A beam cutting across an AC duct route, a column in the middle of a bedroom, a drain pipe passing through a beam, or an electrical room too small for the panels: these are examples of clashes between drawings, one of the most common causes of demolition and rework on site, and of project delays and budget overruns. These clashes look small on paper, but on site they mean breaking out, delays and disputes between owner, contractor and designer. This guide explains why clashes happen between structural, architectural and MEP drawings, examples of them, how to prevent them, and their effect on the permit.
Why Do Clashes Happen?
- Each discipline is designed separately without coordination.
- A change in one set of drawings is not carried over to the others.
- No comprehensive review before approval.
- Using different offices for each discipline without a coordinator.
- Owner changes during design without updating all drawings.
Common Examples
| Clash | Result on site |
|---|---|
| Deep beams in the path of AC ducts | Lowered ceilings or breaking out |
| Columns not matching the architectural plan | Columns inside rooms or doorways |
| Drain openings or services penetrating beams | Dangerous structural weakening |
| Equipment rooms with insufficient space | Costly modifications |
| Bathroom levels ignoring drainage falls | Raised floors or leaks |
| Architectural windows where beams or columns are | Changing the facade or the structure |
Cost of a Clash by When It Is Discovered
| When discovered | Solution | Cost |
|---|---|---|
| During design | Amend the drawing | Almost none |
| At the technical audit | Comments and re-upload | Permit delay |
| During construction | Breaking out and rework | High, with delays |
| After finishing | Demolishing finishes | Highest |
How to Prevent It
- One multidisciplinary office or a coordinator across disciplines.
- A coordination review before upload for approval.
- 3D modelling (BIM) on large projects to detect clashes automatically.
- Documenting every change across all drawings.
- Third-party review for complex projects. Read: Third-party structural review.
- Alert supervision that catches clashes before pouring. Read: Stages of concrete pouring supervision.
Effect on the Permit
The technical audit reviews designs for code compliance, and clashes can send the application back with comments. Read: Why are structural drawings rejected? and What does the municipality review in architectural drawings?.
Effect on Cost
Clashes add unplanned work and extend the duration. Read: How structural design affects cost and Project delays and cost overruns.
Frequently Asked Questions
Who bears the cost of a clash?
It depends on the contracts; prevention through coordination is always cheaper.
Is coordination important in small villas?
Yes, because limited spaces make any clash noticeable. Read: Villa design mistakes.
Is BIM necessary for every project?
It is not necessary for small projects, but very useful in large buildings with many systems.
What should I do if a clash is discovered on site?
Stop work on the affected part, refer to the designer for a documented solution, and do not allow improvised fixes that affect structural elements.
Is it acceptable to drill beams to pass services?
Only if the structural engineer has designed planned openings in advance; random drilling is dangerous.
How Abak Engineering Consultancy Helps
Abak is an accredited engineering office in Riyadh that designs architecture, structure and MEP within one team with a coordination review before approval, and supervises construction to catch any clash before pouring. Learn about our structural design and MEP design services, or For professional support, see our HVAC System Design service. contact us.
Regulatory information is based on the Balady platform and the Ministry of Municipalities and Housing, and procedures may be updated by the competent authority. Last reviewed: October 2026.