Interior window condensation is caused by excessive moisture in the house. It is usually caused by performing daily routines such as: cooking, showering, drying laundry or periodical activities like construction works is. Just by breathing one man produce approximately 2.5 l of fluid.

Today, after the introduction of energy saving measures such as draught proofing, double glazing and cavity wall insulation there is no natural escape route for this stale, humid air, which is now trapped inside the home. As a result, this trapped and stale air, causing condensation on windows, walls and poor indoor air quality.

The collected moisture can corrode steel, rot wood and allow mold growth. Condensation control is an important factor in the success and durability of buildings. Because mold spores and suitable nutrients (cellulose) are virtually always present in dust all that is required to cause mold growth in a building is a sufficient amount of moisture in the micro climate in which the spores exist. Unseen mold can grow out of control, causing indoor air quality problems and negative health impacts for building occupants.

The mold begins to grow on cold surfaces. Surface temperatures must therefore be kept above the mold (critical) temperature. It can be reached by worming up cold surfaces.

The typical example of cold surface appearance is the thermal bridge also known as cold bridges or heat bridges. Thermal bridging generally occur when there is a break in, or penetration of the building envelope (e.g. insulation). Thermal bridges can be caused by:

  • The junctions between the wall and floor (e.g. terrace)
  • The junctions between the wall and roof
  • Holes in the building envelope for pipes and cables
  • Window and door reveals

Example of thermal bridge is shown on the picture below.

The inside wall insulation has break so the coldness is transferred to the interior as a result of that is cold surface in that area. External wall insulation systems can be extremely effective at minimizing cold bridging as is shown on the picture.