Insulation atlas/The envelope
Wall, floor, door, glass: the shell equals its weakest opening.
A calculation that repeats on every project: a 55 dB element beside a 30 dB element is heard close to 30 if the opening is not very small.
Walls
A 200 mm concrete wall often sits in the mid-fifties Rw if it is solid and unpierced. A single gypsum wall with one 12.5 mm layer each side approaches 40 if it is built without bridges, and falls if it is tied to a rigid channel or a pipe is run through it. A decoupled double wall — double studs, or a resilient bar that is not shorted by the wrong screws — with two layers and a cavity fill, is the road toward 60. The detail is drawn in section, not as the sentence ‘soundproof’.
Floors and impact
A heavy slab raises airborne insulation. Impact needs a break: a resilient layer under a floating floor, and a perimeter strip that stops the screed touching the wall. One mortar bridge at the edge brings the knocking back. Carpet improves light impact and is not written as a substitute for a floating floor under a gym.
Doors and glass
An acoustic door is a set: leaf, frame, hinges that do not twist the seal, threshold, and drop seal. The figure printed on the leaf is not the figure of the installed opening. Single glass meets a coincidence dip; unequal double glass with a 50–100 mm cavity goes further for a façade towards a stadium or a street. A continuous aluminium frame without a thermal break can be the bridge.
- Do not average the wall’s Rw with the door’s Rw. Combine them by energy, or measure the opening.
- Every penetration — pipe, cable tray, duct — is closed to the density of the element it pierced.
Rough orders of magnitude from industry literature, for guidance before a system is chosen on its own data. The spread is wide.
| Element | Approximate Rw order |
|---|---|
| Solid door, no seals | About 20–27 |
| Acoustic doorset, well fitted | About 37–45 |
| Single 10 mm glass | About 33–36 |
| Unequal double glass, wide cavity | About 45–52 if the frame is closed |
| Single stud, one layer each side | About 38–45 |
| Decoupled double wall, two layers and fill | About 55–65 |
| Solid concrete 200 mm | Mid-fifties |