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The basics
What is a Hip Truss?
A hip roof buys wind performance and costs you attic space, framing time and money. Whether that trade is worth it is mostly about where you are building.
A hip roof has no gable-end wall to catch wind, and the four-way slope (opens in a new tab) braces itself in every direction. In high-wind zones that difference is worth real money on an insurance premium, and in some coastal jurisdictions it changes what is permitted at all.
Against that, a hip roof costs more to frame, gives up most attic storage, makes ventilation harder because there is far less ridge to vent (opens in a new tab), and leaves nowhere convenient for a gable vent or an attic access door.
- Better wind behaviour No flat vertical wall at roof level, and every slope braces the others. This is the main reason to choose it.
- Less usable attic The four-way slope eats the corners, so the usable rectangle is much smaller than a gable of the same span.
- More framing cost Expect 12 to 18% more for the truss package, plus extra labour hanging jacks off the girder.
- Harder to ventilate Much shorter ridge line, so ridge venting alone rarely moves enough air. Plan the vent strategy early.
The girder is the part to get right
The hip girder carries roughly half the load of the entire hip end concentrated onto two bearing points. It is the truss most likely to be under-specified on a DIY plan, and the one you should never guess at.
The maths
Hip Truss Formula
Hip truss geometry and the step-down series
Each truss moving inward from the end wall gains one step of height and two steps of flat-top width, which is what makes the hip plane come out straight.
Method
How to Calculate a Hip Truss
A hip truss is a common truss with its peak cut off, so it is calculated as a trapezoid: the sloping ends follow the pitch and the flat top spans the middle.
- 1 Set the span Same as any truss, out-to-out of the bearing walls on the narrow dimension of the building.
- 2 Set the flat top width This is the width of the hip truss's flat top chord. The calculator expresses it as a fraction of the span, and a quarter is typical.
- 3 Read the step-down series Each successive hip truss toward the end wall has a shorter flat top and a lower peak, stepping by spacing times pitch over 12.
- 4 Add the girder The hip girder carries every jack truss and is usually doubled or tripled. Budget for it separately, since it is the most expensive truss in the set.
The step between successive hip trusses is fixed by geometry rather than adjusted on site. At 24 in centres and a 6:12 pitch, that is exactly 12 in of drop per truss.
That is what makes the hip plane flat and straight. Getting it wrong shows up as a visible wave along the hip line, and it cannot be corrected with shims once the sheathing is on.
Worked example
A 30 ft span at 6:12 with a quarter-span flat top gives a 7 ft 6 in flat top and an 11 ft 3 in setback each side, putting the top chord 5 ft 7½ in above the bearing. At 24 in centres each step-down truss drops 12 in. Girder sizing is a design question, not a table lookup.
What a typical hip end contains, working from the middle of the building outward.
| Component | What it does | Typical count | Notes |
|---|---|---|---|
| Common trusses | Standard gable trusses through the body of the roof | Most of the roof | Identical to a gable roof truss |
| Hip girder | Carries every jack truss on that end | 1 per hip end | Usually 2 or 3 ply, needs hangers and designed bearing |
| Step-down hips | Flat-top trusses of decreasing height | 3 to 5 per hip end | Each steps down by spacing times pitch over 12 |
| Jack trusses | Short trusses framing from the girder to the corner | 6 to 12 per hip end | Hung off the girder face with truss hangers |
| Corner jacks | Diagonal members forming the hip line | 2 per corner | Often site-cut rather than fabricated |
Note: A hip end typically adds 12 to 18% to the total roof package price versus the same building with gable ends.
The tool
Why Choose Our Hip Truss Calculator
A hip roof is a set of trusses, not one repeated, so the useful tool is the one that shows you the whole set.
- Flat top as a fraction Set the flat top width against the span and see the sloping chords and setback update together.
- Step-down maths shown The drop between successive hip trusses comes straight from spacing and pitch, so the hip plane comes out straight.
- The whole set listed Commons, girder, step-downs and jacks, so nothing gets left off the order.
- Girder flagged, not guessed The tool tells you the girder is a designed component rather than pretending to size it.
More tools
Explore Related Truss Calculators
Calculators that pair with the hip tool, each running the same geometry engine.
- Gable Roof Truss Calculator Live geometry, automatic web pattern selection and a complete material take-off. Open calculator
- Roof Truss Span Calculator Check any span against chord size, species, pitch and load in one pass. Open calculator
- Roof Truss Load Calculator Snow, dead and live load combined into per-truss forces and bearing reactions. Open calculator
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Answers
Frequently Asked Questions
Common questions about hip roof truss calculator.
How do you calculate hip roof trusses?
Start with the common truss geometry for the span and pitch, then set the flat-top width for the hip truss nearest the wall. Every step-down truss behind it gains flat-top width and height at a rate of spacing times pitch divided by 12.
What is a hip girder truss?
The hip girder is the truss the jack trusses hang from. Because it collects the load of the entire hip end, it is normally built from two or three plies fastened together and requires a specific nailing or bolting schedule plus designed bearing at each end.
How many step-down trusses does a hip end need?
Usually three to five, depending on span and pitch. The series continues until the flat top would exceed the span minus twice the setback, at which point a standard common truss takes over.
Are hip roofs more expensive than gable roofs?
Yes, typically 12 to 18% more for the truss package alone, plus extra labour for hanging jacks. In high-wind regions the insurance saving can offset that within a few years.
Can you have an attic room in a hip roof?
It is possible but awkward. The four-way slope eats the corners, so the usable rectangle is much smaller than in a gable of the same span. If a room in the roof is the goal, an attic truss under a gable roof is far more efficient.
Do hip roofs really perform better in high wind?
Post-storm surveys have consistently found hip roofs sustaining less damage than gables, which is why several insurers offer a discount for them. The advantage depends on the whole load path being detailed correctly, not on the shape alone.
References
Hip Roof Sources & Standards
Related calculators on this site, plus the standards and reference works the figures on this page are based on. External links open in a new tab.
Authoritative external references
- WIKI Hip roof, Wikipedia (opens in a new tab)
- WIKI Truss, Wikipedia (opens in a new tab)
- STD ANSI/TPI 1, Truss Plate Institute (opens in a new tab)
- ORG SBCA, truss handling and bracing guidance (opens in a new tab)
- CODE International Code Council, model building codes (opens in a new tab)
Codes and standards are revised on their own cycles. Confirm the current edition adopted in your jurisdiction with your local building department before relying on any figure.