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  • Damp - Types, Causes, Symptoms and Solutions

    8th January 2018

    Damp – Types, Causes and Solutions

    Damp is a word that often sends fear when it comes back in a report or when you are told you have it in your house. But, don’t despair. Once the cause is identified it can be rectified. The difficult part is ensuring that you are fixing the cause and not just masking the symptoms.

    Before we start, what is damp?

    Damp: an excess of moisture in a building that cannot escape which has resulted from water ingress from outside the property or condensation on the inside.



    1. Penetrating damp: caused by water ingress through areas where materials or finishes have degraded or failed. The water makes its way in from the outside of the property and ‘escapes’ on the inside of the property. It often shows up as well-defined patches after heavy rain (typically on the south west facing walls). Exposed areas of the building such as roofs, chimneys and parapets are most susceptible because it is harder to carry out maintenance here. Cracks in pointing and render also allow water to penetrate the walls.


    2. Condensation damp: is caused by moisture in the air within the building condensing on walls and windows throughout the property. This often shows up as mould or water droplets on hard shiny surfaces (such as windows). Energy-saving measures in modern properties that reduce ventilation and keep heat in (e.g. double-glazing) increase humidity. Humidity varies between households depending on the amount of bathing, washing and cooking and whether or not there is a suitable level of extraction of moisture in place. Additionally, walls that are damp from penetrating or rising damp can reduce thermal insulation and increase the chance of moisture condensing as the difference in temperature between the air and the walls increase.



    3. Rising damp: is caused by moisture rising up internal walls from the ground. It isn’t a complete myth but it is also not as common a problem as often claimed. Misdiagnosis of other forms of damp often give rise to the claims of rising damp and incorrect damp solutions which will not solve the issue. Floors can become damp where impervious coverings such as vinyl are installed that inhibit the evaporation of moisture. This forces moisture into the base of walls where it rises through capillary action. While some older properties may not have a damp proof course, rising damp only becomes an issue where breathability is compromised and the moisture cannot naturally evaporate from the floors / walls.


    4. Leaks: plumbing and pipework degrades over time which can cause slow leaks and dampness.



    There are three main factors that can contribute to damp (and with them solutions).

    1. Ventilation (condensation and rising damp): air flow through a property helps to remove moisture in the air and draw moisture away from surfaces such as walls. This is extremely important in older buildings that rely on breathability to remove water from the walls. More modern properties are designed to keep the water out the internal walls but rely on ventilation to prevent moisture building up from general living. This includes the roof space – don’t forget warm air rises (and the moisture in the air with it). This warm air hits the colder surfaces in the roof space (such as the tiles), condenses and can lead to damp/rotting roof timbers.


    2. Heating (condensation damp): heating the property correctly ensures the surfaces do not get too cold and allow hot, moist air to condense. It also helps penetrating damp to evaporate more easily when paired with good ventilation. Insulation also helps to keep the house warm reducing heating bills.


    3. Poor maintenance (penetrating damp): where materials or finishes fail water can penetrate from the exterior into the interior of the property. Where a large amount of water can continually enter without escaping at the same rate, dampness builds up. Examples are cracked render, eroded mortar, slipped tiles or leaking gutters.


    Other factors that can lead to damp

    1. Undersized gutters: If the gutters are not large enough for the volume of rain it has to collect or enough downpipes to remove the water, water can spill over the gutters on a regular basis which then increases the volume of water running down the same area of a wall leading to penetrating damp.


    2. Downpipes: older downpipes made of cast-iron can corrode leading to water running down the wall regularly in the same place. If downpipes discharge into the ground and not into a drain, this water sits near the foundations and can saturate the walls with water (or affect the stability of the ground leading to subsidence).


    3. Chemical Damp Proof Course (DPC): if the root cause of damp in a wall is not rectified, an injected chemical damp proof course can make a damp issue worse. This is because it causes the wall beneath the chemical damp proof course to become saturated further. Internal walls may even be replastered using waterproof cement plaster in order to mask the underlying damp issues.


    4. Cement Render: Cracks inevitably develop through the render which allow water into the wall beneath. However, as cement render is impermeable, it cannot escape or evaporate away. It can also cause condensation to form within the property – the moisture inside the property can’t escape either. The size of the cracks depends on the quality of the render applied, how well it was applied and if there has been any movement, settlement or subsidence affecting the walls.


    5. Floor coverings: old, solid floors that rely on moisture evaporating naturally away must not be covered with impervious coverings that prevent this process from happening. It will cause the floor to saturate potentially leading to rising damp where water is forced into the walls and/or could damage the floor coverings.


    6. Basements/Cellars: these areas were traditionally used as cellars or cold stores and walls were in contact with the ground to ensure they remained cool. They would saturate with water to achieve this and had good ventilation to allow excess moisture to escape. If ventilation is hindered when a basement/cellar is converted it can result in the moisture being forced up into the walls above to try and escape.


    7. High External Ground Levels: very often when new patios or paths are laid around the property, they are built on top of original paths or paving. However, this raises the ground level against the walls of the property. There should be at least 150mm between the damp proof course (DPC) and the ground level. If the ground level is at the height of the DPC the ground can cause a bridge between the two brick layers and allow moisture to transfer. Rainwater bounce approximately 150mm on hard surfaces against the walls which can saturate them over time. Reducing the ground level to at least 150mm below the DPC and installing a shallow gravel filled trench around the walls can help prevent issues.



    1. Condensation: droplets of water on hard surfaces such as windows or walls.

    2. Mould: black mould growth on walls is evidence of condensation damp. It is often seen in kitchens and bathrooms where a large amount of moisture is produced and there is inadequate ventilation.

    3. Fungal growth: this is often as a result of dry rot which does require moisture despite its name. Dry rot requires a moisture content of around 20% and wet rot around 50%. Fungal growth (in particular for dry rot) can occur in areas that aren’t visible such as roof spaces and underfloor boards meaning damage can occur before you’ll realise what’s happening.

    4. Dark patches: usually highlights an area that is saturated with water as a result of penetrating damp.

    5. Peeling wallpaper: can show either condensation damp is present as moisture levels in the room are too high or that damp is rising up the walls.

    6. Wet timbers: usually a sign of penetrating damp or condensation. This is often found in roof timbers or ground floor joists.



    In general there are three main solutions to rectify a damp issue.

    1. Maintenance: ensure that all maintenance is up to date and that there is nowhere that moisture can penetrate the building

    2. Improve ventilation: ensure that where moisture is created in a building it can be extracted and that where the building has been designed to naturally breath it is able to do so (particularly important for older properties)

    3. Improve heating: ensure that the property is kept at a reasonable temperature to help improve evaporation and to reduce the likelihood of moisture in the air condensing on the walls

    The main causes of each type of damp are listed below to give you some idea of where to start looking.

    1. Penetrating: maintenance and repairs are usually key to look for here to prevent water being able to enter the building. Removing any materials that shouldn’t have been used is important such as cement mortar when lime mortar should be used.

    2. Rising: check the DPC is in working order and there is nothing bridging the gap (such as mortar covering the DPC or ground level that is too high around the property. Ensure the walls and floors can breathe (correct mortar and floor coverings used) and ensure water can drain freely away from the property.

    3. Condensation: ensure that the property can breathe through the right level of ventilation and heating within the property.



    Remember, a damp problem doesn’t always need an expensive solution to resolve it. The key is to ensure you correctly diagnose the cause and that your solution is not just a block or mask of the real issue.