Thermal Bridging

Thermal bridging is the term used when there is a break in the continuity of the insulation layer; heat loss occurs through this gap and may increase the likelihood of condensation.

There are two types of thermal bridging:

Repeating thermal bridging (i.e. the joists in an insulated ceiling or the battens in a dry-lined hollow block wall). The indicative U-value tables for floors, walls and roofs contained in this appendix includes provision for this type of repeating thermal bridging when calculating Primary Energy Use and CO~2~ emissions when using the DEAP.
Non-repeating thermal bridging (i.e. around external openings - jambs, heads, sills and thresholds, and junctions between elements - floor/wall and wall/roof junction, etc.). This type of thermal bridging is not taken into account when calculating U-values for floors, external walls and roofs. The use of ACDs will assist in complying with the provisions of TGD L Dwellings 2011 with regard to thermal continuity.

Airtighness

No building is completely air tight; air-tightness is the name given to the level of air permeability given to a building expressed in terms of air leakage. By reducing the amount of heat escape through air leakage, it is possible to reduce the amount of energy consumption, thus eliminating the energy required for the additional heating to compensate loses.

In addition, the warmer air becomes in a dwelling, the greater its ability to carry moisture. If warm air is allowed to escape through unintentional air paths in the building envelope, it may cool in cavities or voids and cause condensation. Issues in air-tightness can cause localized draughts, which in turn may cause discomfort to the occupants.

Air permeability pressure testing of dwellings is a requirement of the Building Regulations 2011 (Amendments to Part L); the use of ACDs will assist in complying with the provisions of TGD L Dwellings 2011 with regard to airtightness.

Thermal Bridging and Airtightness