A warm interior in winter is delightful, especially when one has been out in the weather and is coming home. When we began building homes and public buildings, we used stone, earth, and wood, and heated and cooled with fire and fresh air. We used the natural positioning of windows and doors to encourage the use of sunshine and breeze. As we have improved materials and methods of building, we have had to rely less on the naturally occurring weather patterns, and our interior comfort has grown. But with the changes in interior comfort, we have new challenges to address. One of the most significant in the issue of condensation on interior environments during winter.
The temperature of the air influences the amount of moisture the air carries–this is known as relative humidity. Warm air holds more moisture. We are all familiar with the way that air drops moisture as dew, when it changes temperature from night to day. This same process happens in our interior spaces, when cold exterior air is warmed, then again is exposed to cold.
Single paned windows are colder to the touch that the walls around them. The temperature of the air around exterior walls, window frames, and on glass window panes is colder than the air around the fireplace or heater vent. When the warmer air comes in contact with these colder surfaces, the extra humidity is deposited on the colder surfaces in the form of condensation. This extra moisture around painted surfaces, wallpaper, wooden furniture, panelling, and other elements of the interior that are made or natural or organic materials can cause damage, including peeling paint and wallpaper, warping wood, and the growth of dangerous mould.
Newer buildings, including interior and exterior walls and floors, are made with moisture barriers, vapour barriers, damp-proof materials, and double glazed windows. These super-tight environments see a savings of energy use, but also have their challenges, related to the lack of ventilation. Our first buildings, while they tended to be cold in winter, had a healthy amount of sunshine and ventilation, important to reduce the damaging effects of condensation on the interior health of our spaces.
No one wants to give up heating in winter, or the glorious hot water in indoor baths that puts so much moisture into the winter home. But we also do not want to allow our furniture to be affected or the wallpaper to peel. Several things can be done to improve the relative humidity of the interior, and to reduce the effects of condensation.
Baths and kitchens should have extractor fans of some sort that vent damp air, and fans in the interior space can improve ventilation overall. A careful assessment of areas around exterior doors and window frames is critical, as these are areas that may first see the collection of moisture and damage. Curtains may provide some measure of insulation in front of glass windows. Metal-clad windows are usually the first part of an interior to collect extra condensation.
Basements and foundations should be assessed for damp, and if needed, retrofitting of moisture barriers can be done. A restoration or conservation specialist should assess carefully the condition of raised flooring over a stone or brick subflooring, as these areas are well known for gathering condensation during winter and harbouring mould growth. Retrofitting of insulation in attics and walls includes some new materials and methods, such as blown-in insulation, that does not require extensive renovation.
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