Why does the calculator ask for a moment of inertia instead of a stud depth and gauge?

Because the stiffness of a cold-formed section is not a geometric property you can look up from its outside dimensions. Parts of a thin section buckle locally well before the member as a whole is in trouble, and the effective stiffness that remains depends on the stress level. Manufacturers publish the resulting figure per depth and per gauge, and reproducing those tables from a formula would be inventing them.

My manufacturer's table gives a lower height than this. Which do I use?

The manufacturer's, always. A tabulated limiting height is the lesser of a deflection check and a bending strength check, and it is tied to a tested assembly with a specific track, fastening pattern and liner. This page computes only the deflection half, so where it reads higher than the table, strength is governing and the table is telling you so.

Does adding a second layer of board to the corridor face raise the limiting height?

Not in the way the tables are written. The published heights are for the stud alone, because the board is not connected to the stud in a way that lets the two act as one member, and the liner panel is only friction-fitted between the C-H flanges. Extra board adds weight and fire resistance, not stiffness you may count on.

What transverse pressure should a shaft be designed for?

That is a project decision rather than a property of the wall. Lift shafts see piston effect from car movement, tall shafts see stack pressure that grows with building height, and a smoke control system imposes a pressure difference by design. The figure comes from the mechanical design or the specification, and a perimeter shaftwall must also be checked against wind.

Materials & Quantities

Shaftwall C-H Stud Limiting Height Calculator

How high a C-H shaftwall stud runs unsupported at a given spacing and pressure before its deflection limit, and the share of it a proposed height uses.

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Imperial · sales tax

Design Transverse Pressure

The lateral pressure the shaft enclosure is designed to resist.

Shaft enclosures are designed for a transverse pressure caused by lift piston effect, stack pressure or a smoke control system, and the figure is set by the project rather than by the wall. It is not a wind load; a shaftwall on the building perimeter has to be checked for both, at the greater of the two.

Stud Spacing

Centre-to-centre spacing of the C-H studs along the wall.

Spacing enters twice over. It sets the strip of wall each stud carries, so halving it halves the load per stud; but liner panel widths are fixed, so the spacing is usually decided by the panel rather than by the structure, and the height follows from it.

Effective Moment of Inertia I_eff (×10⁶ mm⁴)

The stud's effective moment of inertia, from the manufacturer's table.

This is where stud depth and gauge enter the calculation. It is not a value you can derive from the nominal dimensions, because a cold-formed section's stiffness depends on which parts of it have buckled locally at the load in question, so it is published per depth and per gauge and must be read from the table for the exact stud specified.

Permitted Deflection Ratio

The deflection limit the specification applies to this wall.

The limit follows the finish, not the fire rating. A shaft face left in bare liner and board is commonly held to L/240; a corridor face carrying tile, stone or a rigid coating is held tighter, because those finishes crack long before the framing is in any distress.

Proposed Unsupported Height

The floor-to-floor height you want to run this stud through.

Unsupported means exactly that: the distance between the top and bottom tracks, or between a track and a real intermediate brace. A ceiling grid, a duct hanger and a run of blocking are not lateral supports, and counting one as though it were is the commonest way a shaftwall ends up over-height.

Maximum unsupported height

18.9 ft

Medium confidence

The proposed height uses 32% of the deflection allowance. This is the deflection-governed limit only — the manufacturer's tabulated limiting height is the lesser of this and a bending strength check, and for heavier gauges and higher pressures it is often strength that governs.

Line load carried by one stud: 10.44 lbf/ft
Deflection at the proposed height: 0.21 in
Allowable deflection at the proposed height: 0.65 in
Deflection allowance used at that height: 32.37 %

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

ASTM C645 (non-structural steel framing members) and ASTM C754 (installation of steel framing to receive gypsum panel products), which is where the practice of selecting studs from a published limiting-height table originates
AISI S100 takes the modulus of elasticity of cold-formed sheet steel as 29,500,000 psi (203,400 MPa); the effective moment of inertia for a given C-H stud depth and gauge comes from the system manufacturer's own limiting height table
Deflection-governed limiting height from elastic beam theory for a uniformly loaded simple span: setting 5wL⁴/(384EI) equal to L divided by the deflection ratio gives L = cube root of 384EI/(5wR)

Inputs used

Design Transverse Pressure: 5.22 psf
Stud Spacing: 24 in
Effective Moment of Inertia I_eff (×10⁶ mm⁴): 0.45
Permitted Deflection Ratio: L/240
Proposed Unsupported Height: 13 ft

Intermediate steps

Line load carried by one stud: 10.44 lbf/ft
Deflection at the proposed height: 0.21 in
Allowable deflection at the proposed height: 0.65 in
Deflection allowance used at that height: 32.37 %

Final result18.93 ft

Confidence note: The proposed height uses 32% of the deflection allowance. This is the deflection-governed limit only — the manufacturer's tabulated limiting height is the lesser of this and a bending strength check, and for heavier gauges and higher pressures it is often strength that governs.

