Alteration of acoustic treatment for condensation control

Part 4: A slight alteration in the concept involves adding an air gap behind the porous absorber while maintaining identical effectiveness

Acoustic Treatment Alteration

The initial approach in Vintage ES Theater II to address acoustic treatment involved incorporating 15 cm of built-in house insulation and supplementing it with an additional 45 cm on walls facing outward. However, the manufacturer’s calculations indicated that adding such a thick insulation layer might lead to condensation issues.

Within the standard external walls, a built-in vapor barrier (6) regulates water vapor diffusion within the structure and acts as an airtight plane. To ensure effective water vapor diffusion, it is necessary to place the barrier in the warm section of the construction.

Adding an extra 45 cm of thermal insulation on the inner side results in the barrier being placed in the outer half of the thermal insulation, potentially causing condensation on a vapor barrier.

The solution? Ensuring a 10 cm gap around acoustic absorbers (filled with insulation) to facilitate sufficient air circulation and mitigate potential moisture problems. This would entail a minor alteration in the design but would also lead to the purchase of less insulation, given that air proves to be nearly as effective in terms of absorption. See the Calculator.

Porous Calculator Absorbers Comparison



Parameters Absorber with air gap Absorber without air gap
Layer 1 thickness 350 mm 450 mm
Air gap 100 mm 0 mm
Layer 2 thickness 150 mm 150 mm
Flow resistivity 5000 Pa.s/m2 5000 Pa.s/m2
Absorption @ 20 Hz 0.384 0.403
Absorption @ 40 Hz 0.613 0.602
Absorption @ 50 Hz 0.662 0.646
Absorption @ 70 Hz 0.718 0.700
Angle of incidence
Porous model Allard and Champoux  Allard and Champoux

Acoustic Treatment Air Circulation


  • 3 Facade insulation, rockwoll (140 mm)
  • 4 OSB board (15 mm)
  • 5 Thermal/acoustic insulation, Knauf NaturBoard FIT rockwoll, (160 mm)
  • 6 Vapor barrier (0.2 mm)
  • 9 Air gap for ventilation (100 mm)
  • a Acoustic absorber w. mineral wool (350 mm)