4.1 Modification of drawings

Modification of drawings is the process of changing existing drawings to reflect new information, correct errors or develop the design further. Drawings are rarely right the first time: clients change their minds, site measurements reveal differences, budgets are cut, regulations require adjustments and the design itself improves as it develops. In CAD, modification is fast and clean compared with erasing and redrawing on paper, but it must be controlled so that every affected drawing is updated and no one builds from outdated information. Example: after reviewing the first layout of a furniture showroom, the owner asks for a larger display area near the entrance, so the designer moves two partitions, rearranges the display units and updates the floor plan, the ceiling plan and the elevations that show the moved partitions.

4.1.1 Reasons for modifying drawings

Changes come from many sources at every stage of a project. Understanding why a change is needed helps the designer judge its effect on cost, time and other drawings. Example: a chama investment group building rental flats asks for a second bathroom in each two-bedroom unit, which affects plans, plumbing layouts and the bill of quantities.

Common reasons

• Client requests: The client changes requirements, adds spaces or prefers different finishes after seeing the first proposals.
• Site conditions: Measurements on site differ from the original drawings, or hidden columns, pipes or beams are discovered.
• Design development: The designer refines the layout, details or finishes as the design progresses.
• Errors and omissions: Mistakes in dimensions, missing items or clashes between elements are found during checking.
• Regulatory requirements: Approving authorities or fire officers require changes to exits, accessibility or fire safety.
• Budget changes: Costs exceed the budget and materials or features must be changed or removed.
• Consultant coordination: Structural, electrical or mechanical consultants need space or positions changed for their services.
• Supplier information: Actual product sizes differ from the assumed sizes used in the drawings.

4.1.2 Types of modifications

Modifications range from small changes in a note to major changes in layout. Classifying the change helps decide which drawings must be updated and how much checking is needed. Example: changing the tile colour in a pharmaceutical distributor's warehouse office is a minor annotation change, while relocating its toilets is a major layout change affecting several disciplines.

4.1.3 Receiving and recording change requests

Every change should be received in writing and recorded before work begins, so that there is a clear record of who asked for what and when. This protects the designer if disputes arise over cost or time. Example: a Montessori school's director sends marked-up PDFs showing where she wants extra storage, and the designer logs each comment in a change register before editing.

Ways changes are communicated

• Marked-up prints: Changes sketched or written on printed drawings by the client or consultant.
• Marked-up PDFs: Comments, clouds and sketches added digitally to PDF drawings.
• Meeting minutes: Changes agreed in design meetings and recorded in the minutes.
• Emails and letters: Written instructions from the client or project manager.
• Site instructions: Formal instructions issued during construction to deal with site conditions.
• Change request forms: Standard forms describing the change, reason, requester and approval.

Information recorded for each change

• Change reference number: A unique number used to track the change.
• Description of the change: What is to be changed and where.
• Reason for the change: Why the change is required.
• Requested by and date: Who asked for the change and when.
• Drawings affected: The list of drawings that must be updated.
• Approval status: Whether the change has been approved, especially if it affects cost or time.

4.1.4 Procedure for modifying drawings

Modifications should follow an orderly procedure so that nothing is missed and earlier versions remain available. Example: an animal feeds factory's office refurbishment designer saves a copy of each drawing before changing the canteen layout, so the original can be shown if the client asks to compare.

1. Review the change request: Read the instruction carefully and clarify anything unclear with the person who requested it.
2. Assess the impact: Identify all drawings, schedules and consultants affected and any effect on cost or programme.
3. Obtain approval where needed: Confirm the change with the client if it affects cost, time or other parties.
4. Preserve the current version: Save or archive the current drawing before editing so the previous state can be recovered.
5. Make the changes in the model: Edit geometry, content and properties in the drawing files.
6. Update related drawings: Carry the change through to plans, elevations, sections, details and schedules that show the same element.
7. Update annotation: Correct dimensions, tags, notes and room names affected by the change.
8. Check the modified drawings: Compare against the change request and check for new clashes or errors.
9. Record the change: Update the change register and prepare the drawings for formal issue.

Impact checks after a modification

• Dimensions: Overall and room dimensions still add up correctly.
• Clearances: Circulation and door swings remain clear.
• Services: Sockets, lights and plumbing positions still suit the new layout.
• Consistency across views: Plans, elevations and sections show the same arrangement.
• Schedules: Door, finish and furniture schedules match the changed drawings.
• Regulations: Exits, accessibility and fire requirements are still met.

Worked example: change in floor area after moving a partition

Change in area = distance moved × length of partition

A partition 4.5 m long in a flower farm's pack-house office is moved 0.8 m to enlarge the manager's office.

Change in area = 0.8 × 4.5

Change in area = 3.6 m², added to the manager's office and taken from the open office

Worked example: cost of a client change

Cost of change = quantity changed × unit rate

A client asks to replace 42 m² of vinyl flooring with porcelain tiles. Vinyl costs Ksh 1,800 per m² and porcelain tiles Ksh 3,200 per m², both installed.

Difference in rate = 3,200 − 1,800 = Ksh 1,400 per m²

Cost of change = 42 × 1,400

Cost of change = Ksh 58,800 extra