IRC Table R602.3(5). A 2x4 under two floors is a dash, not a spacing
Table R602.3(5) sets stud size against height and spacing, and the cell nobody reads is the two-floor column. A 2x4 bearing wall carrying two floors and a roof is a dash: not a tighter spacing you can reach by adding studs, but outside the prescriptive table entirely. This counts your wall and checks the row.
Wall framing takeoff
ft
ft
in
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no.
no.
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Every limit here is a cell in Table R602.3(5). Board feet are on the nominal size, because that is how lumber is billed.
Specification summary
Generated from on .
Reopen that address to reproduce these figures exactly.
Entered
Result
Studs at the spacing entered, against what the table allows
Worked example
A 40 ft exterior wall, 9 ft high, 2x4 studs at 16 in, carrying roof and ceiling only, four corners and two intersections, sheathed.
The row. 2x4 carrying roof-ceiling only allows 24 in on centre up to 10 ft. Your 16 in passes with room.
Studs. 31 in the run plus 10 for corners and tees: 41 studs.
Plates. Sole plus double top over 40 ft is 120 linear ft.
Change it to two floors plus roof and the verdict fails outright: that cell is a dash, and no spacing fixes it.
Go to 2x6 in that condition and the table gives 16 in, which works.
The dash is the finding. Almost every framing calculator will happily hand you a stud count for a 2x4 wall under two floors, and the table simply does not cover it.
The formula
Counting, plus a lookup that can refuse:
studs = ⌊ 12L / s ⌋ + 1 + 2c + t bf = linear ft × nominal t × nominal w / 12
L
wall length, ft
s
stud spacing, in, capped by Table R602.3(5)
c, t
corners and tee intersections. Two extra studs per corner, one per tee
nominal
2 and 4 for a 2x4, not 1.5 and 3.5. Board feet are billed on nominal
plates
sole plus double top is three runs of the wall length
Corner and tee counts vary with the detail used. Two extra studs per corner is a three-stud corner; a California corner or a drywall clip uses fewer, which is the point of them.
A dash is not a small number
Table R602.3(5) is short and it is mostly read for one thing: can I go 24 in on centre. The answer for a 2x4 carrying only roof and ceiling is yes, and that is where most people stop reading.
The columns to the right are where it gets interesting. Add one floor and the 2x4 drops to 16 in. Add a second floor and the cell is a dash. It is easy to read a dash as “the table has nothing to add” rather than what it means, which is that the prescriptive path does not cover the condition at all.
The same is true of the 2x3 row, which is dashes across every bearing column and carries a footnote saying it shall not be used in exterior walls. 2x3 is a nonbearing partition stud and nothing else.
The third thing the table hides is in a footnote: the listed heights are distances between points of lateral support, not floor to ceiling. A sheathed wall is braced continuously and gets the full height. An open-framed wall is not, and R602.3.1 wants sheathing on one side or bridging at 4 ft before the tabulated height means anything.
The cell nobody looks at is the two-floor column
IRC Table R602.3(5), size, height and spacing of wood studs
Stud
Bearing wall height
Roof-ceiling only
One floor + roof
Two floors + roof
Nonbearing height
Nonbearing spacing
2 x 3
-
not permitted
not permitted
not permitted
10 ft
16 in
2 x 4
10 ft
24 in
16 in
not permitted
14 ft
24 in
3 x 4
10 ft
24 in
24 in
16 in
14 ft
24 in
2 x 5
10 ft
24 in
24 in
not permitted
16 ft
24 in
2 x 6
10 ft
24 in
24 in
16 in
20 ft
24 in
IRC Table R602.3(5), size, height and spacing of wood studs, 2021 IRC as adopted in the 2022 Connecticut State Building Code
Read across the 2 x 4 row. Roof-ceiling only: 24 in on centre. One floor plus roof: 16 in. Two floors plus roof: a dash.
That dash is not a tighter spacing you can achieve by adding studs. It means the table does not cover it, and a 2 x 4 bearing wall under two floors and a roof is outside the prescriptive path entirely. The three-storey walk-up framed in 2 x 4 is either engineered or wrong, and it is not a distinction most people know exists.
The other row worth noticing is 2 x 3, which is dashes all the way across the bearing columns and carries its own footnote:
Shall not be used in exterior walls.
Table R602.3(5) footnote a
Height is measured between lateral supports, not floor to ceiling
Listed heights are distances between points of lateral support placed perpendicular to the plane of the wall.
Table R602.3(5) footnote c
A 10 ft bearing wall height assumes the stud is braced against buckling perpendicular to the wall. Sheathing does that continuously, which is why R602.3.1 requires bearing walls to be sheathed on at least one side or bridged at not more than 4 ft. An unsheathed, unblocked stud is not laterally supported and the tabulated height does not apply to it.
