Securely fasten sub-floor to joists.
By using other fasteners, staples and screws and construction adhesive to fasten the sub-floor to the joists, you can help overcome the effects of shrinkage.
Use construction adhesive in addition to nails or staples to enhance the fastening of the sub-floor to the joists. This technique relies initially on the holding strength of the nails or staples to secure the sub-floor to the joists while the construction adhesive sets up. Construction adhesive may provide as much or more holding capacity as nails or staples, depending upon the type of construction adhesive and the conditions under which it is applied.
- One benefit of using construction adhesive is that it is not affected by shrinkage in the same way that mechanical fasteners are affected. Construction adhesive is used only on the top of the joist and therefore shrinkage across the depth if the joist will not affect the connection. Follow the manufacturer's installation instructions.
- The use of screws instead of nails is becoming more common. Some builders are using construction adhesive plus screws in an attempt to eliminate squeaks. Fasteners that are driven 2″ (50 mm) into the joists have good holding strength until the joist shrinks. As the wood shrinks, the amount of fastener that remains embedded in the joists may be reduced by 1/8″ (3 mm) or more. In effect, the fastener releases its hold on the subfloor. This
popping
of the fastener allows the subfloor to move and results in a squeak as shown in Figure 3a and 3b.
Figure 3a - Effect Of Wood Shrinkage On Fasteners - Before Shrinkage Of Joist
Figure 3b - Effect Of Wood Shrinkage On Fasteners - After Drying And Shrinkage Of Joist
- Since screws have 25% to 75% more holding strength than nails of a similar diameter, you may use shorter screws. The shorter the fastener, the less susceptible it will be to
popping
due to shrinkage of the joists. - Ensure fasteners are embedded in joists. Nails or screws which miss the joists can rub against the wood when it is under loading.