Why 3D Walls Look Terrible at Corners - And How to Fix It (Three.js)

Overview

In the previous episode, we solved one of the first big challenges of a 3D home editor: cutting real holes through walls for doors and windows.

In this second devlog, we continue building Pascal, a browser-based 3D home editor inspired by The Sims, and tackle another deceptively simple problem:

Why do 3D walls look terrible at corners?

If you’ve ever built walls by placing boxes from point A to point B, you’ve probably seen overlapping geometry, clipped corners, and broken junctions. In real construction, walls miter together cleanly, regardless of angle or thickness. In Three.js, that behavior has to be built manually.

When Walls Meet

Adding a single wall is easy.

You draw a box between two points and you’re done.

The real problem starts when walls meet.

Add a perpendicular wall and you get an overlap.

Add a diagonal one and suddenly three walls are intersecting in impossible ways.

The first instinct is usually to:

Extend one wall
Shrink another
Let one override the others

These shortcuts fall apart quickly—especially when:

Walls have different thicknesses
Walls meet at any angle
You need predictable, clean geometry for production use

This isn’t a visual issue.

It’s a geometry problem.

In this episode, we solve it properly by:

Breaking the problem down in 2D first
Visualizing the solution before touching 3D
Calculating precise intersection points for wall edges
Building clean polygons at junctions
Extruding those shapes into real 3D walls

This approach works with:

Any wall angle
Different wall thicknesses
Corners and T-junctions

If you’re building level editors, floor planners, configurators, or any serious 3D tool, this is a foundational problem you need to understand.

Resources/Tech Stack

#threejs #js #devlog

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