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43 Burton Street
Devon TQ5 9JA
Tel: 01803859303

  Diagnosing condensation problems and other causes of damp in your home
Please click on a box that describes your problem - you'll find more information and link to a solution
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Black mould
musty smells
mildew on curtains

windows every morning
Dripping in loft or roof space Damp walls near
ground floor level
Damp patches
on outside walls
& wood rot
Damp below
ground level

Black mould  -  Mustiness  -  Poor air quality - Poor health (Top of page)
Diagnosis & Advice


Is there black mould in cold corners or on skirting boards?

Black mould  

Condensation is the main cause of black mould. More than half the homes in the UK suffer some condensation problems.
The mould grows on the coldest corners in the home.

Outside corners and the corner of ceilings ar most affected but with condensation mould can grow anywhere. Visit Condensation solutions

Rising damp leaves salt deposits and moulds cannot tolerate salty water! So if you see mould you suspect there is rising damp is unlikely but not impossible.


Are you aware of bed bugs /dust mites in your home?


Damp beds are ideal conditions for mites and bugs to thrive. Bed bugs do not drink – they get water from the damp air! Condensation is the main cause of dampness in sheet, pillows and bedding.

Dust mites contaminate food and mainly infest damp cupboards.


Does your family suffer from asthma, coughs or allergies?

Damp conditions are a perfect breeding ground for moulds, bacteria and dust mites. 80% of people who are asthmatic are affected by house dust mites. Condensation is often the cause.
Mould and Bacteria Testing Kit from Dryhomes -. Click to find out more.



Musty Smells?


This is associated with condensation which encourages mildew and smell-emitting moulds. Lack of ventilation, low level heating and poor insulation contribute to mustiness.
Homes with sub floors straight on to soil may suffer musty smells – this can be solved by covering the sub floor which is very expensive. Positive ventilation will reduce the problem by not allowing these smells to enter the house.



Does the back of your wardrobe look like this?

mouldy wardrobeThe wardrobe shown was new 2 months before and was not even touching a cold wall.  

This is a classic condensation symptom. Cold damp places are perfect for moulds and fungi to thrive. There is no known reason for this symptom other than condensation.

Move furniture away from cold outside walls where possible and then visit Condensation solutions





Is there mould on your shoes or on leather?

Mould on shoes  

Condensation is allowing mould to grow on the cold surfaces - mould is eating your leather shoes!
Condensation causes £1000’s worth of damage to clothes, furniture, books, shoes and decorations.

High humidity. Does your home feel warm and wet like a jungle ?    

This is the fundamental cause of condensation and more fresh air is required to 'balance' the damp air.

"if your car steams up it is more effective to open a window than turn up the heater"



Is there green mould on the back of picture frames?

Picture frame   Condensation. This picture was hanging on a dry wall! There is no other explanation apart from condensation for this damp.

Do you have mildew on curtains?


Condensation allows moulds to grow consuming the fabric.

Moulds will dry if they do not have water but the stains may not be easy to remove so the fabric is permanently destroyed.



No damp readings on the damp wall?

cond in a corner  

There is a condensation problem early in the morning. Beads of moisture form at about 4am in the morning when the wall is really cold and evaporate later in the day. By the time you measure the damp with a meter the wall is dry

The photo shows a typical pattern: the wall is coldest in the corner. The shape of the black mould mirrors the temperature of the wall surface.

This is when a moisture meter is really useful - if the wall is DRY is caused by condensation. if it's damp there may be a second cause.

Streaming windows (Top of page)


Do you have to wipe the windows nearly every morning?

Wet windows  

This is definitely condensation there is no other cause! water droplets forming on the cold surface. If you leave drops they will evaporate into the air during the day.

On wallpaper and clothes the water soaks in but it's still there

On polished leather the damp tends to stay on the surface which is why the mould attacks so quickly

If you want to end to this nightmare.....

Streaming window


..... visit Condensation solutions

How to stop condensation in the loft or roof space (Top of page)

Drips on loft insulation.


Underside of roof felt has beads of water

White mould on timbers

Rot in roof

Never Install a positive pressure system in a damp loft - it won't work


Dampness, dripping, glistening of water droplets and musty smells means you have a poorly vented roof.
This is can be harmful to the roof timbers.

Mould growth on goods stored in the roof is a sure sign of a condensation problem.

Damp roof voids are prone to rot and insect attack.

Dry rot is unlikely because condensation only occurs under humid conditions and dry rot needs a constant supply of water.

Without management this will become a bigger problem, damp insulation will not be effective and heating bills will rise.


Woodworm holes with fresh dust. Active woodworm like damp timber.


