Air Tightness

This is a new concept to building. To achieve the legal requirement a house should test less than 10m³/(hr/m²) at 50 pascals. This is the very basic standard. Aim to achieve 1.0m³/(hr/m²) or less. Why try? It is now a legal requirement but even more importantly it makes a major improvement to the energy performance of the building.

The performance of the first “airtight houses” I was involved with shocked me. When good airtightness was added to good thermal insulation the heat demand was massively reduced and the comfort greatly improved. How about a 420m² house being heated with wood chip for €270 per year?

Air tightness 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.

Airtightness must be incorporated into the building at design stage. Trades such as plasterers, 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 to wrap them with “Solitex” at building stage. Where slabs are used the plaster must be taken up to the bottom of the slab and the joint between the slab and the wall sealed with plaster. 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.

Testing a house for airtightness is done by reducing the air pressure in the house by 50 pascals. This is equivalent to a 40 kph wind speed outside. Then the technician simply checks around skirting boards, windows, doors and other openings for air coming in. The amount of air escaping from a 13 amp socket will shock you. This is coming via the conduit. The electrician should seal the ends of conduits. Traditionally sealing around the waste pipe at the kitchen sink was unimportant as it was hidden by the kitchen units. Now this is very important as it is very difficult to improve at testing stage.