Anatomy of a wall

A wall is a grid, and every member has a name

Take the boards off an LSF wall and a steel grid is left: two horizontal tracks, one on the floor and one at the top, and between them studs standing every 600 mm. Where there is a door or a window, the grid rearranges itself around the opening. At mid-height, a line of blocking and a strap hold the studs sideways. And somewhere along the wall, an X strap keeps the panel from racking into a parallelogram.

Each of these pieces has a role, and the role decides three things: the section, how it connects to its neighbors and what the engine checks in it. Knowing the name of each piece is what lets you read the bill of materials, the sheet and the CalcSteel check table without stumbling.

The example is the single-story house that runs through the LSF articles: 9 x 7 m, 2.80 m ceiling height, a roll-formed project on the FRAMECAD F325iT. The front wall has a 0.80 x 2.10 m door P1 and a 1.20 x 1.00 m window J1 with the sill at 1.00 m.

• 600 mm: stud spacing, half of the 1.20 m board
• 2.80 m: ceiling height of the example house
• 1.381 kg/m: the C 89x41/39x12x0.95 of every C piece in the wall
• 1.40 m: unbraced length of the stud with the line at mid-height

The front wall, piece by piece

The figure below is the front wall of the house in the CalcSteel 3D view, without boards, seen from outside. The door is on the left, the window on the right, and the colors are the ones the 3D view gives each role: light blue for the track, mid blue for the stud, dark blue for the opening pieces, teal for the header lattice and green for the bracing.

1. Bottom track, fixed to the floor
2. Top track, which closes the top
3. Stud, at 600 mm spacing
4. Corner stud, where the wall meets the side wall
5. King stud, the full-height piece beside the opening
6. Jack stud, which supports the head track
7. Head track, the horizontal track over the opening
8. Lattice header, which carries the load over the opening
9. Cripple above the opening, short, from the header to the track
10. Sill, the bottom of the window
11. Cripple below the sill, short, from the track to the sill
12. Blocking, between two studs
13. Strap, the horizontal strap at mid-height

Two pieces are missing from the picture, and both show up further on: the X strap, placed with the Strap and blocking tool (see Blocking and bracing), and the board, which closes both faces (see What carries load and what only encloses). What the app calls a short stud, numbers 9 and 11, is the cripple of English-language manuals.

Name, label, color, class and section

Every member of the wall is created with a label. On the opening, header and bracing pieces it starts with the role code: KO, JK, HT, BQ. Studs and track segments get M or G and a number, and the app names them by wall and position, such as "montante 3" (stud 3) or "guia inferior" (bottom track). The class groups the members of the same section, and it is through the class that you change the section of many pieces at once.

Why everything comes out in 0.95

A roll-formed project on the F325iT has its section fixed by the machine: every C piece comes out with the stud section. That is why the lattice header, the head track and the sill are also 0.95 mm C 89, 1.381 kg/m. The 1.15 mm that Steel and sections shows in the Header row of the Structure tab applies to the solid header, the one made of full sections, which the opening also accepts.

The strap does not go through the roll former

The strap and the X strap are flat steel strips, the catalog RET 50x0.95, 0.373 kg/m. They are not formed on the F325iT and carry no machine operations: they are cut to length and screwed to the face of the studs. They belong to a tie class, and that has a consequence in the calculation (see What the engine checks).

Colors from the 3D "by role" mode, the default. Sections and weights from the CalcSteel catalog, October 2026. File codes from the app's FRAMECAD connection model.

Three standards give the pieces their names and rules

NBR 16970-2, part of the Brazilian LSF standard, covers structural design: it defines the pieces and says how the panel works. NBR 16970-3 covers interfaces, and it is the one that deals with the window opening and where a cabinet can be fixed. NBR 14762 is the Brazilian standard for cold-formed steel sections, where the checks of each member come from. The items below are the ones this page uses.

The stud fits into the track, and the spacing comes from the board

The fit, the most repeated connection in the house

The stud goes down between the flanges of the track. On the F325iT, when its end does not fit, the machine crushes it (the swage), the track lip is cut where the stud sits, and both pieces come out with the recessed hole (dimple) where the screw goes. That is the fit of the FRAMECAD model, the same at the top and the bottom.

The app's Brazilian market fastening rule calls for 2 wafer-head 4.2x19 screws per end, through the flange. The track works lying flat, fixed to the floor or to the track of the story below, and passes to the support what each stud brings.

On the wall card, the Fit badge counts the joints that touch with no gap, and Web ⊥ wall confirms that every section has its web crossing the thickness of the wall.

