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Understanding Breathability: The Most Misused Term in Conservation

When it comes to caring for old, solid-walled buildings, "breathable" is a term that pops up frequently. It conjures images of walls effortlessly allowing moisture to pass through, keeping homes dry and comfortable. However, this term is often misunderstood, and misapplying it can lead to significant damage in our treasured heritage buildings.

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So, what does "breathable" really mean when companies use it, and what should we understand to protect our buildings properly?

The Movement of Moisture in Walls

Think of your building's walls like a sponge or the roots of a plant. A sponge doesn't just handle mist in the air; it also soaks up liquid spills. Similarly, plant roots don't just absorb humidity; they drink up water from the soil. In both cases, water travels along microscopic "straws" in the material. Walls act in a similar way, pulling water in, carrying it through their core, and releasing it out the other side. This natural process, known as capillary action, is crucial for keeping walls dry. This is where the idea of Rising Damp comes from, often misdiagnosed and missold remedies, when in fact it's about a simple process of moisture absorption and evaporation, obviously minimising the moisture in the first instance is best. Prevention rather than cure. If you have significant damp issues you'll need a damp survey.

The Misuse of "Breathability in Conservation"

Many products labelled as "breathable" focus solely on vapour permeability. However, moisture in our walls tends to be in liquid form, making vapour permeability less important—sometimes even irrelevant. When you see "breathable" on labels for paints, plasters, or insulation, dig deeper into what that really means. If the claim only pertains to water vapour, be cautious. "Breathable but waterproof" is a huge red flag, as these products might trap moisture inside the walls, leading to dampness and structural damage.

True Breathability: Capillary Active and Hygroscopic

True breathability involves supporting the building's ability to handle water in all forms—liquid and vapour. Materials that are capillary active, like non-hydraulic lime, allow walls to naturally transport water from the interior to the exterior, preventing moisture build-up. Furthermore, hygroscopic materials, which absorb and release moisture from the air, help balance indoor humidity. This natural regulation is vital for old buildings which are sensitive to moisture and humidity changes.

The Consequences of Improper Material Selection

Using non-hygroscopic modern paints, for instance, can lead to condensation forming on walls when temperatures drop below the dew point, causing damp and mould. In contrast, hygroscopic limewash absorbs this moisture, preventing condensation and protecting the building.

Making Informed Choices for Heritage Buildings

When selecting materials for repairs or renovations of old buildings, look for those that allow moisture to move in and out and buffer humidity changes. This approach ensures moisture doesn't build up, safeguarding the structure's longevity. Always ask if the product is capillary active and hygroscopic, not just vapour permeable. Often engaging a specialist such as a Chartered Building Surveying practice such as AMS SURVEYS, who can help specific and design building refurbishments and alterations.


The health of an old building lies in its walls' ability to manage moisture effectively. The next time you consider a "breathable" product—be it paint, insulation, or something else—ensure it supports both capillary action and hygroscopic properties. By doing so, you'll help your building stand strong and dry for generations to come.

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Got damp in a heritage or old building find out more about our damp surveys and other specialist heritage services

Here to help, find out more at AMS SURVEYS, contact@amssurveys or call 0151 314 6650

FAQ: Understanding Breathability: The Most Misused Term in Conservation

What does "breathable" mean in the context of building materials?

In building conservation, "breathable" typically refers to materials that allow moisture to pass through. However, true breathability involves supporting a building's ability to handle water in both liquid and vapour forms, ensuring moisture can move in and out effectively without causing damage.

Why is the term "breathable" often misused?

Many manufacturers use "breathable" to describe vapour permeability only. This can be misleading because it overlooks the importance of a material's ability to manage liquid moisture through capillary action. Misuse of the term can lead to selecting products that trap moisture inside walls, causing dampness and structural issues.

What is capillary action, and why is it important?

Capillary action refers to the movement of liquid moisture through tiny channels within a material. This process is crucial for old buildings, as it allows walls to pull in moisture from one side and release it on the other, helping to keep the structure dry and preventing moisture buildup.

How can I determine if a product is truly breathable?

To ensure a product is truly breathable, check if it supports capillary action and is hygroscopic. These properties allow the material to handle liquid moisture effectively and balance indoor humidity by absorbing and releasing moisture from the air.

What are the signs of improper moisture management in walls?

Signs include damp or musty smells, spongy or soft timber, darkened or discoloured wood, peeling paint, and visible mould or mildew. These issues indicate that moisture is trapped within the walls, leading to potential damage.

How can I prevent moisture-related problems in old buildings?

Prevent moisture issues by selecting materials that are capillary active and hygroscopic, ensuring good ventilation, fixing leaks promptly, and maintaining proper drainage around the property. Regular inspections can also help identify and address moisture problems early.

What is hygroscopicity, and how does it benefit old buildings?

Hygroscopicity is a material's ability to absorb and release moisture from the air. In old buildings, hygroscopic materials help regulate indoor humidity, preventing moisture buildup and protecting the structure from damp-related damage.

Are modern paints and plasters suitable for old buildings?

Not always. Modern, non-hygroscopic paints and plasters can trap moisture within walls, leading to condensation, dampness, and mould. It's better to use traditional materials like limewash, which are both hygroscopic and capillary active.

Can "breathable but waterproof" products harm my building?

Yes, products labelled "breathable but waterproof" can trap moisture inside the walls, leading to dampness and structural issues. True breathability requires materials that handle moisture in all forms, not just vapour.

What should I look for in materials for repairing old buildings?

Look for materials that support both capillary action and hygroscopic properties. These materials will allow your building to manage moisture effectively, preventing buildup and protecting the structure over time.


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