What is BRE DIGEST 245
By: admin | Posted on: August 30, 2020
Also called BRE DG 245.
It is part of Building Research Establishment (BRE) digests on authoritative summaries of state of the art on specific topics in construction design and technology. They draw on BRE’s expertise in these areas and provide essential support for all involved in design, specification, construction and maintenance. This particular document can be purchased direct from BRE for just £15.00 here https://www.brebookshop.com/details.jsp?id=287528
This Digest considers the causes of dampness in walls and offers a positive method for diagnosis of rising damp. It suggests possible remedial measures that can be taken to avoid rising damp such as providing a complete moisture barrier by insertion of a physical damp-proof course or the non-traditional method of chemical injection. The repair of plaster damaged by damp is also discussed.
Mechanism of rising damp
For water to rise in a wall, a supply must be available at the base. If the ground surrounding the wall is saturated, this condition is achieved, but if the ground is not saturated the soil will exert a suction that will oppose
the upward capillary pull on the water in the wall. This suction is approximately equivalent to the negative pressure exerted by a column of water extending from the base of the wall to the water table. If the water table falls, the height of the moisture in the wall will drop to a new level provided there is sufficient time for equilibrium to become established. Each period of heavy rain on the ground at the base of the wall will produce a temporary condition of saturation and the water level in the wall will begin to rise again.
The level to which it rises depends on two factors: the amount of evaporation of water from a wet wall and on the resistance to the flow of moisture up the wall. If this resistance is high (as in a material with many fine pores), the effect of evaporation is most marked reducing the appearance of rising damp, but if the wall material has many coarse pores, the height of dampness will be only slightly affected by normal rates of evaporation.
Increasing the heat input to the structure will increase the rate of evaporation from the wall surfaces. The overall effect is to increase the rate of flow of water up the wall but because of the resistance to flow this is likely to be accompanied by a reduction in the height to which the moisture extends.
In addition, evaporation will occur from deep in the pores of the plaster so that the rising damp seems to disappear. In summer, hot weather will increase the evaporation rate and lower the water table so the effect of reducing the appearance of the rising damp can be even more striking.
Water drawn from the soil usually contains a low concentration of soluble salts and the rising water will also dissolve salts present in the bricks or the mortar. When evaporation occurs the salt solution becomes more concentrated at the surface and eventually the salts will crystallise out. This tends to block the pores, reducing evaporation and hence raises the level of dampness. These salts may also be hygroscopic and will absorb moisture from the air above some critical value of relative humidity so that the surface becomes wet during wet weather, although this dampness disappears when the air becomes drier again.
All this suggests that under real, dynamic conditions rising damp in a wall is often in a rather sensitive equilibrium which may be considerably disturbed by changes in the heating of the building and in the level of the water table. The presence of hygroscopic salts tends to obscure any drying associated with such changes by keeping the wall more moist than it would otherwise be. If such salts are removed from the surface by removing the old plaster, and the heating system is improved, it is likely that the apparent dramatic improvement in the appearance of the wall surface will give the impression that the rising damp has been cured when this is not actually the case. It is against this background that the correct diagnosis of rising damp becomes important.
BRE DIGEST 245 is the only way to offer quantitative moisture analysis to prove if a wall has rising damp. This is well documented in the British Standard, BS 6576, BS 5250. BRE digest 245 clearly shows multiple pictures of possible causes of rising damp where there is a physical damp proof course installed that has been bridged by one way or another.
Obviously solid wall properties built before a physical damp proof courses were installed can still have similar causes like high ground levels, modern renders rendered to the floor etc, that can cause rising damp issues. Many older properties also had land drainage incorporated around the property which were installed if an area was deemed to be very wet, which is discussed BRE DIGEST 245. I’ve personally noted this on many of the older historic local buildings I have worked on in the area. This is an extract from my local Bye-laws of the in Warminster Local Board from 1858. Drainage of subsoil and prevention of damp. The house drainage shall be constructed, either with additional eathernware pipe drains or otherwise, as to drain the subsoil of the premises, whenever the dampness of the site appears to the Board to render this necessary; and all the rain-water shall be so drained or conveyed from the roofs of the buildings as to prevent its dripping on to the ground and causing dampness in the walls.
In addition, evaporation will occur from deep in the pores of the plaster so that the rising damp seems to disappear. In summer, hot weather will increase the evaporation rate and lower the water table so the effect of reducing the appearance of the rising damp can be even more striking.
Water drawn from the soil usually contains a low concentration of soluble salts and the rising water will also dissolve salts present in the bricks or the mortar. When evaporation occurs the salt solution becomes more concentrated at the surface and eventually the salts will crystallise out. This tends to block the pores, reducing evaporation and hence raises the level of dampness. These salts may also be hygroscopic and will absorb moisture from the air above some critical value of relative humidity so that the surface becomes wet during wet weather, although this dampness disappears when the air becomes drier again.
