diff --git a/HPXMLtoOpenStudio/measure.xml b/HPXMLtoOpenStudio/measure.xml
index 6136e50ea4..acf153b252 100644
--- a/HPXMLtoOpenStudio/measure.xml
+++ b/HPXMLtoOpenStudio/measure.xml
@@ -3,8 +3,8 @@
   <schema_version>3.1</schema_version>
   <name>hpxm_lto_openstudio</name>
   <uid>b1543b30-9465-45ff-ba04-1d1f85e763bc</uid>
-  <version_id>b20ae61b-bf29-4be9-8e25-a44b3b12c232</version_id>
-  <version_modified>2024-11-16T00:20:48Z</version_modified>
+  <version_id>531c1027-0d75-4343-a8ce-6717ad2b9924</version_id>
+  <version_modified>2024-11-16T04:46:12Z</version_modified>
   <xml_checksum>D8922A73</xml_checksum>
   <class_name>HPXMLtoOpenStudio</class_name>
   <display_name>HPXML to OpenStudio Translator</display_name>
@@ -393,7 +393,7 @@
       <filename>hvac_sizing.rb</filename>
       <filetype>rb</filetype>
       <usage_type>resource</usage_type>
-      <checksum>FEB17D7B</checksum>
+      <checksum>C6F9CE12</checksum>
     </file>
     <file>
       <filename>internal_gains.rb</filename>
@@ -423,7 +423,7 @@
       <filename>math.rb</filename>
       <filetype>rb</filetype>
       <usage_type>resource</usage_type>
-      <checksum>FEB72476</checksum>
+      <checksum>CE6D107B</checksum>
     </file>
     <file>
       <filename>meta_measure.rb</filename>
@@ -693,7 +693,7 @@
       <filename>test_hvac_sizing.rb</filename>
       <filetype>rb</filetype>
       <usage_type>test</usage_type>
-      <checksum>561E6631</checksum>
+      <checksum>E1BC3865</checksum>
     </file>
     <file>
       <filename>test_lighting.rb</filename>
diff --git a/HPXMLtoOpenStudio/resources/hvac_sizing.rb b/HPXMLtoOpenStudio/resources/hvac_sizing.rb
index 152ae72d86..408e380b02 100644
--- a/HPXMLtoOpenStudio/resources/hvac_sizing.rb
+++ b/HPXMLtoOpenStudio/resources/hvac_sizing.rb
@@ -4795,15 +4795,36 @@ def self.get_foundation_wall_above_grade_ufactor(foundation_wall, include_insula
 
     assembly_r = Material.FoundationWallMaterial(foundation_wall.type, foundation_wall.thickness).rvalue
     assembly_r += Material.AirFilmVertical.rvalue + Material.AirFilmOutside.rvalue
-    if include_insulation_layers
-      if foundation_wall.insulation_interior_distance_to_top == 0 && foundation_wall.insulation_interior_distance_to_bottom > 0
-        assembly_r += foundation_wall.insulation_interior_r_value
-      end
-      if foundation_wall.insulation_exterior_distance_to_top == 0 && foundation_wall.insulation_exterior_distance_to_bottom > 0
-        assembly_r += foundation_wall.insulation_exterior_r_value
-      end
+    if not include_insulation_layers
+      return 1.0 / assembly_r
+    end
+
+    ag_depth = foundation_wall.height - foundation_wall.depth_below_grade
+    wall_ins_dist_bottom_to_grade_int = ag_depth - foundation_wall.insulation_interior_distance_to_bottom
+    wall_ins_dist_top_to_grade_int = ag_depth - foundation_wall.insulation_interior_distance_to_top
+    wall_ins_dist_bottom_to_grade_ext = ag_depth - foundation_wall.insulation_exterior_distance_to_bottom
+    wall_ins_dist_top_to_grade_ext = ag_depth - foundation_wall.insulation_exterior_distance_to_top
+    # Perform calculation for each 1ft bin of above grade depth
+    sum_u_wall = 0.0
+    for distance_to_grade in 1..ag_depth.ceil
+      r_wall = assembly_r
+
+      bin_dist_top_to_grade = [distance_to_grade, ag_depth].min
+      bin_dist_bottom_to_grade = distance_to_grade - 1
+      bin_size = bin_dist_top_to_grade - bin_dist_bottom_to_grade # Last bin may be less than 1 ft
+
+      # Add interior insulation R-value at this depth?
+      bin_frac_insulated_int = MathTools.overlap(bin_dist_bottom_to_grade, bin_dist_top_to_grade, wall_ins_dist_bottom_to_grade_int, wall_ins_dist_top_to_grade_int) / bin_size
+      r_wall += foundation_wall.insulation_interior_r_value * bin_frac_insulated_int # Interior insulation at this depth, add R-value
+
+      # Add exterior insulation R-value at this depth?
+      bin_frac_insulated_ext = MathTools.overlap(bin_dist_bottom_to_grade, bin_dist_top_to_grade, wall_ins_dist_bottom_to_grade_ext, wall_ins_dist_top_to_grade_ext) / bin_size
+      r_wall += foundation_wall.insulation_exterior_r_value * bin_frac_insulated_ext # Exterior insulation at this depth, add R-value
+
+      sum_u_wall += (1.0 / r_wall) * bin_size
     end
-    return 1.0 / assembly_r
+    u_wall = sum_u_wall / ag_depth
+    return u_wall
   end
 
