How-To Guide

How to Find Clashes in 2D Construction Drawings

Find coordination conflicts even when you don't have a BIM model

Not every project has a full BIM model, but that doesn't mean you have to wait until construction to find clashes. You can catch a lot of coordination conflicts just by systematically reviewing your 2D PDF drawings. Here's how to do it.

Step 1: Get All the Drawings You Need

To find clashes, you need to compare across disciplines. Gather these:

Architectural floor plans and reflected ceiling plans
Structural framing plans with beam sizes and elevations
Mechanical ductwork plans with duct sizes
Plumbing plans showing pipe routing and sizes
Electrical plans showing conduit runs and panels
Fire protection plans showing sprinkler mains and heads

Step 2: Build a Vertical Reference Map

Most 2D clashes are really about elevation conflicts. You need to know where things are vertically:

Finish Floor Elevation
Architectural sections
Finish Ceiling Elevation
RCP or sections
Bottom of Structure
Structural framing plans or sections
Top of Structure
Structural framing plans
Duct Centerline Elevations
Mechanical plans or sections
Pipe Elevations
Plumbing plans or sections

Step 3: Overlay Drawings on Top of Each Other

Layer different discipline drawings to spot where things might conflict:

PDF Overlay Method

1. Import drawings into Bluebeam or similar software

2. Align them using grid lines or common reference points

3. Set each discipline to a different color

4. Turn down the transparency so you can see overlapping elements

Overlays Worth Creating

• Structural framing over mechanical ductwork

• Structural framing over plumbing risers

• Mechanical over reflected ceiling plan

• All MEP trades together in plenum areas

Step 4: Do the Math on Vertical Conflicts

When you see elements crossing in plan view, you need to check if they actually hit each other vertically:

Plenum Space Check

Available Space = Bottom of Structure minus Top of Ceiling

Required Space = Duct Height + Insulation + Hangers + Clearance

If what you need is more than what you have, you've got a clash.

Beam Crossing Check

When a duct crosses a beam:

Duct Bottom = Duct Centerline minus half the duct height

Beam Bottom = Top of Steel minus Beam Depth

If the duct bottom is lower than the beam bottom, the duct hits the beam.

Step 5: Focus on the Trouble Spots

Some areas have way more clashes than others. Concentrate your effort here:

Corridor Ceilings
All the MEP mains run through corridors, and ceiling heights are usually tight
Mechanical Rooms
Lots of equipment and routing packed into a small space
Vertical Shafts
Multiple risers competing for limited floor area
Beam-Duct Crossings
Main ducts almost always have to cross primary beams somewhere
Column Line Intersections
Columns get in the way of routing that follows the grid

Step 6: Document What You Find

Create documentation that will actually get the clash resolved:

1
Mark the exact location on the plan
2
Note what elements are conflicting and their sizes
3
Include the elevation data that shows why it's a conflict
4
Assign it to the right discipline to resolve
5
Follow up through design revisions

Related Guides

How to Create a Clash Detection Report
Document conflicts in a way that gets them resolved.
Top 5 MEP vs Structural Clashes
Common clash types and prevention strategies.

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