The humidity inside a building can be caused by water infiltration problems or condensation on cold surfaces, such as windows and the inside of the building envelope due to insulation problems or thermal losses or air leaks.

Excessive humidity

The presence of excessive moisture inside a building or inside the structure of the building causes the formation of mold. For this reason, special care must always be taken to prevent or regulate this phenomenon of excessive humidity which can be caused by problems of water infiltration, condensation (inherent to the insulation problem), air through the envelope, inadequate windows or the lack of exhaust fans in the building.

As a precautionary measure, excessive moisture must be avoided at all costs to penetrate the interior of the structure as this moisture affects the integrity of the building materials and may cause premature deterioration of these materials.

Condensation in the attic

© Condensation in the attic

Examples of places where condensation forms

Here are some examples of places where condensation is most commonly formed in buildings that are more prone to excessive moisture and are not built in such a way as to protect the structure against it (such as the lack of steam on the warm side of the insulation]:

  • In older buildings, the presence of high indoor humidity caused by the absence of exhaust fans [combined with low insulation or lack of insulation and steam] ensures that warm, moist air rises to the upper floor through the chimney effect. Then the warm, moist air goes through - without any obstruction - the walls to the outside. As a result, moisture in the air condenses on the cold metal fasteners linking the bricks to the wooden structure. These fasteners, which are usually nails in older buildings, will corrode and detach from the wooden structure. This is why mechanical detachments (called bellies) are found at the top of the brick facings of buildings of the 60 and earlier years. These were not well isolated.
  • In the attic of flat roofs or cathedral, when the roof structure is not ventilated and / or poorly insulated, then the humid air inside penetrates into the cavity of the roof structure and condenses to the interior by touching the cold upper surface of the attic. This causes the degradation of this structure as well as the premature deterioration of the roof covering due to the heat loss - through the roof - and the formation of ice dams on these roofs.
  • The attic that is poorly insulated and poorly ventilated [with air leakage to the attic] can present a condensation problem that affects the wood structure and causes mold formation as well as ice barriers which, in turn, cause water infiltration inwards.
  • If an envelope is poorly executed or if there is no vapor barrier or if insulation is very weak (or poorly distributed), then condensation may occur inside the structure, which will cause premature deterioration of the building envelope.
  • An acrylic exterior cladding that is completely closed at its base - at the junction between this cladding and the foundation walls - may be subject to a condensation problem in the envelope [behind the same cladding]. This will also cause deterioration of the cladding. the wooden structure behind the coating and will cause the presence of mold and fungi.
  • A wet basement due to a non-functional or absent French drain, a problem in the rainwater drainage system, the presence of cracks in the foundations allowing the water to penetrate inwards, all this can cause condensation on the foundation walls (behind the insulation) and thus favor the presence of mold on these walls.
Condensation and mold in the roof structure

© Condensation and mold in the roof structure

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