# Need Help with L-Girder Joists



## [email protected] (Apr 29, 2016)

Hello,
I have finished building my L-girder benchwork and am now about to attach the joists and subsequently my sections of plywood/homosote. My question is simple....should I insure that the plywood extends over the full edge of a joist? I can't imagine being able to screw the 2 edges of adjoining plywood sections onto the top edge of a 1x4 joist, which as you know, is only 3/4" wide. Should I double up the joists where 2 edges of adjoining plywood meet or am I missing something?

Thanks for any help that can be provided,
Mondo


----------



## MichaelE (Mar 7, 2018)

You'll have to run a double joist if your sub-roadbed is not elevated. Like you said, you would have very little to attach both separate pieces to using a single.

However, if the sub-roadbed were elevated you could splice the two pieces of subroadbed together using a splice, screws, and glue.

This is a diagonal splice. That's why it looks like there is more material on one side than the other.

This is where two of my plywood sheets joined on the benchwork before they were cut out of the sheet.


----------



## Mark VerMurlen (Aug 15, 2015)

I do a splice much like Michael has shown above. This helps prevent any kinks in the plywood as it changes height. I overlap on each side of the joint by 3 or so inches for strength and continuity.

Mark


----------



## Nikola (Jun 11, 2012)

If you have a table saw or router, kerf the edges. One under, one over, screw through both into the 1x4.


----------



## MichaelE (Mar 7, 2018)

_"I can't imagine being able to screw the 2 edges of adjoining plywood sections onto the top edge of a 1x4 joist"

_
And if they meet face to face as he has indicated?


----------



## CTValleyRR (Jul 26, 2014)

Just want to confirm that what you're making is benchwork for a layout, not adding on to your house, right?

This does not need to be a massive, load bearing structure. The weight of the plywood you're using is probably more than the layout that's going to be on top of it. A lot of people overengineer their benchwork. It doesn't have to pass building inspection.

The only thing you have to do is make sure that the edges of the two sheets line up vertically. You can just put a 1x3 cleat underneath to make that happen.

You can even dispense with the plywood entirely and use sheets of 2" extruded insulating foam panels.


----------

