Frequently asked questions,
Damp, Dry rot, Mould
Here are some Questions from our site visitors
Answered by our Technical Director Mike Davison cssw
Rising damp & penetrating damp
What's the difference, how can I identify both, are there tell tale signs?
Penetrating damp can be from driving rain, leaking gutters, defective adjoining roof coverings,
defective seals to windows doors etc. Penetrating damp can appear anywhere in a property, upstairs,
roofs, chimeys and in the same places as rising damp too!
Rising damp is where dampness from the ground travels up the wall trough a capillary action and
there is either a defective, failed or no damp proof course installed to stop the progress of the
An inexperienced or untrained surveyor may mistake condensation or penetrating damp or rising damp and
recommend a course of action which will be unnecessarily disruptive and possibly expensive, worst of
all it is also probably not required and will simply disguise the true cause of the problem
All properties are different which is why we offer a full range of damp proofing
solutions. There are many sources of damp in buildings, rising damp, penetrating damp and
condensation are the main types and they are often confused. It is therefore important to get a
reliable and properly trained surveyor to check out the problem fully before arriving at any
conclusions and paying out money for the wrong course of action.
I have condensation in my Victorian conversion flat with black mould on some external walls. I have
double glazing but the problem happens in winter when they're shut.
Would ventilation in windows (e.g. trickle vents) fix it or would passyfier air vents be better to
solve the problem? Ideally I'd like to be able to close the vents when it's really cold as don't have
Condensation is a complex subject, primarily ventilation is the answer but this can be problematic
in the cold e.g during winter. There are lots of opinions on prevention but as any fully trained and
qualified surveyor will confirm, every property is different. Even the lifestyle of the occupants Can
have a major influence.
To cure condensation follow these steps.
1. Do not dry washing on radiators or clothes airers inside if you have any signs of condensation
in your home.
2 Check if anything is introducing damp to the exterior of affected walls, damp = cold = lower surface
temperature and dew point. look especially for leaking gutters, overflows, rising damp, etc. Correct
3. Increase ventilation where practical, IE when cooking close the kitchen door and open the window,
when showering or bathing do the same in the bathroom.
If this does not solve the problem you will need to look at specific types of ventilation.
The airtightness of newer properties and the new building regulations where new properties must pass an
air tightness pressure test mean extractor fans may not be suitable, they can create a negative
pressure which stops them working effectively.
PPU's or positive pressure units are very good for mould but do have some slight
drawbacks, in winter they are bringing minus degree air into your home, this can result in a
temperature drop in the installation area (usually the hallway or landing) but units with pre-heaters
are available and a thermostat activates a heating element below certain temperatures to take the chill
off the incomming air. These units typically start from around £600 + vat fitted.
Builders often recommend passyfier vents, these work on the principle of air movement and pressure
changes - e.g when you open and close a door, but as you do not open and close doors all night when
condensation is at it's worst (not if you want some sleep that is) their efficiency is limited. They
will help to reduce problems on a single room basis but seldom cure condensation problems.
Builders tend to recommend them as they are easy to fit and you do not have to carry out any complex
calculations for them. These are around £150.00 + vat fitted
The best solution is an heat recovery ventilation unit which heats up incoming fresh air using the warm
stale humid air which it exhausts at the same time. The unit contains a matrix through which the warm
humid air from your property is directed as it is extracted to the outside. The fresh but cold external
air is then pulled in across the other side of this matrix warming it up and giving you pre heated
fresh air into your home or property. These fans can now be over 90% efficient heat recovery
and 90% efficient for power consumption. These units efficiently combat condensation and improve air
quality within the home. Some units cost less than a lightbulb to run.
Contact us for further details
Mike Davison cssw
Our neighbours put in a new kitchen about 3 years ago, and put patio doors into the back wall of the
outrigger of their Victorian house, the outrigger shared with our own in a long terrace. We've been
told that under the foundation is normal for a Victorian house, with sandstone probably 3-6 feet under
the surface of the ground. Since their patio doors have gone in, small cracks have appeared above their
doors, and above our own patio doors (both internal and external leafs), which have been in place for
over 15 years I think, and are also in the back wall of the house. I estimate there's about 4 feet of
supporting wall between the patio doors, and another 3 feet of supporting wall to each side to the
outrigger corners. Our patio doors have a substantial steel plate lintel, theirs is a concrete one (I
Since their construction, their new plaster (dot and dab I think) has 2 vertical hairline cracks on
the party wall about 10 feet back into the 18 foot outrigger, whereas our solid plaster wall is fine.
