Does Brick Need to Breathe?
The question “does brick need to breathe?” is one that appears simple on the surface but opens the door to a deeper discussion about traditional construction, moisture movement, building physics, and the long-term health of masonry buildings. It is a topic that is often misunderstood, frequently oversimplified, and sometimes misused in building conversations.
In short, brick itself does not “breathe” in the way a living organism does. However, brickwork systems allow moisture to move, and this movement is essential to the durability and performance of many buildings, particularly older ones. Understanding what this really means helps prevent costly mistakes, structural damage, and unnecessary repairs 💷.
This article explores the science behind brick and moisture, why the idea of breathing exists, how different types of buildings behave, and when breathability genuinely matters.
What People Mean When They Say “Brick Needs to Breathe”
When people say brick needs to breathe, they are usually referring to moisture vapour permeability, not airflow.
Brick walls:
- Do not inhale or exhale air
- Do absorb moisture
- Do release moisture over time
This moisture movement happens through microscopic pores in the brick and mortar. The process is slow, passive, and governed by physics rather than ventilation.
Common Interpretations of “Breathing”
| Phrase Used | What Is Actually Meant |
|---|---|
| Brick needs to breathe | Moisture must escape |
| Wall must be breathable | Vapour can pass through |
| Sealed walls cause damp | Moisture is trapped |
| Traditional buildings breathe | They manage moisture naturally |
The confusion often arises because older buildings were designed differently from modern ones.
The Science: How Moisture Moves Through Brickwork
Brick is a porous material. Under a microscope, a brick resembles a sponge with thousands of tiny interconnected pores.
Moisture moves through brickwork via three main mechanisms:
- Capillary action
- Vapour diffusion
- Evaporation
1. Capillary Action
Water can be drawn into brickwork when it comes into contact with moisture, such as rain or ground water. This is how rainwater soaks into walls and how rising damp can occur.
2. Vapour Diffusion
Water vapour moves from areas of high vapour pressure to low vapour pressure, typically from warm, humid interiors to cooler, drier exteriors. This process is slow but continuous.
3. Evaporation
Once moisture reaches the surface, it evaporates back into the atmosphere. This drying process is crucial for wall health.
If evaporation is blocked, moisture accumulates.
Brick vs Mortar: The Real Breathing Element
Interestingly, mortar plays a bigger role in breathability than brick.
Traditional lime mortars are:
- Softer
- More porous
- Vapour permeable
Modern cement mortars are:
- Harder
- Less permeable
- More resistant to moisture movement
Comparison of Mortar Types
| Property | Lime Mortar | Cement Mortar |
|---|---|---|
| Vapour permeability | High | Low |
| Flexibility | Flexible | Rigid |
| Moisture release | Easy | Restricted |
| Compatibility with old brick | Excellent | Poor |
| Likelihood of trapping damp | Low | High |
In older buildings, moisture is designed to escape through the mortar, not the brick itself. When that pathway is blocked, problems begin.
Do All Brick Buildings Need to Be Breathable?
No. This is a critical distinction.
Whether a brick building needs to “breathe” depends on:
- Age of the building
- Construction method
- Wall thickness
- Presence of cavities
- Internal environment
Building Types and Breathability Needs
| Building Type | Breathability Importance |
|---|---|
| Pre-1919 solid wall | Very high |
| Early 20th century | High |
| Post-1930 cavity wall | Moderate |
| Modern cavity construction | Low |
| Insulated cavity systems | Minimal |
Modern buildings manage moisture using barriers, cavities, membranes, and ventilation systems, rather than vapour permeability through the wall fabric.
Solid Wall Construction and Breathability
Older brick buildings typically have solid walls, often two or more bricks thick, with no cavity.
These walls were designed with the assumption that:
- Rainwater will penetrate
- Moisture will evaporate
- The wall will dry naturally
Blocking evaporation interferes with this design.
Common Solid Wall Characteristics
- No damp proof course or early versions
- Lime mortar throughout
- No cavity for drainage
- High thermal mass
- Slow drying but stable moisture balance
In these buildings, breathability is not optional — it is fundamental to how the structure works 🧱.
Cavity Walls: A Different Moisture Strategy
Cavity walls work on an entirely different principle.
Instead of allowing moisture to pass through the wall:
- Rain penetrates the outer leaf
- Water falls down the cavity
- Moisture is directed out via weep holes
The inner leaf remains dry.
Because of this:
- Vapour permeability is less critical
- Breathability of the brick is secondary
- Moisture management is mechanical rather than passive
What Happens When Brickwork Cannot “Breathe”?
When moisture becomes trapped within brickwork, several problems can occur.
Common Consequences of Trapped Moisture
| Issue | Description |
|---|---|
| Damp patches | Persistent moisture stains |
| Salt crystallisation | White deposits damaging surfaces |
| Frost damage | Expansion cracks in winter |
| Spalling | Brick faces breaking away |
| Timber decay | Wet adjacent timbers |
| Mould growth | Increased internal humidity |
Moisture that cannot escape will find another route, often inward, leading to internal damp problems.
Breathability and Internal Moisture
It is important to understand that most moisture in homes is generated internally, not externally.
Sources include:
- Cooking
- Bathing
- Washing and drying clothes
- Breathing
In a breathable building, vapour can slowly migrate through walls. In a sealed building, moisture must be removed by ventilation.
Neither system is inherently better — but mixing the two causes problems.
The Problem with Hybrid Approaches
One of the most common causes of damp issues is applying modern, impermeable solutions to traditional buildings.
