Types of Lines in Architecture

One of the very first things you learn in architectural school is that a line is the primary component of all architectural drawing...

One of the very first things you learn in architectural school is that a line is the primary component of all architectural drawing and communication. …all designs start as a mere line.

The second thing is the importance of small details, and how something as simple as the thickness of a line can completely alter its entire meaning. 

In this article we aim to help you comprehend these details, and assist you in understanding all the complexities of architecture line types and weights. 

Architecture line types – What are they?

In short, a line type refers to the multiple styles of lines that are used when creating an architectural/ construction drawing, these may consist of a dotted, dashed, long dashed, or simple be a straight solid line for example. Each of these types has a unique purpose and is assigned a specific meaning that it depicts.

Whether you are creating an architectural drawing digitally (on a drafting software like AutoCAD) or manually, line types help to enhance and communicate the intent of drawing – making the drawings easier to understand and read.

Linetypes depict the relationship between objects and their depth, showing which object is closer and which is placed further away, and whether an object/component is placed above or below. Reading through this article will provide you with a comprehensive understanding of these lines and how you can incorporate them into your drawings.

line weights

What typical line types do we use?

One thing to keep in mind before reading further is that while most of the time these lines and their meanings are universally consistent (as shown in our CAD Template Kit), there will of course be exceptions. Not all architects use these lines similarly and their use may vary from firm to firm.

So, it is always a good idea to create a legend that specifies what each line type depicts. 

To help you differentiate and understand universally common line types, we have provided comprehensive descriptions of the typically used line types below:

Solid Line

A solid line is a simple continuous line and represents the visible edges of objects. The thickness of these lines can vary depending on their purpose.

  • Light solid lines: These are used when the objects are not being cut through and are solid projections, e.g. elevation lines.
  • Heavy solid lines: These lines are thicker and darker. They depict those objects that have been cut through in a plane e.g. heavy lines are used in plans as profile lines or cut lines in sections.

Dashed Lines 

A dashed line is made from a series of short equidistant dashes. They are used to depict the edges of anything that is not directly visible in the drawing plane. The lines which use this line type can either be hidden lines or phantom lines and will be discussed in detail in “line type groups” further down in the article.

Dash combination

These lines usually contain some combination of long and short dashes. They are used to depict reference points that do not physically exist but may act as pointers for locating various boundaries or points in our drawings (e.g. required setbacks on a site).

Symbol Lines

“Symbol lines” is an umbrella term for various types of lines that impart some sort of information regarding the drawings. Dimension lines and section cut lines are types of symbol lines. A detailed description of both of these is provided further along in the article.

Tip to remember which line to use…

One thing to keep in mind is that all visible objects are “solid” and can be depicted with a solid line. Whereas, all hidden objects that are not visible in the direct visual plane are “non-solids”, whether they are above or below, will be depicted by a non-solid line.

Why do we use line types?

In any field, professionals and other active participants must communicate with each other. Not just as an act of socializing but to get their ideas across and help others understand their vision. For the ease of this professional communication, people develop a technical language or jargon that is universally understood and accepted.

Similarly, architecture has developed a language of its own as well and one aspect of that language is line types and weights. They make it very easy to communicate our architectural drawings to other professionals in the field

Most drafting softwares such as AutoCAD provides inbuilt options for adding these lines in your drawings which makes it easier and manageable to group similar objects. 

types of lines in architecture

How are different line types used?

Listed below are the general uses of different line types.

Dotted line – Dotted lines are often used interchangeably with dashed lines. They are also used to signify any component that is hidden in a plan or elevation/section view. The choice of using a dotted or dashed line is purely up to the architect.

Solid single line – A solid line is used to depict the visible edges of objects. The object could be a piece of furniture such as a sofa, a table or a counter, etc or it could be a part of the structure e.g. the walls or beams or could be a landscaping element. It is the outline of any component.

Two solid lines with hatch – When two solid lines are placed together and the space between them is filled with a color or a hatch (a patterned fill that specifies the materiality of the object), it signifies a wall. These walls are shown in plans and sections as the hatched walls signify that they have been cut through.

Short dash – Sometimes used interchangeably with dotted lines, these lines are usually used to indicate things that are overhead in a plan or more precisely, above the plan-cut height (usually kept at 4 inches). 

In an elevation, they can be used to depict something that might be hidden behind a door or a wall but has to be shown due to one reason or another.

