diff --git a/Buildings/BoundaryConditions/UsersGuide.mo b/Buildings/BoundaryConditions/UsersGuide.mo
index 676a0770498..c1ec283778d 100644
--- a/Buildings/BoundaryConditions/UsersGuide.mo
+++ b/Buildings/BoundaryConditions/UsersGuide.mo
@@ -18,6 +18,16 @@ and
 Buildings.HeatTransfer.Types.Tilt</a>
 can be used.
 </p>
+<p>
+Note that a ceiling has a tilt of <i>0</i>, and also the solar collector models
+in 
+<a href=\"Buildings.Fluid.SolarCollectors\">Buildings.Fluid.SolarCollectors</a>
+require a tilt of <i>0</i> if they are facing straight upwards.
+This is correct because
+the solar irradiation on a ceiling construction is on the other-side surface,
+which faces upwards toward the sky. Hence, a construction is considered
+a ceiling from the view point of a person standing inside a room.
+</p>
 
 <h4>References</h4>
 <ul>
diff --git a/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo b/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo
index 5f730df6b7b..6c85a9115b1 100644
--- a/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo
+++ b/Buildings/Fluid/SolarCollectors/BaseClasses/PartialSolarCollector.mo
@@ -8,9 +8,11 @@ model PartialSolarCollector "Partial model for solar collectors"
   parameter Integer nSeg(min=3) = 3
     "Number of segments used to discretize the collector model";
 
-  parameter Modelica.SIunits.Angle lat "Latitude";
-  parameter Modelica.SIunits.Angle azi "Surface azimuth";
-  parameter Modelica.SIunits.Angle til "Surface tilt";
+  parameter Modelica.SIunits.Angle lat(displayUnit="degree") "Latitude";
+  parameter Modelica.SIunits.Angle azi(displayUnit="degree")
+    "Surface azimuth (0 for south-facing; -90 degree for east-facing; +90 degree for west facing";
+  parameter Modelica.SIunits.Angle til(displayUnit="degree")
+    "Surface tilt (0 for horizontally mounted collector)";
   parameter Real rho "Ground reflectance";
   parameter Modelica.SIunits.HeatCapacity C=385*perPar.mDry
     "Heat capacity of solar collector without fluid (default: cp_copper*mDry*nPanels)";
@@ -219,7 +221,13 @@ equation
       </p>
     </html>",
     revisions="<html>
-      <ul>
+    <ul>
+    <li>
+    June 25, 2014, by Michael Wetter:<br/>
+    Improved comments for tilt to address 
+    <a href=\"https://github.com/lbl-srg/modelica-buildings/issues/246\">
+    https://github.com/lbl-srg/modelica-buildings/issues/246</a>.
+    </li>
         <li>
           October 8, 2013, by Michael Wetter:<br/>
           Removed parameter <code>show_V_flow</code> in declaration of instance <code>res</code>.
diff --git a/Buildings/HeatTransfer/Types.mo b/Buildings/HeatTransfer/Types.mo
index 232a02ff284..e1f04d35941 100644
--- a/Buildings/HeatTransfer/Types.mo
+++ b/Buildings/HeatTransfer/Types.mo
@@ -72,6 +72,16 @@ heat transfer coefficient for interior (room-side facing) surfaces.
   For example, for a construction that is a floor, use
  <code>Buildings.HeatTransfer.Types.Tilt.Floor</code>.
 </p>
+<p>
+Note that a ceiling has a tilt of <i>0</i>, and also the solar collector models
+in 
+<a href=\"Buildings.Fluid.SolarCollectors\">Buildings.Fluid.SolarCollectors</a>
+require a tilt of <i>0</i> if they are facing straight upwards.
+This is correct because
+the solar irradiation on a ceiling construction is on the other-side surface,
+which faces upwards toward the sky. Hence, a construction is considered
+a ceiling from the view point of a person standing inside a room. 
+</p>
 </html>",
   revisions="<html>
 <ul>
