Unreal Engine DDC: The Derived Data Cache Monster

What the DDC actually is

Derived data is everything Unreal computes from your raw assets: compiled shaders, processed textures, built collision and lighting. The DDC stores those results so the editor does not recompute them on every launch, which is the difference between a project opening in a minute and opening in half a day. Epic's own documentation is blunt about its nature: the local cache is disposable, because everything in it can be rebuilt from the source assets.

The monster part is versioning. Cache entries are keyed by engine version, so upgrading from 4.27 to 5.3 does not reuse the old data — it builds a fresh cache alongside it, and the old one stays forever. A studio machine with two years of engine versions and a dozen projects routinely carries 50–100 GB of DDC that nothing active is reading.

What you can delete, and what it costs

Deleting the local DDC is always safe; the only cost is time. The next editor launch recompiles shaders and reprocesses assets, so the first load of each project is slow, shader compilation hogs the CPU for a while, and then everything is back to normal. The trick is deleting the right subsets so you rarely pay that price in full.

• Local cache: %LOCALAPPDATA%\UnrealEngine\Common\DerivedDataCache — safe to delete wholesale
• After an engine upgrade, remove the subfolders of retired versions first — pure dead weight
• Finished projects: their DDC is dead the day you archive them; delete along with Intermediate and Saved
• Active projects: expect slow first loads and shader recompiles — schedule the delete before a break, not before a deadline
• Teams should stand up a Shared DDC on a network drive so nobody recompiles alone

Housekeeping that keeps it from coming back

The cache regrows, so the habit matters more than the purge. Archive finished projects with their caches stripped, purge retired engine versions after every upgrade, and check the folder size once a month — %LOCALAPPDATA% never tidies up after itself. If you work across many projects, redirecting the cache to a dedicated drive keeps the pressure on C: honest.

Generic disk-cleanup tools do not know this folder exists, which is why multi-gigabyte caches survive every "cleanup" untouched. Kleaner PRO's Space Explorer — top folders by size, with drill-down — is how you catch a quietly grown DDC before guessing does. However you go about it, the rule is the same: know which engine versions you still use, and be ruthless about the rest.

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