The new composite deck feels solid. Step onto the matching stairs and there's a little bounce. The colour may be the same, but the tread boards can need closer supports than the deck surface. Check the stair instructions before assuming the old stringers can stay.
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
On a timber-to-composite stair change, the old stringers looked sound enough to reuse, but their spacing didn't match the selected tread's instructions. We checked the proposed support layout before removing the last usable stair, then included the new stringers and their connections in the price. Reusing timber is only a saving when the resulting assembly works.
Check the top and bottom step after allowing for the new tread thickness and finished landing level. We mark those finished levels before cutting the stair; discovering a mismatch after the border and railing are fitted is a much slower conversation. The decking span table and stair detail answer different questions. Keep both with the drawings and material order.
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.
Have the installer mark the support positions and finished top and bottom steps before the railing goes on. If the old stair needs more than new treads, you'll see why while the work is still accessible. That's a much better time to decide what stays.