All this suggests that under real, dynamic conditions rising damp in a wall is often in a rather sensitive equilibrium which may be considerably disturbed by changes in the heating of the building and in the level of the water table. The presence of hygroscopic salts tends to obscure any drying associated with such changes by keeping the wall more moist than it would otherwise be. If such salts are removed from the surface by removing the old plaster, and the heating system is improved, it is likely that the apparent dramatic improvement in the appearance of the wall surface will give the impression that the rising damp has been cured when this is not actually the case. It is against this background that the correct diagnosis of rising damp becomes important
Experience has shown that it is much more difficult to diagnose the source of dampness in a wall than is generally supposed. It is particularly difficult where the presence of some soluble salts greatly complicates the situation, especially when just a damp meter is being used.
BRE DIGEST 245 is guidance on the diagnosis of rising damp on a rational basis. The basis of the method proposed is to to drill samples, from the wall and measure the free water value and hygroscopic value of the said samples. The aim is to establish whether any dampness damage is caused by rising damp as opposed to other processes, then a location away from other sources like drains, gutter leaks etc. If visible damp or high damp meter readings are located on external and internal walls, ideally many samples should be taken as multiple causes could be causing the symptoms.
Once all of the laboratory analysis is finalised, then we can produce a graph detailing the moisture, and this will help determine the damp issue.
Whilst gravimetric sampling is far superior than using a carbide meter/speedy meter, it is imperative that the guidance in BS: 6576 is used to eliminate other potential causes. An example being that perhaps gravimetrics have proved that rising damp is a cause of the decorative internal spoiling, which is the actual sympton of rising damp. The actual cause of the rising damp could still be something like damaged below ground drainage that would need to subjected to a CCTV drain survey. Gravimetrics and hygroscopic salt analysis sometimes points to there being no nitrates or chlorides present, which then points to drain issues or leaks within the property. This means that finding the root cause, and drying of the building is all that is needed, rather than removing all of the plaster and getting it replaced.
Whilst it sometimes might sound like a slow process and unduly complicated, but no simpler procedure has proved to be reliable.
Some damp issues can cost a small fortune to fix, and so can the amount of errors in damp diagnosis by damp experts. This is why it is imperative that the diagnosis is correct first time.
If you need advice regarding damp issues, give us a shout.
Please don’t contact us for free damp surveys, as this isn’t something we offer. enquiries@completepreservation.co.uk
I have had a series of damp surveys at my old property, and recent repairs haven’t fixed the issue. My house has solid brick walls, which look damp quite high above the floor in some places. Very conflicting advice. The most recent from an independent damp surveyor.
From reading these blogs, the independent claimed to be above the rest, and he hasn’t done any plaster tests, or a drain survey to prove these are functioning. I’m baffled as to why I was charged a large fee without this being carried out, especially as he explained that he could give better advice than the other damp surveyors.
Would you travel to Selby, or could you put me in touch with somebody to carry out a thorough damp survey please?
Hi Charlotte,
It isn’t unusual to get a difference of opinion to be fair. If you have the potential for a dispute because you still have an issue you really need a professional survey. I would of expected an averagely competent independent surveyor to have at least advised you a non invasive survey is of no value in this instance. Send the report to enquiries@completepreservation as I don’t mind having a look at it for you.
I’m having issues with wet walls in our lounge, bathroom is running water down the walls when using the shower, mould on bathroom walls, walls around the shower, mould spots inside the bath (even with cleaning twice a week, bathroom is downstairs by the way) etc.
I’ve had many tests done
Handheld moisture readings, calcium carbide tests, probe tests in the hole from carbide tests, 2 external companies have come and looked and quoted yet my landlord still says there’s no defect with the house.
Cavity wall insulation partly taken out to check the cavity and found a concrete plinth breaching across the cavity above dpc level on the whole front and back external walls.
Carbide tests were:
Kitchen floor: 3.7
Living room wall: 3.5
Bathroom wall: 7.6
Pin test:
Kitchen floor: 15.4%
Living room wall: 42.8%
Bathroom wall: 47.6%
Probe readings in the hole:
Kitchen floor: 44.2%
Living room wall: 60.2%
Bathroom wall: 42.4%
1 surveyor says we have penetrating damp due to the concrete bridge, another says we have rising damp.
All 3 bedrooms upstairs have bad mould on the walls around the windows, when cleaned off it leaves dark black areas in the wall behind the paint.
Any advise or comments would be great.
Thanks.
Hi Richard, those carbide readings are high. The problem with a carbide test it doesn’t differentiate between hygroscopic and capillary moisture. This explains what I mean. https://www.completepreservation.co.uk/2020/06/01/calcium-carbide-meter-speedy-meter-test/
Sounds like you need a decent survey bud
Hi Richard, sorry for the delay! Carbide meters give very limited information. Drop me an email at enquiries@completepreservation and I can see if I can help. the video below might be of use to you.
https://www.youtube.com/watch?v=97yblxM5Ijc
I follow you on YouTube. I would really appreciate some videos on this subject, to help me understand where surveyors go wrong.
Thanks Dan
No probs Dan, and thanks for the follow 🙂
When I get 5 I will upload some… pretty manic at the mo 🙂
Hi Dan, and thanks for the follow. Keep it simple and eliminate any possible causes before coming to a conclusion bud 🙂
Hello Complete Preservation.
