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diff --git a/doc/jenkins-cpp-build.md b/doc/jenkins-cpp-build.md
index 6449ffd..58212a3 100644
--- a/doc/jenkins-cpp-build.md
+++ b/doc/jenkins-cpp-build.md
@@ -285,6 +285,62 @@ This requires the **Git plugin** and **Poll SCM** to be enabled in the job
 config (the schedule can be empty, e.g. just `H * * * *`).
 
 
+## Incremental builds and cleaning the workspace
+
+After the first successful build, Jenkins keeps the workspace directory
+(`/var/jenkins_home/jobs/<job>/workspace/`) between builds. On subsequent
+runs it does a `git fetch` + `git checkout` instead of a full clone, only
+downloading new commits. This makes builds much faster, especially for
+large repositories like the Linux kernel.
+
+The same applies to Docker images: Jenkins pulls the image (e.g.,
+`kernel-builder` or `gcc:latest`) once and caches it locally. Future builds
+reuse the cached image. However, the Docker **container** is always created
+fresh for each build and destroyed when done — only the workspace persists.
+
+Sometimes you need a completely clean build (e.g., to rule out stale object
+files causing issues). Pipeline jobs do not have a "Wipe Out Workspace"
+button in the UI (only Freestyle jobs do). There are two ways to clean it:
+
+### Option A — Delete from host
+
+```bash
+rm -rf /var/jenkins_home/jobs/<job-name>/workspace
+```
+
+The next build will do a fresh clone.
+
+### Option B — Add cleanWs() to Jenkinsfile
+
+Requires the **Workspace Cleanup** plugin. Add a `post` block to
+automatically wipe the workspace after every build:
+
+```groovy
+pipeline {
+    agent {
+        docker { image 'gcc:latest' }
+    }
+
+    stages {
+        stage('Build') {
+            steps {
+                sh 'g++ -o my_app main.cpp'
+            }
+        }
+    }
+
+    post {
+        always {
+            cleanWs()
+        }
+    }
+}
+```
+
+Note: using `cleanWs()` means every build will do a full clone, which is
+slow for large repos. Use it only when you actually need clean builds.
+
+
 ## How DooD works
 
 Jenkins is configured with Docker-out-of-Docker: it mounts the host's