Musty smells in the roof

Moulds growing on cases and goods stored in the roof

Damp in roof

Don't Install a positive pressure system in a damp loft - it won't work



  • Leaking fan vents (ducting with gaps letting damp air into the roof) should be replaced immediately.
  • Turn off light in roof and see how much daylight you can see. If none - you have a 'tight roof' which needs venting.
  • Outside look up at the eaves. Are there any sofit vents?
  • Have tile vents been fitted amongst the slates on the roof itself?
  • Has cladding been added and covered the sofits so the roof cannot breath?
  • Is insulation inside covering the vents?
  • Are water tanks covered to stop evaporation?



Dry homes ventThe "dryhomes roof vent" can be slipped between the joints of the sarking felt to open up enough of a gap to vent the roof.
Fresh dry air from outside enters via spaces between the slates or tiles.



Traditionally sofit vents are installed and where this is not feasible tile vents are added. This is very expensive and time consuming you may be able to use Dryhomes Roof Vents. Check your sarking felt (the material under the slates) has overlapping gaps open the gap and either see daylight or feel a draught.


  • Very cheap and effective
  • Only 1 "dryhomes vent" is needed per 5mtrs of floor space.
  • Quick to install - the average roof would take 1 hour
  • No scaffolding - installation is achieved from inside the roof
  • Can be DIY fitted with no tools

Damp near ground floor level (Top of page)
Diagnosis & Advice


Is there damp at the bottom of the wall on the ground floor?
No mould?

Rising damp  

This is most likely due to rising damp. Rising damp can affect internal and external walls rarely rising more than 3 feet - if it does you may have very high humidity as well…..
What is rising damp? Damp that rises up a wall from the soil under the house. If there is no damp proof course the bricks will absorb the water slowly like a sponge and then evaporate into the house.
There were no effective damp courses in houses built before the 1930’s.
Even with a good damp course there may be bridging of the damp course with mortar in the cavity, or cavity insulation, allowing water from the ground to rise up the wall.
The damp course may have been bridged by a new solid floor on the inside.
Existing damp courses can break down and fail. Then a new damp course needs injecting.



Is the ground level outside higher than the floor?
Is there a raised flower bed, parking area or patio outside?

There are many reasons and wrong diagnosis is expensive so ask a PCA remedial treatment company to investigate.

If you live in 15 miles from Torbay Dampco Ltd will be able to help


The original damp course may have been bridged allowing water to get up the wall. This is particularly a problem in single skin construction. Reduce the ground level.
If the ground level needs to be kept as it is insert a vapour control barrier between the house wall and the raised area.
Have a new damp course injected higher up the wall and the base of the wall ‘tanked’ against penetrating damp. Note that there may be perished plaster inside and without replacing the plaster the wall may fail to dry out.



Salts on the wall surface?

Rising damp salts


 Salts are drawn up with water from the ground where your house is built. The water evaporates leaving a salty deposit which shows as dust or crystals.
This is rising damp but possibly penetrating damp if wall is below ground level.



Rotting skirting boards?

Rotting skirtings


Damp skirtings show the wall is damp. It is most likely caused rising damp. Penetrating damp can also wet a wall. Skirtings can start to rot because of severe condensation but this is rare.



Horizontal line of dampness about 3 feet up the wall?

damp start up a wall  

Look carefully – has there been re-plastering? Some builders use waterproof render to disguise rising damp. Wainscoting* fulfils the same function of hiding problems. Covering up does not solve the problem it merely makes damp rise higher. That is why you can see damp start suddenly high up a wall.

*timber panels about 3ft high around the walls


Springy/ moving floor near a wall?
Does the floor appear to have dropped by the skirting?

There are many reasons and wrong diagnosis is expensive so ask a PCA remedial treatment company to investigate.

If you live in 15 miles from Torbay Dampco Ltd will be able to help


Ends of joists, or the floor plate, have dropped because they have rotted. Usually this is wet rot and is easily rectified. The area can be rebuilt using treated timber. Vapour control barriers (plastic membranes) must be used to protect the new wood from damp masonry. Old timbers, not affected, should be treated with fungicide. Make sure there are adequate air bricks and they are all clear - this helps to keep the floor timbers air dry and prevent wood rot.

Fungus and wood rot (Top of page)

Fleshy fungal growth creamy white jelly?Showers and skirtings.


Plaster fungus is very jelly like and spongy. Spooky! Usually white or creamy. Look for plumbing problems but it can grow on any damp surface – this is not a serious problem but the damp should be identified and stopped. Timbers will be eaten by fungal growth. Check that it is not (the very serious) dry rot – see below.

If you have black mould on the walls you have a condensation problem


White, cream, pink or lilac sheets of fungal growths with  white lacy tendrils.