There is also a first floor crack opened up on both sides of the party wall where the outrigger joins
the main house, but no cracks anywhere else, i.e. on the outer walls of the whole outrigger. There are
what I think are large supporting wooden beams the hold up the back wall of main part of the house, and
there are hairline cracks under both of these, and a few hairline cracks following the panels in our
plasterboard kitchen ceiling (in the outrigger of course). The rest of the building is tickety-boo.
Should I be worried? Is it just minor settlement of the building, or is their lintel not up to the
job and is causing movement in the outrigger? I assume they and their builder used a correctly sized
lintel and got building regs, but I don't know. I know we don't have building regs for our patio doors
(we got an insurance policy as our surveyor picked it up), but you can see our steel plate (5 mm thick
I think) above our door.
I presume we are not liable for any remediation if any is needed. Am I right? I'm guessing the chain
of liability is the builder, then the neighbour's insurance, then our own?
There should be no new settlement on a Victorian house, all settlement should have stopped years
ago. From the sound of your description the first thing I would be looking at is whether there is
enough supporting brickwork left between the two properties and the foundation. By putting two sets of
patios next to each other on the same elevation the weight distribution on the sub strata is reduced to
spot loading through a smaller footprint. This spot loading can in fact push the foundations down into
the earth below whilst the rest of the walls stay put, this movement causes the cracks. If the walls
are of brick construction stepped cracking often occurs. The distance the wall between the patios
travels down into the ground is determined by the compressive resistance of the sub strata.
You will need to appoint a structural engineer to do some calculations and work out what is happening,
the ground may compress a little and then all movement stop or it could keep moving down which will
increase the cracking, cause the patio doors to jam or even lead to collapse in severe cases.
If we are carrying out this type of work we have an engineer check the compressive resistance of the
earth beneath the foundation and loading first, we generally have to underpin the sides of the new
opening with reinforced concrete structural pads prior to cutting the patio door openings out. As this
can be costly, disruptive and time consuming it can be ignored by cowboys or unwitting occupants who do
not want to fork out the extra costs.
Hope this helps
My cellar has black rot due to poor ventilation and is under ground level, but has never flooded
before. I have had several damp-proof companies come to have a look, and some say it must have sump
pump due to BS regulations or something, and others say, no the floor is dry so doesn't need one, just
needs p20 membrane tanking system and humidistat fan. Please advise me, it's alot of money to gamble
and I don't know who to believe.
thanks a million
- kalimills -2nd Mar,
The key to the answer of your question is where you said the room is, 'below ground', to meet the
requirements of the manufacturers membrane system, and British Standards fully, you would need to
install gravity drainage or a sump pump system. The system you mention (Cavity Drain Membrane)
cannot deal with hydrostatic pressure (a build up of standing water behind
the membrane) and if not drained by a pump or gravity drainage system will fail
catastrophically in the event of water build up. Even though the property has not flooded before a slow
build up of ground/rainwater would still be possible. British Standards rule that even if a property
has no record of historic flooding we should assume it may flood in the future!
So the correct answer is yes - in the absences of any reliable gravity drainage you will need a sump
pump in that situation.
Mike Davison cssw (certificated Surveyor in Structural Waterproofing)
- 4th Mar,
I am having issues with my kids bedroom. We live in a rather old property and when we bought it, it
had been sat empty for about 5 years and had a leaky roof so the place was pretty wet! We dried it all
out with dehumidifier's and had the damp course done, roof re done etc. All was fine until I noticed 2
damp patches in one bedroom. These patches are either side of the window (on an external wall)
which has a bank and rather a lot of trees opposite. 1 patch is various distinct damp patches covered
with the small black mold spoors and the other is above the skirting board and again has mold. Both
patches never spread and when I clean the mold off the damp that is left is always in a very distinct
pattern. I open windows at opposite ends of the house to ensure ventilation. No where else in the house
has any issues and I cannot understand if its condensation why its forming there as there is nothing to
cause it. The bathroom has an extractor fan and the door is always shut and this is the only thing
upstairs that I can think could cause the problem.