Examples include:
- Cement pointing on lime walls
- Impermeable wall coatings
- Dense renders
- Modern internal insulation without vapour control
These interventions change how moisture behaves, often with unintended consequences 💷.
Cost Implications of Moisture Trapping
| Issue | Typical Repair Cost (£) |
|---|---|
| Repointing damaged brick | £1,500 – £4,000 |
| Replacing spalled bricks | £2,000 – £6,000 |
| Internal plaster replacement | £1,200 – £3,500 |
| Timber repair due to damp | £800 – £5,000 |
Preventing moisture trapping is often far cheaper than fixing the damage later.
Does Brick Itself Need to Be Vapour Permeable?
Most fired clay bricks are naturally vapour permeable. However, permeability varies significantly depending on:
- Firing temperature
- Clay composition
- Manufacturing process
Brick Types and Vapour Behaviour
| Brick Type | Vapour Permeability |
|---|---|
| Handmade soft brick | High |
| Stock brick | Moderate |
| Engineering brick (Class A/B) | Low |
| Dense modern facing brick | Low to moderate |
In solid wall buildings, pairing low-permeability bricks with impermeable mortar creates a moisture trap.
Breathability vs Waterproofing: Not Opposites
A common myth is that breathability means allowing water in. This is incorrect.
A wall can be:
- Resistant to liquid water
- Permeable to vapour
This balance is what traditional construction aimed to achieve.
Key Differences
| Property | Waterproofing | Breathability |
|---|---|---|
| Stops liquid water | Yes | Usually |
| Allows vapour escape | No | Yes |
| Suitable for solid walls | Rarely | Often |
| Risk of trapped moisture | High | Low |
Problems arise when liquid water is stopped after it has already entered the wall, preventing drying.
Internal Comfort and Breathable Walls
Breathable buildings often feel different to live in.
Occupants commonly report:
- More stable humidity
- Less condensation
- Softer indoor air
- Reduced mould growth (when balanced)
However, breathability alone does not solve ventilation issues. Poor airflow can still result in condensation even in breathable buildings.
Does Brick Need to Breathe in Modern Homes?
In most modern homes, the answer is no.
Modern construction relies on:
- Cavities
- Damp proof membranes
- Controlled ventilation
- Vapour barriers
Breathability through brickwork is not a design requirement because moisture is managed through other systems.
Trying to introduce breathability into modern walls can:
- Reduce thermal efficiency
- Cause interstitial condensation
- Disrupt moisture pathways
Summary: So, Does Brick Need to Breathe?
The most accurate answer is:
Brick does not need to breathe, but many buildings rely on moisture movement through brickwork to remain healthy.
Key Takeaways
- Brick does not exchange air, only moisture vapour
- Breathability is about drying potential
- Solid wall buildings depend on vapour permeability
- Cavity wall buildings do not
- Mortar often matters more than brick
- Trapped moisture causes long-term damage 💷
- Mixing old and new systems is risky
Understanding how a building manages moisture — rather than relying on slogans — is the key to making informed decisions.
🧱 In the end, it is not about whether brick “needs” to breathe, but whether the building was designed to rely on it.
Breathability and Temperature Changes 🌡️
Moisture movement in brickwork is closely linked to temperature. As temperatures rise and fall, vapour pressure within a wall changes, influencing how moisture migrates.
In breathable walls:
- Warm internal air pushes vapour outward
- Cooler external air allows evaporation
- Moisture movement remains gradual and balanced
In non-breathable systems:
- Vapour can condense within the wall
- Moisture becomes trapped at cold surfaces
- Repeated cycles increase long-term damp risk
This is why traditional buildings often perform better during seasonal changes, even without modern insulation, as their walls are able to adapt rather than resist environmental shifts.
Breathability and External Finishes 🧱
External finishes can dramatically affect how brickwork handles moisture.
Dense surface layers can:
- Slow evaporation
- Increase internal moisture retention
- Force damp to migrate inward
More permeable finishes allow:
- Rainwater resistance
- Continued vapour escape
- Surface drying after wet weather
External Finish Impact on Vapour Movement
| Finish Type | Vapour Movement |
|---|---|
| Dense cement render | Very low |
| Acrylic coatings | Low |
| Traditional lime render | High |
| Bare brickwork | Moderate to high |
The finish does not just protect the wall — it controls how moisture behaves within it.
Breathability and Structural Longevity 🏗️
Buildings that can manage moisture effectively tend to last longer. Breathability plays a subtle but crucial role in reducing long-term stress within masonry.
Moisture-related stress includes:
- Freeze–thaw expansion
- Salt crystallisation pressure
- Differential movement between materials
Over decades, these stresses weaken brick faces and mortar joints. Allowing walls to dry reduces internal pressures and extends the lifespan of both materials, often saving thousands of pounds in major repairs.
Common Misconceptions About “Breathing Walls” ❌
The idea of breathing walls has been simplified into misleading soundbites.
Common myths include:
- “Breathable walls let rain straight through”
- “Sealing walls always stops damp”
- “Older bricks are poor quality”
- “Modern materials are always better”
In reality, older bricks were often softer by design, not inferior. Their ability to absorb and release moisture was intentional and integral to the building system as a whole.
When Breathability Becomes Irrelevant 🚧
There are situations where breathability simply does not play a meaningful role.
These include:
- Fully cavity-based wall systems
- Structures with continuous vapour barriers
- Buildings with mechanical ventilation control
- Walls isolated from internal environments
In these cases, moisture is managed through separation rather than diffusion. Expecting brickwork to “breathe” in such systems misunderstands how the building is intended to function.