What this calculation does not cover

Deflection only. Bending strength requires the effective section modulus and yield strength for the same stud, which are published alongside the moment of inertia and are not derivable from it.
Treats the stud as a simply supported span between tracks. Slip track details, deflection heads and intermediate bracing all change the end conditions and the tabulated heights that go with them.
The liner panel is not counted as contributing stiffness. Shaftwall liner is friction-fitted between the studs and is not composite with them, which is why manufacturers publish limiting heights against the stud alone.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations3

ASTM C645 (non-structural steel framing members) and ASTM C754 (installation of steel framing to receive gypsum panel products), which is where the practice of selecting studs from a published limiting-height table originates
AISI S100 takes the modulus of elasticity of cold-formed sheet steel as 29,500,000 psi (203,400 MPa); the effective moment of inertia for a given C-H stud depth and gauge comes from the system manufacturer's own limiting height table
Deflection-governed limiting height from elastic beam theory for a uniformly loaded simple span: setting 5wL⁴/(384EI) equal to L divided by the deflection ratio gives L = cube root of 384EI/(5wR)

Which documents these citations point at

Standards referenced: ASTM C645, ASTM C754 (ASTM International, United States).

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Sizing a Lift Hoistway and an Escalator Welluses this calculator
A hoistway is four separate reservations rather than one rectangle, and a wellway is a hole whose length the rise settles long before the truss exists.
Taking Off Board for Shafts, Soffits and One-Sided Wallsuses this calculator
A riser priced as a two-sided partition buys twice the board, misses the liner completely, and never checks whether the stud height works.
Framing a Cold-Formed Steel Partition

Called something else where you work? Firestopping and cavity barriers — the term in each market, how close the equivalence really is, and the standard that governs it.

How to calculate shaftwall C-H stud limiting height in 6 steps

Design Transverse PressureThe lateral pressure the shaft enclosure is designed to resist.
Stud SpacingCentre-to-centre spacing of the C-H studs along the wall.
Effective Moment of Inertia I_eff (×10⁶ mm⁴)The stud's effective moment of inertia, from the manufacturer's table.
Permitted Deflection RatioThe deflection limit the specification applies to this wall.
Proposed Unsupported HeightThe floor-to-floor height you want to run this stud through.
Maximum unsupported heightThe tool computes the maximum unsupported height from those figures and shows the formula, its sources, and a confidence rating alongside it.

Maximum unsupported height by design transverse pressure

Page defaults, not your figures above.

Design Transverse Pressure	Maximum unsupported height (ft)
4 psf	20.7
6 psf	18.1
8 psf	16.4
10 psf	15.2

Frequently asked questions

Why does the calculator ask for a moment of inertia instead of a stud depth and gauge?: Because the stiffness of a cold-formed section is not a geometric property you can look up from its outside dimensions. Parts of a thin section buckle locally well before the member as a whole is in trouble, and the effective stiffness that remains depends on the stress level. Manufacturers publish the resulting figure per depth and per gauge, and reproducing those tables from a formula would be inventing them.
My manufacturer's table gives a lower height than this. Which do I use?: The manufacturer's, always. A tabulated limiting height is the lesser of a deflection check and a bending strength check, and it is tied to a tested assembly with a specific track, fastening pattern and liner. This page computes only the deflection half, so where it reads higher than the table, strength is governing and the table is telling you so.
Does adding a second layer of board to the corridor face raise the limiting height?: Not in the way the tables are written. The published heights are for the stud alone, because the board is not connected to the stud in a way that lets the two act as one member, and the liner panel is only friction-fitted between the C-H flanges. Extra board adds weight and fire resistance, not stiffness you may count on.
What transverse pressure should a shaft be designed for?: That is a project decision rather than a property of the wall. Lift shafts see piston effect from car movement, tall shafts see stack pressure that grows with building height, and a smoke control system imposes a pressure difference by design. The figure comes from the mechanical design or the specification, and a perimeter shaftwall must also be checked against wind.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.