The objective: Prevent unwanted sound from entering the apartment from the unit next door through the shared party wall in the stairwell. The crew starts by protecting the existing finished wood stair treads with cardboard, paper, and tape, then proceeds to remove the drywall from the party wall.
Soundproofing an existing stairwell involves some special constraints. Removing the skirt board for the stair treads is beyond the scope of this job. So the crew has to leave the skirt board, and the drywall behind it, in place — where it will continue to transmit vibrations through the wall. It’s important to inform clients that some sound may still be heard through this solid point of contact with the neighboring unit. This wall could have been soundproofed more effectively, and far less expensively, had the work been done during the original construction instead of as a retrofit, says contractor Joseph Drago.
Working carefully to avoid damaging an existing water pipe in the wall, the crew removes low-density, open-cell, spray-applied polyurethane insulation from the existing party wall. Open-cell foam transmits sound less readily than high-density closed-cell spray foam, but rock wool fiber performs better than either, so this wall will be re-insulated with special sound-absorbing rock wool.
The existing low-density polyurethane foam insulation can be readily pulled out by hand. The crew puts it in plastic bags and takes it out to a dumpster.
After re-insulating the wall with rock wool fiber, the crew applies sound-blocking mass-loaded sheet vinyl ( Sound Barrier HD) to the studs. Intentionally designed to be soft and massive, the vinyl weighs upwards of 120 pounds per roll. It’s a struggle for a three-man crew to maneuver the heavy rolls into position on site and install the material in the tight quarters of an existing stairwell.
The crew unrolls the mass-loaded sheet vinyl vertically, working along the wall. Joints are positioned between studs (within the stud bays), so that overlaps won’t create a bulge in the wall when drywall is applied.
The low man has to do some heavy lifting, supporting the weight of the roll of sound-deadening sheet vinyl while the men on the staging above position and fasten the material at the top of the wall.
The crew fastens the Sound Barrier HD to the wall studs using a coil nailer loaded with one-inch roofing nails.
The crew seals joints in the sound-deadening vinyl using a 1/16th-inch tape made of the same material, with a polyvinyl acetate (PVA) adhesive. Sealing the joints is critical to the performance of the system: it prevents sound from bypassing the sound-absorbing material through air gaps between the sheets.
The crew measures a drop beam in the ceiling. The sound-deadening material has to be cut to fit any irregularities where the wall meets the ceiling.
The sheet vinyl cuts easily with a razor knife. The technique is to score one face of the material with the knife …
The crew nails the last piece of vinyl into place. After this, a drywall contractor will come on site to re-apply drywall to the wall.