diff --git a/.github/docker/Dockerfile.rhel8 b/.github/docker/Dockerfile.rhel8
index 1861014a71..e7809400d6 100644
--- a/.github/docker/Dockerfile.rhel8
+++ b/.github/docker/Dockerfile.rhel8
@@ -110,15 +110,21 @@ ENV VCPKG_DEFAULT_BINARY_CACHE=/opt/vcpkg-cache
 # ordinary source commits -- nightly rebuilds reuse the previously compiled
 # vcpkg binaries instead of recompiling every port.
 COPY ThirdParty/vcpkg /src/ThirdParty/vcpkg
+COPY ThirdParty/vcpkg-overlay-ports /src/ThirdParty/vcpkg-overlay-ports
 COPY vcpkg.json /src/vcpkg.json
 COPY vcpkg-configuration-rhel8.json /src/vcpkg-configuration.json
 
 # A direct manifest install compiles every dependency into
-# VCPKG_DEFAULT_BINARY_CACHE. The dependency set has no manifest features or
-# overlay ports, and CC/CXX below match the ResInsight configure in the
-# warmup stage and in CI, so the vcpkg ABI hashes match and the cache is
-# reused there. x64-linux is the triplet the vcpkg CMake toolchain defaults
-# to on Linux.
+# VCPKG_DEFAULT_BINARY_CACHE. vcpkg-configuration-rhel8.json's overlay-ports
+# entry ("ThirdParty/vcpkg-overlay-ports") is resolved relative to the
+# directory vcpkg-configuration.json lives in, i.e. /src here, so that
+# directory must be copied in too, not just ThirdParty/vcpkg. CC/CXX below
+# match the ResInsight configure in the warmup stage and in CI, so the vcpkg
+# ABI hashes match and the cache is reused there. x64-linux-release matches
+# the triplet the CI workflows and the warmup stage below pass via
+# VCPKG_TARGET_TRIPLET/VCPKG_HOST_TRIPLET -- using the plain (debug+release)
+# x64-linux triplet here would populate the cache under different ABI hashes
+# and none of it would be reused downstream.
 #
 # After the install, verify the cache contains a plausible number of entries.
 # vcpkg's `files` binary provider stores one .zip per package under
@@ -132,7 +138,7 @@ RUN git config --global --add safe.directory '*' \
  && ( cd /src/ThirdParty/vcpkg && ./bootstrap-vcpkg.sh ) \
  && export CC=/opt/rh/gcc-toolset-14/root/usr/bin/gcc \
  && export CXX=/opt/rh/gcc-toolset-14/root/usr/bin/g++ \
- && ( cd /src && ./ThirdParty/vcpkg/vcpkg install --triplet x64-linux ) \
+ && ( cd /src && ./ThirdParty/vcpkg/vcpkg install --triplet x64-linux-release --host-triplet x64-linux-release ) \
  && vcpkg_zip_count=$(find "${VCPKG_DEFAULT_BINARY_CACHE}" -type f -name '*.zip' | wc -l) \
  && echo "vcpkg binary cache entries: ${vcpkg_zip_count}" \
  && test "${vcpkg_zip_count}" -ge 20 \
@@ -167,7 +173,6 @@ COPY . /src
 # (the command line is part of the hash).
 RUN --mount=type=cache,id=ri-rhel8-buildcache,target=/var/cache/buildcache,sharing=locked \
     git config --global --add safe.directory '*' \
- && cp /src/vcpkg-configuration-rhel8.json /src/vcpkg-configuration.json \
  && source /opt/rh/gcc-toolset-14/enable \
  && ( cd /src/ThirdParty/vcpkg && ./bootstrap-vcpkg.sh ) \
  && export CC=/opt/rh/gcc-toolset-14/root/usr/bin/gcc \
@@ -182,6 +187,9 @@ RUN --mount=type=cache,id=ri-rhel8-buildcache,target=/var/cache/buildcache,shari
       -DRESINSIGHT_ENABLE_HDF5=false \
       -DRESINSIGHT_ENABLE_GRPC=false \
       -DRESINSIGHT_GCC_STDCPP_EXP_PATH=/opt/libstdcxx-exp/lib \
+      -DRESINSIGHT_VCPKG_PROFILE=rhel8 \
+      -DVCPKG_TARGET_TRIPLET=x64-linux-release \
+      -DVCPKG_HOST_TRIPLET=x64-linux-release \
       -DCMAKE_TOOLCHAIN_FILE=ThirdParty/vcpkg/scripts/buildsystems/vcpkg.cmake \
  && cmake --build /src/cmakebuild --target ResInsight-tests -- -j"$(nproc)" \
  && buildcache -s \
diff --git a/.github/workflows/build-rhel8-image.yml b/.github/workflows/build-rhel8-image.yml
index c0b4169c24..80aa42edee 100644
--- a/.github/workflows/build-rhel8-image.yml
+++ b/.github/workflows/build-rhel8-image.yml
@@ -15,6 +15,7 @@ on:
       - ".dockerignore"
       - "vcpkg.json"
       - "vcpkg-configuration-rhel8.json"
+      - "ThirdParty/vcpkg-overlay-ports/**"
       - ".gitmodules"
   workflow_dispatch:
     inputs:
diff --git a/.github/workflows/rhel8-package.yml b/.github/workflows/rhel8-package.yml
index 34ea9cdd29..29f8205ebd 100644
--- a/.github/workflows/rhel8-package.yml
+++ b/.github/workflows/rhel8-package.yml
@@ -78,9 +78,6 @@ jobs:
           cd ThirdParty/vcpkg
           ./bootstrap-vcpkg.sh
 
