Q: I’m planning on framing a landing to break up a long stairway that runs from grade to an upper-level deck. How should the landing be designed—as a separate deck or as part of the stairway?
A: Mike Guertin, a builder and remodeler in East Greenwich, R.I., and the “Deck Workshop” presenter at JLC Live (jlclive.com), responds: I treat a landing as I would a small deck. I design it to handle regular live and dead loads (40 pounds and 10 pounds per square foot, respectively) as well as the concentrated loads imposed by the stairs that attach to it. Just like a deck, a landing needs to have footings, posts, beams, and joists.
Some building officials may consider the landing to be part of the stairway, however, in which case there’s a secondary load requirement (IRC Table R301.5, Minimum Uniformly Distributed Live Loads). It applies to stair treads, but a building official could consider the decking on a landing to be the equivalent of a tread. If so, one of two load requirements would apply: a 40-psf live load or a 300-pound concentrated load acting on an area of 4 square inches—whichever produces the greater stress. Four square inches (2 inches by 2 inches) is a pretty small area. I suppose the 300-pound load occurs where the foot of someone walking on a set of stairs presses on a tread.
If wood-plastic decking is used on the landing, then the landing joists should be spaced at the same distance that the decking’s manufacturer requires for stringer spacing. That distance is product- and brand-specific for composite decking materials.
The minimum size for a landing is 3 feet by 3 feet or the width of the stair sections meeting at the landing—whichever is greater. As shown in the illustration above, the minimum depth is measured from the nosing—not the riser—of the stair. Also, because the bottom of the upper set of stairs will rest on it, the landing must be large enough to fully support the heel of the stringers.
I double up the rim joists to serve as beams because placing separate beams beneath the landing would look too bulky. Then I install 4x4 or 6x6 posts beneath the ends of the rim beam and down to footings, which must reach frost depth if either the landing or the main deck are attached to the house. Diagonal bracing between the posts and the landing frame is needed to resist lateral movement.
I use 2x8s rather than 2x6s for the rim beams and joists. The 2x8 rim beams can usually handle the extra load of stair sections up to 4 feet wide. The only time that this changes is on a landing for a U-shaped stairway, when both sets of stairs bear on one side of the landing. In that case, I install an extra post and footing at the middle of the rim beam to reduce the span.
Posts for the guardrail are attached to the landing frame just as they would be on a deck.
Finally, when designing the landing height and position, keep in mind that the riser and tread cuts don’t need to be equal between the two stair sections. The landing breaks a user’s stride, so the difference doesn’t cause a trip hazard.
This is a revised version of an article that originally appeared in The Journal of Light Construction (jlconline.com).