Very interesting article. My concern is that the independent damp survey that we had had none of this was actually mentioned in it. The surveyor was a Property Care Association member, and had actually ripped us off.
Can you help me get my money back for the survey?
Can you carry out a survey for us in Romsey please?
Sorry to hear this Ray. Unfortunately it is very common for the layperson to be sold an inappropriate survey of a non destructive nature with no sampling. This is because it’s fast for them, which equals more money as time is saved. Independent surveys rarely offer any value, when this isn’t carried out, and once you have the report you have to then find somebody like me for further diagnosis, and to fix the issues.
Check your terms of engagement, and if you have a case complain to the Property Care Association.
I do cover Romsey though if you need further advice. email enquiries@completepreservation with your contact details, and we can go from there.
Best of luck with it anyway
Trying to find another damp specialist that offers this advice along with drainage expertise is literally impossible. It’s either remove concrete, and then plaster in lime, or use a damp meter and inject the wall. A local independent damp surveyor that came with a hefty survey fee told me to install a plastic newton waterproof membrane. This will trap damp and cause further problems down the line I’ve also read. I reckon as you showed on your YouTube videos a damp investigation needs to take place before advising on what could just be a repair that goes wrong shortly after. What areas can you cover please?
Hi Mike,
Unfortunately because of the price of the equipment, and also the time involved in surveying drains, it isn’t something that damp specialists actually carry out. As you’ve probably found out rarely do you find damp specialists actually recommending CCTV drain surveys also. Unfortunately just because you’ve paid for an independent damp survey, it is highly unlikely they have carried out any plaster/mortar sampling following BRE DIGEST 245, along with the guidance in BS 6576. In my opinion its necessary to follow best practice with the British Standards, and then once this has been done, only then can a specification of repair be offered.
Watch this video as it explains along with screenshots and what questions you need to ask a damp surveyor prior to instructing them https://www.youtube.com/watch?v=97yblxM5Ijc
Drop me an email with your details enquiries@completepreservation.co.uk and we can go from there.
Hi Ross, you have been recommended by our friends where you found all sorts of problems with the drains. Could you carry out one of your surveys where you check drains, leaks and take plaster samples like the BRE digest 245 thing?
Sam
Hi Sam, this is something I can carry out for you. send me an email to enquiries@completepreservation.co.uk
Would it be possible to send you the samples from the walls please like BRE digest 245, for you to check and send back the results as I’m 4 hours away from your office? I’m desperate as the local damp surveyors all say something different. I paid £500 for an independent damp survey also with 5* reviews, and they didn’t confirm it was actually rising damp, or do the type of checks with drains you do on YouTube. I need to be sure as I can’t afford to waste any more money or time with this matter
Hi this is something I can do for you.
The general public don’t know what to expect really from a damp survey, so the Google reviews are often good until they actually find what the report doesn’t cover. I don’t know of any independent damp surveyors that offer gravimetric sampling as per BRE DIGEST 245. It is always hidden in the report terms and conditions that this can be offered after the survey has been carried out, but they don’t tell you this before….
Just received my independent damp report survey with no drain survey, no damp plaster sample tests, no salt tests, no thermal imaging, no ventilation tests, no pole camera check survey.
Absolutely furious as this wasn’t cheap, and I was assured he would give the diagnosis.
What is your current lead time for a survey in Somerset please?
This isn’t unusual. But just be aware this might have been mentioned in the terms and conditions. I would need more info please drop me a message at enquiries@completpreservation.co.uk
Surely this is illegal and RICS surveyors shouldn’t be given advice on damp when surveying a house when somebody is buying it. The surveyor we had said damp wasn’t that bad but we have had huge drain issues and leaks that he didn’t find. Currently going through a claim to get this work paid for.
Sorry I don’t really understand what you mean. If you mean about pre purchase survey damp advice, without following this methodology I do agree with you. But unfortunately knowbody allows this type of survey, so the surveyor can only give the best advice on a non invasive survey. Sorry to hear you have a claim going through, and I hope it works out ok for all involved.
Hello,
I found this enlightening. A few months ago, we invested significantly in damp-proofing our property. However, we have recently discovered that our main water supply was damaged by a fence post, which raises the strong possibility that this was the actual cause of the damp issues. I noticed in your videos and posts that you mentioned salt tests and render samples, which were not conducted during our damp-proofing process. Furthermore, there was no inspection of below-ground drains, and plumbing pressure tests were omitted as well. This was a significant financial commitment for us, and we even borrowed money to cover the cost.
Is it possible for you to conduct tests to determine the true cause of the damp issue, and ideally, we would like to explore the possibility of seeking a refund from the damp proofer? Additionally, I’d like to confirm if your services extend to Trowbridge.
Thank you.
Hi, unfortunately this isn’t unusual for damp specialists to not find the root cause.I can help with the diagnostics and a survey to and tests for salts and moisture contents, following BRE DIGEST 245. I do cover Trowbridge also….drop me an email with your details enquiries@completepreservation.co.uk