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Diagnosing and Treating Penetrating Damp in Historic Buildings

Penetrating damp refers to moisture that penetrates a building through the roof, walls and below the ground. It is a serious concern in historic buildings because it can destroy their fabric, including the ceilings, walls, and any timber used in their structure.

Although it can affect any building, older buildings that have not been maintained over the years are at a higher risk due to deterioration. Modern buildings can also suffer from this issue due to poor workmanship and defective downpipes, gutters, tiles, and renderings.

If you are concerned about penetrating damp in a historic building, here’s how to diagnose the issue and rectify it if it is present.

Why Does it Affect Historic Buildings More?

Older buildings have several features that make them more susceptible to penetrating dampness. They often do not have a cavity but use solid wall construction techniques. Proper cavity walls drain water through what are known as weep holes.

However, penetrating damp can still occur in historic buildings with proper cavities if the insulation is not installed properly if the cavities are obstructed or were filled incorrectly, and if the wall ties were installed incorrectly.

Some walls also become porous over time, with the issue getting worse the longer a building stands. Sufficiently porous walls will lead to penetrating damp.

Diagnosing Penetrating Damp

Penetrating damp will typically show up as a patch on a wall, floor, or ceiling, a visual indicator you have an issue you should deal with. Such patches cause local dampness that never dries or goes away regardless of what you do. You might have localised dampness in more than one area of the historic building, pointing to the fact that the damage and issue are far bigger and more serious than anticipated.

You can also identify penetrating damp from the damage it does. A common type of damage caused by penetrating damp is damaged plaster. The plaster will show tear and wear that is not typical for buildings of a specific age, keeping in mind that this tear and wear is normal once a building reaches a certain age.

The plaster might blister or show signs of disintegration and salting. Salting happens when the penetrating water carries salt inside. The most common sign of salting is a fluff-like residue on the affected surfaces.

Mould growth is another sign of penetrating damp and is very serious in occupied historic buildings. Mould associated with damp will lead to a musty or bad odour that worsens over time as the infestation grows. Since it is a fungus, there are many mould species. All these species produce spores, which are their means of reproduction. Some of these spores are harmless, while others can cause serious respiratory illnesses and allergic reactions.

Mould presents as a black or dark green mass anywhere it grows and is very difficult to deal with because of its microscopic pores and its ability to thrive anywhere there is moisture.

Another sign of penetrating damp is damaged internal decoration, with flaking paint and peeling wallpaper.

Lastly, you might notice rotting skirting boards or timber. Water provides the perfect conditions that support rot and decay, so a building might have penetrating damp if it has this issue. The damage can cause the timber to lose its structural strength, putting the building at risk of structural failure.

Exterior Penetrating Damp

Damp is not only an interior issue because it can also affect a building’s exterior. The two most common signs of this issue are moss growth and damaged brickwork. Moss and algae are attracted by and thrive in damp areas. They cause the underlying brickwork to deteriorate over time, and the building will no longer be aesthetically pleasing.

Brickwork can also be damaged by frost. This happens when the water inside the wall freezes when the temperature falls low enough. Water expands as it freezes, and this expansion causes damage that can be mild to extensive depending on how many freezing cycles the building has undergone.

Treating Penetrating Damp

The first step in eliminating this issue is identifying whether a building has it. Since most signs of penetrating damp are visual, an inspection can help you quickly know if you should be concerned. You can also call a specialist to conduct a more thorough survey to identify whether you have a penetrating damp issue, its cause, and the best ways to deal with it.

Rectifying the issue can be as simple as repairing the damaged items. You can repair or replace damaged flashing, fix broken tiles and slates, replace damaged sealant, fill cracks in walls, and repair damaged chimneys.

Historic building owners should also check that their drainage system is working well. These systems can cause water to collect against the building, allowing water to penetrate the building. Drainage systems like gutters can also cause water to flow along the wall instead of following the downpipes. You might have exterior moss growth when this happens, and it is a sign that you need to repair the gutters to stop penetrating damp before it happens.

Doors and windows are also common points of failure and moisture ingress. Cracks, general damage caused by typical wear, and lack of weather protection can all cause damp to get into the property, even when closed.

Building owners can also use several external treatment options to protect their property. These include cladding and colourless water-repellant options. It is best not to paint the building because that will change its visual appearance.

An important thing to remember if you use these exterior treatments is that the increased impermeability of the walls they are used on can cause surface condensation inside the building. They should, therefore, only be used where there are no other options and with the strict supervision of an experienced specialist.

While crucial for life, water can cause a lot of damage to buildings. Penetrating damp can damage walls and timber support structures, increasing the likelihood of structural failure. The mould that grows due to moisture inside a building causes serious illnesses and allergic reactions that can require urgent care. For this and other reasons, historic building owners must know how to identify signs of penetrating damp and how to treat it.

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