One person told us it was condensation and the another didn't seem to think it was!
shed any light?
- M. E. copland -1st Sep,
The black spot mould is condensation.
This can be caused by cold bridging or dampness within the walls.
Basically the affected areas are colder than the rest of the wall creating a dew point on the walls
where the moisture from the ambient air within your property condenses more readily than the higher
Things to look for-
Gaps where moisture or cold air can enter the fabric of the building
Dot'n'dab plasterwork where the adhesive dabs form a cold bridge from an outside wall
Leaks from roofs
Leaks from gaps to lintels or sills.
The leaks can be through quite small cracks gaps or openings and can be some distance from the internal
signs as water/moisture can run from point of entry and settle in a different place.
Also possible that interstitial condensation is forming within a cavity and causing damp patches or
mortar is lying on wall ties forming a cold bridge.
Or If wall ties have corroded this can cause a gap in the mortar and allow moisture/cold air to cross
the cavity. This can often be seen by horizontal splitting in mortar courses/gaps in external
These issues can be detected quite easily by a trained professional and inspections are often
If in the North East area drop us a line and I will inspect the problems for you.
Mike Davison cssw
- 12th Sep,
Hi I just moved into a house that has had both chimney breasts removed downstairs. Upon removing the
wallpaper I have noticed damp and the skirting boards rotted at the bottom. What could be the cause of
this? Any help appreciated..
- ata_75 -3rd Sep,
Most chimneys were constructed without a damp proof course, the heat from the fire would pull any
moisture out of the brickwork and up the flue. of course when the open fire is removed any dampness
will now manifest itself through the plastering if a suitable dpc has not been installed. Have the area
checked out to see if it is rising or penetrating damp. An expert will tell you straight away.
Mike Davison cssw
I have an old damp patch on the bottom of my kitchen wall. I have recently made enquiries about
cavity wall insulation and have been told I cannot proceed until the damp is stopped. I believe this
was caused by a blocked gutter which overflowed when it rained, bounced back up on to the wall and
through any gaps in the mortar. We have had the gutter cleared out and I'm in the process of getting
the gutter fixed. I have also filled up any holes I could see, and am in the process of getting the
walls properly checked out, in case I have missed any. The internal wall is discoloured (looks like the
oil from Kitchen paint) and there are two very small bubbled patches, but the wall doesn't feel damp
anymore. However, I believe it still must be because I occasionally get dead woodlice on the floor in
the area. How would I be able to check and tell for sure whether the damp has been resolved and has
Thank you for taking the time to read this and reply.
- claire3278 -10th Oct,
There are a number of issues which could explain the problem you describe.
The gutter will certainly not have helped but it is unlikely that would have caused a damp patch on the
internal skin of a cavity wall if there were no other underlying problems.
The cavity wall insulation people will not do your walls until damp issues are resolved as the cavity
wall insulation may exacerbate the problem, originally cavity walls were built for several reasons, the
cavity formed part of the exterior ventilation of the property, it prevents the cold bridging of the
solid wall and allows the outer leaf to get wet from rain etc whilst the internal leaf remains dry as
it is not connected by brickwork to the extern.
The issue you have is most likely due to cold bridging, where mortar droppings from the original
bricklayers fell down the cavity during construction, this formed a thermal bridge between the outer
and inner leafs and during winter conducts the cold/damp from the outer leaf to the inner one. This can
then cause condensation to form on the internal cold spot (because of the lower dew point) and the wall
becomes damp, however the damp is from the surface of the wall and not rising damp. this problem gets
worse in the cold and damp of winter but can appear to improve in warm summer months.
You would be best to get a qualified surveyor to check it out. If you get a RICS surveyor you will
usually get good advice and a hefty fee, if you get a reputable remedial and damp proofing surveyor the
report is usually free but they may not fully understand the problem and advise a damp proof course
that is not needed.
Check to see if they have CSRT or CSSW after their name, it generally means they have been properly
trained and certified as competent to do the job.
Mike Davison cssw
- 12th Oct,
The damp is in patches is in some parts around the bay. Seems particularly bad in the corner. Damp
seems to have wicked to an internal wall also. We have recently added additional ventilation bricks as
they were covered by turf on the outside. We have dug a small trench around the outside of the bay
though yet to finish with drainage pipe/shale.
