Basic Floor Framing Layout, Point Loads, and Making Plywood Fit

Floor joist layout options that ensure the subfloor sheets begin and end where you want them to
Floor framing begins after the foundation is ready and the mud sills are installed. Typically, there's a beam somewhere because floor joists cannot usually span a full house width. Usually, the beam is level with the mud sills, and the joists sit on both.

Floor joist layout options 16 o.c. or 24 o.c.?
Before laying out the mudsills, let's look at some layout options. Subflooring and other sheet goods come in four-foot by eight-foot sheets. Both four feet and eight feet are divisible by 16 inches.

Every sixteen inches is marked on tape measures with a black arrow. They're also divisible by 24 inches, marked with a red square.

For joists that are to be placed 16 inches on center (o.c.), mark a layout line 15-1/4 inches in from the end of the mudsill. This puts the center on the host at 16 inches and each successive joist 16 inches apart so that an eight-foot piece of subflooring will end in the middle of a joist, where the next sheet will begin.

Run the joist ends past each other
Rather than cutting every joist to butt into another on top of the beam, run them past each other. This eliminates a lot of cutting.

However, it places the sister joist on the opposite side of the layout line, so this needs to be remembered. When laying out the beam, place Xs on both sides of the line, indicating which direction the joist runs.

This ought to keep all of the joists running straight and square so that the subflooring will install smoothly.

Locate and account for point loads
But before putting down subflooring, locate and transfer point loads. Atop this beam will sit a bearing wall that carries half the ceiling weight. This wall sits directly over the beam, so the load is transferred directly.

If the wall is more than a joist depth away from the beam, you either need to put the beam in a different place or you need a backup plan.

The roof is carried by the outside walls. Within those walls are places that have extra concentrations of weight, such as trimmer studs under headers. These studs need to be fully supported with blocks that transfer the weight to the mudsill, which transfers it to the foundation.

In this opening, the trimmers are fully supported by the doubled joists below, but this one has a larger load that is not fully supported. The best option is sistered joists that can pick up the load.

Don't sabotage the insulators
One other thing to think about before laying subflooring is how difficult it will be to insulate that last little joist cavity after it's covered. It will never be easier to insulate that before putting down subflooring.

Planning ahead means not going backward.

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[sprankthetank]

This was perfect. I sent this to all my volunteers and the day went smooth.

[mustharieazeez]

This video was awesome, helped me a lot to build my shed

[Stan_CentralFla]

Great tip: mark first joist at 15.25” from end of mud sill. Thank you!

[TorontoRealtorAndre]

Amazing. Simple and great visuals so a dummy like me can understand.

[Deep_Divers]

Great video! Is the blocking between the joists required by code or just good practice? Also, could you have just added additional blocking under the trimmers vice adding an entire joist to transfer the load?

[wolfplex]

Just cut a scrap piece of 2x4 spacer to 14.5 inches and you'll always be 16 on center.

[ShinnahWilde]

Where should the sheathing layout shift for the staggered joists if the sheets don't break at the bearing wall?

[danwhitaker]

Do you need double joist at partition walls that run parallel to the joists? And what do you do when a vertical plumbing pipe aligns with double joist at a “wet” wall

[sef]

This makes no sense, you can’t be 16” OC on both sides of the house if you sister your floor joists.