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Drafting conventions: scale orientation

The set up construction documents contains numerous pages, like a book, as well as a table of contents (but not an index). The page order has already been described. Although the bound drawings resemble a book, they are not exactly a "narrative" with a clear beginning and end. Each drawing is somewhat self-sufficient, sometimes entirely so, while others are incomprehensible without being placed in a larger context.

One way to understand the organizational structure of such drawings is to think of the floor plan as the key drawing, to which all other drawings somehow relate. The primary means of linking these other drawings is through a linear progression from plan to section to detail (or from plan to large-scale plan). Thus, it is usually impossible to start with a detail and work backwards; rather, the way to understand the place of the detail in the overall building design is to find it, i.e., be referred to it, from a section drawing, which was in turn "found" from the floor plan.

Further, the way these drawings are keyed together is through section and detail symbols.

Orientation: All plans should have the same orientation, ideally with "north" pointing up. This includes site plans, floor plans, large-scale plans, and plan details. The same is true of sections and detail sections.

If the entire plan doesn't fit on a single sheet, use matchlines to patch together pieces of the larger plan.

True north/plan north: A site plan may be oriented with "true north" pointing up, but with the building axes (and such axes usually, but not always, can be discerned) having a different orientation, not corresponding to the N-S or E-W geographical directions. In such cases, create a "plan north" in order to "straighten up" the building plans, while still being able to refer to elevations and directions with the N-S-E-W designations.

The official north arrow symbol for such contexts is shown like this:

...but in other contexts the dotted arrow is reserved for "magnetic north" (rarely used) with true north shown as in the sketch.

Grid lines: Use vertical and horizontal "grid" lines, primarily to designate structural items, especially columns, but also load-bearing walls or shear walls. Can also be used to show a "module" that may not be related to the structure. Vertical grid lines have "bubbles" at the top (numbered from left to right), while horizontal grid lines have "bubbles" at the right, lettered from bottom to top. Do not use the letters O or I (which resemble the numbers 0 and 1). See "Symbols Module" for more details. (PDF page 633; the symbol section begins on PDF page 609).

It is possible to use fractional designations between primary grid lines, e.g., 3.5 between 3 and 5; or C.5 between C and D.

It is OK to omit the grid lines in a multistory building where a column is no longer present within a given floor plan. Note that the structural drawings maintain the grid line in the floor plan view immediately above the point where a column "drops off," since the structural plan for a given level is interested in the support for that level, which occurs under the floor:

Coordinate system: The building can be oriented both horizontally and vertically in the following ways: on the site plan, a point can be dimensioned to some "benchmarks" or property lines, and the angle of the building's primary grid lines can be measured to some site boundary line. On the building section, a datum can be established as the ground-floor elevation, usually set arbitrarily as 100', but also related to the actual "National Geodetic Vertical Datum" which are used to coordinate such things as drainage and grading. A note indicating this relationship should be placed on the site plan.

Drawing layout:

For each drawing in a "drawing block," show (a) title, (b) identifying number, and (c) scale.

Each drawing should be subdivided into discrete areas, to the extent possible, for different types of information, including grid lines, dimensions, notations, and the so-called "leaders" connecting notations to the drawing itself.

The most important drawing on a sheet (the one referred to, or used, the most) occupies the bottom-right position; then the next drawings are prioritized from bottom to top and from right to left. Note that this instruction is inconsistent with the coordinate system outlined previously (numbering the modules from left to right in "sheet organization").

Drafting detail: Details should be appropriate to the scale of the drawing and the drawing's intent (what information needs to be conveyed). A "double line" to show a steel stud in a 1/4"=1'-0" scale plan is "useless data." Note that this notion still considers the "drawing" as being separate from the building model. How one reconciles these two divergent approaches (i.e., drawing versus model), especially in B.I.M, is an interesting question.

Still, given the ideal world where the architect still can control the drawings qua drawings (sorry for the "qua," but I've always wanted to insert that term into a course), the following guidelines apply:

• Drawings are abstract and need not be "realistic"
• Be economical in use of lines: use only what is necessary
• Be aware of legibility when drawing is plotted at chosen scale

Scale: Choose appropriate scales based on the information to be conveyed. This includes graphic, dimensional, and textual content. The scale can be numeric or graphic, and should be integrated with the drawing title and designation, as follows:

Note that the graphic scale is optional if the drawings are not anticipated to be reduced or enlarged.

Try to use scales that are typical for the drawing type (e.g., floor plan) and convention (e.g., metric, architectural, or engineering). Refer to table below (based on "Common Scales") on PDF page 348. Note that there are times when different scales should be used: use your judgment.

* Note that where floor plans are drawn at 1/8" = 1'-0", it is possible to shown "enlarged plans" (large-scale plans) at 1/4" = 1'-0".

Try to use a single scale on each sheet, where possible: note that this is not always feasible. Whatever choice is made, the scale must be shown separately for each drawing on the sheet.

For CAD drawings that are created from a full-size model, note that the notes, leaders, dimensions, etc. must correspond to the final scale of the plot.