Lines, lettering, symbols and abbreviations

If drawings are a language, lines are its alphabet. Every line on a construction drawing has a weight, a pattern and a meaning: a thick continuous line might be a wall cut through on a plan, a thin dashed line an object hidden above or below, a long chain of dashes and dots a center line or grid line. Symbols and abbreviations then add vocabulary, packing a great deal of information into a small space. This lesson teaches the alphabet and the common vocabulary: line types and weights, lettering and notes, material hatches, reference symbols, tags, and the abbreviations that fill every set. Each set has a legend that defines its own symbols, and the legend always governs, but most sets follow similar conventions, so learning the common ones lets you read quickly and spot when a set does something unusual.

Line weights

Line weight is the thickness of a line. Drawings use a hierarchy of weights so that the most important information stands out:

• Heavy (thick) lines show objects cut by the plane of a plan or section, such as walls, columns and slabs in section, and the outline of the building on a site plan.
• Medium lines show objects seen beyond the cut but not cut, such as the edges of countertops, steps or a window sill seen in elevation.
• Light (thin) lines show dimensions, leaders, hatching, grid lines and other annotation, and minor surface features.

On a well-drawn floor plan, a quick glance shows the walls in bold, the furniture and fixtures lighter and the dimensions lightest of all. This hierarchy makes plans readable at a glance. When drawings are printed poorly, reduced too far or viewed on a small screen, line weights can be lost, which is one reason to view important sheets at full size or zoom in on the PDF.

Line types

Line type, or pattern, tells you what kind of object a line represents. The most common types are:

Some lines change meaning by discipline. On civil drawings, dashed lines with letters, such as a line marked "W" or "SAN", show buried water mains or sanitary sewers; on electrical drawings, lines between symbols show circuits; on mechanical drawings, single lines can represent pipes and double lines ductwork. The discipline's legend sheet explains these.

Existing, new and demolished work

On renovation and addition projects, drawings must distinguish existing construction to remain, existing construction to be removed and new work. Common conventions are:

• Existing to remain: lighter or gray lines, sometimes screened (shown at reduced intensity).
• Existing to be removed: dashed lines, often on separate demolition plans, with demolition notes or keynotes.
• New work: bold, solid lines, often with a hatch or fill for new walls.

Many sets include separate demolition plans before the new construction plans. Reading both together is essential, because the demolition plan tells you what must go before the new work can start, and items shown dashed on a demolition plan are work in the contract, with real cost and real hazards such as asbestos or structural support.

Lettering, notes and keynotes

Text on drawings is kept short and consistent. Most drawings use upper-case sans-serif lettering, whether hand-drawn in the past or generated by CAD today, because it remains legible when reduced. Text comes in several forms:

• View titles: the name of each view with its number and scale, such as "2 WALL SECTION, SCALE 1:20".
• Labels and leaders: short text with a thin line (the leader) pointing to the object it names.
• General notes: numbered notes that apply to the whole sheet or the whole discipline, often placed on the first sheet of each discipline. Structural general notes, for example, give design loads, material strengths and standards.
• Sheet notes: notes that apply only to the sheet on which they appear.
• Keynotes: numbered or coded tags on the drawing that refer to a list of notes on the same sheet, keeping the drawing uncluttered. Some offices tie keynotes to specification section numbers, so a keynote such as 09 21 16.A refers to a gypsum board item in that specification section.

General notes are easy to skip and costly to miss. They often contain requirements that appear nowhere else on the drawings, such as "Provide blocking for all wall-mounted equipment", "All dimensions are to face of stud unless noted otherwise" or "Contractor to verify all existing conditions before starting work".

Material indications and hatches

In sections and plans, the cut surfaces of materials are filled with hatch patterns that indicate the material. A few patterns are almost universal:

• Concrete: a random pattern of dots and small triangles representing aggregate.
• Masonry (brick or block): diagonal lines, with concrete block often drawn as diagonal lines with a different spacing or cross-hatching.
• Earth: a pattern of short diagonal strokes, sometimes with dots, below grade.
• Gravel or granular fill: small circles or stones.
• Wood: an X through dimensional lumber cut in section, or a grain pattern for finished wood; plywood shown with layered lines.
• Steel: solid fill or close diagonal lines for small sections.
• Insulation: a loopy wavy line for batt insulation and a cross-hatched or diagonal pattern for rigid insulation.
• Gypsum board, plaster and finishes: often too thin to hatch and drawn as single or double lines with labels.

Hatches only show the general material. The exact product, strength and grade come from labels, notes and the specifications. A concrete hatch does not tell you the concrete strength; the structural general notes or the specifications do.