   # Calculates the foundation wall below grade effective U-factor according to Manual J Section A12-4.
@@ -4832,22 +4853,27 @@ def self.get_foundation_wall_below_grade_ufactor(foundation_wall, include_soil,
 
     # Perform calculation for each 1ft bin of below grade depth
     sum_u_wall = 0.0
-    wall_depth_above_grade = foundation_wall.depth_below_grade.ceil
-    for distance_to_grade in 1..wall_depth_above_grade
+    for distance_to_grade in 1..foundation_wall.depth_below_grade.ceil
       # Calculate R-wall at this depth
       r_wall = wall_constr_rvalue - Material.AirFilmOutside.rvalue
-      bin_distance_to_grade = distance_to_grade - 0.5 # Use e.g. 2.5 ft for the 2ft-3ft bin
-      r_soil = (Math::PI * bin_distance_to_grade / 2.0) / ground_conductivity
-      if (distance_to_grade > wall_ins_dist_top_to_grade_int) && (distance_to_grade <= wall_ins_dist_bottom_to_grade_int)
-        r_wall += wall_ins_rvalue_int # Interior insulation at this depth, add R-value
-      end
-      if (distance_to_grade > wall_ins_dist_top_to_grade_ext) && (distance_to_grade <= wall_ins_dist_bottom_to_grade_ext)
-        r_wall += wall_ins_rvalue_ext # Exterior insulation at this depth, add R-value
-      end
+      bin_dist_top_to_grade = distance_to_grade - 1
+      bin_dist_bottom_to_grade = [distance_to_grade, foundation_wall.depth_below_grade].min
+      bin_size = bin_dist_bottom_to_grade - bin_dist_top_to_grade # Last bin may be less than 1 ft
+      bin_avg_dist_to_grade = (bin_dist_top_to_grade + bin_dist_bottom_to_grade) / 2.0
+
+      # Add interior insulation R-value at this depth?
+      bin_frac_insulated_int = MathTools.overlap(bin_dist_top_to_grade, bin_dist_bottom_to_grade, wall_ins_dist_top_to_grade_int, wall_ins_dist_bottom_to_grade_int) / bin_size
+      r_wall += wall_ins_rvalue_int * bin_frac_insulated_int
+
+      # Add exterior insulation R-value at this depth?
+      bin_frac_insulated_ext = MathTools.overlap(bin_dist_top_to_grade, bin_dist_bottom_to_grade, wall_ins_dist_top_to_grade_ext, wall_ins_dist_bottom_to_grade_ext) / bin_size
+      r_wall += wall_ins_rvalue_ext * bin_frac_insulated_ext # Exterior insulation at this depth, add R-value
+
       if include_soil
-        sum_u_wall += 1.0 / (r_soil + r_wall)
+        r_soil = (Math::PI * bin_avg_dist_to_grade / 2.0) / ground_conductivity
+        sum_u_wall += (1.0 / (r_soil + r_wall)) * bin_size
       else
-        sum_u_wall += 1.0 / r_wall
+        sum_u_wall += (1.0 / r_wall) * bin_size
       end
     end
     u_wall = sum_u_wall / foundation_wall.depth_below_grade
diff --git a/HPXMLtoOpenStudio/resources/math.rb b/HPXMLtoOpenStudio/resources/math.rb
index f351ead325..e6d61b5abe 100644
--- a/HPXMLtoOpenStudio/resources/math.rb
+++ b/HPXMLtoOpenStudio/resources/math.rb
@@ -34,7 +34,7 @@ def self.interp4(x, y, x1, x2, y1, y2, fx1y1, fx1y2, fx2y1, fx2y2)
           + (fx2y2 / ((x2 - x1) * (y2 - y1))) * (x - x1) * (y - y1)
   end
 
-  # Calculate the result of a biquadratic polynomial with independent variables.
+  # Calculates the result of a biquadratic polynomial with independent variables.
   # x and y, and a list of coefficients, c:
   #
   # z = c[1] + c[2]*x + c[3]*x**2 + c[4]*y + c[5]*y**2 + c[6]*x*y
@@ -52,7 +52,7 @@ def self.biquadratic(x, y, c)
     return z
   end
 
