Factors that compromise insulation

Moisture

With an airtight building, consideration also must be made to appropriate ventilation and moisture control. Excessive humidity and/or condensation can be significant issues. Excessive moisture (or invisible humidity) can rot construction materials and/or encourage microbial growth eg. mold, bacteria. Moisture can also drastically reduce the effectiveness of insulation by creating a thermal bridge. Damp materials may lose most of their insulating properties. The choice of insulation often depends on the means used to manage moisture and condensation on one side or the other of the thermal insulator.

Thermal bridge

Thermal bridges are points in the building envelope that allow heat conduction to occur. Since heat flows through the path of least resistance, thermal bridges can contribute to poor energy performance. A thermal bridge is created when materials that are poor insulators come into contact. Wood and rubber are poor insulators - thus heat can flow through joists and studs.

Poor construction technique can create thermal bridges or areas which are inaccessible to further insulation. When bulk insulation becomes wet it acts as conductor rather than an insulator of heat, and can therefore also form a thermal bridge. Incorporating inaccessible voids within the wall cavity which do not allow the interposition of insulation can be another source of thermal bridging.

Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging. The bridging has to be rebuilt with smaller or more insulative materials. A common example of this is an insulated wall which has a layer of rigid insulating material between the studs and the finish layer.