I forgot to mention, it has rained before and the damp has not been visible. The house was left
empty for 1 day and the temperature dropped, not sure now whether it is condensation and not rising
- k_webb -9th Oct,
It is impossible to diagnose your problem without a thorough inspection of your property and it's
individual circumstances. See my other answer with a description of 'cold bridging'.
Do not follow any course of action until someone who knows what they are talking about has had a look
or it could prove both costly and unnecessary.
Mike Davison cssw
I think I have an interesting one for you...
I have had a problem with damp patches appearing around my ground floor chimney breast and I would
have though I first noticed an issue around 2 years ago. This is an INTERNAL wall and the construction
is SINGLE SKIN brick. In June 2011, I commissioned an independent damp survey (CSRT qualified surveyors
independent of any supplier) to try and identify the root cause of the problem.
The surveyor took damp measurements of the affected wall and created a damp profile. The moisture
meter indicated elevated readings ranging from 70 - 90% in the plaster of the chimney breast and 40 -
60% in the plaster of the adjacent wall. The skirting boards were 20%. Up to 1m the readings are fairly
consistent and at approx 1m the damp readings stop entirely.
At my instruction floorboards were not lifted due to an existing laminate floor that I can't afford
to replace at present. Samples of brickwork were not taken and the surveyor inspected the house from
the outside but did not get up onto the roof or go into the loft.
The survey report identified the "cause" as being rising damp due to a missing or ineffective dpc in
the chimney breast. Also possible bridging from the concrete hearth and associated earth mound allowing
moisture to track up the brickwork and plaster. Unable to confirm whether the hearth is in-situ due to
Recommendation is to install a dryzone or vandex dpc in the bottom row of brick above floor level
and replaster with sand+cement incorporating salt inhibitor. Plaster not to project more than 25mm
below top of new skirting and min gap to floor of 25mm.
HOWEVER, from visual inspection over a period of time, the damp patches on the wallpaper gets worse
very quickly during periods of heavy rain and gradually dries out over a period of several weeks when
there is a dry spell (all too rare in north Manchester!).
The gas fire came out today and the hearth behind was full of rubble and soot. I have cleaned all of
this out. I have had a couple of lads come out to quote for the
So then based on the above, is my problem:
a) Rising damp as diagnosed by the surveyor
b) Penetrating damp from a leaking chimney
c) Condensation being hygroscopic salts in plaster drawn through from brickwork behind.
d) Some combination of the above/ other
And based on that diagnosis. Do I:
a) Hire a dpc Contractor as per recommendation
b) Get a roofer to see what is what up top and fix any problems there as a first try.
c) Buy a dehumidifier and run it hard for a few weeks.
Sorry for the essay, hope you found it an interesting one, any more info just ask, look forward to
- davebee -27th Sep,
Your problem is probably a combination of issues, chimney breasts were usually constructed with no
DPC, the roaring hot fire used to pull all the damp ot of the masonary and evaporate it up the flue,
when the fire was removed, rising damp could have taken hold however the problem with chimneys is that
they often have a rubble filled void either side of the fire opening, this makes injection unsuitable
as the moisture would rise through the rubble and beyond the dpc (bridging) and then affect the walls
from the inside-out. Also you could have problems with interstitial condensation and with your
description you could also have an open chimney allowing rain/moisture to leak down the flue and
collect in the debris at the bottom.
Sorry if I threw a few more spanners into the works, but a far deeper investigation is required to
get to the bottom of this.
And FYI rising damp can go well beyond 1m depending on wall construction, the only way to tell if the
damp is rising or not is with a calcium carbide test.
Mike Davison cssw
Damp and condensation expert
- 13th Oct, 2011
Passyfier vents or heat exchange units?
Condensation is forming in one room in my ground-floor Victorian conversion on the windows and some
of the walls.
passyfier vents or heat exchange units?
- jason_32 -14th Nov,
Heat exchange units are always the better option, they are bringing fresh pre heated air into your
home and not just allowing freezing cold air (depending on external temp) into it.
