Ventilation and its role in a dry home

Historic buildings weren't likely to have been built damp. If they were the timbers would have rotted and the building would have fallen down years ago. Many historic buildings have survived centuries and yet significant timber decay can be observed over decades. So why are some so damp now?

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An often overlooked aspect of old buildings was the extensive trickle ventilation. Consider that all windows and doors likely had some degree of draught and fireplaces were not only open, they were in constant use. This provides dry heat and enormous amounts of ventilation up the chimney.  Compare that with a house that has sealed up fireplaces and modern UPVC windows and doors. The old house has become airtight. The problem is that the house has also been modernised with moisture producing shower, kettle, hot water taps, washing machine and tumble dryer. Combine all of this with what are often comparatively cold (compared to the inner leaf of a cavity wall) solid walls and you have a recipe for condensation.

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Houses need to be ventilated. Fix the root of the problem. The moisture. They also need to be heated constantly at a low temperature. Solid walled buildings act like storage heaters. They have a high specific heat capacity and low thermal conductivity. They take a long time to warm up and cool down. Heating the walls intermittently won't give them time to warm up, meaning a cold wall and increased chances of condensation. 

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Strategies for Effective Ventilation in Historic Buildings

1. Understanding the Building’s Original Ventilation System: Assess how the building was originally designed to ventilate. Restoring or adapting these systems can often provide effective, non-intrusive ventilation.

2. Controlled Ventilation: Installing controlled ventilation systems like extractor fans in kitchens and bathrooms can help remove moisture at the source. Care should be taken to ensure that these systems are sympathetic to the building’s aesthetics and structural integrity.

3. Use of Dehumidifiers: In areas where humidity levels are particularly high, dehumidifiers can be an effective solution. However, they should be used judiciously to avoid excessively dry conditions that can be just as harmful.

4. Sympathetic Upgrades: When upgrading windows or doors, consider options that maintain a degree of natural ventilation. For instance, windows designed with trickle vents can provide a balance between modern efficiency and traditional airflow.

5. Regular Maintenance: Regularly check and maintain ventilation pathways. This includes cleaning vents, chimneys, and ensuring that any modern installations are functioning correctly.