This matters most during construction, when a wall is stood and left unsheathed over a weekend, and in garages and basements where one face is often left open.
A habitable attic assembly supported by 2 x 4 studs is limited to a roof span of 32 feet.
Table R602.3(5) footnote b
And that footnote catches the increasingly common bonus room over a garage: put a habitable attic on 2 x 4 studs and your roof span is capped at 32 ft regardless of anything else in the table.
Openings do not save you much framing
The intuition is that a window is a hole, so it removes studs. In practice each opening deletes a few common studs and adds a header, two king studs, jack studs at each end and cripples above and below.
On a typical window it is close to a wash. On a door it is often more material than the studs it replaced, because the header is a multi-ply member and the jacks stack.
Size the header on the header calculator, which carries all 549 cells of Table R602.7(1) and tells you the jack stud count, including the case where the code lets you use a framing anchor instead.
Steel studs are a different code entirely
Cold-formed steel framing is not in Table R602.3(5). It has its own provisions in IRC Chapter 6 and its own standard, AISI S230 for prescriptive residential framing, with member designations that encode web depth, flange width and steel thickness rather than a nominal size.
A steel stud is specified as something like 350S162-33: 3.5 in web, 1.625 in flange, 33 mil steel. The thickness is the variable that matters and it is the one nobody quotes, so two studs of the same depth can differ substantially in capacity.
This calculator counts wood. The stud and plate counts transfer to steel framing directly, since the layout arithmetic is identical, but nothing in the table above applies to it.
Advanced framing, and what it is actually saving
Studs at 24 in rather than 16, two-stud corners, single top plates with aligned framing, and no cripples under windows: the package usually called advanced framing or optimum value engineering.
It is permitted where the table permits it, which is the point of checking the row rather than assuming. A 2x6 wall carrying roof and ceiling gets 24 in outright. A 2x4 carrying a floor does not.
What it saves is less lumber and more insulation: fewer studs means less thermal bridging, and on an exterior wall that is usually worth more than the timber. What it costs is that every opening has to line up with the layout, which is a design decision rather than a framing one.
Frequently asked questions
Can 2x4 studs be spaced 24 inches apart?
Yes for a bearing wall carrying roof and ceiling only, up to 10 ft between points of lateral support, per Table R602.3(5). With one floor plus roof-ceiling it drops to 16 in. With two floors plus roof-ceiling the table prints a dash: not permitted at all.
Can a 2x4 wall carry two floors?
Not under the prescriptive table. Table R602.3(5) shows a dash for a 2x4 bearing wall supporting two floors plus a roof-ceiling assembly. Go to 2x6 or 3x4, which are permitted at 16 in, or have the wall engineered.
How tall can a stud wall be?
For bearing walls the table gives 10 ft for every listed size, measured between points of lateral support rather than floor to ceiling. Nonbearing walls go higher: 14 ft for 2x4, 16 ft for 2x5 and 20 ft for 2x6.
What does laterally unsupported height mean?
The distance between points that brace the stud perpendicular to the wall. Sheathing does that continuously. R602.3.1 requires bearing walls to be sheathed on at least one side or bridged at not more than 4 ft, and without that the tabulated height does not apply.
Can I use 2x3 studs?
Only in nonbearing interior walls, up to 10 ft at 16 in on centre. Footnote a to Table R602.3(5) says 2x3 shall not be used in exterior walls, and every bearing column for it is a dash.
How many studs do I need for a 40 foot wall?
Thirty-one at 16 in on centre for the run itself, plus extras at corners and intersections. Four corners at two extra studs each and two tee intersections at one each brings it to 41.
Why are board feet calculated on the nominal size?
Because that is how lumber is sold and billed. A 2x4 measures 1 1/2 by 3 1/2 in, so about 34% of every board foot you pay for is not physically present. It is the convention rather than a trick, but it means board feet and cubic feet of wood are different numbers.
Does a habitable attic change the stud requirement?
Yes. Footnote b limits a habitable attic assembly supported by 2x4 studs to a roof span of 32 ft. Beyond that the studs go to 2x6 regardless of what the rest of the table allows.
How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.
Figures on this page last checked against the source documents on 2026-09-08. Codes are amended locally; confirm against the edition your jurisdiction enforces.
A dash means not permitted. Where Table R602.3(5) prints one, the prescriptive path does not cover the condition and the wall must be designed. Tabulated heights are between points of lateral support, so an unsheathed, unbridged wall does not get them. Steel studs are a different standard entirely.