I going to build a kids playroom in a third floor attic area. The floor joists are 2×6’s, spaced 16″OC. The roof rafters are 2x8s. There are currently 4 dormers already installed but covered up by the roof rafters. The area is appx. 38’x24′ We plan to use the existing slope of the roof for a vaulted ceiling giving us 14′ at the center peak. Permits are pulled so no short cuts anywhere. I am a residential remodeler.
This is going to be a high use, gymnasium type of room for 5 active kids. A key concern I have is to install the right soundproof and impact friendly floor. I don’t want the entire house to develop cracks or have it sound like a herd of elephants are up there. The house is a saltbox design with a bonus room over the garage. It is about 12 years old and very well constructed.
From your experience, what do you recommend for a floor?
Replies
First off, there is no such thing as soundproof.
The greatest single thing you can do to help with impact noise is to install deep carpet over a good quality (relatively dense) 1/2" thick pad.
The limitations most often encountered are money to spend and thickness of the floor system.
A good sound attenuating floor would be, from the ceiling up: Two layers of 5/8" drywall with Green Glue between them, your floor joists with R-13 batt or loose fill insulation between them (fiberglass or cellulose), 3/4" t&g subfloor, glued and nailed/screwed to joists, second layer of 3/4" subfloor set in Green Glue over the first, all joints staggered, also fastened to joists (screws are better for second layer), dense pad, thick carpet.
The above sandwich adds 1-1/2" to the thickness of a much cheaper system, and half the thickness is in each level, i.e., half upstairs and half in the room below. (The cheaper system is single 1/2" drywall and single 3/4" subfloor.)
If drywall is already there, the second layer with the Green Glue is the part that makes the big difference. Ditto with the subfloor.
If you've got more money and more headroom upstairs to play with, there are ways to get better performance, but they are a lot more work than what I described, which will give very satisfactory performance and is more error-tolerant than some methods are.
Bill
So what is the span on the 2x6 joists? 12'?
Hi Barry, the span of the floor joists are 12' overlapping on a load bearing wall running the width of the house in the center.
Were there rooms up there before? How old is the house? The joists seem a little undersized for what you are intending. I'd probably be worried about the kids bouncing on them besides the sound issue.
Barry E-Remodeler
There were no previous rooms in the attic. It is an unfinished area. Yes, I am concerned about the floor joist size. If we do have to add additional support, I got a neat reply advising me to install new floor joists, independant of the existing joists, thereby isolating sound and impact transmission from the floor to the walls and areas below.
The idea of the estrapping is to isolate the ceiling from the joists, but since it is probably finished below, the secondary separated joist system is the better idea especially since 2x6 would not do well as floor joists
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I believe the new independent joists would have to be installed in such a way that they are shimmed up so the bottom of the new floor joist does not have contact with the ceiling below, and the top of the new floor joist is higher than the top of your existing floor joists so the subfloor is off of the existing floor joists. Breaking up the contact of finish floor above from finish ceiling below in addition to insulating the cavity should baffle the noise transmission.
Did largely the same thing a couple years ago. No thuds, cracks or complaints.
The largest quantity of sound transmission will come from the direct transmission of impact to the ceiling below. Sistering new joists to the old to handle the new loads will turn your 2nd floor ceiling into a diaphragm when the kids jump almost regardless of how thick you go.
The best thing we did that resulted in a quiet floor was to use entirely new floor joists independent from the celing below. We needed new joists anyway for the loads, so the extra work in slotting them in between the existing ceiling wasn't too great.
You didn't mention spans or supporting wall information, so all normal structural requirements will still apply.
Obviously, padding, choice of floor, etc. will also have an impact. In our case we went with hardwood floors throughout and area rugs in the kids area. Cathedral ceilings tend to make a room pretty 'live' in terms of acoustics, so add as much fabric to the room as you can when doing the interior design.
Excellent advice. Thanks also for bringing to my attention the sound generated from a vaulted ceiling.
You're welcome.
As I see your existing joists overlap on the center wall, any new floor joist system would need to be acoustically isolated from this point to minimize the vibrations.
Given that going with full 24' spanning joists is probably overkill and prohibitive on several fronts, you might consider some type of rubber bushing/pad such as are used in home theater installations. Just a thought... have fun.
Edited 2/18/2007 7:30 pm ET by Thaumaturge
Homasote makes some structural underlayment that has impact-deadening properties. Try their website.
Best is to use strapping under the floor joists to hang the ceiling below, then sandwhich homasote between plywood and plywood on the floor above and carpet - thick padded on the floor
I'm not sure what you mean about the dormers being covered with rafters though ...???
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When the home was built, the roof rafters were installed as they normally would be. As an afterthought, I surmise, they then installed 4 dormers each fully framed out with functioning windows. There is a rafter that runs the full length from the eave to the top of the attic through the center of each dormer opening that we'll have to cut out and brace. I suppose the builder did'nt bother to finish the dormers since they were in a attic.
Probably intended only as dummy dormers then. You'll have to double up the rafters they sit on and let in headers if you cut rafters out.
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I love this forum. You're 100% right. Thanks.
Here is some more info.http://www.soundproofing.org/infopages/channel.htm