Humidity inside a building can be caused by water infiltration problems or by condensation on cold surfaces, such as windows and the inside of the building envelope due to insulation problems, heat loss, or air leaks.
Excessive humidity
Excessive humidity inside a building or within its structure leads to mold growth . Therefore, it is crucial to take steps to prevent or address this excessive humidity, which can be caused by water infiltration, condensation (related to insulation problems ) , air leaks through the building envelope, inadequate windows, or a lack of exhaust fans.
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.
Examples of places where condensation forms:
The following are some examples of where condensation most commonly forms in buildings that are more prone to excessive moisture and are not constructed to protect the structure from it [such as the absence of a barrier. steam from the hot side of the insulation]:
1. In older buildings, high humidity levels inside, caused by the lack of exhaust fans (combined with poor insulation or the absence of insulation and a vapor barrier), cause warm, humid air to rise to the upper floor through the stack effect . This warm, humid air then passes unimpeded through the walls to the outside. Consequently, the moisture in the air condenses on the cold metal fasteners that connect the bricks to the timber frame. These fasteners, which are usually nails in older buildings, will corrode and detach from the timber frame. This is why we find mechanical detachments (called "bellies") at the top of the brickwork on buildings from the 60s and earlier. These buildings were not well insulated.
2- In the attic of flat or cathedral roofs, when the roof structure is not ventilated and/or poorly insulated, then the humid air inside enters the cavity of the roof structure and condenses inside. inside by touching the cold upper surface of the attic. This causes the degradation of this structure as well as the premature deterioration of roof coverings due to heat loss – through the roof – and the formation of ice dams on these roofs.
3- The attic that is poorly insulated and poorly ventilated [with air leaks to the attic] may have a condensation problem that affects the wooden structure and causes the formation of mold as well as ice barriers which, to their tower, cause water to seep inwards.
4- If an envelope is poorly executed or if there is no vapor barrier or if insulation is very weak (or badly distributed), then condensation can arrive inside the structure, which will lead to premature deterioration of the building envelope.
5- An exterior acrylic cladding that is totally closed at its base – at the junction between this cladding and the foundation walls – may be subject to a problem of condensation in the envelope [behind this same cladding]. This will also cause the deterioration of the wooden structure behind the coating and will cause the presence of mold and fungus.
6- 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 water to penetrate inwards, all this can cause condensation on the foundation walls (behind the insulation) and thus promote the presence of mold on these walls.
Condensation and mold in the roof structure