Insulation atlas/Detail · double leaf
A double wall wins if the cavity stays a cavity. A bridge turns it back into one wall.
The rough mass law: doubling the mass of a single leaf adds about 6 dB, until coincidence appears. A cavity goes beyond that if it is not tied.
What kills the cavity
Two light leaves with an air cavity behave better than one heavy leaf of the same total mass when they are separated: independent studs or a resilient channel, a porous quilt in the cavity to damp resonance, and no screw that reaches both faces. A continuous screw, a single metal stud, a floor that runs under the wall, and a ceiling that runs over it are all bridges. The double wall’s natural resonance is pushed below the speech range by heavier leaves or a wider cavity. If the resonance stays in the middle of speech, the sentence is heard despite a good figure on paper.
The quilt in the cavity is not the room absorber in the catalogue. It is a detail of the wall build. A class A ceiling panel is not used instead of it, and its figure is not pasted onto an Rw line.
Elsewhere in the atlas
- Detail · floating floorA floating floor is mass on a resilient layer. One rigid point is enough to spoil it.
- Detail · penetrationsA small hole puts a ceiling on the insulation of a large wall. The rough rule is known before the measurement.
- Detail · junctionsA good wall loses where it meets the floor, the ceiling and the façade.