Inspector told me my collar ties don't count as rafter ties.

Your inspector is correct—collar ties and rafter ties are different members that serve different structural purposes.

Rafter Ties are horizontal members installed between opposing rafters (perpendicular to the rafters), typically in the bottom third of the rafter span. They resist the outward thrust created by roof loads pushing the rafters apart, which would otherwise push the exterior walls outward. Rafter ties are usually 2x4, 2x6, or larger lumber, installed every 4–8 feet vertically.

Collar Ties are installed between rafters on the same side (parallel to the ridge), typically in the upper third of the rafter span. They resist uplift forces on the roof (like wind uplift) by tying opposing rafters together near the ridge. Collar ties are usually 2x4 or 2x6, installed every 4 feet or so.

Key Difference:

• Rafter ties resist horizontal outward thrust (walls pushing out).
• Collar ties resist vertical uplift (roof being lifted off).

Code Reference: Per IRC R802.4, ceiling joists and rafter ties must be installed to resist rafter thrust. IRC R802.5 requires collar ties where ceiling joists are not continuous or where specified for uplift resistance.

Bottom Line: If your rafters are not adequately tied at the base (bottom third), you need proper rafter ties. Collar ties alone won’t prevent wall spread. You likely need both, depending on your roof design and load path.

If you're unsure about sizing or spacing, consult a structural engineer or experienced framer.

They are not the same. The inspector is correct.

Rafter Ties (Ceiling Joists)

• Function: Resist the outward thrust of rafters pushing the walls apart. They form the bottom chord of a structural triangle.
• Location: Lower third of the rafter span (typically sitting on top of the wall plates).
• Code: IRC R802.5.2 (prescriptive tables) or engineered design. Required unless you have a structural ridge beam.
• Sizing: Table R802.5.2 based on span, spacing, slope, and snow load. Often 2x4, 2x6, or 2x8.

Collar Ties (Collar Beams)

• Function: Resist wind uplift and keep the ridge from separating. They do not stop wall spread.
• Location: Upper third of the rafter span (high in the attic).
• Code: IRC R802.5.2 (Exception) & R802.4.6.
• Sizing: Minimum 1x4 (nominal) or 2x4, spaced max 4 ft. o.c. Nailed per Table R602.3(1) (typically 3-10d or 4-8d per end).

The Rule of Thumb:

• Low = Structural (Rafter Tie). Holds walls in.
• High = Uplift (Collar Tie). Holds ridge together.

If you only have collar ties high up: You have no resistance to wall spread. Your ridge will sag and walls will bow out. You must install proper rafter ties at the plate line or install a structural ridge beam (engineered) to carry the load to posts.

Fix: Sister 2x material to the rafters at the plate line per Table R802.5.2, or hire an engineer to spec a ridge beam.