Airtightness is essential to prevent heat loss via the fabric of the building and maximise the effectiveness of thermal insulation thus reducing energy consumption. For example, an 80m2 house with poor airtightness requires the same energy to heat as a 400m2 house with the same thickness of thermal insulation, but which has a very high standard of airtightness.
Air tightness must be incorporated into the building at design stage. Trades such as plasters, electricians and plumbers need training as the concept of airtightness is new to most sites. Block and mortar are not airtight, neither is plasterboard and skim. Sand cement plaster is airtight. Around the ends of first floor joists air tightness is difficult. The best method of addressing this is ensuring you build your home with Campion Insulated Concrete Panels.
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Many people are aware of draughts coming from recessed lights. Normally this cold air is coming from the cavity – and it is costing you money and comfort.
When we talk of air tightness, what we’re essentially speaking about is the elimination of draughts. In other words when we want fresh air, we open a window or slide the cover of a vent across, and we have the fresh air that we want. Draughty buildings provide fresh air whether we want it or not. In winter when ambient external temperatures may be only three or four degrees and we like to relax indoors in temperatures around twenty degrees, we end up footing the bill for warming-up any incoming air. The less cold air that we have to heat the better – so air tightness or air control saves money. Airtight buildings offer another economic benefit – they don’t let much warm air escape either
When we blow up a balloon we create what we call a static pressure inside it. If we then form an opening at the valve which is tiny compared to the surface area of the balloon then all the air will escape very quickly at high velocity,” explains McHugh. “Now if the wind blows against the side of our house, a similar kind of static pressure builds up. Any small openings which exist in the building, such as around window frames, pipes, and so on, will allow air through, in the form of draughts
Air Leakage (or infiltration) is the flow of outside air into and out of a building. It is not planned by the designers and is due to imperfections in the building ‘envelope’ (or outer skin).
It will typically take place through:
- joints, gaps and cracks in the construction
- gaps created where the structure penetrates the outer skin of the building
- cracks around door and window openings
- gaps where services enter the building
Air leakage will have detrimental effects on the buildings thermal performance, comfort levels and energy efficiency.
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