Finishing Basement: Insulation between 1st floor

Old 04-28-13, 10:30 AM
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Finishing Basement: Insulation between 1st floor

I'm finishing off my basement and was planning on using some standard fiberglass insulation between the basement and the 1st floor for both sound deadening and insulation for the basement.

My question is, is this standard practice and is one layer of insulation for 2x4 walls enough or should I go with product made for 2x6 walls or maybe two applications for 2x4 walls?
Old 04-28-13, 10:45 AM
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Fiberglas will be "iffy" for sound suppression. Without decoupling the ceiling from the joisting, your best bet would be something like Roxul. A little more expensive than fiberglas, but denser and a better R rating per inch.
Old 04-28-13, 01:30 PM
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Unless you're not heating the basement, there's no reason to insulate. I'm not talking about sound transmission here, just want to make sure you understand what you're getting out of this.
Old 05-16-13, 12:37 PM
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Hi, Brubakes, I’m Dave Wolf – senior research and development program leader at ********. My passion is building science, and I’ve worked on extensive air sealing research throughout my career, so just wanted to see if I could offer some help.

Mitch17 – you make a good point, which I wanted to elaborate on. It doesn’t seem like there is a reason to deter heat, so installing insulation would be purely for sound reduction. Sound will pass to/from the basement through the floor in two ways: 1) pressure fluctuations inside the cavity, which fiberglass insulation will do a great job of dampening, and 2) vibration through floor joists, which no type of insulation can notably minimize.

For the floor cavity insulation, we’d recommend installing R-19 fiberglass insulation (typically used for 2x6 walls), because this thicker product will address a wider frequency (longer amplitude) of noise waves than would the thinner R-13 product. This will help sound reduction throughout your basement.

If you haven’t drywalled the ceiling yet, you may also want to add a thin gasket-like material between the bottom of the floor joists and the drywall to dampen structure-borne vibrations. We have a product called F******R that can be used for this purpose. This product is a sill gasket and is designed to stop air leakage between the sill plate and the foundation, but it would also work in your noise control application. It typically comes in a 5-1/2” wide roll, which you would need to cut down to about 1-1/2” wide strips for placement on the bottom side of the floor joist. It can be fastened with staples until the drywall is eventually installed.

I hope that helps.

Last edited by chandler; 05-16-13 at 01:24 PM. Reason: Remove advertising
Old 05-16-13, 01:25 PM
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Mineral wool is superior to fiberglass for sound deadening, but more expensive. If you want to go with the less expensive fiberglass, I would definitely use the R-19 batts, as Dave suggested. With either material, they can, and probably should, be unfaced - you don't need any moisture barrier in this application.

I'm not convinced that installing any buffer between the joists and the drywall will help. Drywall attached to the framing will transmit vibration coming through the framing regardless. Maybe Dave is thinking the resilient material would help dampen the amplification?

I would install a suspended ceiling, as Chandler suggested - even if it was a suspended frame for screwing drywall to.
Old 05-18-13, 08:01 PM
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Oops, hope this isn't too late for the original poster... here is an answer to a similar question I just gave;

Roxul STC 52;

Fiberglass STC 50, #10- 5/8"GWB each side; 1/2" GWB is STC 46.

Compare different thickness changes of insulation only in same stud configuration; pp.15 and pp.17;

Density is a biggie;


If a techie; Research Highlight 2000-109 Summary Report For Consortium On Fire Resistance And Sound Insulation Of Floors: Sound Transmission Class And Impact Insulation Class Results (CMHC Canada Mortgage and Housing Corporation)

Resilient channels = 4-7 STC improvement, neoprene isolators = 8-11, pp.3;

Last, but not least, lol; Georgia-Pacific HushBoard Sound Deadening Board


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