Install Collar Ties
Keeping your roof together. Collar ties are horizontal members connecting opposing rafters, preventing them from spreading apart under load and keeping the ridge intact.
Why Collar Ties Matter
A conventional roof works like a triangle - the rafters push outward at their bases while the ridge holds them together at the top. Collar ties are horizontal members that connect opposing rafters in the upper portion of this triangle, preventing the rafters from separating at the ridge under snow loads, wind uplift, or the roof's own weight. Without this connection, rafters can slowly spread apart, causing the ridge to drop, walls to bow outward, and eventually catastrophic roof failure. In attic conversions, existing collar ties often limit headroom at the most usable part of the space. The temptation is to remove them, but doing so without proper engineering can compromise your entire roof structure. Understanding how collar ties work - and what alternatives exist - is essential for a safe, successful conversion.
Tools & Materials You'll Need
Step-by-Step Guide
Assess Existing Collar Ties
Before modifying anything, understand what you're working with:
- Count existing collar ties and note their spacing (every rafter pair? Every other?)
- Measure current collar tie height from floor to underside
- Note lumber dimensions (1x6, 2x4, 2x6?)
- Check connection type (nails, bolts, metal connectors?)
- Look for any signs of stress (pulling away, split wood, gaps)
- Photograph existing configuration for engineer review
Warning: Never remove existing collar ties or ceiling joists without engineer approval. Even temporary removal during construction can allow roof spread that's difficult to reverse.
Calculate Required Sizing
Engineering determines what collar ties must handle:
Factors Affecting Size:
- Rafter span (eave to ridge)
- Roof pitch (steeper = more thrust)
- Expected loads (snow, wind)
- Collar tie height position
- Spacing (every pair or alternating)
Typical Specifications:
- 1x6 for light loads, short spans
- 2x4 for moderate spans
- 2x6 for longer spans or heavy loads
- Every rafter pair or max 4' spacing
- Within upper 1/3 of rafter length
Engineering Note: If converting to cathedral ceiling without collar ties, your engineer will typically specify a structural ridge beam supported by posts. This changes the roof from a thrust-based system to a beam-supported system.
Mark Installation Height
Position collar ties for maximum headroom within code requirements:
- Calculate upper third of rafter span from ridge (code requirement)
- Add desired finished ceiling thickness below collar tie
- Mark height on rafters at both ends of the space
- Snap chalk line between marks for consistent height
- Verify height provides adequate headroom (7' minimum at center)
- Transfer marks to each rafter pair receiving collar ties
Height Strategy: Install collar ties as high as structurally allowed. Every inch higher means more headroom in your finished space. But don't exceed the upper-third limit without engineering approval.
Cut and Install Collar Ties
Measure, cut, and secure each collar tie:
Measuring and Cutting:
- Measure between rafters at marked height
- Each collar tie may be slightly different length
- Cut ends square for full bearing on rafter face
- Or angle-cut to match rafter slope if end-nailing
Fastening Options:
- Nails: Minimum 3 - 10d nails per end (face-nail through rafter into tie end, or toe-nail)
- Bolts: Two 1/2" bolts per end for heavy loads
- Metal Connectors: Simpson H2.5A or similar - strongest, easiest
- Screws: Structural screws per manufacturer specs
Pro Tip: Metal connectors like Simpson H2.5A clips make collar tie installation faster and more reliable than nailing. They cost more but provide consistent, code-approved connections.
Ridge Beam Alternative (If Removing Ties)
If your engineer approves collar tie removal for cathedral ceiling:
- Install structural ridge beam sized for roof loads (often LVL or glulam)
- Support beam ends on posts carrying loads to foundation
- Mid-span posts may be required for longer ridges
- Rafters connect to beam with metal hangers
- Install temporary shoring before removing existing collar ties
- Remove collar ties only after ridge beam is fully installed and supported
Typical Ridge Beam Sizing:
- 10-foot span: 3.5" x 9.25" LVL or larger
- 16-foot span: 3.5" x 11.875" LVL or larger
- 20+ foot span: Multiple LVL plies or engineered beam
- Always verify with structural engineer
Pro Tips
- ✓Consider exposed collar ties as a design feature - stained wood ties can add character to attic rooms
- ✓If collar ties double as ceiling joists for a flat ceiling, ensure they're sized for both functions
- ✓Install collar ties before removing temporary bracing from other structural work
- ✓Check for plumb and level after installation - crooked collar ties make ceiling installation difficult
- ✓Use construction adhesive in addition to mechanical fasteners for the strongest connection
Frequently Asked Questions
What's the difference between collar ties and ceiling joists?▼
Collar ties connect opposing rafters in the upper third of the roof to prevent rafters from separating at the ridge under load. Ceiling joists span from exterior wall to exterior wall at the attic floor level, preventing walls from spreading outward from roof thrust. Both serve structural purposes but at different locations. In attic conversions, ceiling joists are often the floor you're standing on, while collar ties may limit headroom and be candidates for modification.
Can I remove collar ties to gain headroom?▼
Collar ties can often be relocated higher or removed entirely, but only with proper engineering. If removed, you typically need to install a structural ridge beam supported by posts at each end (and possibly mid-span) that carries roof loads down to the foundation. This converts the roof from a "tied rafter" system to a "supported ridge" system. Never remove collar ties without an engineer's approval and specified alternative structure.
How high should collar ties be installed?▼
Building codes typically require collar ties to be installed in the upper third of the rafter span, measured from the ridge. For a 12-foot rafter length, this means within 4 feet of the ridge. Installing them lower doesn't provide the same structural benefit and may not meet code. The higher you can install them while still providing adequate connection strength, the more headroom you'll preserve.
What size lumber should collar ties be?▼
Collar tie sizing depends on rafter span, roof pitch, and spacing. Common specifications are 1x6 or 2x4 lumber installed at every rafter pair or every other pair. Your structural engineer will specify the exact size based on your roof design. Connections matter as much as lumber size - code typically requires at least three 10d nails per end, though metal connectors provide stronger, more reliable connections.