-  # Calculate the result of a quadratic polynomial with independent variable.
+  # Calculates the result of a quadratic polynomial with independent variable.
   # x and a list of coefficients, c:
   #
   # y = c[1] + c[2]*x + c[3]*x**2
@@ -70,9 +70,9 @@ def self.quadratic(x, c)
     return y
   end
 
-  # Calculate the result of a bicubic polynomial with independent variables.
+  # Calculates the result of a bicubic polynomial with independent variables.
   # x and y, and a list of coefficients, c:
-
+  #
   # z = c[1] + c[2]*x + c[3]*y + c[4]*x**2 + c[5]*x*y + c[6]*y**2 + \
   #     c[7]*x**3 + c[8]*y*x**2 + c[9]*x*y**2 + c[10]*y**3
   #
@@ -91,6 +91,17 @@ def self.bicubic(x, y, c)
     return z
   end
 
+  # Calculates the overlap distance of two 1D line segments.
+  #
+  # @param min1 [Double] min value of line 1
+  # @param max1 [Double] max value of line 1
+  # @param min2 [Double] min value of line 2
+  # @param max2 [Double] max value of line 2
+  # @return [Double] overlap distance
+  def self.overlap(min1, max1, min2, max2)
+    return [0.0, [max1, max2].min - [min1, min2].max].max
+  end
+
   # Determine if a guess is within tolerance for convergence.
   # If not, output a new guess using the Newton-Raphson method.
   #
diff --git a/HPXMLtoOpenStudio/tests/test_hvac_sizing.rb b/HPXMLtoOpenStudio/tests/test_hvac_sizing.rb
index 1fb1b7731f..b04bbcb7f1 100644
--- a/HPXMLtoOpenStudio/tests/test_hvac_sizing.rb
+++ b/HPXMLtoOpenStudio/tests/test_hvac_sizing.rb
@@ -1678,6 +1678,54 @@ def test_manual_j_basement_wall_below_grade_ufactor
     end
   end
 
+  def test_foundation_wall_non_integer_values
+    tol = 0.01 # 1%
+
+    # Test wall insulation covering most of above and below-grade portions of wall
+    fwall = HPXML::FoundationWall.new(nil)
+    fwall.height = 5.0
+    fwall.depth_below_grade = 1.5
+    fwall.type = HPXML::FoundationWallTypeSolidConcrete
+    fwall.thickness = 4.0 # in
+    fwall.insulation_interior_r_value = 10.0
+    fwall.insulation_exterior_r_value = 0.0
+    fwall.insulation_interior_distance_to_top = 0.3
+    fwall.insulation_exterior_distance_to_top = 0.0
+    fwall.insulation_interior_distance_to_bottom = 4.9
+    fwall.insulation_exterior_distance_to_bottom = 0.0
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_below_grade_ufactor(fwall, false, nil)
+    assert_in_epsilon(10.25, rvalue, tol)
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_above_grade_ufactor(fwall, true)
+    assert_in_epsilon(9.6, rvalue, tol)
+
+    # Same as above but test exterior wall insulation
+    fwall.insulation_interior_r_value = 0.0
+    fwall.insulation_exterior_r_value = 10.0
+    fwall.insulation_interior_distance_to_top = 0.0
+    fwall.insulation_exterior_distance_to_top = 0.3
+    fwall.insulation_interior_distance_to_bottom = 0.0
+    fwall.insulation_exterior_distance_to_bottom = 4.9
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_below_grade_ufactor(fwall, false, nil)
+    assert_in_epsilon(10.25, rvalue, tol)
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_above_grade_ufactor(fwall, true)
+    assert_in_epsilon(9.6, rvalue, tol)
+
+    # Test small coverage of below-grade portion of wall, no coverage of above-grade
+    fwall.insulation_exterior_distance_to_top = 4.4
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_below_grade_ufactor(fwall, false, nil)
+    assert_in_epsilon(2.7, rvalue, tol)
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_above_grade_ufactor(fwall, true)
+    assert_in_epsilon(1.2, rvalue, tol)
+
+    # Test small coverage of above-grade portion of wall, no coverage of below-grade
+    fwall.insulation_exterior_distance_to_top = 2.3
+    fwall.insulation_exterior_distance_to_bottom = 3.5
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_below_grade_ufactor(fwall, false, nil)
+    assert_in_epsilon(1.0, rvalue, tol)
+    rvalue = 1.0 / HVACSizing.get_foundation_wall_above_grade_ufactor(fwall, true)
+    assert_in_epsilon(2.1, rvalue, tol)
+  end
+
   def test_multiple_zones
     # Run base-zones-spaces-multiple.xml
     args_hash = {}