[jfguerrero1]

Does anyone know what is the largest size screw that can be put into a 2"x4" (on the 1 1/2" side) without compromising the strength of the board?

I have trusses that are made of 2"x4" between the first and second floor that I want to drill and add a piece of horizontal 2"x8" so that I can use it to support AND brace a half wall in the second floor bathroom. The half wall will be 40" tall (2"x6" construction), tiled and with 50" tall 3/8" thick glass on top. The wall will be 100" long. In the current design, the half wall runs parallel to the trusses and falls between 2 trusses.

In the attached picture I show what my trusses look like. They are 'generally' 16" o.c. (some are more - up to 20" o.c.). and 16" (top to bottom). In the picture I have also drawn in a horizontal 2"x8" (a ghostly yellow) with the expected placement of screws to secure to the 2"x4" truss. I also show, in gray, joist brackets I would add, then in solid yellow is another 2"x"8" to span (perpendicular) to the next truss, with a similar 2"x8" horizontal board attached and joist brackets to support the 2"8" being added.

I am wondering if I can use 1/4" screws with predrilled holes to secure the boards, or is that too large for the 1 1/2" side of the 2"x4"? Should I use a #10 screw instead?

Thank you in advance for reading this and your feedback.

 

[Old Thomas]

Re: what is the largest size screw that can be drilled into the side of a 2"x4"

I use 3” torx drive deck screws. Their shank is long enough so they pull the boards tight together.

 

[SeniorSitizen]

Re: what is the largest size screw that can be drilled into the side of a 2"x4"

I'd probably use a #12 construction screw

 

[Chris616]

Re: what is the largest size screw that can be drilled into the side of a 2"x4"

Any reasonable sized screw and screw pattern that you choose to use it going to have little to no impact on the trusses if you predrill to avoid cracking. You’re also not adding any significant load to the trusses, so you don’t need to be concerned with that.

Are you planning this work because one or both ends of the half wall are detached from any other structure, so you’re concerned about its lateral stability? I did something similar, using angle iron bolted to the end of the half wall framing and to the joist below the floor. That made it very solid compared to typical open railings or half walls, but not so solid that I would have tiled it or added glass on top, both of which aren’t going to react well to even a bit of movement.

Chris

 

[jfguerrero1]

Re: what is the largest size screw that can be drilled into the side of a 2"x4"

Thanks everyone for the replies.

Chris616. Yes, one end will not be attached to a wall. I have uploaded a hand drawn layout. I need to secure the 1/2 wall to the trusses below for stability and because of the glass going on top of the wall. I'll be using some Simpson 8 1/2 inch - 10 guage holdown brackets and 5/8 threaded rods at 2 locations.

 

[Nealtw]

Re: what is the largest size screw that can be drilled into the side of a 2"x4"

I would cut 3 holes in the floor for the ends of the wall studs and block them below the floor.

 

[HotRodx10]

Re: what is the largest size screw that can be drilled into the side of a 2"x4"

Assuming the trusses are aligned, I would attach 12" 2x4's flat (spacer block) centered on top of 24" 2x6's, and screw the 2x6's to the side of the vertical members of the trusses. That way, you're not relying on half the thickness of a 2x4 to support the load.