Last updated July 28, 2026
TRUSS draws elevations of open-web floor trusses — the parallel-chord trusses used in timber floor framing, with a web of diagonals between top and bottom chords. You give it the truss depth, the size of the chord and web members, and the web spacing, and it draws the elevation.
Drawing one of these by hand is tedious and drawing several at different depths is worse, because the web geometry has to be reworked each time. That is exactly the job a parametric routine is for.
It is by Bob Thomas of Thomas Enterprises in San Rafael, California, and it is part of a small family — the same author’s rafter routines and cabinet elevations are also on this site, and all three are built the same way.
Both files must stay together
The archive holds TRUSS.LSP and TRUSS.DWG, and the author’s licence is built around the pair: they may be freely copied provided the two remain together and the header stays intact, so people know what the program does and he gets the credit. His words at the end of that paragraph are “Use and enjoy…”.
The drawing file is not documentation. Extract both into the same folder on your support file search path or the routine will not have what it needs.
The four values it remembers
The author names them in the header, which is more courtesy than most routines of this age extend. All the routine’s variables are local except four, which hold your last answers so they can be offered as defaults next time:
- th — truss height, the overall depth of the truss.
- cw — component width, the width of the chord and web members.
- ch — component height, their depth.
- ws — web spacing, how far apart the diagonals sit.
Because those four persist, drawing a run of trusses at the same specification is a matter of pressing Enter through the prompts. And because they are named, you can check for a clash with your own variables before you load it — the author explicitly suggests renaming them if they conflict.
Expect imperial defaults
The author is American and the companion routines in this family use inches throughout, so expect the same here. That does not stop it working — type metric numbers and you get a metric truss — but the defaults offered will not be sensible starting points for Australian timber sizes.
If you use it regularly, editing the default values to your own standard chord sizes is worth the few minutes. They are set near the top of the file and the header tells you which is which.
Command reference
The file defines a single command, TRUSS.
How to load it
Unzip Truss.zip, put both files in one folder on the support file search path, then load TRUSS.LSP with APPLOAD. Our AutoLISP guide covers loading and the search path.
Step-by-step usage
- Type TRUSS.
- Give the truss height, then the component width and height for the chords and webs.
- Give the web spacing.
- Place the truss. Run it again for the next one — your four values are remembered.
Draw one and dimension it before using the output on a real drawing, so you know the values you typed produced the geometry you expected.
Compatibility notes
The companion routines from the same author reference Release 10, which puts this around 1990. Written-for rather than tested-on, by a wide margin. It is parametric geometry built from standard functions, which is the sort of code that tends to survive; the accompanying DWG is old enough that current AutoCAD will still open it.
Plain AutoLISP with no dialog boxes and no Express Tools calls, so nothing requires the full product; LT users on LT 2024 or later, the release that brought AutoLISP to LT, should be able to run it. See what runs on AutoCAD LT.
Download
| Name: | TRUSS |
| Description: | This file contains a parametric program that creates elevation drawings of floor trusses. All variables are local except those used to carry defaults, as follows: th = default truss height, cw = default component width, ch = default component height, ws = default web spacing. |
| Type: | AutoCAD AutoLISP Routine |
| Author: | Bob Thomas |
| File Size: | 7 Kb |
| Cost: | Free |
| Worked on: | AutoCAD |
| Download File: | Truss.zip |
Related routines
- RAFTER — the same author’s rafter and roof truss routines.
- CABINET — his parametric cabinet elevations.
- WALLS — the structure the trusses sit on.