diff --git a/.gitea/workflows/build-iso-windows.yaml b/.gitea/workflows/build-iso-windows.yaml
index 1509e48..bb95671 100644
--- a/.gitea/workflows/build-iso-windows.yaml
+++ b/.gitea/workflows/build-iso-windows.yaml
@@ -184,6 +184,15 @@ jobs:
           # RUNNER_TEMP is per-job/ephemeral. Keep the latest validated build at a
           # stable path so it can be retrieved (e.g. for VM boot-testing) out of band.
           New-Item -ItemType Directory -Force 'C:\silvermetal\out' | Out-Null
+          # The ISO is already built + validated; free the build working set (extracted ISO
+          # tree + the mounted/expanded install.wim + the 5GB base ISO) BEFORE the ~5GB persist
+          # copy, or the single-volume runner runs out of space mid-copy. The ISO itself lives
+          # in RUNNER_TEMP\out (untouched) and the SBOM/SHA uploads read from there too.
+          $before = [math]::Round((Get-PSDrive C).Free/1GB,1)
+          Remove-Item "$env:RUNNER_TEMP\smbuild" -Recurse -Force -ErrorAction SilentlyContinue
+          Remove-Item "$env:RUNNER_TEMP\base.iso" -Force -ErrorAction SilentlyContinue
+          $after = [math]::Round((Get-PSDrive C).Free/1GB,1)
+          Write-Host "   freed build working set: C: ${before}GB -> ${after}GB before persist"
           Copy-Item "$env:RUNNER_TEMP\out\*" 'C:\silvermetal\out\' -Force
           Get-ChildItem 'C:\silvermetal\out' | ForEach-Object { Write-Host $_.Name }