TryBuildCalcFraming Resources
Hip Roof Framing Guide (Common, Hip & Jack Rafters)
A hip roof isn't just a gable roof with slanted ends — it uses three distinct rafter types that each follow their own length formula, and getting the relationship between them wrong is the single most common source of layout mistakes on a first hip-roof framing job.
Last updated: September 6, 2026
A hip roof frames every wall plate with a slope back toward the ridge, which means the corners need their own dedicated rafter type — and that single difference from a gable roof cascades into three distinct rafter geometries that all have to agree with each other at the hip line.
This guide covers what each rafter type does, how hip and jack rafter lengths are actually derived, and the layout mistakes that most commonly show up on a first hip-roof framing job.
Common, Hip, and Jack Rafters at a Glance
| Rafter Type | Path | Structural Role | Cut Complexity |
|---|---|---|---|
| Common Rafter | Straight, perpendicular to wall plate and ridge | Primary roof slope member, same as a gable roof | Simplest — a single plumb cut and a single bird's-mouth seat cut |
| Hip Rafter | Diagonal, from an outside wall corner to the ridge (17" unit run) | Structural corner member; carries the jack rafters on both sides | Most complex — compound (double-bevel) cuts at both the ridge and the seat |
| Jack Rafter | Shortened common rafter, wall plate to hip rafter | Ties the wall plate to the hip; series shortens toward the corner | Moderate — a single-bevel compound cut where it lands against the hip |
The hip rafter's diagonal path is why it uses a 17" unit run on a framing square instead of the common rafter's 12" — it's covering the diagonal of the same corner square, not a straight run.
How Jack Rafter Lengths Are Derived
Jack rafters don't get measured individually from scratch — each one is derived from the last using a fixed shortening step:
- Common difference = on-center spacing × the common rafter's length multiplier for the roof pitch.
- Illustrative example: at 16" O.C. on a 6:12 pitch (common multiplier ≈1.118), each jack is roughly 17-7/8" shorter than the previous one.
- The full common rafter length is the starting point; each jack in the series is the previous jack's length minus the common difference.
- A shortening allowance (roughly half the hip rafter's diagonal thickness) is then deducted at every hip-side cut so the pieces actually seat correctly against the hip.
Worked Example — Jack Rafter Series on a 6:12 Hip
16" O.C. Spacing, 6:12 Pitch
Illustrative example — actual lengths depend on the specific common rafter length and layout for the roof in question.
| Rafter | Length (before shortening allowance) | Step from Previous |
|---|---|---|
| Common rafter | 13'-4" | — |
| Jack 1 (nearest hip) | 11'-10" | −17-7/8" |
| Jack 2 | 10'-4" | −17-7/8" |
| Jack 3 | 8'-10" | −17-7/8" |
Each jack in the series is simply the previous jack's length minus the fixed common difference — the shortening allowance at the hip-side cut is applied on top of these lengths, not included in them.
Common Mistakes
Using the Common Rafter's 12-Inch Unit Run for Hip Layout
A hip rafter's diagonal path across the building corner uses a 17-inch unit run on a framing square, not the 12-inch run used for common rafters — using the wrong unit run produces a hip rafter that's the wrong length across its entire run, not just slightly off.
Forgetting the Shortening Allowance
Cutting the hip rafter and its jack rafters to their exact theoretical centerline lengths, without deducting the shortening allowance (roughly half the hip's diagonal thickness) at the ridge and hip intersections, leaves rafters sitting slightly proud and throws off the ridge line and hip corner fit.
Spacing Jack Rafters Differently from the Common Rafters
Jack rafters need to follow the same on-center spacing as the common rafters along the same wall plate — inconsistent spacing between the jack run and the common run creates uneven sheathing bearing and breaks the common-difference formula the jack lengths are calculated from.
Estimating Hip Roof Material and Labor the Same as a Gable Roof
Hip framing needs more individual pieces (a hip rafter and a full jack series on every hip corner instead of one continuous common rafter run), more waste from the compound cuts, and meaningfully more layout and cutting time — pricing a hip roof off gable-roof assumptions consistently underestimates both material and labor.
Not Verifying Local Code Adoption and Edition
Rafter sizing and span figures are published by code (in the US, the IRC) and both the numbers and which edition is locally adopted can differ by jurisdiction — confirm the exact table and edition in force before finalizing real rafter sizes.
Relevant Standards and References
Rafter length geometry (unit run, common difference, shortening allowance) is universal trigonometry, but member sizing against load is code-specific.
| Region | Relevant Codes / Guidance |
|---|---|
| United States | IRC Chapter 8 covers roof framing generally; ANSI/TPI 1 governs engineered wood truss design where a hip roof is truss-framed rather than stick-framed |
| Europe / UK | Structural timber roof member design is generally governed by Eurocode 5 (BS EN 1995), with wind and snow actions from Eurocode 1 (BS EN 1991), alongside national building regulations |
| India | IS 883 covers design of structural timber in building construction, though light-frame stick-built hip roofs are less common than RCC roof construction |
| Australia / New Zealand | AS 1684 (Residential Timber-Framed Construction) covers rafter, hip, and jack member sizing and spacing for timber-framed roofs |
| General guidance | Rafter length formulas (unit run, common difference, shortening allowance) are geometric and universal, but member sizing against load always needs region-specific span tables. |
Final Verdict
Hip roof framing is genuinely more involved than a gable roof — it needs a hip rafter with its own 17" unit run, a full jack rafter series derived from the common difference, and a shortening allowance applied at every hip-side cut. Getting the three rafter types' relationship right up front avoids the fit problems that show up at the ridge and hip corners otherwise.
- Use the 17" unit run for hip rafter layout — not the common rafter's 12" run.
- Derive jack rafter lengths from the common difference (spacing × pitch multiplier), stepping down from the full common rafter length.
- Apply the shortening allowance at every ridge and hip-side cut, not just the hip rafter itself.
- Keep jack rafter spacing consistent with the common rafter spacing along the same wall plate.
- Price hip roof material and labor separately from a gable-roof estimate — more pieces, more waste, and more layout time.
- Confirm the exact table and code edition your local authority has adopted before finalizing real rafter sizes.
Related calculators
Use these calculators when you need to turn this reference information into project quantities:
- Hip Roof Calculator
Find common, hip, and jack rafter lengths and counts from your roof's footprint and pitch.
- Rafter Calculator
Size the common rafters that a hip roof's jack rafters are cut down from.
Related resources
- Rafter vs. Truss: Which Should You Use?
A practical comparison of stick-built rafters and prefabricated roof trusses — cost per square foot, achievable span, usable attic space, installation speed, and design flexibility — to help decide which fits a given roof.
- Rafter Span & Sizing Guide
How rafter span, spacing, roof pitch, and ground snow load relate to each other — reading a rafter span table correctly, why snow load can cut allowable span dramatically, and how pitch changes the load a rafter actually sees.