Is damp always visible – 4 places damp can hide

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Most people will begin to worry about damp when the visible signs start to appear. These can include:

  • Damp patches on surfaces in the home
  • Mould growth
  • Damage to internal decoration
  • Deterioration of woodwork.

When the signs are not visible, it can be much more difficult to diagnose. This means it can be harder to find and repair damp problems.

In some cases, you may not even be aware there is a damp issue, until the visual signs become more obvious.

There are several instances when damp might not be visible, such as:

  • Damp structural timbers – A common place for this, is the ends of timber joists that are housed into the brickwork of your property.
  • Excess moisture trapped in the masonry – This can be the result of penetrating damp, rising damp, and even condensation.
  • Damp behind furniture and appliances – This can be behind movable furniture and appliances around the home, as well as fixed items such as kitchen units.
  • Condensation in cold unused areas, such as attics – If moisture can enter cold areas in your home, it will naturally find the dew point and cause condensation. Over time this problem can escalate, and mould growth will occur.

All the above can be hidden away and not visible to the homeowner. However, there may be other signs such as a damp musty smell.

You may also be in the process of buying or selling a home. If this is the case, the initial survey may have flagged up a potential damp issue. This will usually be due to high damp meter readings.

Below we will look at each of the issues mentioned above, as well as ways you can identify each type of damp.

Damp structural timbers

This is quite a common issue, it is usually caused by two main damp problems, rising damp, and penetrating damp.

The issue occurs due to the timber joists being housed into the masonry. This alone is not an issue and is quite standard practice. However, if damp penetrates through the outer wall, or rises from the ground below, this can soak into the timber joists.

Due to this occurring under the floorboards, it is not a visible issue. However, there may be other signs, such as a damp smell.

Once the timber deteriorates enough, this may become noticeable as a sag, or bounce in the floor. At this point you must fix the issue. If this is affecting multiple timbers, it could result in the floor completely failing and falling through.

A good builder, or a local joiner should be able to fix your floor joists without too much disruption.

This will usually involve taking up the floorboards and cutting back the affected timbers, then overlapping and fixing new joists.

The most important thing to consider with this issue, is that you resolve the damp problem first. Simply replacing the timber will not solve your problem. If the defect causing damp remains, then the new timber will face the same fate.

Ideally you should have a damp inspection carried out by a professional. You can easily find reputable damp companies in your local area, via online comparison sites.

Most of the companies will offer a free survey or inspection.

Click here to view profiles of damp proofing experts in your area

Moisture trapped in the masonry

If this is an issue you are currently facing, then it is highly likely it was flagged up during a survey, such as a home buyers report.

If there is no visible damp, the only other way to come to this conclusion, would be testing walls yourself with a damp meter. There are some good affordable options available if you want to check this yourself. You can see our favourite damp proof meters here

If a surveyor suspects there may be damp, this will often be due to readings they have obtained, during their survey. This is usually not conclusive and will require a more specialist damp survey.

Walls are porous, so it is not uncommon for them to contain a certain level of moisture.

Also, higher levels of moisture can be quite common after damp issues have been repaired in the past.

For example, let us assume a situation where penetrating damp was repaired in the past.

Once the repair work has been carried out, water is no longer able to enter the property. However, it is highly likely that there is still excess moisture in the walls.

For this reason, it is essential after any damp proofing work, that walls are thoroughly dried out. If you simply redecorate and cover it up without drying, the moisture will be trapped and may resurface later.

If you are in this situation and you do need a damp survey, Click here

damp behind furniture

Damp behind furniture is not usually visible. However, once you move items, it is quite common to find damp and mould behind them.

This is particularly true if your furniture backs onto a cold external wall.

Cold walls act as a dew point, if you combine this with the lack of airflow behind most pieces of furniture, it is clear to see why damp occurs.

Basically, warm moist air travels behind the furniture. Then due to a lack of air circulation and a cold surface (the wall), water condenses and soaks in. Over the longer term this will nearly always result in mould growth.

Whilst this type of damp is not visible until you move your furniture, the mould will create a damp and musty smell.

If you do smell damp, this is the first place you should look. Find any furniture that backs onto walls and look behind it. Especially those items that back onto cold external walls.

For fixed items, such as kitchen units and fitted bedroom units, you may need the help of a professional joiner or handyman.

Also, you should try and improve ventilation. If moisture in the air is extracted in some way, you will have far less issues with condensation.

Condensation in your attic

Warm moist air rises and is attracted to cold surfaces where it can condense. For this reason, if moisture can enter your attic, it will settle on the inside surface of your roof and attic walls.

For many of us, the attic is a space that we rarely enter. In some instances, we use it for storage, and we may only go up there once a year to grab our Christmas tree.

It is important that you try to avoid damp in your attic. There is a lot of exposed structural timber in most lofts and if you are unlucky enough to have a damp issue, the worst-case scenario is rot setting in.

Once rot sets into timber, it can spread quickly, and this can result in a huge bill to repair or even replace your roof timbers. This is not that common, but it can happen, and it can be expensive to repair.

There is also the potential for mould growth. Again, this can spread and result in further problems down the line.

To avoid condensation in your loft there are a few things you can do.

  1. Firstly, make sure you try to stop moisture getting up there. Make sure the attic is sealed off from the rest of the house.
  2. Reduce relative humidity in other areas of the house by improving ventilation.
  3. Make sure your attic is well ventilated
  4. Consider placing a dehumidifier in your attic occasionally to remove any built-up moisture. You can see how a dehumidifier can help by clicking here.


As you can see, damp is not always visible. This article mentions just a few examples of how damp can go undetected.

To avoid hidden damp issues, you should try to keep an eye out for any of the other signs. This can include high levels of condensation on windows. This would indicate an issue with high humidity.

Any damp musty smells should be investigated.

Also, keep an eye out for other defects that might point you to a damp problem, such as bounce in certain areas of your floor.