Long dash – Visually, these are similar to short dashed lines except the dashed segments are longer. These lines are generally used to portray unseen or hidden objects that may not be visible in the drawing but have some importance. They may also depict objects that are much higher up than those depicted by short dashed lines.

In site plans, the existing contours may also be shown with long dashed lines while the new/artificial contours will be portrayed with light solid lines.

Short and long dash – The short and long dash is a combination line type and can be used for various reasons but is usually used to depict reference points or symbol lines. A legend will usually be required to specify exactly what they depict.

Curved line – A curved line on a plan is mostly placed at an opening and is normally a light solid line (although some architects draw the curve with a dotted line). It is specifically used to represent a hinged, swinging door and the position of the curve will convey where the extent of the door’s swing will be. 

lines in architecture

Line type groups

As explained previously, the exact constituents of these groups might change depending on the architect but for general comprehension, we can divide line types into the following groups.

Centrelines – As the name suggests, centrelines are used to mark the centers of an object for alignment purposes. These are also a branch of dashed lines and use a combination of long and short dashes. 

Centrelines do not depict “solid” objects and are simply used to depict the position of an object in that specific plane. Centrelines may also include a CL symbol, short for Center Line, to not confuse the reader.

Dimension lines – These are light continuous lines that show two extreme points of a line and also include a numerical value that provides us with the exact dimension of that line. They may contain an arrowhead at both ends.

Extension line – Extension lines (or thin lines) show the end limits of the object that is being dimensioned. They help us understand which exact dimension is being shown and are placed perpendicular to the dimension lines.

Section cut lines – These are heavy lines on a plan that usually consist of a dot-dash combination and represent the exact position from which a section has been cut.

Section cut lines always have an arrow or some other type of symbol at their ends which signifies the direction from where the section is to be viewed, and may also include a letter such as A or A’ to signify the section’s assigned name.

Section lines – Thin lines that are drawn at an angle of 45 degrees, and are used as a sort of hatching to signify that an object has been cut through in a section.

Phantom lines – Depict major overhead features like overhangs, roof extensions, beams, and details on the ceiling, as well as overhead openings. So any features that are above the cut height are shown with dashed lines and are called phantom lines. They may also be used to depict the alternate positions of movable objects such as an open/closed door.  

Hidden lines – Hidden lines are used to show obscured edges of an object in an architectural drawing. They are also used to depict a completely hidden object, for example, structures under the earth or on a lower floor. Hidden lines are typically dashed lines.

Object line – Object lines are heavy or light solid lines and are used to signify the outlines of all visible objects being drafted.

Boundary line – Boundary lines also called property lines, are dashed lines that show the extent of the plot where your building is to be constructed.

Border line – It is very important to create an understandable composition on an architectural drawing to not create a confusing jumble. Border lines help with this composition. They are solid continuous lines that help to distinguish different drawings (each floor plan can be in its separate bounding box) and the title block from the rest of the drawing.

Break line – Break lines are used to depict objects that have the same shape for the entirety of their length and may be too long to fit in the drawing (e.g. stairs). They are also used to break apart sections of an object for ease of understanding.

The three types of break lines are:

  • Cylindrical break lines: Used to show the cut section of a cylindrical object so that it may be shortened or broken in half for better viewing.
  • Short break lines: Heavy wavy lines are used to depict the broken-off section of a flat object.
  • Long break lines: These indicate that the further part of an object has not been shown or has been removed.

Leader line – Leader lines are thin lines used as pointing or guiding lines that point towards a specific object that may require a note. They are usually drawn at a 45° angle and should not parallel to dimension/extension lines or section cut lines.

line types

Architectural line weights – What are they?

Line weight is the thickness or visual density (lightness/ darkness) of a line. It refers to the strength or heaviness of a line against a background. Varying line weight helps us to distinguish between objects that are placed at different visual/physical hierarchies.

In any scaled architectural drawings, these visual line weights help in making them more readable.

Commonly in architecture school, when students start manual drafting, they are introduced to drafting pens. Each of these pens has a distinct thickness that allows us to create line weights easily, notating the difference in element. 

Types of line weights

The various types of line weights that you need to know about before making an architectural drawing have been explained in the following section. The numeric value mentioned next to the name is the thickness or “point” of the pen/line:

Construction lines (6H-4H, ~0.05mm – 0.1mm / 0.18 – 0.25 pt) – These are usually the lightest lines present in the drawing. Their primary purpose is to help in creating the basic geometry during the initial design process. They are visible enough to assist in the drawing but are light enough that they can be erased later on.

