Index: src/Plugins/Wti/Wti.IO/Builders/SoilLayer2D.cs
===================================================================
diff -u -rf97fbfa34ad013491cc6ec609a9ef097be6625b7 -r4f83a029b2b4967a5f9e91dcd2ce06ecbbd09ddb
--- src/Plugins/Wti/Wti.IO/Builders/SoilLayer2D.cs	(.../SoilLayer2D.cs)	(revision f97fbfa34ad013491cc6ec609a9ef097be6625b7)
+++ src/Plugins/Wti/Wti.IO/Builders/SoilLayer2D.cs	(.../SoilLayer2D.cs)	(revision 4f83a029b2b4967a5f9e91dcd2ce06ecbbd09ddb)
@@ -47,26 +47,20 @@
                 
                 if (outerLoopIntersectionHeights.Count > 0)
                 {
-                    Collection<Tuple<double, double>> outerLoopIntersectionHeightPairs = new Collection<Tuple<double, double>>();
-                    AddOrderedStartAndEndPairsIn1D(outerLoopIntersectionHeights, outerLoopIntersectionHeightPairs);
-                    foreach (var heightPair in outerLoopIntersectionHeightPairs)
-                    {
-                        result.Add(new PipingSoilLayer(heightPair.Item2));
-                    }
-                    bottom = outerLoopIntersectionHeightPairs[0].Item1;
-
                     IEnumerable<Collection<double>> innerLoopsIntersectionHeights = InnerLoops.Select(loop => GetLoopIntersectionHeights(loop, atX));
                     IEnumerable<Tuple<double, double>> innerLoopIntersectionHeightPairs = GetOrderedStartAndEndPairsIn1D(innerLoopsIntersectionHeights).ToList();
+                    IEnumerable<Tuple<double, double>> outerLoopIntersectionHeightPairs = GetOrderedStartAndEndPairsIn1D(outerLoopIntersectionHeights).ToList();
 
-                    bottom = EnsureBottomOutsideInnerLoop(innerLoopIntersectionHeightPairs.ToList(), bottom);
+                    var currentBottom = outerLoopIntersectionHeightPairs.First().Item1;
+                    var heights = new List<double>();
+                    heights.AddRange(innerLoopIntersectionHeightPairs.Where(p => p.Item1 >= currentBottom).Select(p => p.Item1));
+                    heights.AddRange(outerLoopIntersectionHeightPairs.Select(p => p.Item2));
 
-                    foreach (var heightPair in innerLoopIntersectionHeightPairs)
+                    foreach (var height in heights.Where(height => !innerLoopIntersectionHeightPairs.Any(tuple => HeightInInnerLoop(tuple, height))))
                     {
-                        if (heightPair.Item1 > bottom)
-                        {
-                            result.Add(new PipingSoilLayer(heightPair.Item1));
-                        }
+                        result.Add(new PipingSoilLayer(height));
                     }
+                    bottom = EnsureBottomOutsideInnerLoop(innerLoopIntersectionHeightPairs, currentBottom);
                 }
             }
             return result;
@@ -86,31 +80,40 @@
             return newBottom;
         }
 
-        private bool BottomInInnerLoop(Tuple<double, double> tuple, double bottom)
+        private bool HeightInInnerLoop(Tuple<double, double> tuple, double height)
         {
-            return bottom < tuple.Item2 && bottom >= tuple.Item1;
+            return height <= tuple.Item2 && height > tuple.Item1;
         }
 
+        private bool BottomInInnerLoop(Tuple<double, double> tuple, double height)
+        {
+            return height < tuple.Item2 && height >= tuple.Item1;
+        }
+
         private IEnumerable<Tuple<double, double>> GetOrderedStartAndEndPairsIn1D(IEnumerable<Collection<double>> innerLoopsIntersectionPoints)
         {
             Collection<Tuple<double,double>> result = new Collection<Tuple<double, double>>();
             foreach (var innerLoopIntersectionPoints in innerLoopsIntersectionPoints)
             {
-                AddOrderedStartAndEndPairsIn1D(innerLoopIntersectionPoints, result);
+                foreach (var tuple in GetOrderedStartAndEndPairsIn1D(innerLoopIntersectionPoints))
+                {
+                    result.Add(tuple);
+                }
             }
             return result;
         }
 
-        private static void AddOrderedStartAndEndPairsIn1D(Collection<double> innerLoopIntersectionPoints, Collection<Tuple<double, double>> result)
+        private static Collection<Tuple<double, double>> GetOrderedStartAndEndPairsIn1D(IEnumerable<double> innerLoopIntersectionPoints)
         {
+            var result = new Collection<Tuple<double, double>>();
             var orderedHeights = innerLoopIntersectionPoints.OrderBy(v => v).ToList();
-            while (orderedHeights.Count >= 2)
+            for (int i = 0; i < orderedHeights.Count; i = i+2)
             {
-                var first = orderedHeights[0];
-                var second = orderedHeights[1];
-                orderedHeights.RemoveRange(0, 2);
+                var first = orderedHeights[i];
+                var second = orderedHeights[i+1];
                 result.Add(new Tuple<double, double>(first, second));
             }
+            return result;
         }
 
