What is the difference between a ridge board and a ridge beam?

A ridge board is a non-structural member that rafters nail into; the roof structure relies on the ceiling joists or collar ties to resist rafter thrust. A ridge beam is a structural member that supports the rafters from above, eliminating the need for ceiling ties.

How deep should the ridge board be?

The IRC requires the ridge board to be at least 1 inch nominal depth and not less than the cut end of the rafter. In practice, use a board one size deeper than the rafters for easy nailing.

Can I use a 2×6 ridge with 2×6 rafters?

Technically yes, if the cut end of the rafter fits against the ridge. However, a 2×8 ridge makes nailing much easier and provides better alignment. The cost difference is minimal.

How do I splice a ridge board?

Splice at a rafter location. Butt the two ridge pieces together at the rafter, then nail a scab plate (plywood or dimensional lumber) across the joint on one or both sides. The splice must align with the rafter for load transfer.

Do I need a ridge board for a hip roof?

Yes, but it's shorter. A hip roof's ridge length equals the building length minus twice the rafter run (since hip rafters fill the triangular ends). For a square building, the ridge length is zero—just a point where four hips meet.

When is a structural ridge beam required?

A ridge beam is required when there are no ceiling joists or collar ties to resist the horizontal thrust from the rafters, such as in cathedral ceilings or vaulted rooms. The beam must be sized by an engineer.

Ridge Board Length Calculator

Calculate ridge board length for gable and hip roofs. Includes gable overhang extensions and recommends ridge board depth.

Building Length

Left Gable Overhang

Right Gable Overhang

Rafter Size

Max Board Length

Total Ridge Length

43.0 ft

including overhangs

Boards Needed

16-ft boards

Recommended Depth

2×10 or larger

for 2x8 rafters

Planning notes, formulas, and examples

About the Ridge Board Length Calculator

The ridge board sits at the peak of a gable roof and provides a nailing surface where opposing rafters meet. Its length must match the building length plus any gable overhang (rake) extensions on each end. Getting the ridge board length right is critical for starting your roof framing on track.

This ridge board length calculator takes the building length and gable overhang dimensions to compute the total ridge board length. It also recommends the proper ridge board depth based on your rafter size—the IRC requires the ridge board to be at least as deep as the cut end of the rafter.

For a standard gable roof without overhangs, the ridge board simply equals the building length. Adding gable overhangs with lookout rafters or fly rafters extends the ridge past the end walls.

When This Page Helps

Ridge boards must be ordered at the correct length and depth before framing begins since they set the alignment for every rafter. This calculator ensures you order the right material, including splices if the building is longer than available lumber lengths.

How to Use the Inputs

Enter the building length (exterior wall to exterior wall).
Enter the gable overhang distance at each end (0 if flush gable).
Select the rafter size to determine the recommended ridge board depth.
Read the total ridge board length and material requirements.
If the total length exceeds standard lumber lengths, the calculator shows the number of splice pieces needed.

Formula used

Ridge Length = Building Length + Left Overhang + Right Overhang
Ridge Depth ≥ Rafter depth (one size larger recommended)
Boards needed = ceil(Ridge Length / Max board length)

Example Calculation

Result: 43 ft ridge board (2×10 or larger)

A 40-foot building with 1.5-ft overhangs on each end needs 40 + 1.5 + 1.5 = 43 linear feet of ridge board. Using 2×8 rafters, the ridge should be at least 2×10 depth. Three 16-ft boards with staggered splices will cover 43 feet.

Tips & Best Practices

Use a ridge board one size deeper than the rafters (e.g., 2×10 ridge for 2×8 rafters).
Splice ridge boards at rafter locations with a scab plate nailed across the joint.
Set the ridge board perfectly level and straight—it sets the plane for the entire roof.
Support the ridge temporarily with posts and braces until enough rafters are installed.
A ridge beam (structural, usually 4× or LVL) is different from a ridge board and must be engineered.
For buildings over 30 feet long, use a string line to check ridge straightness during framing.

Ridge Board Material Options

Standard ridge boards are made from dimensional lumber (2×8, 2×10, 2×12). For very long buildings, LVL ridges provide a single straight, warp-free member that eliminates the need for splices. LVL is especially popular for exposed ridges in timber-frame style construction.

Setting the Ridge

The most common method is to set temporary posts at each end and every 8–12 feet to support the ridge at the correct height. Install a pair of rafters at each end first, then fill in the common rafters, alternating sides to keep the ridge plumb.

Cathedral Ceilings and Structural Ridges

When the ceiling follows the roof slope (cathedral or vaulted ceilings), there are no horizontal ceiling joists to resist rafter thrust. In this case, a structural ridge beam is required. The beam must be designed to carry half the roof load and typically consists of a 4× or larger LVL, glulam, or steel member supported by posts at each end.

Sources & Methodology

Last updated: February 8, 2026

Frequently Asked Questions

A ridge board is a non-structural member that rafters nail into; the roof structure relies on the ceiling joists or collar ties to resist rafter thrust. A ridge beam is a structural member that supports the rafters from above, eliminating the need for ceiling ties.