Reference symbols

Reference symbols connect views across the set (Lesson 1). Their exact shapes vary by office, but the common ones are:

• Section symbol: a circle divided by a horizontal line, with the view number above and the sheet number below, attached to a cut line, with an arrow or solid triangle showing the direction of view.
• Detail callout: a circle or rounded boundary drawn around the area to be enlarged, connected to a bubble with the detail number and sheet number.
• Elevation marker: a circle or square with one to four arrows or triangles, each with a view number, showing the directions of interior or exterior elevations.
• View title: placed under each view, with a bubble repeating the view number and the sheet from which it is referenced, plus the title and scale.
• Grid bubble: a circle at the end of each grid line containing a letter or number.
• Match line: a heavy line with a label where a large plan continues on another sheet, such as "Match line, see A-103".
• North arrow: shows plan north, sometimes alongside true north if the building is rotated from the compass.
• Spot elevation: a symbol, often a small cross or target with a number, giving the height of a point (Lessons 3 and 5).
• Revision cloud and delta: a scalloped cloud drawn around changed work with a triangle containing the revision number (Lesson 11).

Tags

Tags identify individual items and link them to schedules or legends. Most sets use a different shape for each kind of tag so they are easy to tell apart, for example:

• Door tags: a circle or ellipse with the door number, often matching the room number, such as 104A for the first door into room 104.
• Window tags: a hexagon or diamond with a window type, such as W3.
• Wall or partition type tags: a diamond, rectangle or flag with a code that refers to a wall type legend showing its construction, height and fire rating.
• Room tags: a rectangle with the room name and number, sometimes with the finish code or area.
• Equipment tags: a rectangle or circle with an equipment code, such as AHU-1 for an air handling unit or P-2 for a pump, referring to an equipment schedule.
• Fixture tags: letters or numbers beside plumbing or lighting fixtures, such as WC-1 for a water closet type or L4 for a light fixture type.

Tags are powerful because they keep drawings uncluttered: instead of writing the full construction of every wall, the drawing shows a small tag and the legend shows the construction once. The price of that efficiency is that you must look up every tag. A wall tag that reads 2B might mean a one-hour fire-rated assembly to the underside of the deck above, which is very different from the non-rated partition to the ceiling beside it.

Abbreviations

Drawings use abbreviations heavily. Every set should include an abbreviations list, and you should check it rather than guess, because abbreviations differ between offices and disciplines. Some are nearly universal:

A few abbreviations deserve special attention because they shift responsibility or scope:

• TYP means the item shown applies everywhere the same condition occurs, even where it is not drawn. One typical detail might govern hundreds of locations.
• SIM means similar: the condition is like the one shown, but not identical, so you must work out the differences, and ask if they are unclear.
• UNO or UON means the note applies unless the drawings say otherwise somewhere else, so you must look for the exceptions.
• NIC means not in contract: the item is shown for coordination but is provided by others, such as the owner or another contractor.
• VIF means verify in field: the dimension or condition must be confirmed on site before work proceeds, and the contractor carries that responsibility.
• NTS means not to scale: never scale the view.

Legends and the general sheets

The front of each set, and the first sheet of each discipline, normally contain legends: tables defining the symbols, line types, hatches and abbreviations used. Electrical and mechanical legends are especially long, because those drawings rely heavily on symbols. A set may contain several legends, one per discipline, and they may contradict each other: a circle with a letter might be a door tag on architectural sheets and a light fixture on electrical sheets. Always read each discipline's legend before reading its plans.

Some US public owners, such as federal agencies, state departments of transportation and large school districts, publish their own symbol and abbreviation standards that consultants must follow, and some projects in areas with large Spanish-speaking workforces add Spanish translations of key safety and general notes.

Dimensions as symbols

Dimensions are themselves a kind of symbol, drawn with thin dimension lines, extension lines that run from the object to the dimension line, and terminators such as arrowheads, ticks (short diagonal slashes, the usual choice on architectural drawings) or dots. The number written on the dimension line is the figured dimension. Lesson 3 explains how to read dimension strings and calculate missing dimensions; for now, notice that a dimension string usually runs between specific reference points, such as a grid line, the face of a stud, the center line of an opening or the face of concrete. The reference point is part of the information: a dimension "to face of stud" and one "to face of finish" differ by the thickness of the gypsum board.

Reading conventions as a professional

Experienced readers combine these conventions into a fast scanning technique. On a plan, they first see the heavy lines (walls and structure), then read the grid and overall dimensions, then the tags and room names, then the notes and keynotes, and finally follow references to sections and details. They look for anything that breaks the pattern: a wall with a different hatch, a dashed line that suggests something overhead, a cloud showing a revision, a "VIF" note or an "NIC" item. These anomalies are where questions, risks and extra costs hide.