Rafter ties vs collar ties: what inspectors check

What a rafter tie does

A pitched roof wants to spread. Each rafter pushes down and outward on the wall below it. Without something holding the two sides together, the top of the wall can lean out and the ridge can sag.

A rafter tie is the horizontal member that resists that outward push. It connects the rafters on opposite sides of the roof, at or near the wall plate. In a conventionally framed roof, the ceiling joists often do this work. That is why an inspector looks at where the ceiling joists run, how they connect to the rafters and whether they bridge all the way across.

Think of a triangle. The two rafters are the sloped sides, and the tie is the base. Take the base away and the triangle can flatten.

What a collar tie does

A collar tie connects opposite rafters in the upper part of the roof. Its job is different: it helps keep the two roof planes from separating at the ridge, for example when wind pulls up on the roof. It is not the member that holds the walls in.

That distinction matters on a site. A framer who installs a few boards high in the attic and calls them "ties" has installed collar ties. If the roof has no ceiling joists at the plate and nothing else resisting thrust, those boards do not replace a rafter tie.

Side by side

What the inspector checks

You are looking for the right member in the right place, with the right connection. A practical sequence:

1. Identify the framing system. Is this conventional rafter and ceiling joist framing, or a roof with a ridge beam, or a truss roof? Trusses carry their own engineering, so you check them against the drawings and the manufacturer's information.
2. Find the ties. Look for ceiling joists running parallel to the rafters and lapped or connected across the building. Look for separate ties where the ceiling joists do not span.
3. Check where the ties sit. A tie raised above the plate works less efficiently, so the code adjusts the allowed rafter span. Our span table walkthrough shows that adjustment in a worked example with invented numbers. To see how pitch and run turn into sloped rafter length and roof angle, use the rafter length calculator.
4. Check the connections. A tie that is not nailed to the rafters is a board that happens to be nearby. Look at the fastening, not just the presence of lumber.
5. Check the conditions that change the answer. Spacing, roof slope, whether the ceiling is attached to the rafters and the snow load for your area all change what is allowed.

Conditions that change the answer

The same roof can pass or fail when one input changes. A few to watch:

• Ceiling joists that do not span the building. If they stop at a bearing wall in the middle, ask how the thrust is resisted.
• Raised ties. The higher the tie, the more bending the rafter takes below it.
• Ceiling attached or not. The rafter tables treat these cases differently.
• Spacing that differs from the plans. Measure it on site.

Finding it in your own IRC

The B1 is open book, so the skill is finding the provision quickly. Start in the roof and ceiling chapter, Chapter 8. Rafter sizing sits in section R802.4.1 and ceiling joist sizing in R802.5.1. For the 2021 edition, a raised-tie adjustment is in Table R802.4.1(9). For the 2024 edition, we have not confirmed the table numbers here, so read them from your own book.

Use the index for the tie provisions and write the section number on a tab. Section numbers can move between editions, as the 2021 or 2024 IRC guide shows for alarms, egress and stairs, so tab the book you will actually bring. This site cites sections by number only. The rules themselves are in your licensed copy.

A five-minute practice drill

1. Pick a roof section from a set of plans you can draw on.
2. Mark where the rafters meet the plate and where the ceiling joists run.
3. Ask: what resists the outward thrust? Where is it connected?
4. Find the section in your IRC and time yourself. Aim for under two minutes, which is the pace the B1 allows per question.
5. Write the section number on your tab.

Roof and ceiling construction is 14% of the B1 outline. See where it sits among the other areas in the outline guide, and keep the pace in mind from how hard the B1 really is. The free 10-question check at /icc-inspector shows exactly which areas to study first, roofs included.

FAQ

What's the difference between a rafter tie and a collar tie?

A rafter tie is low, at or near the wall plate, and resists the outward thrust of the roof on the walls. A collar tie is higher, in the upper part of the roof, and keeps the roof planes from separating at the ridge.

Are ceiling joists rafter ties?

In conventional framing they often serve as the rafter ties, provided they are properly connected to the rafters and run across the building. Where they do not, the roof needs separate ties.

Where is this in the IRC?

Look in Chapter 8, roof and ceiling construction. Rafter sizing is in R802.4.1 and ceiling joist sizing is in R802.5.1. Use your book's index for the tie provisions themselves.

Does it change between the 2021 and 2024 editions?

Numbering and tables can differ. The 2021 rafter tables are R802.4.1(1) through (8), with an adjustment in R802.4.1(9). Check the 2024 numbers in your own book before you tab it.