- 26th Nov,
We are in the process of buying an attractive Victorian home in a good road. We have secured a good
price and it is in reasonable condition for its age, with the vendors living there for 25 years and it
is well presented, half of it has been refurbished and the kitchen is new and good quality. The survey
has come up with some maintenance issues which are to be expected. However, off the side of the house
is an extension which was originally a garage and has been extended backwards to become the kitchen
(this was done before the current vendor over 25 years ago). The garage is 16 x 8.5 and the kitchen on
the back of that is 22 x 8.5. It has a flat roof which was replaced this summer.
However the surveyor has noticed that the kitchen wall "may" be of single-skin brick with a
timber-frame inner lining. It isn’t thick enough to be cavity or solid. There was no obvious feel of
insulation nor any obvious ventilation. "Unless they have been very clever", he would guess that any
insulation is either minimal or non-existent. He doubts that there is any insulation (or not much) in
the wall lining. If they do claim to have insulation then he suggests i ask how the roof is ventilated
as there was no sign of anything.
How concerned should i be about this? I have read that mortgage companies don't like such
construction. We have secured a mortgage on the property but used an independent surveyor so he said
the mortgage company "might not notice". Would a roof company re-do the roof with a 20 guarantee and
not provide adequate ventilation and insulation? If they provide us with proof of building regs does
this mean that the insulation is adequate at least in the roof?
We could obviously not change the roof because of the construction, how much would it cost to
demolish and rebuild such a structure if we had to in the future? Is this a reason to secure a lower
If you can help and offer an opinion on this I would be very grateful. I don't want to buy something
that is not mortgage able in the future. I don't want to have a kitchen that is a cold and mouldy. The
vendors have lived there happily for 25 years and seem to be perplexed by our concerns because the
extension has been there for so long and the refurbishments they have done have been very good
I am awaiting their vendors information which should include the relevant paperwork for the new
roof, what should i be looking for? In short, would you buy this house, i don't want to pay alot of
money for something that isn't what is seems???? Many thanks for your help and apologies if i haven't
explained this very well my knowledge of construction is zero but i am trying to learn very
- greenpeel1969 -16th Nov
Email your surveyor and ask him directly for advice as to what to do, and any indicative costs for
his recommendations, this is what you have already paid him for. Remember - you can't re-negotiate
after the purchase so make sure you get to the bottom of it before you complete.
It is quite an easy job to add insulation on top of a flat roof and re-felt it (assuming you have the
height to do this) and insulation can be attached externally and rendered if need be. If this work is
required you will need to know the cost for negotiation prior to purchase, so ask your surveyor
directly and follow his advice or the same problem will only come back and haunt you when you come to
Mike Davison cssw
- 11th Feb
A plumber supplies a verbal estimate to fit a bathroom. Say £1950.00. Including labour and materials
to install the bathroom assuming fitting of bath, sink, toilet and radiator.
The customer is a very competent person experienced in a wide range of building work. However, too busy
to carry out the plumbing installation. As they are projecting the installation, measure all out doing
the joinery work, tiling, painting etc. To get the job as required up to 50% of the installation
assistance is supplied to the plumber without questioning, assistance just given and accepted. 75% of
the installation materials are available free issue and taken without question from the customer,
copper pipes & fittings, soil pipes, the plumber supplies hep pipe but takes the customers stock
copper pipe to trade etc. Some of the work the plumber caries out is not to satisfaction. I.e. loose
pipes need re-bracketing and further chasing out and is rectified in the absence of the plumber to move
on with the install. All holes cored for waste and soil pipe with customers core drill. Plumbers drill
is said to not be suitable to core engineered brickwork. The fitting of most equipment is prepared and
carried out by the customer for the plumber just to fit pipes. Bath, sink, wall hung toilet frame. The
plumber has spent approx 50 hours installing the bathroom. This is a generous time given due to plumber
spending up to 2 hours a day on their mobile running their business.
The customer expected the price to be less than £1950 as most materials were supplied and assistance
supplied. Equipment was fitted ready for piping up. A lot of time has been paid for by the customer for
the plumber to speak business on his phone, visit plumbers merchant for the bathroom equipment
installation advice etc.
The plumber requests the verbal estimated price for the job £1950. Where would the customer stand
requesting a discount? Customer has requested a breakdown of the price but still said to be a fixed
It is always difficult to advise with only one side of a story, however I hope this helps.