The 600 mm spacing is half of the 1.20 m board, and that is what 16970-2 asks for in item 4.1: a module that is a submultiple of the board, so that every joint has a stud behind it. The app's Brazilian market offers 400 and 600 mm, with 600 selected. The app always counts the grid from the same corner of the project, not from the start of each wall, so that parallel walls and stacked stories have their studs on the same line. Every wall closes with a stud at each end, even if the last bay comes out shorter than the spacing.

At the corner there are two studs, one from each wall

Where two walls meet in an L, each one has its own stud at the corner, with its web crossing its own thickness. The wall that runs to the corner closes with its end stud; the one that butts against it gets a stud of its own, the corner stud, label QN, oriented in its plane. In the FRAMECAD model that is the corner: two studs, one from each wall, screwed to each other, with no closed box and no clip. The same applies to the T joint.

The corner is where foreign manuals talk about a double stud: in the finished wall, there are two pieces side by side. The market fastening rule calls for hex-head 4.8x19 screws in a zigzag, every 200 mm, at the corner, the T and the X.

The example house has four L corners, and the card of each wall shows it in the 4 joints · 4 L badge.

How the pieces of the wall meet

The app's FRAMECAD connection model has four kinds of joint. In a fit, the end goes in between the flanges of the other piece. In an overlap, the piece passes over the flanges of the other, with its web notched. In bearing, it only rests against it. And in a mid-span crossing, two pieces cross away from their ends. When the receiving piece shows its open side, it is a fit; when it shows its web, it is an overlap.

The window: the opening interrupts studs, and something has to carry their load

Window J1 is 1.20 m wide. At 600 mm spacing, two studs would fall inside the opening. They do not just disappear: the load that would come down through them is carried by the header, which hands it sideways to the studs that frame the opening. That is why the opening is the part of the wall with the most pieces per meter.

King stud (KO). Full height, from the bottom track to the top track, on each side of the opening. It holds the wall beside the window against the wind.

Jack stud (JK). Set against the king stud, it rises to the head track and supports it. The house uses the Single option of the opening dialog, one jack stud per side.

Head track (HT). The horizontal track over the opening, at the top of the window, at 2.00 m. The pieces above rest on it.

Header. Here, a lattice header: a chord on top, the head track below and verticals and diagonals between the two, 300 mm deep, the default of the opening dialog.

Cripples (CT and CB). The upper ones go from the header to the top track; the lower ones, from the bottom track to the sill.

Sill (SL). The bottom of the window, installed open side down: the lower cripple goes into its open side, as a fit.

The door, with dimensions, and the back-to-back king stud

The door repeats the window without the sill: a full-height king stud on both sides, a jack stud up to the head track at 2.10 m, the 0.30 m lattice header above and, from it to the top track, two cripples. The door has a 0.80 m opening and the header spans all of it.

Back to back

In the FRAMECAD model the king stud sits back to back with the jack stud, like the pair of brackets ][: the king stud with its open side facing away from the opening, the jack stud and the end post of the header with their open side toward the opening. The two webs touch and are screwed through the web, with hex-head 4.8x19 screws every 600 mm, at least two, under the market rule.

Lattice or solid

The opening dialog offers a lattice header, the one in this house, or a section header. The section header is solid: Box (two sections lip to lip), I (two sections back to back through the web) or Single, and it rests on the jack stud. It is the one that uses the section from the Header row of the Structure tab, the 1.15 mm C, and it is covered in detail in Headers.

Blocking and strap: the line that cuts the stud in half

A 2.80 m stud in compression, on its own, buckles sideways in a single wave, from floor to ceiling. If a piece holds it at mid-height, the wave has to fit in 1.40 m, and the force it can take rises a lot, because the critical load falls with the square of the length. That piece is the bracing line: a strap, the horizontal strap screwed to the face of the studs, and blocking, pieces of section lying flat between two studs, which give the line something to bear against.

The wall is created already braced

Every new LSF wall in CalcSteel is created with one line at mid-height: with a 2.80 m ceiling height, the stud has 1.40 m unbraced. The strap goes on one face and stops at door and window openings; in each continuous run of it, blocking goes into the first and the last bay between studs, so the line has something to anchor to at both ends, and every 3.60 m, under the market rule. It is the same piece as the Strap and blocking tool: you can remove, change or add lines with it.

The market rule, in the tool

When you place bracing with the tool, the app's Brazilian market rule divides the height into equal parts of at most 1.25 m, counting the tracks. With a 2.80 m ceiling height that gives two lines, at 0.93 m and at 1.87 m, and the stud has 0.93 m unbraced.

Where it meets another wall, the strap of the butting wall stops at the face of the continuous one, without crossing it; the strap of the continuous wall runs to the end. The blocking passes over the flanges of the studs with its web notched: that is the overlap of the FRAMECAD model. And the line only counts as restraint because it is perpendicular to the stud and has strength and stiffness, as NBR 16970-2 requires in items 7.1 and 7.2.