-      - name: Use RHEL8 vcpkg configuration
-        run: cp vcpkg-configuration-rhel8.json vcpkg-configuration.json
-
       - name: Configure CMake
         env:
           CC: /opt/rh/gcc-toolset-14/root/usr/bin/gcc
@@ -103,6 +100,9 @@ jobs:
             -DRESINSIGHT_ENABLE_HDF5=false \
             -DRESINSIGHT_ENABLE_GRPC=false \
             -DRESINSIGHT_GCC_STDCPP_EXP_PATH=/opt/libstdcxx-exp/lib \
+            -DRESINSIGHT_VCPKG_PROFILE=rhel8 \
+            -DVCPKG_TARGET_TRIPLET=x64-linux-release \
+            -DVCPKG_HOST_TRIPLET=x64-linux-release \
             -DCMAKE_TOOLCHAIN_FILE=ThirdParty/vcpkg/scripts/buildsystems/vcpkg.cmake
 
       - name: Build install target
diff --git a/.github/workflows/rhel8-unit-tests.yml b/.github/workflows/rhel8-unit-tests.yml
index 6f41cb7510..bfe994c65d 100644
--- a/.github/workflows/rhel8-unit-tests.yml
+++ b/.github/workflows/rhel8-unit-tests.yml
@@ -80,9 +80,6 @@ jobs:
           cd ThirdParty/vcpkg
           ./bootstrap-vcpkg.sh
 
-      - name: Use RHEL8 vcpkg configuration
-        run: cp vcpkg-configuration-rhel8.json vcpkg-configuration.json
-
       - name: Configure CMake
         env:
           CC: /opt/rh/gcc-toolset-14/root/usr/bin/gcc
@@ -104,6 +101,9 @@ jobs:
             -DRESINSIGHT_ENABLE_HDF5=false \
             -DRESINSIGHT_ENABLE_GRPC=false \
             -DRESINSIGHT_GCC_STDCPP_EXP_PATH=/opt/libstdcxx-exp/lib \
+            -DRESINSIGHT_VCPKG_PROFILE=rhel8 \
+            -DVCPKG_TARGET_TRIPLET=x64-linux-release \
+            -DVCPKG_HOST_TRIPLET=x64-linux-release \
             -DCMAKE_TOOLCHAIN_FILE=ThirdParty/vcpkg/scripts/buildsystems/vcpkg.cmake
 
       - name: Build
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 84c360044b..55ceb795bd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,6 +23,10 @@ include(FetchContent)
 # subdirectory CMakeLists.txt files pull in via their own find_package().
 set(CMAKE_FIND_PACKAGE_TARGETS_GLOBAL TRUE)
 
+# Must be include()'d before project() -- see cmake/ResInsightVcpkgProfile.cmake
+# for why.
+include(cmake/ResInsightVcpkgProfile.cmake)
+
 project(ResInsight)
 
