diff --git a/etc/bashrc b/etc/bashrc
index 30241548cd..a949d5e11e 100644
--- a/etc/bashrc
+++ b/etc/bashrc
@@ -136,6 +136,11 @@ projectDir="$HOME/OpenFOAM/OpenFOAM-$WM_PROJECT_VERSION"
 #   * on a 32-bit OS this option is ignored (always 32-bit)
 #export WM_ARCH_OPTION=64
 
+# [FOAM_EXTRA_CXXFLAGS]
+# Additional compilation flags - do not inherit from the environment.
+# Set after sourcing or via <prefs.sh> to avoid surprises.
+unset FOAM_EXTRA_CXXFLAGS
+
 ################################################################################
 # NO (NORMAL) USER EDITING BELOW HERE
 
diff --git a/etc/config.csh/unset b/etc/config.csh/unset
index c3405cd65e..94dc6f8490 100644
--- a/etc/config.csh/unset
+++ b/etc/config.csh/unset
@@ -9,8 +9,7 @@
 #     Copyright (C) 2016-2019 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
-#     This file is part of OpenFOAM, licensed under GNU General Public License
-#     <http://www.gnu.org/licenses/>.
+#     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
 #
 # File
 #     etc/config.csh/unset
@@ -46,20 +45,15 @@ endif
 
 unsetenv WM_ARCH
 unsetenv WM_ARCH_OPTION
-unsetenv WM_CC
-unsetenv WM_CFLAGS
 unsetenv WM_COMPILER
 unsetenv WM_COMPILER_ARCH
 unsetenv WM_COMPILER_TYPE
 unsetenv WM_COMPILER_LIB_ARCH
 unsetenv WM_COMPILE_OPTION
-unsetenv WM_CXX
-unsetenv WM_CXXFLAGS
 unsetenv WM_DIR
 unsetenv WM_HOSTS
 unsetenv WM_LABEL_OPTION
 unsetenv WM_LABEL_SIZE
-unsetenv WM_LDFLAGS
 unsetenv WM_MPLIB
 unsetenv WM_NCOMPPROCS
 unsetenv WM_OPTIONS
@@ -75,6 +69,11 @@ unsetenv WM_PROJECT_VERSION
 unsetenv WM_SCHEDULER
 unsetenv WM_THIRD_PARTY_DIR
 
+# Older variables
+
+# Before 1906
+unsetenv WM_CC WM_CXX WM_CFLAGS WM_CXXFLAGS WM_LDFLAGS
+
 
 #------------------------------------------------------------------------------
 # Unset FOAM_* environment variables
@@ -84,8 +83,9 @@ unsetenv FOAM_APPBIN
 unsetenv FOAM_APP
 unsetenv FOAM_CODE_TEMPLATES
 unsetenv FOAM_ETC
+unsetenv FOAM_EXTRA_CXXFLAGS
+unsetenv FOAM_EXTRA_LDFLAGS
 unsetenv FOAM_EXT_LIBBIN
-unsetenv FOAM_INST_DIR
 unsetenv FOAM_JOB_DIR
 unsetenv FOAM_LIBBIN
 unsetenv FOAM_MPI
@@ -102,6 +102,10 @@ unsetenv FOAM_USER_APPBIN
 unsetenv FOAM_USER_LIBBIN
 unsetenv FOAM_UTILITIES
 
+# Old variables
+
+# Before 1812
+unsetenv FOAM_INST_DIR
 
 #------------------------------------------------------------------------------
 # Unset MPI-related environment variables
diff --git a/etc/config.sh/unset b/etc/config.sh/unset
index 3676b19c20..4b9bcbf15f 100644
--- a/etc/config.sh/unset
+++ b/etc/config.sh/unset
@@ -6,11 +6,10 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2016-2019 OpenCFD Ltd.
+#     Copyright (C) 2016-2020 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
-#     This file is part of OpenFOAM, licensed under GNU General Public License
-#     <http://www.gnu.org/licenses/>.
+#     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
 #
 # File
 #     etc/config.sh/unset
@@ -35,19 +34,14 @@ foamOldDirs="$WM_PROJECT_DIR $WM_THIRD_PARTY_DIR \
 
 unset WM_ARCH
 unset WM_ARCH_OPTION
-unset WM_CC
-unset WM_CFLAGS
 unset WM_COMPILER
 unset WM_COMPILER_TYPE
 unset WM_COMPILER_LIB_ARCH
 unset WM_COMPILE_OPTION
-unset WM_CXX
-unset WM_CXXFLAGS
 unset WM_DIR
 unset WM_HOSTS
 unset WM_LABEL_OPTION
 unset WM_LABEL_SIZE
-unset WM_LDFLAGS
 unset WM_MPLIB
 unset WM_NCOMPPROCS
 unset WM_OPTIONS
@@ -63,6 +57,10 @@ unset WM_PROJECT_VERSION
 unset WM_SCHEDULER
 unset WM_THIRD_PARTY_DIR
 
