The deck feels solid. The stairs have a little bounce. Those two observations can coexist because the surface boards and stair treads do not necessarily use the same support spacing.
A stair is its own assembly, not a strip of deck tipped downhill.
Read the row for the exact board
In the 2026 Trex stair guide, page 36, Enhance 1x6 treads have a maximum stringer spacing of 9 inches on centre. The listed Signature, Transcend, and Select 1x6 profiles use 12 inches. The guide also specifies minimum stringer support and fastening requirements.
Those are product-specific examples, not dimensions to transfer to another brand or a different profile. Check the current instructions for the supplied material, including any more restrictive detail in its installation system.
More than one measurement controls the stair
| Item | Why it belongs on the drawing |
|---|---|
| Stringer spacing | Supports the chosen tread product across the stair. |
| Stringer design | Carries the stair between its top connection and landing. |
| Tread overhang | Must fit the product detail rather than a preferred visual edge. |
| Finished rise and run | Must account for the actual tread and landing finishes. |
The manufacturer's instructions and the applicable Ontario requirements both need to be satisfied. A US model-code reference in a product guide is not a substitute for the local stair design.
Resurfacing is where the assumption sneaks in
Old wood treads can come off cleanly, leaving stringers that look reusable. Before replacing them with composite, compare their spacing and condition with the new product's requirements. Also check the top and bottom step after allowing for the change in tread thickness.
The decking span table and the stair detail answer different questions. Keep both with the project drawings so the person ordering the material and the person building the stairs are working from the same information.
Ask for the complete stair price
Include any additional stringers, connections, landing work, and railing changes in the resurfacing quote. "New composite treads" can otherwise describe a finish while leaving its supports undecided.
It is a modest detail to settle at a desk. It is an irritating detail to revisit with a finished railing in the way.