Index: Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/HeightStructuresFailureMechanismSectionResult.cs
===================================================================
diff -u -r7308fa5293c97e6dc38f36aeaff089e41a5fca51 -rbe5396964501c20d142d21dcf39a2a859bbcb472
--- Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/HeightStructuresFailureMechanismSectionResult.cs	(.../HeightStructuresFailureMechanismSectionResult.cs)	(revision 7308fa5293c97e6dc38f36aeaff089e41a5fca51)
+++ Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/HeightStructuresFailureMechanismSectionResult.cs	(.../HeightStructuresFailureMechanismSectionResult.cs)	(revision be5396964501c20d142d21dcf39a2a859bbcb472)
@@ -35,6 +35,7 @@
     public class HeightStructuresFailureMechanismSectionResult : FailureMechanismSectionResult
     {
         private double tailorMadeAssessmentProbability;
+        private double manualAssemblyProbability;
 
         /// <summary>
         /// Initializes a new instance of <see cref="HeightStructuresFailureMechanismSectionResult"/>.
@@ -46,7 +47,8 @@
             SimpleAssessmentResult = SimpleAssessmentResultType.None;
             DetailedAssessmentResult = DetailedAssessmentResultType.Probability;
             TailorMadeAssessmentResult = TailorMadeAssessmentProbabilityCalculationResultType.None;
-            tailorMadeAssessmentProbability = double.NaN;
+            TailorMadeAssessmentProbability = double.NaN;
+            ManualAssemblyProbability = double.NaN;
         }
 
         /// <summary>
@@ -88,5 +90,29 @@
                 tailorMadeAssessmentProbability = value;
             }
         }
+
+        /// <summary>
+        /// Gets or sets the indicator whether the combined assembly should be overwritten by <see cref="ManualAssemblyProbability"/>.
+        /// </summary>
+        public bool UseManualAssemblyProbability { get; set; }
+
+        /// <summary>
+        /// Gets or sets the manually selected assembly category group.
+        /// </summary>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="value"/> is not in range [0,1].</exception>
+        public double ManualAssemblyProbability
+        {
+            get
+            {
+                return manualAssemblyProbability;
+            }
+            set
+            {
+                ProbabilityHelper.ValidateProbability(value, null,
+                                                      RingtoetsCommonDataResources.ArbitraryProbabilityFailureMechanismSectionResult_AssessmentProbability_Value_needs_to_be_in_Range_0_,
+                                                      true);
+                manualAssemblyProbability = value;
+            }
+        }
     }
 }
\ No newline at end of file
Index: Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/HeightStructuresFailureMechanismSectionResultTest.cs
===================================================================
diff -u -r7308fa5293c97e6dc38f36aeaff089e41a5fca51 -rbe5396964501c20d142d21dcf39a2a859bbcb472
--- Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/HeightStructuresFailureMechanismSectionResultTest.cs	(.../HeightStructuresFailureMechanismSectionResultTest.cs)	(revision 7308fa5293c97e6dc38f36aeaff089e41a5fca51)
+++ Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/HeightStructuresFailureMechanismSectionResultTest.cs	(.../HeightStructuresFailureMechanismSectionResultTest.cs)	(revision be5396964501c20d142d21dcf39a2a859bbcb472)
@@ -48,6 +48,8 @@
             Assert.AreEqual(TailorMadeAssessmentProbabilityCalculationResultType.None, sectionResult.TailorMadeAssessmentResult);
             Assert.IsNaN(sectionResult.TailorMadeAssessmentProbability);
             Assert.AreSame(section, sectionResult.Section);
+            Assert.IsFalse(sectionResult.UseManualAssemblyProbability);
+            Assert.AreEqual(double.NaN, sectionResult.ManualAssemblyProbability);
         }
 
         [Test]
@@ -87,5 +89,46 @@
             // Assert
             Assert.AreEqual(validValue, sectionResult.TailorMadeAssessmentProbability);
         }
+
+        [Test]
+        [SetCulture("nl-NL")]
+        [TestCase(-20)]
+        [TestCase(-1e-6)]
+        [TestCase(1 + 1e-6)]
+        [TestCase(12)]
+        public void ManualAssemblyProbability_InvalidValue_ThrowsArgumentOutOfRangeException(double newValue)
+        {
+            // Setup
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var result = new HeightStructuresFailureMechanismSectionResult(section);
+
+            // Call
+            TestDelegate test = () => result.ManualAssemblyProbability = newValue;
+
+            // Assert
+            string message = Assert.Throws<ArgumentOutOfRangeException>(test).Message;
+            const string expectedMessage = "De waarde voor de faalkans moet in het bereik [0,0, 1,0] liggen.";
+            Assert.AreEqual(expectedMessage, message);
+        }
+
+        [Test]
+        [TestCase(0)]
+        [TestCase(1e-6)]
+        [TestCase(0.5)]
+        [TestCase(1 - 1e-6)]
+        [TestCase(1)]
+        [TestCase(double.NaN)]
+        public void ManualAssemblyProbability_ValidValue_NewValueSet(double newValue)
+        {
+            // Setup
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var result = new HeightStructuresFailureMechanismSectionResult(section);
+
+            // Call
+            result.ManualAssemblyProbability = newValue;
+
+            // Assert
+            Assert.AreEqual(newValue, result.ManualAssemblyProbability);
+        }
     }
 }
\ No newline at end of file