The X strap holds the whole wall against the wind

Blocking and strap hold each stud. Holding the wall is the job of another piece. Pushed sideways by the wind, a grid of studs and tracks with simple connections racks into a parallelogram. The X strap, two diagonals of steel strap from the foot of one standing piece to the head of another, prevents that: one of the diagonals stretches and holds.

In the app it is placed with the Strap and blocking tool, X strap type. The section is RET 50x0.95, the same as the strap, and by default the X strap goes on both faces of the wall: on one face only, it would twist the stud. The angle to the horizontal stays between 30° and 60°, and automatic placement aims for 45°.

Strap is thin sheet: it stretches well and cannot take compression. In each wind direction, the diagonal in tension does the work. That is why the X has two diagonals, and why the engine calculates the strap as a tie (see What the engine checks).

Three jobs: carry, brace and enclose

Carries load

Track, stud, corner stud, king stud, jack stud, head track, header, cripples and sill. They take the weight of the roof, the ceiling and the wall itself, plus the wind, and carry it all down to the foundation.

Braces

Blocking and strap, which hold each stud sideways; X strap, which holds the whole panel. They carry almost no gravity load, but without them the load-bearing pieces buckle too early.

Only encloses

Boards, insulation, membrane and finishes. They add weight and pass the wind to the grid but, by default in the app, they do not count as structure.

The weight of the enclosure

Default for the app's Brazilian market: 35 kgf/m² of wall, about 0.34 kN/m².

The default board is 1.20 x 2.40 m. Outside, 11.1 mm OSB, fastened with bugle-head 4.2x32 screws every 150 mm at the edges and 300 mm in the field, a water-resistive membrane and 10 mm cement board; in the middle, 50 mm mineral wool; inside, 12.5 mm standard gypsum board. The board enters the calculation as weight and as the surface that takes the wind and passes it to the studs.

The wall in the app: one click and the card tells you what it is

Click a wall in the 3D view or in plan and it turns orange, with a card underneath. The front wall of the house shows up as Parede 4 (wall 4), exterior, 9.00 m.

The buttons in the top row open the outputs of the wall: Sheet, Panel plan, Details, Connections, Typicals, Project cut list and Open view. The outputs have pages of their own: LSF sheets, Standard details and Cut list, takeoff, DXF and IFC; Connections opens the Connections panel. The Edit button opens the wall to work on it piece by piece, and Editing tools walks through it.

Each piece, its own check

The LSF engine builds the member model of the whole house, computes the forces for each combination and checks each member under NBR 14762, with the LSF rules of NBR 16970-2 on top. The role of the piece decides what goes into the calculation.

The force in the bracing line

For each braced stud, NBR 16970-2 (7.2) requires a force Fbr = 0.004·NSd and a stiffness Sbr = 2·γr·NSd/Lbc, with γr = 1.35. The engine adds up the shares of all the studs the line braces, combination by combination, up to the point where it is anchored, and checks strap and blocking with that sum, in a step of its own: the line does not enter the member model of the house.

Why the strap leaves the model

A strap in compression buckles under almost nothing. If the model kept it, it would carry a compression it cannot carry. In each combination the engine removes the diagonal in compression and redoes the calculation, and only the one in tension stays, as in the real wall.

And what stays with the designer

Knowing what the engine does not check is as useful as knowing what it does. Three items of the wall stay outside the member calculation and are the responsibility of the design.

1. The strength of the connections. The number of screws at each joint comes from the market fastening rule: it is a construction rule, and the app counts and lists it. The strength of the self-tapping screw, in shear and pull-out, is item 10.5 of NBR 14762, and it is not part of the member checks.
2. Anchorage to the foundation. The anchors that hold the bottom track to the foundation and keep the wall from overturning and lifting under wind are item 6 of NBR 16970-2. The support reactions come out of the calculation; designing the anchorage is up to the project.
3. The board as structure. With the board bracing switches off, the default, the board is only weight and wind surface. Turning a switch on makes the engine count on it, and the responsibility for that choice is yours.

The Brazilian market fastening rule

Default values for the app's Brazilian market, editable, based on the IFSul LSF handbook and the OSB DATec 015. The 200 mm spacing at the corner is the app default.

The wall, in one line

Tracks on the floor and at the top → studs every 600 mm, counted from the corner of the project → one stud from each wall at the corner → around the opening, king stud, jack stud, head track, header and cripples → a line of blocking and strap at mid-height → X strap in both directions → board that encloses and adds weight.

The example so far

• 9 x 7 m: single story, four L corners
• 2.80 m: ceiling height
• P1 J1: 0.80 x 2.10 door and 1.20 x 1.00 window
• 1.40 m: unbraced stud