What Are Line Types and Line Weights

One of the biggest challenges architecture students have is using the correct line weights and line types in their drawings. Incorrect drawing conventions can cause problems because people cannot read drawings properly when you present drawings with inaccurate line weights and line types. Your ideas are unclear, they don’t get adequately communicated, and you do not know if people understand your work correctly.

Architectural drawings use a unique language to communicate our idea about the built form. We use lines, text, symbols, hatching and colour in certain combinations and ways. These different drawing conventions come together to communicate specific information.

Learn more… “An Introduction To Architectural Drawing Systems”

Architecture uses different drawings throughout the design process to communicate various ideas and information. Every architectural drawing will use line types and line weights in similar ways to communicate similar information about our design. All technical drawings created by architects, draftspeople, engineers or industrial designers will use line weights and line types in similar ways.

Let’s start by clarifying what line types and line weights are.

  • Line type is the style of a line. Line types can be a pattern of dots, dashes, text and symbols and be broken and not continuous. Or they can be solid and continuous.
  • Line weight is the thickness of a line.
  • Line colour is the colour of the line when printed. Note that CAD programs will allow you to set up your lines in an infinite range of colours on the screen. Colour helps you identify different layers of information while you are working. But our final drawings will be printed in black, white and grey. When we cannot rely on colour, we must rely on our line types and weights!

Architectural Line Types

Every line in your drawing is going to be a particular type. We start with some simple line types:

  • Solid – Elements that are seen or visible.
  • Dashed – Elements that exist but are not seen or visible help explain the 3-dimensional form and spaces. For example:
    • On a plan, we may show the edge of the roof dashed over or the edge of an overhead cupboard above a kitchen bench.
    • On a plan, you may show the outline of a significant basement level below the ground.
    • On an elevation or section, you may show the outline of a significant element hidden behind.
  • Long dash-short dash – Reference points that do not exist as a physical element but are points in space that help us locate our design. These can appear on plans, sections and elevations. When read across multiple drawings help us understand the three-dimensional volume of space that we design and build within. Long dash-short dash lines include:
    • Site Boundaries – The edges of the site and the area you can design and build within.
    • Boundaries Setbacks – The extent of the area you need to set the building back from the boundary to comply with local building regulations.
    • Grid references – A dimensioned grid set out from a critical point on the site boundary defines points from which to set out the building. A grid reference is dimensioned and locates points in space through an X and Y-axis grid.
      • Plans show grid reference as letters left to right horizontally across the page and numbers vertically top to bottom down the page.
      • Sections and elevations will either show a numbered or letters grid reference across them, depending on how they are oriented.

Learn more… “What Are The Most Essential Architecture Design Drawing Conventions?“

How To Use Architectural Line Types

To determine which line type to use, look at your drawing as a representation of the final built form and ask yourself:

  • Can I see this element in real life? If yes, then solid.
  • Is this a hidden element, or has it been removed in a plan or section? If yes, does it help explain the overall volume or form if shown on the drawing? If yes, then show dashed. If not, then leave it off.
  • Is there a non-existing reference or point in space that will help orient the viewer or understand where a physical element exists in space? If yes, this shows as a setback, boundary or grid that is the same across all your drawings.

Other Line Types

As an architect, mastering these three different line types will take you a long way in your drawings.

However, we will be coordinating and reading drawings from other disciplines such as landscape designers, civil, structural and mechanical engineers, and show drawings from manufacturers. So it is essential to understand that other professions may communicate different types of information in different ways.

When you see line types in a drawing beyond solid, dash and long dash-short dash, look for a key or legend somewhere on the individual drawing or in the drawing set. This will tell you exactly what each line represents.

Architectural Line Weights

Architectural line weights refer to the thickness of lines in a drawing. Any scale drawing representation will use lines of different thicknesses. Thicknesses within an individual drawing and across a drawing suite help communicate information about drawn elements and how different elements relate to one another.

To understand line weights in the simplest way possible, I want to take you back to a time before computers, software and CAD systems. Architects once created all their drawings with pen and paper.

When I was at university, we started our first year with a basic architectural drawing set. It included a compass, three pencils, an eraser, some ink and four technical drawing pens. These pens came in a range of different thicknesses – 0.25mm, 0.35mm, 0.5mm and 1.0mm. Sometimes you might buy an extra thin pen at 0.18mm, but these were very easy to break.

So why am I telling you this?

Because with these four or five pens, you could create every architectural drawing. You can create every architectural drawing on software with only 4-5 line weights.

You might have many different pens or the ability to create infinite line weight on software, but you don’t need them. You only need 4, maybe 5 line weights at the most.

  • 0.7mm – Thickest
  • 0.5mm – Thick
  • 0.35mm – Thin
  • 0.25mm – Thinner
  • 0.18mm – Thinnest

These thicknesses are an excellent place to start. They were used in technical drawing pen sets for decades. They work. You don’t need to reinvent the wheel!

If you are using a felt pen or CAD software, you can slightly adjust the thicknesses. Before starting a hand drawing, choose your pens and figure out which one you will use for thickest, thick, thin, thinner and thinnest. It would help to make sure the line thicknesses are different and work together. Remember, felt pens can change over time.

How To Use Architectural Line Weights

We use architectural line weights slightly differently in each drawing. But let’s start with plan, section and elevation and refer to line weights as thickest to thinnest.

  • Section and cut plan – Thickest for the section through the ground line. Thick for the cut-through primary elements such as walls, floor and roof. Thin for secondary cut elements such as doors and windows. Thinner for tertiary element outlines such as toilets, benches and furniture. I would also use this thickness for drawing conventions such as text, annotations or dimensions. And finally, you can use the thinnest pen or a pencil for material details and texture.
  • Elevation – Again the thickest for the section through the ground line. Thick for the foreground or what is closest. Thin for the mid-ground and thinner for the background. Again, use this thickness for drawing conventions such as text, annotations or dimensions. And finally, you can use the thinnest pen or a pencil for material details and texture.
  • Top Plan – The top plan is the same as the elevation, except no section is cut through the ground.

The table gives you a good summary of how to use the line weights for each drawing type.

What Next?

As you start to research and find different drawings that communicate well, save them. Start to create a library of examples and drawing styles that you like. Over time, you will see different adjustments to the actual line weights. Still, the philosophies of thickest to thinnest very much stay the same. Look at drawings that you find hard to read and understand. Find where the line types and weights are not being used or misused. Consider what you would do differently with line weights and line types to improve the drawing.

They will become second nature once you understand line types and line weights and practice reading drawings. You will notice them when they don’t exist. On your next project, make a real effort to create a clear strategy for your line weights and line types using the guidance above.

Until next time…

Liz at ArchiMash