Dimensional Tolerances in Construction and for Surface Accessibility

1.2 Best practices for drawing

1.2.1 Use the plus - or - minus symbol (±) after a dimension when it must be made clear what the expected tolerance is. This should be coordinated with the specification requirements. Although current practice dictates that tolerances only be included in the specifications, many workers reading the drawings do not read the specifications so it makes sense to show critical tolerances on the drawings as well. Also include a general note stating that no additional allowances either plus or minus will be allowed. For example, use a format such as 6' - 4" (±1/8") or 1930 (±3 mm).

1.2.2 Use datum dimensioning referenced to a primary or secondary control point on the construction site when the position of one item is particularly important. Do not dimension it based on one or more dimensions in a string.