THERMAL BYPASSING

Thermal bypassing is complex and is often confused with airtightness. A thermal bypass occurs where air is allowed to move through, around and between the insulation, in effect bypassing the benefit of the insulation. Therefore, it is possible to have a very airtight house but still have thermal bypassing resulting in lower thermal performance. The important issue in relation to thermal bypassing is the location of the thermal insulation and its relationship with the air barrier. Where there is separation of the thermal insulation from the air barrier, then a thermal bypass can exist. The air barrier and the thermal insulation should always be in the same plane and be in contact with one another.

Thus, by constructing a building with a high level of airtightness and ensuring that the air barrier is kept in contact with the thermal insulation layer, thermal bypassing can be effectively eliminated from the structure. This can significantly reduce actual space heating requirements, bringing realised dwelling emissions far closer to design values than is routinely observed.

Material contained in this section will include:

• Selection of insulation material
• Thermal mass
• Thermal bypasses
• Sequencing of construction processes
• Placing of insulation
• Continuity of the insulation layer
• Buildability