We are putting in a new ceiling in our basement area which is now used as a studio.  We would like to soundproof the basement activity from the upstairs home activity.  My question is, can regular fibreglass be used as soundproofing?  If not, is it possible to purchase a sound proofing type of insulation that we can put in between the basement ceiling and the living room floor?

There are lots of different ways to develop what the construction industry calls a “sound transmission class rating" (STR) between floors or in walls between rooms. Your carpet or vinyl flooring, plywood sub-floor, floor joists and ceiling in the basement all reduce sound transfer. Each component in this assembly is better or less effective at blocking sound than other components in the assembly. For instance, carpets transfer less sound than vinyl flooring. The floor joists readily transmit sound because solid wood is a resonator. To reduce sound transfer, select additional layers of materials that have proven sound blocking abilities. Then, add as many of these materials to the floor assembly as you can afford. Generally, the more layers you add, the better the sound control.

Building technologists have found that one of the best materials for sound control is a 50 mm (1-1/2 inch) concrete topping installed on the top-side of the sub floor in combination with other sound control materials. This is the way designers and builders get such quiet suites in commercial buildings such as hotels and apartment blocks. However, this is not very practical in an existing residence like yours.

So, the most common solution is to do exactly what you propose. Fiberglas insulation is one of the most frequently used “home owner friendly” materials for controlling sound transfer. Install at least R20 Fiberglas insulation between the floor joists in the basement. If you have 2x10 floor joists and you can afford the extra cost, you can increase your STR rating by installing R32 Fiberglas insulation. Don't compress the Fiberglas batts because it is the dead air that breaks the sound transfer. Another great soundproofing material is blown cellulose insulation. This material usually requires an installer with the equipment to "full fill" the joist cavities with cellulose. The blown cellulose is held in place with a fibre-mesh membrane stapled to the underside of the floor joists. Because the cellulose is densely packed when it is forced into the joist cavities under pressure, it will probably achieve better sound control than Fiberglas insulation. However, due to the labour and material costs, blown cellulose will probably be a more expensive solution.

Whether you choose Fiberglas or cellulose, you can still go one step further. After the insulation is installed, you can install sound bar (resilient channels) at 16 inches on centre, across the underside of the floor joists. Then attach your 1/2 inch or 5/8 inch ceiling drywall to the sound bar. The air gap that the sound bar creates between the drywall and the floor joists further reduces sound transfer through the floor joists to the both areas above and below the floor assembly. The thicker the drywall layer, the more you decrease the amount of sound transfer. As mentioned previously, the more layers of material you install the more you reduce sound transfer. For example, some folks install a layer of "donna conna" sound board on the underside of the floor joists, then they re-install the resilient channels and a drywall ceiling. The STR you achieve will be proportionate to the layers of materials you install and the amount you can afford to invest.

Note: Thanks to Max Hoedeman for noting that the Code still permits only one set of winders in a flight of stairs.

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This article was written by Steven Cannon, a Registered Building Official and partner in Lynch Building Inspection Services Ltd. of Nelson, British Columbia. It originally appeared in The Nelson Express.

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