Fan like invasion of dry timber with white thin skin of mycelium.

Soft, spongy central body?

Red spore dust?

Timber has deep, hollow cracks going across the grain.

Eaten timber has no strength and may be easily broken.

Nearby timbers can be not affected at all.

Dry rot under floor

dry rot hidden behind panels

Dry rot seen


This is Dry rot and should be tackled immediately as it is invasive and expensive to treat. Call a PCA member immediately and get professional advice.
About 80% of cases of true dry rot are caused by faulty plumbing so get a plumber in if there is any local pipe work so he can check for leaks. Plumber Yellow Pages
Dry rot needs a permanent source of water such as damp under the house so investigate this possibility. The water may only be a small constant drip. For this reason dry rot is rare in roofs because rain is intermittent and the dry rot will die of thirst.

Note: Dry rot is so called because it can transport water, via mycelium, from the source of water to dry timbers. As soon as the timber has been wetted the fungus can start digesting it. Dry rot is the only wood rot that can attack dry timber!

Click on this photo to see how destructive and invasive dry rot can be.

TIP. DIY. Expose the mycelium as soon as possible to assist drying and slow down the invasion – cut water supply to any leaking pipes immediately – rip out loose, rotted timber and fungus and cart away.

There are many reasons and wrong diagnosis is expensive so ask a PCA remedial treatment company to investigate.

If you live within 15 miles from Torbay call Dampco Ltd
straight away. Dry rot should be treated quickly.


White or brown feathery fungus on  wet timber?

Shallow cracking along the grain of the wood?


Wet rot in beam  

This is usually a brown rot, probably cellar fungus. Timbers are rotten on the surface but tend to have some strength

To kill wet rot you need to dry the area and replace affected timbers. There are many types of wet rot and all can be treated in the same way.

We recommend you have a survey  from a damp proofing specialist to confirm it is not dry rot. See above.

Damp patches on outside walls (Top of page)

Black mould on the ceiling?

Black mould on ceiling  

Classic condensation. Often when insulation is missing or substandard as this makes the ceiling cold. The pattern of mould may be in patches where there are no joists as in the photo. Note that the warm joists can be ‘seen’ where there is no mould. Upgrade the insulation and control the humidity.
   "an old couple, who lived with this for 10 years, had been ‘sold’ new gutters but there was no problem with penetrating damp"

Damp patches on walls near the ceiling on downstairs rooms?    

Leaking plumbing – check for bathroom and radiators on the floor above. Most common leaks are shower trays then bath seals where tiles meet the walls. WC foul pipes can break inside walls. Small drips may cause big problems. If there is a kitchen above something could be leaking – washing machine pipes often leak.
This is a common cause of dry rot outbreaks. Plumber or tiler Yellow Pages.
TIP – Check under washing machines for leaks – many people are not aware of leaks until they fall through the rotten kitchen floor! 


Grass in gutters?
Faulty rain water goods?
Leaking overflow pipes?

    These are all common causes of penetration through walls especially in older property. Damp is always worse after rain and especially bad after wind and rain.  Routine maintenance is the answer. Builder Yellow Pages

Damp below a chimney stack or valley in upstairs bedrooms?
Damp bedroom ceiling/wall?

Poor chimney  

Most faults with flashings are near where the stack meets the slates.
It could also be because no damp course was built in the chimney stack to stop water migrating down into the house.
Penetrating damp can occur if the stack is porous, badly pointed, has cracked or substandard render or is badly painted. Is the stack in a good condition? See photo!  builder / roofer Yellow Pages



Damp patch in middle of ceiling?

Poor insulation  

Leaking water tank or loose slates. Have a look and call plumber / roofer Yellow Pages

The grey mould in the photo shows a condensation problem on the coldest part of the ceiling - maybe loft insulation is not laid properly.

Grey stains on the wall shows a condensation problem.


Cavity wall.

Patterns of damp patches on walls about 1 mtr apart.


In cavity construction this may be damp migrating across wall ties. Externally problems of corroded wall ties are indicated by horizontal cracking which can also cause penetrating damp. Check to see if heights of outside cracks correspond to inside damp – damp may appear lower but not higher up the wall. PCA survey.
It may be condensation on the cold ties as they make a “ cold bridge” to the outside. Condensation also occurs on dry lined walls which have been fixed by blobs of adhesive, known as dabs. If the wall is lined it will be hollow when tapped – try tapping the damp spot to see if it is a solid dab. Note that lined walls often cover defects and penetrating damp may be the problem.


Cavity Walls.Damp patch or uneven patches in middle of a cavity wall?


