TRUSSFRAME draws a complete roof truss — top chords, bottom chord and the full web pattern — from four numbers and one pick point.
What TrussFrame does
Six standard configurations:
King Post a single vertical post from bottom chord to peak. Short spans
Fink the common "W". The most widely used domestic truss, and
the most material-efficient of the six for medium spans
Howe verticals in tension, diagonals sloping toward the peak
Pratt the mirror of Howe - diagonals slope toward the heels,
which puts them in tension instead of compression
Belgian a simplified Fink with fewer web members
Fan webs radiating from the heels toward the peak
How to use it
- Load the routine with
APPLOAD, or put it on your support file search path. - Type
TRUSSFRAME. - Choose the pattern.
- Give the span, the rise, and the lumber width and thickness.
- Pick the left heel.
How it works
One drawing engine and a small table, not six near-identical routines. Every one of these trusses is the same triangle with a different set of web members inside it.
Four points frame the truss: the two heels, the midspan point on the bottom chord, and the peak directly above it at the given rise.
The rafters and the bottom chord are divided into equal parts. How many differs per truss — a Fink quarters its rafters, a Howe thirds them — and those two divisors are the first two numbers in each table entry.
Every division point gets a short name, and the webs are lists of those names. The Howe pattern reads literally as E A F B P3 C G D H — a single zigzag from the left heel across to the right. Adding a seventh truss type means adding one line to the table, not writing another function.
Lumber thickness is applied as AutoCAD extrusion thickness, so the truss comes out as a 3D object with real depth rather than a flat diagram. THICKNESS is put back afterwards, so the setting does not leak into whatever you draw next.
Lumber width becomes the polyline width, so the chords and webs are drawn at their true scantling rather than as single lines.
Notes and limits
- Six patterns, one table entry each.
- The truss has real depth via extrusion thickness.
- This is geometry, not a design. Member sizes and connections are an engineer’s call.
- One undo group covers the truss.
Download and details
| Name | TrussFrame — draw a timber roof truss in six standard web patterns |
| Download | TrussFrame.lsp — 12.6 KB, plain AutoLISP source. Downloads directly; no zip to unpack. |
| Type | AutoCAD AutoLISP routine |
| Command | TRUSSFRAME |
| Requires | nothing beyond a CAD platform with AutoLISP. |
| Source size | 12.6 KB, 308 lines |
| Error handling | Yes — a *error* handler restores every system variable it changed, on cancel as well as on error. |
| Undo | The whole operation is wrapped in a single undo group, so one U reverses all of it. |
| Compatibility | AutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer. |
| Author | YZ, August 2026 |
| Licence | Free to use, supplied “as is” with no warranty. |
References
- TRUSS LISP — parametric floor truss elevations
- RAFTER LISP — rafters and cuts for the same roof
- ROOFPITCH LISP — the pitch triangle behind the numbers
- More free AutoLISP routines on this site
- Wisey’s Steel Shapes — free structural steel section drawing program