Install permanent 2x4 diagonal bracing between posts and beams. Required per A3.4 detail 02 since deck exceeds 2' above grade.
Per A3.4 detail 02: "IF HEIGHT OF DECK IS TO BE GREATER THAN 2' ABOVE GRADE, 2X4 WOOD DIAGONAL BRACING IS TO BE USED"
What the bracing does: The diagonal 2x4s form triangles between the posts and beams. Triangles don't flex — they lock the frame against side-to-side movement (called "racking"). Without bracing, a tall deck can sway when someone jumps or leans against a rail.
Bracing Geometry (per A3.4 detail 02)
Each brace forms a 45° triangle:
One end attaches to the beam, 2'-0" out from the post
Other end attaches to the post, 2'-0" down from the beam
Brace length: about 2'-10" from bolt hole to bolt hole (hypotenuse of a 24"×24" triangle)
Cut angle: 45° at each end
One brace per corner. Bolt through beam 2'-0" from post face; bolt through post 2'-0" below beam. 3/8" × 8" carriage bolts, washers on nut end. Per plan, all 4 outer post-beam intersections per beam get a brace (12 braces total for 3 beams).
2 per brace (one at each end) × 12 braces = 24 needed + buffer
3/8" flat washers (hot-dip galv)
~30
One under each nut (washer goes on the nut side, not the carriage bolt head side)
3/8" hex nuts (hot-dip galv)
~30
One per bolt
Part A: Bracing Layout
Step 1: Understand Where Braces Go
1Plan bracing locations before cutting anything.
Braces go on the OUTSIDE face of the frame (where they're visible)
Along each of the 3 beam columns (running perpendicular to pool): braces triangulate between each adjacent pair of posts and the beam above them
Total braces per column: 4 (one on each side of each of the 2 post-to-beam junctions between the 3 posts)
Total across all 3 columns: 12 braces
Step 2: Mark Brace Positions on Beam and Post
2At each post-beam junction, mark the two brace attachment points.
Mark on the beam: 2'-0" (24") out from the face of the post
Mark on the post: 2'-0" (24") down from the bottom of the beam
The brace will run diagonally between these two marks
Part B: Cut and Install Braces
Step 3: Cut Each 2x4 Brace
3Cut each 2x4 brace to length with 45° angles on both ends.
Brace length (long-point to long-point): about 34" (this is 24" × √2 for the hypotenuse of a 24"×24" triangle)
Set Speed Square to 45° and mark cut lines on the 2x4
Both ends cut at 45°, angled so the ends sit flat against the beam and post
Cut 12 braces total (allow a few extras for miscuts)
Label them so you know which are for which locations
Cut ONE brace first, test-fit it in one location, and confirm the geometry works before cutting the remaining 11.
Step 4: Bolt Each Brace
4Per A3.4 detail 02: attach each brace with two 3/8" x 8" carriage bolts.
Hold the brace in position, angled between the beam and post marks
Mark the bolt hole locations on the brace (centered on the 2x4, about 1" in from each end)
Remove brace, drill 3/8" hole through the brace at each mark
Hold the brace back in position, use it as a guide to drill 3/8" holes through the beam (one hole) and through the post (one hole)
Insert a 3/8" x 8" carriage bolt at each end (bolt head on the brace side, since carriage bolt heads are smooth and don't need a wrench)
On the far side (through the beam or post), add washer and nut
Tighten with 9/16" socket wrench until snug
Carriage bolt orientation: The rounded carriage bolt head has a square shoulder just below it that bites into the wood, so the bolt won't spin when you tighten the nut. Insert the bolt so this square shoulder embeds into the BRACE (soft PT wood). If you insert it backwards, tightening the nut will just spin the bolt.
Step 5: Repeat for All Locations
5Install all 12 braces (4 per beam column × 3 columns).
Part C: Verify
Step 6: Test for Lateral Movement
6Push and shake the deck to check for movement.
Grip a corner post at deck level, push firmly side-to-side
Minimal movement = properly braced
Noticeable racking (frame twisting) means more bracing needed or bolts need tightening
Completion Checklist
All 12 diagonal braces installed (4 per column × 3 columns)
Each brace has 2 carriage bolts (top end and bottom end)
All carriage bolt heads on the brace side, nuts on the beam/post side
All bolts have washers under the nuts
All nuts tightened firmly with 9/16" socket wrench
Deck feels solid — no visible racking when pushed sideways
Common Problems & Fixes
Brace doesn't fit — angle is wrong
Verify the marks on beam and post are BOTH 24" from the post-beam junction. Re-cut the brace at exact 45° angles. Speed Square makes this easy.
Bolt spins when tightening
Carriage bolt is backwards. The square shoulder must embed into the wood on the head side. Remove, flip, reinsert.
3/8" bit is tight in the hole
Use a 7/16" bit instead — carriage bolt will still hold securely and slides in more easily.
Deck still feels wobbly after bracing
Check that all post-anchor nuts are torqued to 55-60 ft-lbs. Check hurricane ties are fully screwed. Verify no beam-post bolts are loose. If still wobbly, add more bracing at outer corners.
Drill bit too short
A 3/8" bit needs to reach through the brace (1-1/2") + beam (3") or post (5-1/2") = at least 5" to 7" of drilling depth. A 6" or 8" long twist bit works.