+# Older variables
+
+# Before 1906
+unset WM_CC WM_CXX WM_CFLAGS WM_CXXFLAGS WM_LDFLAGS
 
 #------------------------------------------------------------------------------
 # Unset FOAM_* environment variables
@@ -72,8 +70,9 @@ unset FOAM_APPBIN
 unset FOAM_APP
 unset FOAM_CODE_TEMPLATES
 unset FOAM_ETC
+unset FOAM_EXTRA_CXXFLAGS
+unset FOAM_EXTRA_LDFLAGS
 unset FOAM_EXT_LIBBIN
-unset FOAM_INST_DIR
 unset FOAM_JOB_DIR
 unset FOAM_LIBBIN
 unset FOAM_MPI
@@ -90,6 +89,10 @@ unset FOAM_USER_APPBIN
 unset FOAM_USER_LIBBIN
 unset FOAM_UTILITIES
 
+# Old variables
+
+# Before 1812
+unset FOAM_INST_DIR
 
 #------------------------------------------------------------------------------
 # Unset MPI-related environment variables
diff --git a/etc/cshrc b/etc/cshrc
index b63ba3e4ed..9c3e9a03e2 100644
--- a/etc/cshrc
+++ b/etc/cshrc
@@ -138,6 +138,11 @@ set projectDir=`lsof +p $$ |& \
 #   * on a 32-bit OS this option is ignored (always 32-bit)
 #setenv WM_ARCH_OPTION 64
 
+# [FOAM_EXTRA_CXXFLAGS]
+# Additional compilation flags - do not inherit from the environment.
+# Set after sourcing or via <prefs.csh> to avoid surprises.
+unsetenv FOAM_EXTRA_CXXFLAGS
+
 ################################################################################
 # NO (NORMAL) USER EDITING BELOW HERE
 
diff --git a/wmake/rules/General/Clang/c++ b/wmake/rules/General/Clang/c++
index aa379895cc..4bba0cb569 100644
--- a/wmake/rules/General/Clang/c++
+++ b/wmake/rules/General/Clang/c++
@@ -14,9 +14,12 @@ c++WARN     = \
     -Wall -Wextra -Wold-style-cast \
     -Wnon-virtual-dtor -Wno-unused-parameter -Wno-invalid-offsetof \
     -Wno-undefined-var-template \
-    -Wno-unknown-warning-option
+    -Wno-unknown-warning-option \
+    $(FOAM_EXTRA_CXXFLAGS)
 
 c++LESSWARN = \
     -Wno-old-style-cast -Wno-unused-local-typedefs \
     -Wno-tautological-undefined-compare -Wno-shift-negative-value \
     -Wno-null-pointer-arithmetic
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/General/Gcc/c++ b/wmake/rules/General/Gcc/c++
index 15b7870a3e..337a7dfe73 100644
--- a/wmake/rules/General/Gcc/c++
+++ b/wmake/rules/General/Gcc/c++
@@ -13,9 +13,12 @@ ptFLAGS     = -DNoRepository -ftemplate-depth-100
 c++WARN     = \
     -Wall -Wextra -Wold-style-cast \
     -Wnon-virtual-dtor -Wno-unused-parameter -Wno-invalid-offsetof \
-    -Wno-attributes -Wno-unknown-pragmas
+    -Wno-attributes -Wno-unknown-pragmas \
+    $(FOAM_EXTRA_CXXFLAGS)
 
 c++LESSWARN = \
     -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds \
     -Wno-deprecated-declarations \
     -fpermissive
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/General/Icc/c++ b/wmake/rules/General/Icc/c++
index 2119fe8faf..e0ad375d2a 100644
--- a/wmake/rules/General/Icc/c++
+++ b/wmake/rules/General/Icc/c++
@@ -14,7 +14,10 @@ c++WARN     = \
     -Wall -Wextra \
     -Wnon-virtual-dtor -Wno-unused-parameter -Wno-invalid-offsetof \
     -Wno-unknown-pragmas \
-    -diag-disable 327,654,1125,1292,2289,2304,11062,11074,11076
+    -diag-disable 327,654,1125,1292,2289,2304,11062,11074,11076 \
+    $(FOAM_EXTRA_CXXFLAGS)
 
 c++LESSWARN = \
     -diag-disable 1224,2026,2305
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/General/Pgi/c++ b/wmake/rules/General/Pgi/c++
index b089aab167..e1f41b9425 100644
--- a/wmake/rules/General/Pgi/c++
+++ b/wmake/rules/General/Pgi/c++
@@ -10,5 +10,9 @@ ptFLAGS     = -DNoRepository
 # - Standard warnings
 # - Less restrictive warnings (may be needed for flex++, CGAL, etc.)
 
