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Installation and use

What to know before insulating a drywall partition

6 min read · Written by our team · Updated 26 Sept 2026

Gloved hands fitting an insulation slab between the metal studs of a drywall partition, with red sound arcs stopping at the wall.
In short

Insulation in a drywall partition delivers the expected sound insulation only when the whole system is built right: choose a wall system with supporting data, fill the whole face of the cavity without gaps and without packing it too tightly, seal leaks around the wall edges and penetrations, and place outlets correctly. Small mistakes on site can cut the sound insulation a lot.

Before you start: settle the wall system

  • An STC or Rw belongs to the whole wall system. If you need the figure a manufacturer states, use the boards, framing, stud spacing, cavity depth and insulation in those details. See What are STC and Rw
  • Check that the insulation thickness suits the cavity depth
  • If the wall must be fire-rated, follow the tested system and have a qualified designer or installer take responsibility. Substituting materials yourself may mean the wall no longer matches what was tested

Fitting the insulation

  1. Fill the whole face of the cavity — cover the full space between studs with no gaps at the top, bottom or sides. NRC research found that partly filling a cavity works less well than covering its whole face with the same amount of material
  2. Cut to fit — the SCG Cylence ZoundBlock installation guide says to measure and cut the slab slightly larger than the space so it holds itself in place, and to install from the bottom up
  3. Don't over-pack — don't force insulation thicker than the cavity so it pushes on both boards. NRC research notes that overfilling a cavity with fairly dense, rigid material risks sound travelling through the material itself
  4. Stop it slumping — in tall walls or ceilings, fix it as the manufacturer recommends so it doesn't slide and leave gaps later
  5. Look after facings — if the insulation has a film or wrap, such as a moisture barrier, avoid tearing it unnecessarily, and keep the material dry before installation

More on gaps and compression in Gaps and compression in insulation.

Sealing leaks and penetrations

  • Wall perimeter — seal joints between the wall and the floor, ceiling and side walls with acoustical sealant or as the wall system specifies
  • Board joints — tape and finish board joints properly
  • Pipes and cables through the wall — close the gaps around them fully
  • Walls and ceilings — for sound separation between rooms, a wall that stops at the suspended ceiling can let sound go round over it. See Sound transmission and flanking

Outlets and services in the wall

  • Don't place outlet boxes back to back on both sides of the wall. NRC research found that the position of metal outlet boxes can affect a wall's sound insulation
  • Seal around outlet boxes as the designer or wall-system manufacturer recommends

Electrical work must be done by a qualified electrician

Moving outlets, running cables or working near live wiring in the wall must be done by a qualified electrician. This article explains the acoustic principle only; it is not an electrical guide.

Safety during installation

Cutting and handling glass wool or stone wool can irritate the skin, eyes and airways. Wear gloves, long sleeves, eye protection and a dust mask as the manufacturer's safety information advises, and work in a ventilated area. See Is stone wool safe?

Common mistakes

  • Filling only half the cavity, or leaving gaps at the edges
  • Forcing in insulation thicker than the cavity so the boards bulge
  • Not sealing the wall perimeter, or leaving gaps around pipes
  • Outlet boxes placed back to back
  • Building the wall only up to the ceiling and expecting the result of a full-height wall
  • Changing materials or stud spacing from the documented design and still quoting the original STC

For the principles behind this, see Why cavity insulation improves a wall's sound insulation.

See solution: Noise from next door / neighbours

Sources

  • National Research Council Canada — Construction Technology Update No. 1, Control of Sound Transmission through Gypsum Board Walls (Warnock & Quirt, 1997)
  • National Research Council Canada — Construction Technology Update No. 27, Effect of Electrical Outlet Boxes on Sound Isolation of Gypsum Board Walls (Nightingale, Quirt & Sultan, 1999)
  • SCG — SCG Cylence ZoundBlock installation guide
  • USG — Sound Control Manual (perimeter caulking)
  • ROCKWOOL (Thailand) — Safe 'n' Silent Pro data sheet

Related products

Categories and example products for this topic

Sound insulation
  • ROCKWOOL Safe 'n' Silent Pro — Stone wool slab for drywall stud cavities, in four density grades, Pro 330–380
  • SCG Cylence ZoundBlock — 50 mm for galvanised steel framing; 100 mm for timber or structural steel framing
  • ISO NOISE Standard — Glass wool batt in a clear PE bag, 0.60 × 1.20 m, installed in the bag in the stud cavity
  • ISO NOISE Premium — 100% polyester batt in a PE bag, 65 mm, for drywall and ceiling cavities
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