Windows Update Says Not Enough Disk Space: The Permanent Fix
Where to Find the 20 GB
Short answer: Windows 11 feature updates need roughly 20 GB free on the system drive. The fastest route is Settings > System > Storage > Temporary files, where ticking "Windows Update Cleanup" and "Previous Windows installation(s)" typically reclaims 10-25 GB on its own. If that is not enough, clear the SoftwareDistribution download folder and run a DISM component store cleanup.
The error code 0x80070070, or the message that Windows needs more space to install, means the update never got started. The good news is that the cause is almost always temporary data: old update packages, the previous Windows installation and abandoned downloads. This guide walks through where to reclaim space in order, how much each step typically returns, and what to change so it does not happen again.
Key Takeaways
- Windows 11 feature updates require roughly 20 GB of free space on the system drive.
- The biggest single win is usually "Windows Update Cleanup" plus "Previous Windows installation(s)" — together 10-25 GB.
- The SoftwareDistribution\Download folder can be emptied safely; Windows re-downloads whatever it still needs.
- DISM /Online /Cleanup-Image /StartComponentCleanup shrinks the component store safely, whereas deleting WinSxS by hand breaks the system.
- Reserved Storage holds about 7 GB for updates and can be disabled, but doing so only postpones the problem.
- If Windows offers to use an external USB drive, that works — but needing it every time means your system drive is permanently too full.
Why Does a Windows Update Need So Much Space?
A feature update does not need only as much space as the package it downloads. Windows first downloads the package, then expands it into a working area, installs the new system files, and keeps the previous version for rollback throughout. Three copies coexist on the disk for a while.
That is why a 4 GB update package can demand 20 GB of free space. Most of it is released once installation completes, but the Windows.old folder stays behind for 10 days.
Monthly security updates are far more modest, typically wanting a few hundred megabytes to a few gigabytes. The "not enough space" error almost always appears on major version updates rather than routine patches.
The Biggest Win: Windows Update Cleanup
Settings > System > Storage > Temporary files is the screen most users never open, and it holds the largest single win. The "Windows Update Cleanup" entry contains old update files that are no longer needed once installed, and it alone can reach 5-10 GB.
"Previous Windows installation(s)" is the Windows.old folder and typically holds 15-30 GB. Clearing it means giving up the ability to roll back to your previous Windows version; if the current version is running fine, you can tick it safely.
The same list includes "Delivery Optimization Files" (update fragments shared with other PCs) and the classic "Temporary files". Ticking all four together covers the full 20 GB requirement on most machines.
Advanced Cleanup: SoftwareDistribution and DISM
C:\Windows\SoftwareDistribution\Download is where Windows Update keeps the packages it downloads. Failed and abandoned update attempts accumulate here and grow into gigabytes over time. Deleting the contents is safe; Windows re-downloads whatever it needs.
The correct order is to stop the services first: in an administrator command prompt run net stop wuauserv and net stop bits, delete the folder contents, then bring the services back with net start wuauserv and net start bits. Deleting without stopping the services produces in-use errors on the locked files.
The second advanced step is the component store. DISM /Online /Cleanup-Image /StartComponentCleanup removes superseded component versions from WinSxS and can reclaim several gigabytes. Never touch the WinSxS folder by hand — this command is the only method that does that job safely.
Reserved Storage and the External USB Offer
Since Windows 10 version 2004 there is a feature called Reserved Storage: Windows sets aside roughly 7 GB on the system drive for updates and temporary files. Its entire purpose is preventing this exact error.
You can release that space with DISM /Online /Set-ReservedStorageState /State:Disabled in an administrator command prompt. Be careful though: it reclaims 7 GB while making future update failures more likely. If your drive runs permanently on the edge, the fix is to free real space rather than remove the safety buffer.
If Windows offers to plug in an external USB drive during the update, that is a legitimate route and a 32 GB stick will do. Still, having to repeat it for every update is a clear signal that the system drive is permanently overfull.
Making Sure It Does Not Happen Again
Solving this error once buys you a few months. The durable fix is keeping a 20 GB buffer permanently free on the system drive. Turning on Storage Sense and letting it clear temporary files and the recycle bin automatically is the first step.
The second step is seeing where the space goes on a regular basis. Disk Mop's Disk Analysis draws the drive as a treemap so a folder that is growing becomes obvious; Cache Cleaner collects close to twenty categories on one screen, from Windows temporary files to browser caches; and scheduled cleanup turns all of it into a weekly task.
You can download Disk Mop free and try it with limited features; the Pro version is a one-time $19.90 payment for a lifetime license. It runs on Windows 10 and 11 (64-bit) and macOS 12 or later.
Frequently Asked Questions
How much free space does a Windows update need?
Windows 11 feature updates require roughly 20 GB of free space on the system drive. Monthly security updates need far less, typically a few hundred megabytes to a few gigabytes. The required space is shared between the downloaded package, the temporary files it expands into, and the previous version kept for rollback.
What does error 0x80070070 mean?
That code means insufficient disk space, and the update stops before starting. The fix is to reclaim space: use Settings > System > Storage > Temporary files to remove Windows Update Cleanup files and previous Windows installations, then empty the SoftwareDistribution download folder.
Is it safe to delete the SoftwareDistribution folder?
Deleting the contents of its Download subfolder is safe; Windows re-downloads whatever packages it still needs. Stop the services first with net stop wuauserv and net stop bits in an administrator command prompt, and restart them with net start afterwards.
Should I disable Reserved Storage?
Usually not. Reserved Storage is a buffer of about 7 GB set aside so updates always have room, and it exists precisely to prevent this error. It can be disabled with DISM /Online /Set-ReservedStorageState /State:Disabled, but that makes update failures more likely. Freeing real space is the better fix.
Can I use an external USB drive for the update?
Yes. When there is not enough room, Windows offers to use external storage, and a 32 GB USB stick is sufficient. It is a valid solution but a temporary one; if you need it for every update, your system drive is permanently too full.
Can I delete Windows.old after the update?
Yes. Windows.old only lets you roll back to the previous version within 10 days, and it is deleted automatically after that period. If the new version is working fine, remove it immediately via Settings > System > Storage > Temporary files by ticking "Previous Windows installation(s)" and reclaim 15-30 GB.
Verdict
The fix for "not enough disk space" follows a clear order: clear Windows Update Cleanup and previous Windows installations from the Temporary files screen, then empty the SoftwareDistribution download folder, then run a DISM component store cleanup if needed. Those three steps cover the required 20 GB on most machines with room to spare.
Disabling Reserved Storage and using an external USB drive both work, but both only postpone the problem. If your drive is on the edge at every update, the real issue is permanent fullness.
The durable answer is maintaining a 20 GB buffer on the system drive at all times. Turn on Storage Sense, put cleanup on a schedule, and check where the space is going from time to time.
Make Room Before the Next Update
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