A drainage layout has the supply run, the waste run and the hot water run side by side, and all three are continuous lines. Printed in black and white, nobody can tell them apart. An AutoCAD linetype library solves exactly that: one linetype per service, with the symbol letters sitting inside the line itself.
This article publishes the Institute's set of 14 types, each one loaded and drawn for real on AutoCAD 2027. For the whole discipline of producing a drawing set, the Institute runs an AutoCAD course for construction.
Forty-five and fifty-nine ship with the software, and still not enough
Counted directly in the linetype files of the 2027 release on the machine:
| File | Linetypes | Used for |
|---|---|---|
acad.lin | 45 | Imperial drawings |
acadiso.lin | 59 | Metric drawings |
That sounds generous until you open them. Almost all of it is variations on dashed, dash-dot and centre lines in three sizes each. Types carrying a discipline symbol — water, drainage, power, buried services — are not there in any form a Vietnamese drawing set would use.
The Institute's set: 14 linetypes
The set falls into four groups, and every type was loaded into AutoCAD 2027 and drawn as a real line to check it.
| Group | Name | For |
|---|---|---|
| Basic | IIC_KHUAT | Hidden line |
IIC_TIM | Centre line, grid line | |
IIC_RANH | Site boundary | |
IIC_CAPNGAM | Buried services, general | |
| Water | IIC_CAPNUOC | Cold water supply, letter N |
IIC_THOATNUOC | Foul drainage, letters TN | |
IIC_NUOCNONG | Hot water, letters NN | |
IIC_THOATMUA | Rainwater, letters TM | |
| Power and data | IIC_DIEN | Power, letter E |
IIC_THONGTIN | Data and telecoms, letter T | |
| Other | IIC_GAS | Gas, letter G |
IIC_PCCC | Fire main, letters PC | |
IIC_TUONGRAO | Fence line | |
IIC_HAN | Weld line |
Loading the whole set into a fresh drawing: 14 of 14 went in, taking the drawing's linetype table from 3 entries to 17.
The reason to keep an AutoCAD linetype library rather than draw services as coloured continuous lines comes down to how drawings are actually consumed. Colour survives on screen and dies at the printer, and it dies again in every photocopy a site engineer makes of the sheet. A symbol embedded in the line survives all of that, which is why the convention exists in the first place.
Loading a linetype: three steps with the dialogs
Loading a linetype is far simpler than installing a hatch pattern: one .lin file holds as many definitions as you like, and no search path has to be registered. The screenshots come straight from AutoCAD 2027.
Step 1 — download the file and keep it somewhere findable.
iic.lin is a few kilobytes. Unlike a hatch pattern you do not need to keep it long term: once loaded, the definitions live in the drawing and deleting the source file costs nothing.
Step 2 — open the manager and click Load.
Type LT and press Enter. The Linetype Manager opens, and a new drawing shows only ByLayer, ByBlock and Continuous. Click Load… at the top right.
Step 3 — point at the file and pick what you need.
The Load or Reload Linetypes dialog opens, reading acad.lin by default. Click File… and point at the iic.lin you downloaded. The list switches to the Institute's 14 types, with a description column that sketches each pattern in characters so you can read it at a glance.
Hold Ctrl to pick several at once, or right-click and choose Select All to take the whole set. Click OK twice and it is done.
Unlike a hatch pattern, a linetype is copied into the drawing when loaded, so the recipient of the drawing sees the correct linework without the .lin file.
Complex linetypes: the letters live inside the line
The eight types in the water and power groups are the valuable part of the set, because they are complex linetypes — the line carries text, not just dashes and dots.
Autodesk describes the category on its linetype customisation page: "A complex linetype can contain embedded shapes that are saved in shape files. Complex linetypes can denote utilities, boundaries, contours, and so on."
The practical gain is obvious once you have drawn one external works plan. Four runs pass within a metre of one another, and printed in black and white the layer colours mean nothing. With these utility linetypes, the reader sees N, TN, E and PC repeating along each run and knows immediately which is which, without consulting a legend.
One caveat: the text inside the line takes the drawing's STANDARD text style. If your template has changed STANDARD to another font, the letters change with it, and that is expected behaviour rather than a fault.
