diff --git a/scripts/build_native_fvs.sh b/scripts/build_native_fvs.sh
new file mode 100755
index 0000000..b41e5d5
--- /dev/null
+++ b/scripts/build_native_fvs.sh
@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+#
+# Build native FVS shared libraries for pyfvs parity testing.
+#
+# Compiles each requested FVS variant from the USDA Fortran source into a
+# loadable shared library (FVS<variant>.so) and installs it to ~/.fvs/lib,
+# where pyfvs.native and the parity suite discover it.
+#
+# Usage:
+#   scripts/build_native_fvs.sh                 # build all pyfvs variants
+#   scripts/build_native_fvs.sh sn ls ne        # build a subset (lowercase codes)
+#
+# Environment:
+#   FVS_SRC   FVS source checkout   (default: ~/Projects/ForestVegetationSimulator)
+#   FVS_LIB_PATH / LIBDIR  install dir (default: ~/.fvs/lib)
+#   JOBS      max concurrent variant builds (default: 4)
+#
+# Requires: gfortran, gcc, make. The volume/NVEL git submodule is initialized
+# automatically if absent (the build fails without it).
+set -uo pipefail
+
+FVS_SRC="${FVS_SRC:-$HOME/Projects/ForestVegetationSimulator}"
+LIBDIR="${LIBDIR:-${FVS_LIB_PATH:-$HOME/.fvs/lib}}"
+JOBS="${JOBS:-4}"
+LOGDIR="${LOGDIR:-$FVS_SRC/bin/_build_logs}"
+
+# pyfvs-implemented variants (10 + EC). FVS ships 20 geographic variants total.
+PYFVS_VARIANTS="sn ls cs ne pn wc ec ca ws op oc"
+
+# --- child mode: build a single variant (re-invoked by xargs below) ----------
+if [ "${1:-}" = "--build-one" ]; then
+	v="$2"
+	lib="FVS${v}.so"
+	mkdir -p "$LIBDIR"
+	( cd "$FVS_SRC/bin" && rm -rf "FVS${v}_buildDir" && make "$lib" ) \
+		> "$LOGDIR/build_${v}.log" 2>&1
+	if [ -f "$FVS_SRC/bin/$lib" ]; then
+		cp "$FVS_SRC/bin/$lib" "$LIBDIR/$lib"
+		codesign -s - "$LIBDIR/$lib" >/dev/null 2>&1 || true   # macOS ad-hoc sign
+		echo "OK    $v  ->  $LIBDIR/$lib"
+	else
+		echo "FAIL  $v  (see $LOGDIR/build_${v}.log)"
+	fi
+	exit 0
+fi
+
+# --- main dispatch -----------------------------------------------------------
+if [ "$#" -gt 0 ]; then VARIANTS="$*"; else VARIANTS="$PYFVS_VARIANTS"; fi
+
+# Ensure the NVEL volume library submodule is present.
+if [ ! -f "$FVS_SRC/volume/NVEL/beqinfo.inc" ]; then
+	echo "Initializing volume/NVEL submodule..."
+	git -C "$FVS_SRC" submodule update --init --recursive
+fi
+
+mkdir -p "$LOGDIR" "$LIBDIR"
+export FVS_SRC LIBDIR LOGDIR
+
+echo "Building variants: $VARIANTS  (JOBS=$JOBS, install -> $LIBDIR)"
+printf '%s\n' $VARIANTS | xargs -P "$JOBS" -n1 "$0" --build-one
+echo "Done. Installed libraries:"
+ls -1 "$LIBDIR"/FVS*.so 2>/dev/null || echo "  (none)"
diff --git a/src/pyfvs/native/BUILD.md b/src/pyfvs/native/BUILD.md
index ac474b7..5bb1d22 100644
--- a/src/pyfvs/native/BUILD.md
+++ b/src/pyfvs/native/BUILD.md
@@ -3,6 +3,38 @@
 Instructions for building the native FVS Fortran shared libraries for use
 with `pyfvs.native` validation bindings.
 
+## Quick build (recommended)
+
+From the pyfvs repo, build and install all variants the parity suite needs:
+
+```bash
+scripts/build_native_fvs.sh            # all 11 pyfvs variants -> ~/.fvs/lib
+scripts/build_native_fvs.sh sn ls ne   # or a subset (lowercase codes)
+```
+
+The script compiles each variant from the FVS Fortran source (default
+`~/Projects/ForestVegetationSimulator`) via the repo's own makefile, installs
+`FVS<variant>.so` into `~/.fvs/lib`, and ad-hoc code-signs on macOS.
+
+**Gotcha:** the FVS source tree's `volume/NVEL` (National Volume Estimator
+Library) is a **git submodule**. A fresh clone/restore leaves it empty and the
+build fails with `No rule to make target '../volume/NVEL/beqinfo.inc'`. The
+script initializes it automatically; to do it by hand:
+
+```bash
+git -C ~/Projects/ForestVegetationSimulator submodule update --init --recursive
+```
+
+Then run the parity suite. The parity tests are auto-marked `parity` and the
+default pytest config deselects them (`-m "not slow and not parity"`), so you
+**must** opt in explicitly:
+
+```bash
+uv run pytest tests/parity/ -m parity
+```
+
+The manual, single-variant steps below are kept for reference.
+
 ## Prerequisites
 
 ### macOS
@@ -26,7 +58,8 @@ sudo apt install gfortran make
 ### 1. Clone the FVS repository
 
 ```bash
-git clone https://github.com/USDAForestService/ForestVegetationSimulator.git
+# --recursive pulls the volume/NVEL submodule (required for the build)
+git clone --recursive https://github.com/USDAForestService/ForestVegetationSimulator.git
 cd ForestVegetationSimulator
 ```