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Heat Moisture & Air Movement

Precise, predictable performance – engineered to exceed Building Regulations

Building science is all about understanding how various elements of a building are impacted by the movement of heat, moisture and air within. An appreciation of the fundamental principles of this very complex subject is usually enough to demonstrate how closed timber panel construction overcomes many of the environmental and structural issues inherent in other forms of building.

heatmoves1Conduction, convection and radiation

Heat moves via conduction (through materials), convection (warm air rising, replaced by cool air), and radiation (by heat-producing sunshine).

The rate of heat lost in a house is determined by the temperature difference from the outside, the surface area of the building, air leakage and thermal resistance (insulation).

Warm air is buoyant, and warm air will rise, meaning extra insulation should be placed at the ceiling or roof.

Also, warm air holds more moisture than cooler air. There is more moisture in a warm house than the cool outside, which means water vapour will try to move to the outside unless a vapour barrier is installed. When warm air contacts a cool surface, there will be condensation.

heatmoves4There doesn’t have to be a leak for moisture to get into a wall. A pressure difference can cause moisture to move into walls. Because warm air holds more moisture than cooler air, there is a higher concentration of water vapour in the warm inside air than the cooler outside air. Particles in an area of high concentration will move to an area of lower concentration, and will move right through vapour permeable materials, including building materials.

Air movement

Wind is simply moving air, and wind blowing on a building’s surface will create a positive pressure. There will be an equal negative pressure on the leeward side of the house.heatmoves3