Assign linetypes to layers, not to individual objects
Once the set is loaded there is one more decision, and it affects the whole drawing set rather than one sheet.
| How it is assigned | What happens when it has to change |
|---|---|
| Straight onto each object | Every object on every sheet has to be reselected |
Onto the layer, objects left ByLayer | Change one row, the whole set follows |
The second is the only approach that survives a package of thirty sheets. Set up one layer per service — MEP-CAP-NUOC, MEP-THOAT-NUOC, MEP-DIEN — give each layer its linetype, and draw with objects set to ByLayer. When the client changes the symbol convention you edit one row in the layer table.
Building a proper layer set is covered in our article on layers in AutoCAD.
A habit worth forming on infrastructure work: put the layers and the linetypes into the practice template once. Every new drawing then starts complete, nobody has to remember to load anything, and the whole team draws the same symbols. That is a large part of what separates a practice producing coordinated sets from one where every engineer has a personal convention.
The ltscale variable: why the line still looks continuous
This is the most common question after loading, and it is not a fault in the file.
The same drawing, the same 14 types, one number changed:
LTSCALE | A 2,600-long line reads as |
|---|---|
| 1 | Minute fragments; the letters are illegible |
| 30 | Clear dashes, with N, TN and PC readable |
The reason: the set is defined in millimetres, with a dash 12 units long. On a line 2,600 long that repeats more than two hundred times, so it reads as continuous. Multiply the scale and it resolves.
A useful starting point is the reciprocal of the plot scale: a sheet at 1:100 begins at LTSCALE 100 and gets adjusted by eye from there. What matters is that the value is a property of the sheet, not of the file you downloaded.
The right number for your drawing depends on the plot scale. Choosing the ltscale variable and the related CELTSCALE is covered in detail in our article on linetypes in AutoCAD, which also shows how to write your own definitions.
Choosing a downloadable set without wasting an afternoon
Search for a linetype set and dozens come back, most sharing three problems.
| Common problem | Consequence |
|---|---|
| Defined in inches | Loaded into a millimetre drawing, the pattern shatters or disappears |
Complex types calling .shx shape files not included | They load, but drawing one reports a missing shape file |
| Names that clash with the standard types | Existing linework in the drawing changes appearance on load |
The third is the most damaging and the least anticipated. A set naming its types DASHED or CENTER overwrites the standard definition on load, and every existing object using that name changes immediately. A plan that was correct is suddenly wrong, with nothing to explain why.
The Institute's set avoids all three: metric definitions, text drawn from an existing style rather than an external shape file, and every name prefixed IIC_ so nothing of Autodesk's is touched. The matching hatch pattern set is in our article on an AutoCAD hatch pattern library.
Three things often repeated that are not true
| Often repeated | What was measured on the 2027 release |
|---|---|
The .lin file has to travel with the drawing | Linetypes are copied into the drawing on load; the file is not needed |
| A line still showing continuous means a broken file | The same file at LTSCALE 30 resolved perfectly |
One .lin file can only hold one definition | This set holds 14, and all 14 loaded |
Frequently asked questions
Is an AutoCAD linetype library worth setting up for a small job?
For one sheet, probably not. From the point where two services share a drawing, it pays for itself the first time the sheet is printed in black and white.
Which command loads a linetype library?
Type LT for the Linetype Manager, click Load, then File, and point at the .lin file.
Loaded, but the lines still look continuous.
Raise LTSCALE. The set is metric, so a large drawing needs a value in the tens.
Does the recipient of my drawing need the .lin file?
No. The definitions are copied into the drawing on load, so it opens correctly anywhere.
The letters inside the line show in the wrong font.
They follow the drawing's STANDARD text style. Change that style's font and the letters change with it.
How do I remove a type I loaded by mistake?
Open LT, select it and click Delete. A type still in use is refused, so change those objects first, or run PU and pick Linetypes to clear every unused one at once.
Can I add my own definitions to this file?
Yes. Open iic.lin in a text editor and copy the existing two-line pattern: a name and description line, then the numeric line.