What size nail should I be using to build a 2x2 soffit around a duct? Everything I've read just says use nails, but never mentions what size/type. Thanks for any help!

 

You will want approximately 1/2 to 2/3rds of your fastener to penetrate into the wood to which you are fastening. Using a 2x2 you would use a 12 penny nail. You will find out, however, this large of a nail will split the 2x2 because of reduced surface tension normally associated with framing lumber. My suggestion is to use a 2 1/2" finish screw, and place the 2x2 to where you are driving your fastener across the grain rather than with the grain. The finish screw will have a smaller head and you will have to buy a #1 square drive bit, but they will hold just fine for the boxing. Post back if we can help further.