diff --git a/charts/certimate/DESIGN.md b/charts/certimate/DESIGN.md
index 25f8fb72..f3182bef 100644
--- a/charts/certimate/DESIGN.md
+++ b/charts/certimate/DESIGN.md
@@ -28,6 +28,12 @@ Disabling persistence is a breaking, explicit choice: users must set
 keeps disposable CI and demo installs available while preventing accidental loss
 of certificates, ACME accounts, provider credentials, and workflow state.
 
+Certificate workflows create temporary processing files under `/tmp`. The chart
+mounts a dedicated ephemeral `emptyDir` there so these workflows remain
+functional while `securityContext.readOnlyRootFilesystem` stays enabled. Operators
+can set `tmpStorage.sizeLimit` to bound the volume and apply the same value as the
+container's ephemeral-storage request and limit.
+
 ## Exposure
 
 The chart supports Kubernetes Ingress and Gateway API HTTPRoute. TLS termination is expected at the ingress controller or gateway. Certimate itself remains an internal HTTP service.
diff --git a/charts/certimate/README.md b/charts/certimate/README.md
index 7979d4cc..7bc87dd2 100644
--- a/charts/certimate/README.md
+++ b/charts/certimate/README.md
@@ -11,6 +11,8 @@ This chart packages the official `certimate/certimate:v0.4.30` image and follows
 - explicit `persistence.ephemeral=true` opt-in for disposable emptyDir installs
 - default resource requests and memory limit for scheduler and Kubescape hygiene
 - restricted ServiceAccount token mounting by default
+- ephemeral writable `/tmp` storage while the container root filesystem remains read-only
+- optional `tmpStorage.sizeLimit` with matching ephemeral-storage request and limit
 - Kubernetes Ingress and Gateway API HTTPRoute support
 - optional NetworkPolicy with explicit additional egress for ACME DNS APIs, DNS, SMTP, webhooks, and target deployment systems
 - ExternalSecret support for environment variables or other integration secrets
diff --git a/charts/certimate/templates/deployment.yaml b/charts/certimate/templates/deployment.yaml
index 331af9b2..a0fa3403 100644
--- a/charts/certimate/templates/deployment.yaml
+++ b/charts/certimate/templates/deployment.yaml
@@ -1,4 +1,24 @@
 {{/* SPDX-License-Identifier: Apache-2.0 */}}
+{{- if eq .Values.persistence.mountPath "/tmp" }}
+{{- fail "persistence.mountPath must not use the reserved mountPath /tmp" }}
+{{- end }}
+{{- range .Values.extraVolumeMounts }}
+{{- if eq (get . "mountPath") "/tmp" }}
+{{- fail "extraVolumeMounts must not use the reserved mountPath /tmp" }}
+{{- end }}
+{{- end }}
+{{- range .Values.extraVolumes }}
+{{- if eq (get . "name") "tmp" }}
+{{- fail "extraVolumes must not use the reserved volume name tmp" }}
+{{- end }}
+{{- end }}
+{{- $resources := deepCopy .Values.resources }}
+{{- if .Values.tmpStorage.sizeLimit }}
+{{- if not (hasKey $resources "requests") }}{{- $_ := set $resources "requests" dict }}{{- end }}
+{{- if not (hasKey $resources "limits") }}{{- $_ := set $resources "limits" dict }}{{- end }}
+{{- $_ := set (get $resources "requests") "ephemeral-storage" .Values.tmpStorage.sizeLimit }}
+{{- $_ := set (get $resources "limits") "ephemeral-storage" .Values.tmpStorage.sizeLimit }}
+{{- end }}
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -105,13 +125,16 @@ spec:
             timeoutSeconds: {{ .Values.probes.readiness.timeoutSeconds }}
             failureThreshold: {{ .Values.probes.readiness.failureThreshold }}
           {{- end }}
-          {{- with .Values.resources }}
+          {{- with $resources }}
           resources:
             {{- toYaml . | nindent 12 }}
           {{- end }}
           volumeMounts:
             - name: data
               mountPath: {{ .Values.persistence.mountPath | quote }}
+            - name: tmp
+              mountPath: /tmp
+              readOnly: false
             {{- with .Values.extraVolumeMounts }}
             {{- toYaml . | nindent 12 }}
             {{- end }}
@@ -126,6 +149,13 @@ spec:
           {{- else }}
           emptyDir: {}
           {{- end }}
+        - name: tmp
+          {{- if .Values.tmpStorage.sizeLimit }}
+          emptyDir:
+            sizeLimit: {{ .Values.tmpStorage.sizeLimit | quote }}
+          {{- else }}
+          emptyDir: {}
+          {{- end }}
         {{- with .Values.extraVolumes }}
         {{- toYaml . | nindent 8 }}
         {{- end }}
diff --git a/charts/certimate/tests/templates_test.yaml b/charts/certimate/tests/templates_test.yaml
index e418814d..f20afb63 100644
--- a/charts/certimate/tests/templates_test.yaml
+++ b/charts/certimate/tests/templates_test.yaml
@@ -96,3 +96,60 @@ tests:
       - equal:
           path: spec.template.spec.containers[0].resources.limits.cpu
           value: 500m
+  - it: provides writable temporary storage with a read-only root filesystem
+    template: templates/deployment.yaml
+    asserts:
+      - equal:
+          path: spec.template.spec.containers[0].securityContext.readOnlyRootFilesystem
+          value: true
+      - contains:
+          path: spec.template.spec.containers[0].volumeMounts
+          content:
+            name: tmp
+            mountPath: /tmp
+            readOnly: false
+      - equal:
+          path: spec.template.spec.volumes[1].name
+          value: tmp
+      - equal:
+          path: spec.template.spec.volumes[1].emptyDir
+          value: {}
+  - it: rejects an extra volume mount that duplicates the reserved tmp path
+    template: templates/deployment.yaml
+    set:
+      extraVolumeMounts:
+        - name: custom-tmp
+          mountPath: /tmp
+    asserts:
+      - failedTemplate:
+          errorMessage: extraVolumeMounts must not use the reserved mountPath /tmp
+  - it: rejects persistence mounted at the reserved tmp path
+    template: templates/deployment.yaml
+    set:
+      persistence.mountPath: /tmp
+    asserts:
+      - failedTemplate:
+          errorMessage: persistence.mountPath must not use the reserved mountPath /tmp
+  - it: rejects an extra volume using the reserved tmp name
+    template: templates/deployment.yaml
+    set:
+      extraVolumes:
+        - name: tmp
+          emptyDir: {}
+    asserts:
+      - failedTemplate:
+          errorMessage: extraVolumes must not use the reserved volume name tmp
+  - it: bounds temporary storage when configured
+    template: templates/deployment.yaml
+    set:
+      tmpStorage.sizeLimit: 1Gi
+    asserts:
+      - equal:
+          path: spec.template.spec.volumes[1].emptyDir.sizeLimit
+          value: 1Gi
+      - equal:
+          path: spec.template.spec.containers[0].resources.requests.ephemeral-storage
+          value: 1Gi
+      - equal:
+          path: spec.template.spec.containers[0].resources.limits.ephemeral-storage
+          value: 1Gi
diff --git a/charts/certimate/values.schema.json b/charts/certimate/values.schema.json
index c35a798f..c8699258 100644
--- a/charts/certimate/values.schema.json
+++ b/charts/certimate/values.schema.json
@@ -59,6 +59,13 @@
     "externalSecrets": { "$ref": "#/definitions/externalSecrets" },
     "probes": { "$ref": "#/definitions/probes" },
     "resources": { "type": "object" },
+    "tmpStorage": {
+      "type": "object",
+      "required": ["sizeLimit"],
+      "properties": {
+        "sizeLimit": { "type": "string", "default": "", "pattern": "^$|^[0-9]+(\\.[0-9]+)?(Ei|Pi|Ti|Gi|Mi|Ki|E|P|T|G|M|k)?$" }
+      }
+    },
     "test": {
       "type": "object",
       "properties": {
diff --git a/charts/certimate/values.yaml b/charts/certimate/values.yaml
index 797dfd02..cca08110 100644
--- a/charts/certimate/values.yaml
+++ b/charts/certimate/values.yaml
@@ -136,6 +136,10 @@ resources:
     cpu: 500m
     memory: 512Mi
 
+tmpStorage:
+  # -- Optional limit for writable /tmp storage. When set, the same value is applied to the container ephemeral-storage request and limit.
+  sizeLimit: ""
+
 test:
   resources:
     requests: