You can see daylight under the deck post, and it is holding up a rather large part of your backyard. Before you slide a wedge into the gap, check the metal base: that space may be there to keep the timber out of moisture.

Identify the connector, not just the gap

Simpson Strong-Tie's post-base discussion explains standoff connections and moisture exposure. The product, anchor, fasteners, and load requirements must work together. Its US examples do not establish an Ontario design for your deck.

Do not hide the part you need to inspect

Decorative post wraps and later landscaping can collect debris or conceal the base. Keep the intended drainage and inspection access. If the wood is soft, the connector is heavily corroded, or the support has shifted, have it assessed. Adding a wedge underneath does not establish that the post or anchor is sound.

Before the next step

  • Locate the connector model and installation detail.
  • Check whether landscaping or trim blocks drainage.
  • Refer movement, decay, or missing fixings for assessment.

Ask the carpenter to point out the connector and show you the intended clearance. Once you know what belongs there, you'll also know whether next spring's mulch needs to stop a little short.