Many old cob and stone cottages in Cornwall suffer from high internal humidity. While these buildings can be warm and dry, they require careful treatment. Homeowners often invest heavily inmodern damp and mould solutions, only to find them ineffective or even counterproductive.
Impact of Humidity on Heating Efficiency
One significant issue is the impact of high humidity on heating efficiency. Warm air with high humidity releases moisture as it cools, leading to condensation forming on windows and cold walls. This condensation then evaporates, consuming heat energy meant for warming the room.
This phenomenon is further exacerbated by the slow warming of cob and stone walls, which have a high thermal mass.
If cob or stone walls are damp, moisture from them evaporates into the internal living space, leading to further evaporation and heat loss. This can manifest in various ways, such as plaster deterioration and the formation of salt crystals on the plaster surface.
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Impact of Damp Walls on Heating Efficiency
In addition to encouraging the formation of condensation, damp cob and stone walls have a much lower thermal efficiency than dry ones. The higher the moisture content of a wall is, the more readily heat is able to pass through it. The moisture content of a wall can be reduced by addressing any external flaws in the drainage, guttering, weather detailing and finishes. This is a more effective long term approach than retrofitting insulation internally.
Choose a Breathable Finish
Breathable finishes like lime and clay offer a valuable solution. Externally, they allow walls to shed excess moisture to the outside, preventing excessive internal dampness. Internally, they provide moisture mass, effectively absorbing and releasing moisture vapor to regulate humidity levels. This inherent moisture-absorbing property also reduces the likelihood of condensation forming on these finishes.
It's crucial to remember that breathable finishes are just one part of the solution. Proper weatherproofing, drainage, and rainwater goods are equally important.
To effectively address these issues and improve your home's thermal performance, an assessment by an experienced building surveyor specialising in historic properties, such as Muddy Mortars, is highly recommended.
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