         private Collection<double> GetLoopIntersectionHeights(HashSet<Point3D> loop, double atX)
Index: test/Plugins/Wti/Wti.IO.Test/Builders/SoilLayer2DTest.cs
===================================================================
diff -u -r2423a70958e7fecfc92afa462c34194cc695a81e -r4f83a029b2b4967a5f9e91dcd2ce06ecbbd09ddb
--- test/Plugins/Wti/Wti.IO.Test/Builders/SoilLayer2DTest.cs	(.../SoilLayer2DTest.cs)	(revision 2423a70958e7fecfc92afa462c34194cc695a81e)
+++ test/Plugins/Wti/Wti.IO.Test/Builders/SoilLayer2DTest.cs	(.../SoilLayer2DTest.cs)	(revision 4f83a029b2b4967a5f9e91dcd2ce06ecbbd09ddb)
@@ -309,27 +309,109 @@
             var innerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
                 "6",
                 "........",
+                "...12...",
                 "........",
+                "...43...",
+                "........",
+                "........"));
+
+            var innerLoop2 = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+                "6",
+                "........",
+                "........",
                 "...12...",
                 "........",
                 "........",
                 "...43..."));
 
-            var innerLoop2 = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+            var layer = new SoilLayer2D
+            {
+                OuterLoop = outerLoop,
+                InnerLoops =
+                {
+                    innerLoop,
+                    innerLoop2
+                }
+            };
+
+            // Call
+            double bottom;
+            var result = layer.AsPipingSoilLayers(3.5, out bottom).ToArray();
+
+            // Assert
+            Assert.AreEqual(1, result.Length);
+            Assert.AreEqual(4.0, bottom);
+            CollectionAssert.AreEquivalent(new[] { 5.0 }, result.Select(rl => rl.Top));
+        }
+
+        [Test]
+        public void AsPipingSoilLayers_OuterLoopInnerLoopOnBorderBottom_ReturnsTwoLayers()
+        {
+            // Setup
+            var outerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
                 "6",
+                "..1..2..",
                 "........",
+                "........",
+                "........",
+                ".4....3.",
+                "........"));
+
+            var innerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+                "6",
+                "........",
+                "........",
                 "...12...",
                 "........",
                 "...43...",
+                "........"));
+
+            var layer = new SoilLayer2D
+            {
+                OuterLoop = outerLoop,
+                InnerLoops =
+                {
+                    innerLoop
+                }
+            };
+
+            // Call
+            double bottom;
+            var result = layer.AsPipingSoilLayers(3.5, out bottom).ToArray();
+
+            // Assert
+            Assert.AreEqual(2, result.Length);
+            Assert.AreEqual(3.0, bottom);
+            CollectionAssert.AreEquivalent(new[] { 5.0, 1.0 }, result.Select(rl => rl.Top));
+        }
+
+        [Test]
+        public void AsPipingSoilLayers_OuterLoopInnerLoopOverlapTop_ReturnsOneLayer()
+        {
+            // Setup
+            var outerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+                "6",
                 "........",
+                "..1..2..",
+                "........",
+                "........",
+                ".4....3.",
                 "........"));
 
+            var innerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+                "6",
+                "...43...",
+                "........",
+                "...12...",
+                "........",
+                "........",
+                "........"));
+
             var layer = new SoilLayer2D
             {
                 OuterLoop = outerLoop,
                 InnerLoops =
                 {
-                    innerLoop2,
                     innerLoop
                 }
             };
@@ -340,11 +422,52 @@
 
             // Assert
             Assert.AreEqual(1, result.Length);
-            Assert.AreEqual(4.0, bottom);
-            CollectionAssert.AreEquivalent(new[] { 5.0 }, result.Select(rl => rl.Top));
+            Assert.AreEqual(1.0, bottom);
+            CollectionAssert.AreEquivalent(new[] { 3.0 }, result.Select(rl => rl.Top));
         }
 
         [Test]
+        public void AsPipingSoilLayers_OuterLoopInnerLoopOnBorderTop_ReturnsOneLayer()
+        {
+            // Setup
+            var outerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+                "6",
+                "..1..2..",
+                "........",
+                "........",
+                "........",
+                ".4....3.",
+                "........"));
+
+            var innerLoop = PointCollectionHelper.CreateFromString(String.Join(Environment.NewLine,
+                "6",
+                "...43...",
+                "........",
+                "...12...",
+                "........",
+                "........",
+                "........"));
+
+            var layer = new SoilLayer2D
+            {
+                OuterLoop = outerLoop,
+                InnerLoops =
+                {
+                    innerLoop
+                }
+            };
+
+            // Call
+            double bottom;
+            var result = layer.AsPipingSoilLayers(3.5, out bottom).ToArray();
+
+            // Assert
+            Assert.AreEqual(1, result.Length);
+            Assert.AreEqual(1.0, bottom);
+            CollectionAssert.AreEquivalent(new[] { 3.0 }, result.Select(rl => rl.Top));
+        }
+
+        [Test]
         public void AsPipingSoilLayers_OuterLoopVerticalAtX_ThrowsException()
         {
             // Setup