Depending on circumstances quotes can be changed and estimates can be changed i.e. if the work is
added to or reduced or takes longer that the time expected due to unforeseen circumstances, but a fixed
price can not be changed unless agreed by both parties.
Hindsight is a wonderful thing but you have gone about this the wrong way and unfortunately he seems to
have taken advantage of that.
Legally I suspect you do not have a leg to stand on.
Try talking to him, he may be prepared to replace the materials he has used if he calculated them into
his price - otherwise you may just have to pay up and learn from experience - you will know better next
time. This shows the need for only employing decent trustworthy businesses to do your work.
Mike Davison CSSW
- 11th Feb,2012
I live in an old cottage set on a Pennine hillside which has a vaulted cellar.
The cellar is currently damp and in really wet conditions water can be seen at the edges of the flag
The water is only ever in one corner of the room but the opposite corner appears dry (in fact I have
ran a hose pipe down there for a few hours and the water totally drained away).
When I lifted some flag stones I had a dig around to see what the ground was like underneath and
after only about 1" of digging I hit solid bedrock.
It looks like the water is due to a natural water course which runs along this bedrock.
Therefore it doesn't look like installing a sump pump would be possible as I would need to literally
chisel into the rock. Also as the house is old I wouldn't want to try and alter the natural water
course which the house has always been sat on.
Given that the water is only ever in one corner and the level of water never comes above the flag
stones (I have been watching for about 3 years now) would I get away without a sump pump if I were to
try and use a membrane tanking system ?
Otherwise would a more traditional concrete + DPM type floor be better as this would raise the floor
level 3 or 4 " ?
Any advise would be appreciated.
- lee -26th Apr,
You can only use cavity drain membrane in a tanking situation if it has drainage or a sump pump. The
system is not designed to cope with static water pressure and any build up would certainly result in
failure. The British standard for this type of system tells you that even if there is no history of
flooding we must assume that some flooding will occur in the future.
The pump does not necessarily have to go in the damp corner - if there is earth elsewhere in your
cellar you could dig there and form a drain to that point.
Mike Davison cssw
- 27th April 2012
Skirting boards butted-up and not
I have just had a conservatory makeover which included plastering walls and fitting skirting boards. The
contractor has used pencil round boards. Internal joints have been simply butted-up (and not scribed) and
external mitres don't fit perfectly. He is trying to tell me that it's perfectly normal to butt-up (even
though it looks rubbish) and it is to be expected that external mitres are not flush. When I get round to
decorating, apparently I should put caulk in the hole caused by butting-up and filler in the mitres. I want
the boards stained not painted by the way. My view is that if the internal joint can't be scribed (too
flimsy they say) then they should mitre (not square they say). Surely a decent carpenter can deal with
walls that are not square and do an internal mitre at say 44 degrees instead of 45?
- neiltheblue -17th Sep,
A decent joiner will always do a mitre to external corners and scribe the internals with the profile
scribe to the wall least visible.
Give them a reasonable deadline and refuse to pay till they put it right, if they don't put it right by
the deadline employ a craftsman joiner to do the work and knock his bill off their price.
Simple as that.
People like that get us all a bad name.
What I am getting at here is do I buy the tiles and adhesive myself then get a tiler to come in and
lay the floor or will they get the materials for me?
If I get the tiles myself will they know what adhesive to use?
These may sound like silly questions but we are just about to exchange on our first home and we are
clueless about anything remotely DIY related!
- heathershouse -4th Jul, 2011Flooring
There are no hard and fast rules here, some Tilers will charge a percentage for supplying the materials
and some won't, often the tilers can buy at such a discount that they can add a handling charge and
still be cheaper than you would pay if you purchased them yourself.
Invite several companies to quote, request a full breakdown of all costs, ie tiles, adhesive, grout,
tile edge (if needed) and compare them. Remember to ask for the broken down price in writing and a
reference from a recent customer.
Mike Davison cssw
Mike is our Technical Director, He is probably the most experienced Damp,
Timber and basement waterproofing expert in the North of England. Mike carries out our
more technical inspections and provides our training courses and technical advice. Mike has
never been beaten. If you have a problem and need a definitive answer, put him to the test and ask the
question...email us and he will give you a personal reply and we may even publish it
Use the contact form here