diff --git a/terraform_shelly/AGENTS.md b/terraform_shelly/AGENTS.md
new file mode 100644
index 0000000..7b6e3e1
--- /dev/null
+++ b/terraform_shelly/AGENTS.md
@@ -0,0 +1,40 @@
+# Shelly Fan Control Agent Documentation
+
+This directory manages the configuration, code templating, and deployment for the Shelly Plug S (Gen 3) that controls the cellar ventilation fan to prevent mold.
+
+## Domain Structure & Key Files
+
+*   **[main.tf](file:///Users/moritz/src/infrapuzzle/terraform_shelly/main.tf)**: Coordinates rendering the JavaScript template and executing the Python upload script.
+*   **[variables.tf](file:///Users/moritz/src/infrapuzzle/terraform_shelly/variables.tf)**: Defines MAC addresses for the Bluetooth sensors, safety parameters, and the mold calculation coefficients.
+*   **[scripts/Taupi-4.0.js](file:///Users/moritz/src/infrapuzzle/terraform_shelly/scripts/Taupi-4.0.js)**: The source Shelly control script containing the logic for parsing Bluetooth BTHome events, calculating dew points, evaluating mold danger, and switching the relay.
+*   **[scripts/Taupi-4.0.templated.js](file:///Users/moritz/src/infrapuzzle/terraform_shelly/scripts/Taupi-4.0.templated.js)**: The locally generated script rendering the variables passed from Terraform. Do not edit directly.
+*   **[scripts/upload.py](file:///Users/moritz/src/infrapuzzle/terraform_shelly/scripts/upload.py)**: Helper script executing during `terraform apply` to upload the templated script to the Shelly device over local HTTP RPC commands.
+
+## Architecture Decisions
+
+### 1. Linear Isopleth Approximation (LIM I)
+To determine if indoor relative humidity is high enough to warrant ventilation, we use a linear approximation of the **Lowest Isopleth for Mould (LIM I)** curve developed by Klaus Sedlbauer for biodegradable substrates (like wood or wallpaper). 
+
+Between $5^\circ\text{C}$ and $25^\circ\text{C}$, the critical relative humidity threshold is calculated dynamically based on room temperature ($T$):
+
+$$RH_{crit}(T) = 80\% - 0.5 \cdot (T - 10)$$
+
+*   At $10^\circ\text{C}$, the critical threshold is $80\%$.
+*   At $20^\circ\text{C}$, the critical threshold is $75\%$.
+
+### 2. Room-to-Wall Safety Buffer (15%)
+Since the sensor measures ambient room air, but mold grows on colder outer wall surfaces, we must compensate for the thermal gradient.
+*   **Physical Effect**: A $5^\circ\text{C}$ drop in temperature between room air ($20^\circ\text{C}$) and the wall surface ($15^\circ\text{C}$) causes the local relative humidity at the wall to spike from $60\%$ to $82\%$, crossing the mold germination threshold.
+*   **Action**: We apply a **$15\%$ safety buffer** to the threshold. This targets keeping the ambient room air relative humidity below **$60\%$** (when the room is at $20^\circ\text{C}$) to keep wall surfaces safely below $80\%$ relative humidity.
+
+The fan is only allowed to run if:
+
+$$\text{humidity\_innen} \ge RH_{crit}(T) - 15\%$$
+
+---
+
+## Sources & References
+
+*   **[BoeserBob/Taupi-4.0](https://github.com/BoeserBob/Taupi-4.0)**: The original upstream Shelly dew point ventilation controller repository.
+*   **[Klaus Sedlbauer Biography (Wikipedia)](https://de.wikipedia.org/wiki/Klaus_Sedlbauer)**: The researcher who developed the Lowest Isopleth for Mould (LIM) curves at Fraunhofer IBP.
+*   **[WUFI Biohygrothermal Model](https://wufi.de/en/wufi-software/wufi-bio/)**: Fraunhofer IBP documentation explaining dynamic mold growth and spore germination models.
diff --git a/terraform_shelly/main.tf b/terraform_shelly/main.tf
index 25ec756..aa4fc79 100644
--- a/terraform_shelly/main.tf
+++ b/terraform_shelly/main.tf
@@ -1,13 +1,17 @@
 locals {
   templated_code = templatefile("${path.module}/scripts/Taupi-4.0.js", {
-    sensor_aussen_mac  = var.sensor_aussen_mac
-    sensor_innen_mac   = var.sensor_innen_mac
-    taupunktschwelle   = var.taupunktschwelle
-    mindesttemperatur  = var.mindesttemperatur
-    mindesthumi        = var.mindesthumi
-    schaltzeit         = var.schaltzeit
-    battery_warngrenze = var.battery_warngrenze
-    lost_connection    = var.lost_connection
+    sensor_aussen_mac         = var.sensor_aussen_mac
+    sensor_innen_mac          = var.sensor_innen_mac
+    taupunktschwelle          = var.taupunktschwelle
+    mindesttemperatur         = var.mindesttemperatur
+    mindesthumi               = var.mindesthumi
+    schaltzeit                = var.schaltzeit
+    battery_warngrenze        = var.battery_warngrenze
+    lost_connection           = var.lost_connection
+    critical_humi_base        = var.critical_humi_base
+    critical_humi_temp_coeff  = var.critical_humi_temp_coeff
+    critical_humi_ref_temp    = var.critical_humi_ref_temp
+    critical_humi_buffer      = var.critical_humi_buffer
   })
 }
 
