forum, so a bit tongue tiede, but you are being fed a lot of rubbish. Do your research – try googling damp in old houses, and go from there…

Rising damp is referred to in two documents referenced several times in this conversation- from Historic Scotland and SPAB. Presumably their is some foundation for its inclusion.

Lynda says:
8 October 2013

I have a 1900 mid terrace bungalow with sandstone frontage. I have recently noticed a wet patch in one of my living room corners which is spreading upward & along the front wall. It is now approx 1m high x 50cm wide. I recently replaced all original leaking gutters, facia & soffits with new upvc gutters & down pipes. Hopefully this will help the problem long term but how do I treat the internal dampness as it doesn’t appear to be drying out? Is there anything I can use on the sandstone to prevent water penetrating?

Many Thanks


Traditional solid stonemasonry walls work differently from modern cavity construction inasmuch as they absorb moisture in wet conditions and then allow it to evaporate in more clement weather. The application of a proprietary waterproofing agent, for example one of the clear repellant systems, will actually act to trap water within the stone and accelerate decay. It is to be avoided at all cost.

When assessing the condition of such a wall, important things to check are the condition of the mortar joints. Is mortar missing, allowing water to penetrate far more quickly and deeply than would normally be expected? Have cement repairs been undertaking, potentially trapping water within the core? Are there hard surfaces like tarmac paths around the base which may be encouraging splashback wetting?

My advice would be to ensure adequate heating and ventilation to the affected areas, keeping a close eye on it for a few more months in order to see whether it might be slowly drying out. Continue to check for leaks at heating and water pipes, drains, and so on.

Lynda says:
8 October 2013

Having inspected the mortar joints there are 2 small pieces missing. Also the area in front of the sandstone has a mesh membrane with decorative chips lying up against the stone, could this be adding to the problem?


My advice would be to have a look at the Historic Scotland Inform guides; there’s a good one on dampness generally, and you might also want to look at the ones on stone/pointing:




There will be English equivalents by SPAB and others, but the underlying advice is likely to be broadly similar.

Mils says:
9 October 2013

Does anyone have any views or experience of using a specialist membrane system on a chimney breast to deal with salt damaged plaster? This has been suggested to us as an alternative to hacking all the plaster off the walls and replacing it but I can’t find much information on the pros and cons.

Many thanks for your help

Heritage House says:
9 October 2013

Yes – save your money – take salty plaster off, allow to dry, brush salts off, and plaster in lime.. paint with breathable paints..

Dry Rot says:
9 October 2013

Hi Mils,

Chimneys with salt contamination can be a long term problem due to the aggressive hygroscopic salt content from the flue gasses. These are not common efflorescent salts, so of course you cannot just brush them off, as this only removes the salts which are not a problem and leaves the problem salts behind.

These salts are in the old plaster and have arrived there, either due to a leak at stack level/ingress of rain down the stack and/or very high RH’s in the flue, which can lead to some of the salts (ammonium sulphates and Nitrates), becoming deliquescent. This means they are then mobile in liquid form, so they migrate to the warm side of the wall – ie the plaster.

All the repairs in the world will not remove the salts, so the plaster must come off. The naked brick will be hygroscopic too so merely applying a lime plaster will not change that. Remember Mils, most of the water added to any mix – cement or lime, is not required for setting (even less so with lime), it is just there to make the product trowelable. So of course much of the ‘free’ water is absorbed into the masonry as plastering proceeds; plasterers call this ‘suction’. The clean tap water thus absorbed will dissolve salts already in the brickwork and become salty.

Now then, as the lime plaster dries evaporation at the face will draw that moisture through and hey presto – hygroscopic lime plaster and a return of damp patches, particularly in humid weather.

The solution is either use a harder material, such as cement render which is dense and less likely to allow passage of water (salts can’t walk so only move in solution). OR – ensure that the new plaster is not in contact with the brickwork at all, either via a membrane or by a lathing system to allow dry lining with plaster board.

Both methods have merit but whatever you do, do not apply plasterboard using dot and dab plaster onto naked brickwork; the gyroc adhesive loves salt! And remember that if the masonry is very soft and friable the dry lining or membrane method is preferred; so too with listed or historic property. The aim is a dry surface for decoration so focus on that.

‘Salt Damp’ is the search term to use to look into this in more detail if you want to delve deeper.

Good luck with it


Heritage House says:
9 October 2013

You cannot, and should not, ever trap salts or anything else into the structure. By using cement, you are condemming your property to more problems in the long term. Even the name dry rot has connotations – try googling damp in old houses and see what you come up with – we can’t give references in this forum, so are really about as useful as a needle in a haystack – but what you have been advised is rubbish. Keep it simple – let it breathe, remove salts, and keep everything breathing – it will sort itself out.

With respect, a membrane method is not normally recommended for the care of historic stonemasonry walls whether friable or otherwise. I know of no such advice from HS/EH/SPAB or even authors such as Ashurst.

The objective should be to stop water entering the historic fabric, not to manage it through plastic membranes fixed to the internal face. Failure to do so simply means that the deterioration of the masonry continues, albeit unseen.

Robusto says:
9 October 2013

A lot of damp problems on chimney breasts are caused by hygroscopic salts caused by the burning of coal over many decades (sulpherous fumes result in large amounts of sulphates permeating the bricks and mortar around the chimney). In such cases you can’t really deal with the source of moisture.

I agree that membranes have the disadvantages of lack of breathability and causing damage to the underlying fabric due to the large number of fixing plugs required. However I would contend that they are probably the least bad option in the circumstances and have the advantage to the homeowner that they are pretty much guaranteed to solve the problem. It is easy to forget that not all old houses are national treasures and sometimes the occupants just want an effective and simple solution.


Yes and no:

1. If the flue is no longer used, then vent it at the head and foot in order to minimise build-up of dampness.

2. Have it swept before sealing (or if easy access is available) in order to try and remove sooty material which may contribute to the problems.

3. Make sure that the flashings, copes, pargings, and weatherings are all tight in order to minimse the scope for water penetration.

4. Strip back the linings and ensure that the masonry is in good order. if the brick or stone is affected to the stage where it has lost its matrix then consider indenting and/or localised repointing.

5. If the level of salt contamination is so bad that it cannot be replastered, then I would strap & line over membrane applicaiton inasmuch as the former IMHO traps the dampness within the stone and can exacerbate underlying weakening issues.

Of course caution is always required when strapping & lining potential problem walls in order to ensure that you’re not merely concealing a problem and creating a potential safe haven for a nasty rot outbreak.

Realist says:
9 October 2013

The trouble with using lime in a situation like this is that it is very slow to cure. Therefore salts will have a chance to migrate into the lime plaster during the curing period and if they are hygroscopic (likely on a chimney breast) they will continue to attract moisture from the air.

This problem could possibly be reduced by using a hydraulic lime or Roman Cement (effectively a very hydraulic lime), but if I was paying for it I’d probably use a lower risk approach – e.g. the plaster membrane.


Putty plasters: finishing coats aside, there’s a blast from some hairy experiments we all did in the 1990s. I can’t remember the last time I saw someone using anything other than a hydraulic mix, even on listed proeprties, although I acknowledge that shrinkage and a need to tamp back become an issue.

Whether such plasters are suitable for post WWII houses is very much debatable, given the additional cost and risk involved. We perhaps have to be careful that someone doesn’t mention clay plasters, I suppose.

One thing is clear, however: never use gypsum based plasters anywhere there is a meaningful risk of salt or water ingress. In my experience they’ll be off like the proverbial greyhounds if problems do occur. Limelite may be far from perfect – they term “lime” is indeed misleading – but in a modern building it’s probably the most realistic solution once the underlying dampness has been sorted.

Dry Rot says:
9 October 2013

There are some folk on this forum who believe that only they have a right to give advice and when they see advice which is contrary to advice they give, they become outraged, petulant and abusive.

In my experience this sort of reaction is usually the result of fear and poor self-esteem. It is also an abuse of this group, which from what I can see is there to allow consumers to get some advice and weigh up the pros and cons of that (though the title invites scepticism).

Rising damp is common and an age old problem. Some however, market their own brand of expertise by using the age old method of scaremongering and abusing others.

I’m reminded of the crack-pot doctor who caused the MMR scandal… no evidence for it, just pandering to the neurotic public and the worried well. Kids have measels now because of that.

As for me, it’s water off a ducks back – I lecture to trainee RICS surveyors on damp diagnosis and have many RICS freinds, who ask me for damp advice and recommend me to clients too. I have met students with more knowledge than some of the ‘experts’ here, who scream and shout abuse about people they have never even met.

Respect others – be true and honest. Don’t let the cynical few spoil your enjoyment of the gift of learning.

and…………Buyer beware