In houses, multiplexes and condo buildings, noise from the floor above or below can be a major disturbance. After all, who wants to hear what the neighbour’s watching on TV, or be subjected to an amateur musician’s practice sessions (with emphasis on the word “amateur”)?
Sound insulation is the solution for anyone who needs peace and quiet to concentrate at home, including students and teleworkers.
Although walls can be a factor in transmitting noise, this article will focus on the issue of improving the sound resistance of floor/ceiling assemblies in existing wood-frame buildings.
Types of noise
What kinds of noise bother you? To effectively curb the decibel level, you first need to define the problem. Experts recognize two types of noise:
Airborne (also called “ambient”) sounds
- These sounds are caused by voices, a ringing telephone, a radio playing, etc.;
- They are transmitted through the air and then through floors and ceilings or openings in vertical building elements;
- Filling cavities using sound-absorbing material, such as fibre insulation, is a proven method of attenuating this kind of noise.
- These sounds are caused by something making direct contact with a surface: a dropped object, a child running, someone walking in high heels, etc.;
- They travel because the impact creates vibrations in the construction elements (like wood joists and beams, for example) that connect walls, floors and ceilings.
Reducing impact sounds in an existing building is a challenging project. The key to success is to decouple construction materials that are connected to each other, i.e., the floor covering, joists, wood furring strips, and ceiling covering. There are two ways to do this:
- On the ceiling side, by installing flexible metal channels, called resilient furring strips, to support the ceiling covering below;
- On the floor side, by installing a resilient subfloor beneath the floor covering.
Successful techniques for better sound absorption
If you want to take action to keep the decibels at the right “level,” here are two effective methods.
A – With removal of the existing ceiling
- Remove the ceiling covering and the wood furring strips from the joists;
- Fill the spaces between the floor joists with glass fibre or cellulose fibre insulation (batt or bulk). Good to know: studies have shown that no type of insulation of this type delivers better sound-absorption performance than the others.
- Install resilient furring strips spaced 24 in. (61 cm) on-centre (o.c.) beneath the floor structure;
- Install two layers of ½ in. (12 mm) Type X gypsum wallboard, screwed to the furring strips, with the second layer joints offsetting the base layer joints by 12 in. (300 mm) or more;
- Apply flexible caulk (acoustic sealant) around the entire edge of the wall/ceiling junction between the two layers of gypsum board.
B – Without demolition
If you want to keep the existing ceiling and improve its sound insulation, you can build an additional ceiling under it. Tests conducted for Canada Mortgage and Housing Corporation (CMHC) have proven the effectiveness of the following method:
- Screw standard 2½ in. (64 mm) metal studs to the wood furring strips of the existing ceiling, spaced at 24 in. (61 cm) o.c.;
- Fill the spaces between the studs with 2½ in. (64 cm) pink glass fibre batt insulation;
- Attach a layer of ½ in. (12 mm) gypsum board to the studs.
What about floors?
Another key to improving sound insulation from one floor to another is rethinking the floor covering.
Acoustic membranes designed for use with “floating” floors, i.e., with no nails or screws connecting the boards to the structure, decouple the materials. This reduces both airborne and impact noise.
- The thicker and denser the membrane, the more sound will be attenuated
- As for the floor finishing, the softer it is, the less impact sound will be conducted.
If you have an issue with noise travelling between floors, the rest is up to you: by implementing the corrective actions suggested here, you’ll find the peace and quiet you’ve been looking for.
Research Project on the Noise Isolation Provided by Floor/Ceiling Assemblies in Wood ConstructionPDF file, MJM Acoustical Consultants Inc. for Canada Mortgage and Housing Corporation (CMHC).