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1 b 31S 63 125 250 BOO Ik 2 k 4 k THIRD OCTAVE BAND CENTER FREQUENCY, Hz

Figure 12.26 Separately Supported Wood Floor

Figure 12.26 Separately Supported Wood Floor

2 x H mm (3/A") Plywood Slued and Screwed

33 x IIO mm f2 x 3.) Stepped Mid Span Blocking

ISO mm (b" In,) Batt Insulation

Figure 12.27 Sources of Floor Squeak

Non Bedded Nail

Uneven Joists No Slue

Noise Transmission in Floor Systems 449 Figure 12.28 Truss Joists with Stepped Blocking

Uneven Joists

Nail squeak also can occur in a wood floor when the joists are of an uneven height. In these cases, the diaphragm does not make contact with the top of the joist and, in time, can move up and down on a nail, even one embedded in the joist. These conditions are particularly difficult to locate and remedy after the fact. Liberal application of panel adhesive to the top side of the joist before the plywood is installed will bond the subfloor to the joist and help fill in gaps that may be present. Factory manufactured truss joists can provide a better size consistency, which helps problems due to the variability in lumber. With truss joists, however, it is more difficult to construct stepped blocking since a spacer piece is required to fill the webbing, as illustrated in Fig. 12.28.

Hangers

Squeak can also occur when metal hangers are used to support the joists. In these cases the nails securing the hanger to the joist may rub on the hanger as the joist deflects. If the lumber varies in size, the diaphragm may not make contact with the joist and a gap will result. The best solution in these cases is to shim the joist so the top is even, and to glue the plywood down before nailing. It is preferable to frame the joists on the top plate of the bearing wall rather than being carried on wall-mounted metal hangers.

Nailing

A smooth nail, which does not grip the wood, is more prone to squeak than a ribbed nail. Ribbed or ring shank nails are helpful in preventing squeak since the wood is less likely to move vertically. Floor panel materials fabricated from strands of wood glued together are more prone to squeak than plywood since the high glue content material abrades and leaves a small hole where the nail can rub. Panel screws along with glue can give additional protection against squeak since they grip the wood more firmly. Drywall screws can be used; however, they are thinner than panel screws and more prone to break off.

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