What airtightness conditions are needed to meet the regulations?

Airtightness is defined as the result of having a protective system that prevents the passage of water in liquid or vapor form through a construction or any of its exterior enclosures. Therefore, to achieve that a room or a complete building is airtight, a surface must be created through which rainwater does not enter the interior of the building. When these conditions are given, it must be taken into account that the building will no longer be ventilated spontaneously, through infiltrations that may appear in the exterior envelope. Therefore, a hybrid or mechanical ventilation system must be installed to ensure the quality of the indoor air.

The Technical Building Code hereinafter referred to as C.T.E., in its Basic Document HS. "Health", outlines the requirements related to the degree of airtightness that must have walls, floors, facades, and roofs..

• Walls: the degree of impermeability of a wall is defined in the CTE based on two factors: the presence of water and the soil permeability coefficient. The presence of water can be:
  • Low: when the underside of the floor in contact with the ground is above the water table.
  • Medium: when the underside of the floor in contact with the ground is at the same depth as the water table or less than two meters below it.
  • High: when the underside of the floor in contact with the ground is two or more meters below the water table.

• Floors: C.T.E. requires a minimum degree of impermeability (from grade 1 to grade 5) for floors that are in contact with the ground against the penetration of water and runoff that may occur within it, as reflected in the following table:

• Facades: the minimum degree of impermeability required for facades against precipitation penetration is set in the C.T.E. based on the rainfall zone, geographical area, and the wind exposure degree corresponding to the location of the building. This last varies according to the height of the building's crown above the ground, the corresponding wind zone at the location point, and the type of environment in which the building is located: area near the sea, rural area, or urban area.
• Roofs: for the roof of a building to achieve the degree of impermeability required by the C.T.E., it must have the following construction elements:
  • System for forming slopes when the roof is flat or when it is inclined and its supporting structure does not have the slope suitable for the type of protection and waterproofing that is going to be used.
  • Vapor barrier placed below thermal insulation when condensation is anticipated in that element.
  • Thermal insulation.
  • Separation layer under the thermal insulation, the waterproofing layer, or in other locations depending on the type of roof used.
  • Waterproofing layer when the roof is flat or when it is inclined and the slope formation system does not have the minimum required slope.
  • Roofing, when the roof is inclined, unless the waterproofing layer is self-protected.
  • Water drainage system that includes gutters, drains, and overflows.