Extreme impact sound transmission between floors
Recently I have been wondering if the way I built my house in 1978 caused some extreme impact sound transmission issues. The house is 24×36, 2 floors above a walk-out/garage basement foundation set into a hillside.
Basement ceiling has a 36′ steel girder down the middle supported at 12′ and 24′ by columns (stacked 12″ CMU). The first floor joists are SYP 2×10@16″OC with 12′ span and 3/4″ T&G plywood subfloor glued and nailed. Second floor joists are SYP 2×12@24″OC with 12′ span and 3/4″ T&G plywood subfloor glued and nailed. All walls are 2×6@24″. Wall layers (outside->in) are 5/8″ RB&B redwood plywood, 1/2″ CDX sheathing, 2×6 stud, 5/8″ T-111 pine exterior siding used as interior paneling. T111 instead of drywall provided an indestructible interior surface, great when raising children.
The worst problem has been impact noise passing from the first floor 12×24 kitchen/dining space to the directly-above second floor master bedroom. We have no problems with thru-air sound transmission. Loud conversation in the kitchen/dining area is barely audible upstairs. However first floor impact noise is another story. Opening kitchen drawers is heard loudly in the bedroom. A microwave oven buzzing on the kitchen counter can be clearly heard. Even typing on a keyboard on the breakfast counter sounds like a dull rumble above.
A triple 2X12 first floor ceiling beam supports the interior ends of the bedroom floor joists. The beam spans 8′ from an end wall to a 4X6 post, then 4′ more to a load bearing partition. The center of the bedroom floor is directly over the 8′ and 4′ unsupported portions of the beam. The kitchen is U shaped with a breakfast counter located in the space under the 8′ beam span and work counters that wrap two exterior walls.
Severe noise seems to be coupled directly from the kitchen counters and cabinets through the exterior walls or triple 2X12 beam to the bedroom wall and floor surface above. The 2nd floor bedroom has padded carpet but this does little to abate impact noise from the first floor. Walking around in the kitchen/dining area also causes thud noises that are heard and felt above. Usually impact noise is thought of as impact on an upper floor coming though the ceiling of the floor below. We have the opposite problem – impact on the stiff first floor is coupling through walls and beam support post to the second floor walls and floor.
Perhaps the extreme impact sound transmission occurs because the entire house structure and finish is wood. Floor joists are stiff SYP covered with 3/4 plywood. Walls are 5/8 plywood on both sides. Kitchen cabinets are wood screwed firmly to the exterior wall studs and interior T111 plywood. Kitchen counters use 1″ plywood substrate screwed firmly into the cabinet tops. So everything in the second floor bedroom and the kitchen/dining floor below is a single density (wood) and its all joined tightly together.
We have lived with the impact noises but now are planning a master bedroom renovation. If there is any way to reduce the impact noise level I want to consider it. Also we are planning a house addition that will be about 26×26. I want to understand what I did wrong so I dont do the same thing again. For the addition, I could probably clear span the 26′ length with 16″ I-joists. Or I could make it like the existing house with a basement steel girder and first floor load bearing walls/ceiling beams to halve the joist span to 13′. Is one approach less susceptible to impact sound transmission between floors than the other ?
Any comments or advice would be appreciated.