 # Include common settings
diff --git a/cmake/ResInsightVcpkgProfile.cmake b/cmake/ResInsightVcpkgProfile.cmake
new file mode 100644
index 0000000000..b83551a1f2
--- /dev/null
+++ b/cmake/ResInsightVcpkgProfile.cmake
@@ -0,0 +1,67 @@
+# Select an alternate vcpkg-configuration.json without renaming/copying any
+# tracked file. The vcpkg toolchain
+# (ThirdParty/vcpkg/scripts/buildsystems/vcpkg.cmake) defaults
+# VCPKG_MANIFEST_DIR to CMAKE_SOURCE_DIR only when it is not already defined,
+# and it must see the final value before project() triggers toolchain-file
+# processing. This file must therefore be include()'d from the root
+# CMakeLists.txt before project() is called -- code that runs after project()
+# is too late.
+#
+# A profile's vcpkg-configuration file is expected at
+# "vcpkg-configuration-${RESINSIGHT_VCPKG_PROFILE}.json" in the source root,
+# e.g. vcpkg-configuration-rhel8.json for -DRESINSIGHT_VCPKG_PROFILE=rhel8.
+# vcpkg.json is copied alongside it so both manifest files live in the same
+# directory, as vcpkg requires; the copy is regenerated on every configure so it
+# can never drift from the root vcpkg.json.
+set(RESINSIGHT_VCPKG_PROFILE
+    ""
+    CACHE
+      STRING
+      "Optional vcpkg-configuration profile, e.g. 'rhel8' to use vcpkg-configuration-rhel8.json"
+)
+if(RESINSIGHT_VCPKG_PROFILE)
+  set(_resinsight_vcpkg_profile_config
+      "${CMAKE_CURRENT_SOURCE_DIR}/vcpkg-configuration-${RESINSIGHT_VCPKG_PROFILE}.json"
+  )
+  if(NOT EXISTS "${_resinsight_vcpkg_profile_config}")
+    message(
+      FATAL_ERROR "RESINSIGHT_VCPKG_PROFILE='${RESINSIGHT_VCPKG_PROFILE}' but "
+                  "${_resinsight_vcpkg_profile_config} does not exist"
+    )
+  endif()
+
+  set(_resinsight_vcpkg_manifest_dir
+      "${CMAKE_BINARY_DIR}/vcpkg-manifest-${RESINSIGHT_VCPKG_PROFILE}"
+  )
+  file(MAKE_DIRECTORY "${_resinsight_vcpkg_manifest_dir}")
+  configure_file(
+    "${CMAKE_CURRENT_SOURCE_DIR}/vcpkg.json"
+    "${_resinsight_vcpkg_manifest_dir}/vcpkg.json" COPYONLY
+  )
+  configure_file(
+    "${_resinsight_vcpkg_profile_config}"
+    "${_resinsight_vcpkg_manifest_dir}/vcpkg-configuration.json" COPYONLY
+  )
+
+  # overlay-ports/overlay-triplets entries (e.g.
+  # "ThirdParty/vcpkg-overlay-ports") are resolved by vcpkg relative to the
+  # directory vcpkg-configuration.json lives in. Since the copy above now lives
+  # under the build tree instead of the source root, rewrite those repo-relative
+  # "ThirdParty/..." paths to absolute paths so they still resolve to the real
+  # source tree.
+  file(READ "${_resinsight_vcpkg_manifest_dir}/vcpkg-configuration.json"
+       _resinsight_vcpkg_profile_json
+  )
+  string(REPLACE "\"ThirdParty/" "\"${CMAKE_CURRENT_SOURCE_DIR}/ThirdParty/"
+                 _resinsight_vcpkg_profile_json
+                 "${_resinsight_vcpkg_profile_json}"
+  )
+  file(WRITE "${_resinsight_vcpkg_manifest_dir}/vcpkg-configuration.json"
+       "${_resinsight_vcpkg_profile_json}"
+  )
+
+  set(VCPKG_MANIFEST_DIR
+      "${_resinsight_vcpkg_manifest_dir}"
+      CACHE PATH "" FORCE
+  )
+endif()
diff --git a/vcpkg-readme.md b/vcpkg-readme.md
index a1464d2f9d..e22a7cf4dc 100644
--- a/vcpkg-readme.md
+++ b/vcpkg-readme.md
@@ -16,11 +16,26 @@ The `baseline` field in each configuration file pins the vcpkg registry to a spe
 
 ## RHEL8 CI usage
 
-The workflow `.github/workflows/rhel8-unit-tests.yml` copies `vcpkg-configuration-rhel8.json` over `vcpkg-configuration.json` before invoking cmake:
+Selecting the RHEL8 configuration does not rename or overwrite the tracked
+`vcpkg-configuration.json`. Instead, the root `CMakeLists.txt` accepts a
+`RESINSIGHT_VCPKG_PROFILE` cache variable. When set, it copies `vcpkg.json`
+and `vcpkg-configuration-<profile>.json` into a profile-specific directory
+under the build tree and points vcpkg's `VCPKG_MANIFEST_DIR` at it, before
+`project()` triggers the vcpkg toolchain file. This must happen before
+`project()`: the toolchain file only defaults `VCPKG_MANIFEST_DIR` to
+`CMAKE_SOURCE_DIR` when the variable is not already defined, and it reads
+that value while processing `project()`.
 
-```yaml
-- name: Use RHEL8 vcpkg configuration
-  run: cp vcpkg-configuration-rhel8.json vcpkg-configuration.json
+The workflows `.github/workflows/rhel8-unit-tests.yml` and
+`.github/workflows/rhel8-package.yml` (and `.github/docker/Dockerfile.rhel8`)
+select the RHEL8 baseline by passing this flag to `cmake`:
+
+```
+cmake -S /src -B /src/cmakebuild -G Ninja \
+  ... \
+  -DRESINSIGHT_VCPKG_PROFILE=rhel8 \
+  -DCMAKE_TOOLCHAIN_FILE=ThirdParty/vcpkg/scripts/buildsystems/vcpkg.cmake
 ```
 
-This ensures vcpkg uses the RHEL8 baseline without affecting other CI runs.
+This ensures vcpkg uses the RHEL8 baseline without affecting other CI runs,
+and without ever mutating a tracked file in the source tree.