[MEP Center Engineering]

Starter question — a frequently asked question posted by the MEP Center team to open this forum. Share your own experience below.

Our office is setting up CAD and BIM templates for MEP drawings. Every project currently uses different layer names, sheet numbers and text sizes, and consultants complain when files are exchanged.

• Which standards exist for layer naming, sheet numbering and file naming?
• What text heights and line weights are practical at 1:50 and 1:100?
• What must a title block and revision table contain?

[MEP Center Engineering]

Use one documented office standard based on an international scheme: ISO 13567 or the US National CAD Standard (AIA layer guidelines) for layers, ISO 19650 naming fields for files, ISO 128 line widths and ISO 3098 text heights; then follow any client or project standard in the BIM execution plan where it overrides yours.

Layers

• ISO 13567 structures layer names into fields: agent responsible, element, presentation and optional fields such as status and sector.
• US NCS / AIA uses a discipline designator followed by major and minor groups, e.g. a mechanical HVAC group with separate minor groups for supply, return and exhaust.
• Whatever scheme is chosen: separate systems (supply, return, cold water, hot water, drainage), equipment, annotation, dimensions and hatches; keep new, existing and demolished on separate layers; do not draw on layer 0 except inside blocks.

Sheets and files

• ISO 19650 file naming uses fields such as project, originator, volume or system, level or location, type, role and number. Agree the codes once per project.
• Sheet numbers by discipline and series, e.g. mechanical plans, sections, details, schematics in separate number ranges, with one sheet list per discipline.
• Sheet sizes from ISO 216: A1 594 x 841 mm and A0 841 x 1189 mm for plans; keep one size per drawing set where possible.

Worked example: text height and line weights

Minimum plotted text height of 2.5 mm (ISO 3098 series 1.8, 2.5, 3.5, 5, 7 mm) for notes, 3.5 mm for room names and tags, 5 mm for titles. In a model drawn in millimetres at 1:1:

• At 1:100, 2.5 mm plotted text = 2.5 x 100 = 250 mm in the model; 3.5 mm = 350 mm.
• At 1:50, 2.5 mm = 125 mm; 3.5 mm = 175 mm.

Annotative text or view-scale text avoids recalculating this by hand. For line weights, ISO 128 uses a series with a ratio of about √2: 0.13, 0.18, 0.25, 0.35, 0.5, 0.7, 1.0 mm. A common MEP practice is to plot the architectural background thin and grey (0.13-0.18 mm), services in 0.25-0.5 mm, and the main system being described heavier so it reads first.

Title block and revisions

• Project name and location, client, consultant, drawing title, drawing number, scale(s) at the stated sheet size, date.
• Status and suitability code (e.g. for information, for approval, for construction).
• Revision table: revision code, date, description, drawn, checked, approved; revision clouds on the drawing for the current revision.
• Drawn, checked and approved names, and a north point and key plan on plans.

Common mistakes

• Text that is readable on screen but below 2.5 mm when plotted at A3 for site use.
• Colours used to mean systems on screen but plotted in black, so systems cannot be told apart; use line types and labels as well.
• Legends that do not match the symbols actually used on the sheet.
• External references with absolute paths that break when files are exchanged.

Related: MEP drawing standards: layers, sheet numbers, title blocks, MEP shop drawing review checklist.

Check the edition of the code that applies to your project.

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