-c++WARN     =
+c++WARN     = \
+    $(FOAM_EXTRA_CXXFLAGS)
+
 c++LESSWARN =
+
+#------------------------------------------------------------------------------
diff --git a/wmake/wclean b/wmake/wclean
index c7ebcd7bab..3317a802fe 100755
--- a/wmake/wclean
+++ b/wmake/wclean
@@ -7,7 +7,7 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2017 OpenCFD Ltd.
+#     Copyright (C) 2017-2020 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM.
@@ -37,37 +37,52 @@
 #     lnInclude directories generated for libraries.
 #
 #------------------------------------------------------------------------------
-Script=${0##*/}             # Use 'Script' for error messages in wmakeFunctions
-. ${0%/*}/scripts/wmakeFunctions        # Source wmake functions
+Script="${0##*/}"           # Use 'Script' for error messages in wmakeFunctions
+. "${0%/*}/scripts/wmakeFunctions"              # Source wmake functions
 
-usage() {
-    while [ "$#" -ge 1 ]; do echo "$1"; shift; done
-    cat<<USAGE
+printHelp() {
+    cat<<HELP_INFO
 
 Usage: $Script [OPTION] [dir]
        $Script [OPTION] target [dir [MakeDir]]
 options:
-  -a | -all         Same as the 'all' target
+  -a | -all         All subdirectories, uses Allwclean, Allclean if they exist
   -s | -silent      Ignored - for compatibility with wmake
-  -help             Print the usage
+  -h | -help        Display short help and exit
+  -help-full        Display full help and exit
 
 Clean up the wmake control directory Make/\$WM_OPTIONS and remove the
 lnInclude directories generated for libraries.
 
-The targets correspond to a subset of the 'wmake' special targets:
-  all               All subdirectories, uses any Allwclean or Allclean
-                    files if they exist
+HELP_INFO
+
+cat<<HELP_TAIL_FULL
+Special targets:
+  all               Same as -all option
   exe | lib | libo | libso
-                    Clean Make, any *.dep files and lnInclude directories
   empty             Remove empty sub-directories for the requested dir.
                     If executed in the main project directory, it will also
                     remove deprecated object directories and respective binaries
                     that refer to no-longer-existing source code.
 
-USAGE
+HELP_TAIL_FULL
+    exit 0 # clean exit
+}
+
+# Report error and exit
+die()
+{
+    exec 1>&2
+    echo
+    echo "Error encountered:"
+    while [ "$#" -ge 1 ]; do echo "    $1"; shift; done
+    echo
+    echo "See '${0##*/} -help' for usage"
+    echo
     exit 1
 }
 
+
 #------------------------------------------------------------------------------
 # Parse arguments and options
 #------------------------------------------------------------------------------
@@ -78,16 +93,20 @@ MakeDir=Make
 while [ "$#" -gt 0 ]
 do
     case "$1" in
-    -h | -help*)
-        usage
+    -help-f*)   # Full help
+        printHelp -full
+        ;;
+    -h | -help*) # Short help
+        printHelp
         ;;
     -a | -all | all)
         targetType=all
         ;;
     -s | -silent)    # Ignored - for compatibility with wmake
+        export WM_QUIET=true
         ;;
     -*)
-        usage "unknown option: '$1'"
+        die "unknown option: '$1'"
         ;;
     *)
         break
diff --git a/wmake/wmake b/wmake/wmake
index 8bc070eb4b..ce1a2185a7 100755
--- a/wmake/wmake
+++ b/wmake/wmake
@@ -7,7 +7,7 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2017-2019 OpenCFD Ltd.
+#     Copyright (C) 2017-2020 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM.
@@ -94,19 +94,22 @@ cat<<HELP_FULL
 HELP_FULL
 fi
 
-cat<<HELP_TAIL
+cat<<HELP_TAIL_COMMON
   -pwd              Print root directory containing a Make/ directory
-  -version | --version  Print version, which is the same as -show-api
+  -version | --version  Print version (same as -show-api)
   -h | -help        Display short help and exit
   -help-full        Display full help and exit
 
 A general, easy-to-use make system for multi-platform development
 with support for local and network parallel compilation.
 
-The 'target' is a Makefile target:
-  e.g., platforms/linux64GccDPOpt/.../fvMesh.o
+HELP_TAIL_COMMON
 
-or a special target:
+if [ -n "$1" ]
+then
+cat<<HELP_TAIL_FULL
+Makefile targets:   platforms/linux64GccDPInt32Opt/.../fvMesh.o (for example)
+Special targets:
   all | queue       Same as -all | -queue options
   exe               Compile statically linked executable
   lib               Compile statically linked archive lib (.a)
@@ -116,10 +119,23 @@ or a special target:
   updatedep         Compile dependencies only (in case of broken dependencies)
   objects           Compile but not link
 
-HELP_TAIL
-    exit 1
+Environment
+  FOAM_EXTRA_CXXFLAGS
+
+HELP_TAIL_FULL
+else
+cat<<HELP_TAIL_BRIEF
+Some special targets (see -help-full for details):
+  all | queue       Same as -all | -queue options
+  exe               Executables
+  lib libo libso    Libraries
+
+HELP_TAIL_BRIEF
+fi
+    exit 0 # clean exit
 }
 
+
 # Report error and exit
 die()
 {