Do you have cavity insulation? Inferior cavity insulation, from a few years ago, has been ciga logoresponsible for some penetrating damp problems. Have a PCA survey to investigate. If insulation is found to be the problem the faulty insulation must be removed.
TOP TIP - check if wall insulation is covered by  long term CIGA insurance - they should pay your costs 


Damp patch or patches in middle of a wall? Single 9” brickwork on older homes


In solid construction rain can migrate through bricks and across stones.
POINTING. Care should be taken to maintain the pointing particularly where it is difficult to do – behind down pipes etc.
RENDERING. Some solid walls are rendered to stop this damp. Be aware that very small HORIZONTAL cracks in render are the worst for damp as they can suck in rain as it comes down the wall.
Renders may crack because of drying stress or movement and these cracks must be repaired.
On poor backgrounds, weak renders or badly keyed surfaces the render can be ‘blown’. This means that the bond has broken down and the render is peeling off. Test this by tapping the surface for hollowness. Occasionally there are individual patches of blown render and these must be replaced or monitored.
If you decide to re-render make sure there is a good bond on the substrate, PVA and adhesives should be considered. The dubbing out coat should be weaker than the final coat and without a waterproofer. The final coat may have a waterproofing additive. Make sure the render is carefully cured  by keeping damp for up to 4 weeks to prevent cracking and strengthen the render.
Lime mortars can be considered as they are less prone to cracking but they are expensive. Always use lime on cob construction to allow movement – lime has the advantage of being easily repaired.
 NB Take local advice….these are only general notes.... we are not experts in this field
PAINTING. Where the walls are painted look carefully at the surface for small holes – many tiny pin holes can cause big damp problems.
LININGS. Older homes were lined inside with lathe and plaster inside to disguise the penetrating damp. This will work if the wall has time to dry between rains but lathes can be attacked by wet rot over a long period of wet weather – tap the wall inside to detect movement or/and listen to plaster falling down the ‘cavity’
 DIY. Painter or builder Yellow Pages



Dark patch on chimney breast?

    In older houses the chimney stacks may be full of coal tar which bleeds out on the stone/brick. Interstitial condensation causes the staining. Vent the stack by fitting air bricks on each floor where fireplaces are blocked.
Sometimes the wall will benefit from re-plastering to remove the tar or use stain block to cover it up.
DIY - Builder - Yellow Pages.

Odd damp patch usually at the back of the house?

There can be many reasons but don’t rule out a broken water pipe within the wall.
I have found old lead pipes, with beaten ends, leaking since a local "handyman" chopped it off. Most commonly these pipes are near the back of the house and originally fed the WC.



Damp when it rains?
Damp under windows


Penetrating damp can usually be solved by routine maintenance. Handyman or builder. On rare occasions the rain comes from the ‘wrong direction’ blown by strong winds – unusual small damp patches and odd drips appear - unless this is persistent the damp will dry out in a few days.
Note that condensation is always worse on damp days due to the air being very humid. Normally this is a short term problem.


Damp below ground level (Top of page)
Cellars     Rooms below ground are prone to condensation and ground water penetration. The most serious problems in cellars can be that the damp will cause wet rot or dry rot in the floor above – it is worth a look at the joist ends where they meet the wall and poke the wood with a bradawl to see if it is spongy. If a damp meter shows 18-22% I would recommend a survey. See below. It is sometimes cheaper and stronger to support joist ends with a wall than replace joist ends. Care must be taken to isolate all timbers from damp masonry.


Damp proofing basement conversions.


Call in the experts to design a system to waterproof below ground level.
Control the ground water BEFORE starting any conversion. See below.
Note: Note that conversions are only desirable when light, airy and dry – otherwise they will not enhance the value of your home and will not be fit for purpose.
Ventilation is not an optional extra!

Basement flats.    

Flats are prone to all manner of problems but chiefly condensation and sometimes penetrating damp.
Inadequate ventilation is a primary cause of misery for people living below ground level. The lack of windows, lack of general airflow between the rooms and poor ventilation make unhealthy conditions inevitable.
Humidity controlled fans – sometimes ducted – will assist the ventilation. See Condensation solutions

Damp ingress after prolonged rain in rooms below ground?




After prolonged wet spell, when the land has little chance to dry out and water pressure builds up, the water table is raised,. All land has water underneath and this water reservoir is an underground lake. Heavy rain adds water and the ‘lake’ level rises. The height of the water surface is known as the water table. If the water table rises under the property it can create pressure in a basement and any waterproofing should be designed to either withstand such pressure or remove the water to reduce the pressure.
Many basements never have a problem because of the location or the nature of the subsoil but well designed habitable areas below ground level must be built with potential problems in mind. This is why you need a PCA survey. It is worth paying for a survey to save costs later