The key to maintaining Traditional Buildings
When we talk about breathability in buildings, what we’re really referring to is vapour permeability - the ability of building materials to allow water vapour to pass through them. This doesn’t mean that buildings “breathe” in the way living organisms do. It’s a simplified term that describes a building fabric’s ability to manage moisture in vapour form, letting it evaporate out rather than becoming trapped within the walls or floors.
Every material in a building holds some level of moisture - even when we think of them as being “dry.”
Traditional buildings were constructed with materials that could safely absorb, hold, and release this moisture without damage. These materials work as part of a balanced system. If vapour is allowed to enter but not leave - usually because modern, impermeable materials have been used - problems like rising damp, internal mould, and frost damage to brickwork can occur.
Let’s look at some of the most common types of traditional wall construction:
Solid Brick Walls
Usually built without a cavity, these walls rely on their thickness and the use of lime-based mortars to handle moisture. Rainwater and ground moisture may be absorbed into the wall, but it can also evaporate back out thanks to the permeability of the materials.
Brick and Rubble Walls
Often concealed behind lime render, these walls use a mixture of dressed stone, rubble, and brick with lime mortar. These need to remain vapour-open. If modern render or pointing traps moisture inside, the wall can slowly become saturated and begin to degrade.
Cob Walls
Made from clay, straw, and sometimes sand, cob walls are extremely vapour-permeable. They can tolerate moisture provided it can evaporate out. These walls should never be sealed or covered in cement-based renders or paints.
Timber Frame
Old timber-framed buildings rely on lime-rendered or lime-plastered infill panels and breathable finishes. If these are replaced with modern gypsum plasters or cement renders, the reduced breathability can lead to timber decay from trapped moisture.
Traditional buildings used lime-based mortars and finishes for good reason. Lime is a flexible, vapour-permeable material that accommodates small movements and allows moisture to travel through the wall structure and evaporate harmlessly. These finishes are designed to:
Lime plaster inside the home performs a similar role: helping regulate internal humidity by absorbing excess moisture and releasing it slowly when the air is drier.
Damp-Proof Courses and Membranes: A Modern Invention
Many traditional buildings never had a DPC, and that doesn’t make them defective. They were designed to tolerate a degree of moisture and manage it through permeability. As long as the construction materials remain breathable, the walls can take in and release moisture in a balanced cycle without harm.
Problems start when impermeable modern materials are introduced into a breathable structure. These can disrupt the natural moisture cycle and cause damp-related damage.
When lime mortar is replaced with a harder, dense sand-and-cement mix:
Dense cement renders applied to the external face of traditionally built walls trap any absorbed moisture inside the structure. This often results in:
Modern gypsum plasters are too rigid and impermeable to cope with the dynamic moisture levels in traditional walls. They can crack, blow off, or become discoloured when used inappropriately on older buildings.
It’s important to remember that some traditional buildings that have had modern materials added may not show immediate signs of damage. In these situations, monitoring may be a good alternative to costly immediate interventions. You can track wall and air moisture levels over time using:
This evidence-led approach allows you to delay major works until re-rendering, plastering, or repointing is needed anyway - and to do them sympathetically when the time comes.
Even a well-maintained traditional building will carry some moisture. What matters is how that moisture is managed. You can help by:
Traditional buildings were designed to function as systems - with breathable materials that manage moisture naturally. When we interfere with that system by adding hard, impermeable modern materials, we can cause more harm than good.
Understanding vapour permeability - and respecting the role of lime-based materials -is essential for anyone maintaining, repairing, or retrofitting a traditional home. With thoughtful materials choices and a focus on moisture movement, these buildings can remain healthy and durable for centuries to come.
Many of the traditional buildings across North Devon are located within conservation areas or are listed buildings, meaning there are legal protections in place that control what types of work can be carried out. These heritage properties often feature materials and construction techniques that are completely different from modern building methods - and they require a sympathetic approach to inspection, maintenance, and repair. In areas like Barnstaple, Bideford, and Clovelly, it's not unusual to find cob walls, lime-washed stone, or timber framing concealed behind modern alterations. Understanding the significance of these original elements is key to preserving their long-term value and character.
At Nova Surveyors, our lead surveyor Shaun Watts is a Certified Historic Building Professional and acts as an assessor for the RICS and ICE Conservation Accreditation Schemes. This expertise ensures we can provide sound advice on working with traditional materials, and where necessary, help guide repairs in line with best conservation practices. Whether you're maintaining a listed cottage or planning upgrades to a property in a conservation area, we can help you avoid common pitfalls that lead to damp, decay, or enforcement issues - while ensuring your work remains compliant with heritage and planning requirements.