While they are usually erased once the drawing is complete, sometimes they are kept intact to assist explanations or for visual/aesthetic aids.

Light lines (4H-2H, ~0.10mm / 0.3 – 0.4 pt) – These are slightly darker than construction drawings but they must be clear and visible as these are used for symbol lines (dimension lines, extension lines, and section lines) or curved lines (for door swings) and sometimes might be used for landscaping/vegetation as well.

Medium lines (F-H, ~0.2mm / 0.5 – 0.6 pt) – Medium lines are used to depict most of the non-structural objects on a drawing such as furniture or doors/windows etc.

Bold lines (HB-B, ~0.3mm-0.4mm / 0.7 – 1 pt) – These are the second darkest lines on an architectural drawing and are used to draw the primary boundaries or the outermost silhouette of the buildings/object that will distinguish it from the ground.

Cut lines (B+, 0.4mm and above / 1 pt and above) – Cut lines are the darkest lines on a drawing and are used for walls, columns, and all other structural or non-structural components that are being cut through by a sectional plane.

Architecture line weights

Thicker vs. Thinner lines

All architectural drawings, whether they are showcasing a plan, section, or elevation, are providing us with a specific and unique view of our building. And one of the most important pieces of information stored in these is the knowledge of what object is placed in the front and which is at the back. 

And since these architectural drawings are mostly flat two-dimensional images, it can be very hard to distinguish between the myriad of lines if they were all of the same thickness. That is where line weights come in.

The thicker lines are used to depict objects that are at the very front (closest to us) and the thinner lines are used for objects at the back (or are further away from us). Even in 3-dimensional or orthographic drawings, the line weight is a symbol of its hierarchy and position.

Why are line weights important?

Line weights are one of the most important aspects of an architectural drawing. It can be the paramount factor that contributes to the legibility of your drawing. Following are some points which will further elaborate on its importance.

Depth of objects – When creating a 2D drawing of a 3D composition, as architects always do, it is very important to create a sense of depth between objects. Otherwise, the drawing might seem to be an incoherent jumble of lines.

Relationship of objects – When two objects have varying weights, it helps us to understand the relationship they have with not just one another, but also with space. It depicts where exactly and in what position those objects are placed.

Hierarchy – Creating hierarchy is the primary purpose of line weights, e.g. important objects will be thicker while those that do not require more attention (e.g. construction lines) will be thinner.

Readability – When you assign line weights to different options, it allows the reader to distinguish between two objects, otherwise, all components might seem to be melding into each other. In this way, line weights can increase the readability of our drawings.

If you are looking to learn more about line weights and their importance, the below video is a great guide for beginners:

How to create and use different line weights

There are multiple ways to incorporate line weights in our architectural drawings and different architects have different preferences. But for your ease, we have listed below some of the most prominent and simplest ways to use and create line weights:

Thickness – The easiest way is to use a different pen. Or you can simply draw over a line multiple times, to make it seem darker and thicker.

Varying Density – Apart from using a thicker pen, you can create the impression of more weight by drawing lots of lines close to each other. In this way, you can create a distinction between lines and objects.

Variety – Using multiple line weights and types in your drawing will make it easier to understand. You can create variety not only by using different line weights but also by changing the colors of these lines e.g. all doors could be in red and all windows could be blue.

Proximity – As explained above, when using line weights keep in mind the proximity of the objects. So the ones at the front must be the darkest/thickest and they can keep getting lighter the further away they are.

Distinction – Keep in mind that the crux of using line weights is to create hierarchies between various objects. So once you have decided on the internal hierarchy of all components within your drawing, you can start to assign them line weights so it is easier to distinguish between them.

Materiality – Another way to use line weights is to incorporate them into the hatching of your drawings. Depending upon the scale, it is sometimes possible to hatch your drawings so that they show what material the objects are made of. For example, using crisscross diagonal lines to depict soil or two closely spaced diagonal lines to show brick. You can also use a marker or pen to fill the walls that have been “cut” in a section or plan (this process is called Poche).

To sum up

Overall, it is pretty clear that without concise management and usage of line types and line weights, it would be almost impossible to create successful architectural drawings. By incorporating the above-mentioned techniques, we can not only make our drawings more readable but also visually pleasing.

Happy drawing!

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