Adding a landing breaks up longer flights of stairs, improving comfort and looks, and reducing stair-jack spans.
The 300-pound point load mentioned in the code relates directly to the tread material (usually decking) and the spacing between jacks. The stronger the decking, the greater the allowable space between the jacks, and the fewer jacks you’ll need to cut.
Make stairs wider than the code minimum of 3 feet. They’re more inviting, and two people can easily pass each other.
A framing square aligned on the riser and tread dimensions is used to lay out the notches on the jacks.
Lay out the bottom riser cut, then mark the cut on the bottom of the jack so the riser is one tread thickness shorter than all the others.
Don’t overcut the jack notches with a circular saw, as shown here. It weakens the jack. Cut just up to the intersecting lines.
After carefully cutting the first jack and checking its fit, use it as a pattern to lay out the remaining jacks.
When cutting the remaining jacks, be careful to take out the layout marks. Doing so will make these jacks exactly the same as the pattern jack.
Pressure treatment doesn’t reach the interior of most framing lumber, so cutting exposes untreated wood. Coat all cuts with end-cut preservative.
A 2x8 the width of the stair is supported by scraps of framing lumber. Commercially available hardware secures the jacks to the 2x8.