diff --git a/terraform_shelly/scripts/Taupi-4.0.js b/terraform_shelly/scripts/Taupi-4.0.js
index 24754a0..c62aa8f 100644
--- a/terraform_shelly/scripts/Taupi-4.0.js
+++ b/terraform_shelly/scripts/Taupi-4.0.js
@@ -23,6 +23,11 @@ var mindesthumi        = ${mindesthumi};                 // [%]  ...und RHinnen
 var schaltzeit         = ${schaltzeit};                 // [s]  Schaltbedingung prüfen alle X Sekunden
 var battery_warngrenze = ${battery_warngrenze};                 // [%] wenn dieser Schwellwert unterschritten ist blinkt der Plug rot
 var lost_connection = ${lost_connection};                  // [s] Zeit nach der frische Sensordaten gekommen sein müssen um tote Verbindungen zu finden
+//========== Kritische Feuchte-Konfiguration (Schimmelgefahr) ==========
+var critical_humi_base       = ${critical_humi_base};          // [%] Kritische relative Feuchte bei Referenztemp.
+var critical_humi_temp_coeff = ${critical_humi_temp_coeff};    // [%/°C] Steigung des Grenzwerts pro °C
+var critical_humi_ref_temp   = ${critical_humi_ref_temp};      // [°C] Referenztemperatur
+var critical_humi_buffer     = ${critical_humi_buffer};        // [%] Sicherheitspuffer
 //===== Ende Sensor-Konfiguration === AB HIER MUSS NICHTS MEHR GEÄNDERT WERDEN =====================================
 
 var taupunkt_aussen;
@@ -59,6 +64,13 @@ function schalten() {
     return;
   }
 
+  // Kritische Feuchte (Schimmelgrenzkurve) berechnen
+  var rh_crit = critical_humi_base - critical_humi_temp_coeff * (temperatur_innen - critical_humi_ref_temp);
+  var rh_activation = rh_crit - critical_humi_buffer;
+  var is_critical = humidity_innen >= rh_activation;
+
+  print("Schimmelprüfung: T_innen =", temperatur_innen, "°C, RH_innen =", humidity_innen, "%, RH_crit =", rh_crit, "%, Aktivierung ab =", rh_activation, "%, Kritisch =", is_critical);
+
 // Sicherheitsprüfung kommen regelmäßig frische Daten von den Sensoren?
   lost_connection_innen = lost_connection_innen + schaltzeit
   lost_connection_aussen = lost_connection_aussen + schaltzeit
@@ -82,8 +94,9 @@ if (battery_innen < battery_warngrenze ||
     farbring(100,0,0,100);
    }
 
- // Schaltlogik (immer schalten, der Shelly schaltet nur, wenn er schalten muss).
-  if ( temperatur_innen > mindesttemperatur &&
+  // Schaltlogik (immer schalten, der Shelly schaltet nur, wenn er schaltet muss).
+  if ( is_critical &&
+    temperatur_innen > mindesttemperatur &&
     humidity_innen > mindesthumi &&
     taupunkt_innen > taupunkt_aussen + taupunktschwelle
   )
@@ -141,9 +154,12 @@ function checkBlu(event) {
 
 // Haupt-Timer für Steuerlogik
 Timer.set(schaltzeit * 1000, true, function () {
+  var rh_crit_t = (typeof temperatur_innen !== "undefined") ? (critical_humi_base - critical_humi_temp_coeff * (temperatur_innen - critical_humi_ref_temp)) : undefined;
+  var rh_act_t = (typeof rh_crit_t !== "undefined") ? (rh_crit_t - critical_humi_buffer) : undefined;
+
   print("----- Steuerung alle", schaltzeit, "s -----");
-  print("Innen: T =", temperatur_innen, "°C, RH =", humidity_innen, "%, Tp =", taupunkt_innen, "Batterie: ", battery_innen, " % ");
-  print("Außen: T =", temperatur_aussen, "°C, RH =", humidity_aussen, "%, Tp =", taupunkt_aussen, "Batterie: ", battery_aussen, " % ");
+  print("Innen: T =", temperatur_innen, "°C, RH =", humidity_innen, "%, Tp =", taupunkt_innen, "°C, Aktivierung ab RH =", rh_act_t, "% (Batterie:", battery_innen, "%)");
+  print("Außen: T =", temperatur_aussen, "°C, RH =", humidity_aussen, "%, Tp =", taupunkt_aussen, "°C (Batterie:", battery_aussen, "%)");
   schalten();
 });
 
diff --git a/terraform_shelly/variables.tf b/terraform_shelly/variables.tf
index b18b4e6..3fcc853 100644
--- a/terraform_shelly/variables.tf
+++ b/terraform_shelly/variables.tf
@@ -49,3 +49,27 @@ variable "lost_connection" {
   description = "Time in seconds after which data is considered stale, causing the fan to turn off for safety"
   default     = 600
 }
+
+variable "critical_humi_base" {
+  type        = number
+  description = "Critical indoor relative humidity [%] at reference temperature (for mold warning curve)"
+  default     = 80
+}
+
+variable "critical_humi_temp_coeff" {
+  type        = number
+  description = "Temperature coefficient [%/°C] for the mold warning curve"
+  default     = 0.5
+}
+
+variable "critical_humi_ref_temp" {
+  type        = number
+  description = "Reference temperature [°C] for the mold warning curve"
+  default     = 10
+}
+
+variable "critical_humi_buffer" {
+  type        = number
+  description = "Safety buffer [%] subtracted from the critical relative humidity threshold"
+  default     = 15
+}