My question has to do with screws, tension, and pre-drilling.
At Home Depot I bought 1/4" diameter hot dipped galvanized (HDG) wood screws for drilling into pressure treated wood. The exact make and model:
1/4" x 3" HDG
"Pre-Drilling Not Required"
UPC 7 07392 53960 5 (707392539605)
Simpson has a webpage with information on their screws:
SDS & SD Wood Screws
On that webpage they have a link to their engineering document:
Strong-Drive Screw Applications
The Simpson Strong-Drive® wood screw has a hex washer head
for easy driving. The built-in reamer and type 17 tip allows for
installation without predrilling. Predrilling may be necessary
depending on the type and moisture content of wood. Refer to
the 2001 NDS Section 11.1.4 for drill diameter requirements.
Bold/Italics added for emphasis. Now, why I'm confused:
The documentation they provide for the screws seems to contradict their selling point for the screws (no pre-drilling). Pressure treated wood obviously has a high moisture content and will shrink. How important is pre-drilling, and what type of bit do I pre-drill with for a 1/4" diameter screw?
I am worried I will lower the withdrawal load (tension) if I predrill. At the same time I don't want the wood splitting on me when it shrinks. What do you guys think? How do I get the maximum withdrawal load? What if I do 1/16 pre-drill? Does anyone know what the NDS (National Design Specification) says for pressure treated wood pre-drilling? What do you guys think?