diff --git a/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/mount.conf b/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/mount.conf
index dad6c229df2b..7113acc881a9 100644
--- a/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/mount.conf
+++ b/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/mount.conf
@@ -20,8 +20,20 @@ extraMounts:
       mountPoint: /sys/firmware/efi/efivars
       efi: true
 
-# Ensure the right fmask/dmask is set on the ESP, as it will be
-# picked up by nixos-generate-config later
+# Btrfs subvolume layout for NixOS
+# Empty subvolume for / means no subvolume (top-level) for GRUB compatibility
+btrfsSubvolumes:
+    - mountPoint: /
+      subvolume: ""
+    - mountPoint: /home
+      subvolume: /home
+    - mountPoint: /nix
+      subvolume: /nix
+
+# Mount options by filesystem type
+# nixos-generate-config picks these up for hardware-configuration.nix
 mountOptions:
     - filesystem: efi
       options: [ fmask=0077, dmask=0077 ]
+    - filesystem: btrfs
+      options: [ compress=zstd, noatime ]
diff --git a/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/partition.conf b/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/partition.conf
index 3e067e8d2343..75d04cec9dfa 100644
--- a/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/partition.conf
+++ b/pkgs/by-name/ca/calamares-nixos-extensions/src/config/modules/partition.conf
@@ -12,11 +12,29 @@ userSwapChoices:
 
 luksGeneration: luks2
 
+defaultFileSystemType: "ext4"
+
+availableFileSystemTypes:
+    - ext4
+    - btrfs
+    - xfs
+    - f2fs
+
 showNotEncryptedBootMessage: false
 
+bios:
+    mountPoint: "/boot"
+    minimumSize: 512MiB
+    recommendedSize: 1GiB
+    label: "BOOT"
+
 partitionLayout:
-    - name: "root"
+    - name: "boot"
       filesystem: "ext4"
+      mountPoint: "/boot"
+      size: 1GiB
+    - name: "root"
+      filesystem: "unknown"
       noEncrypt: false
       mountPoint: "/"
       size: 100%
diff --git a/pkgs/by-name/ca/calamares-nixos-extensions/src/modules/nixos/main.py b/pkgs/by-name/ca/calamares-nixos-extensions/src/modules/nixos/main.py
index 5987724728f8..e9bee7a245d4 100644
--- a/pkgs/by-name/ca/calamares-nixos-extensions/src/modules/nixos/main.py
+++ b/pkgs/by-name/ca/calamares-nixos-extensions/src/modules/nixos/main.py
@@ -45,6 +45,15 @@ cfgbootbios = """  # Bootloader.
 
 """
 
+cfgbootbiosbtrfs = """  # Bootloader.
+  boot.loader.grub.enable = true;
+  boot.loader.grub.device = "@@bootdev@@";
+  boot.loader.grub.useOSProber = true;
+  # Use provided UUIDs instead of blkid probing (required for btrfs subvolumes)
+  boot.loader.grub.fsIdentifier = "provided";
+
+"""
+
 cfgbootnone = """  # Disable bootloader.
   boot.loader.grub.enable = false;
 
@@ -360,6 +369,46 @@ def catenate(d, key, *values):
     d[key] = "".join(values)
 
 
+def fix_btrfs_subvolumes(hardware_config, partitions):
+    """
+    Fix btrfs subvolume configuration in hardware-configuration.nix.
+
+    nixos-generate-config generates incorrect subvol options for btrfs
+    by setting them to mount points instead of actual subvolume names.
+    This function corrects the subvol options to match what Calamares configured.
+    """
+    # Map of mount points to their correct btrfs subvolume names
+    # These match what is configured in mount.conf btrfsSubvolumes
+    # Root uses top-level (no subvolume) for GRUB compatibility
+    subvol_map = {
+        "/home": "home",
+        "/nix": "nix",
+    }
+
+    # Check if root is actually btrfs
+    root_is_btrfs = False
+    for part in partitions:
+        if part.get("mountPoint") == "/" and part.get("fs") == "btrfs":
+            root_is_btrfs = True
+            break
+
+    if not root_is_btrfs:
+        return hardware_config
+
+    libcalamares.utils.debug("Fixing btrfs subvolume configuration")
+
+    # Fix subvol options for each mount point
+    # nixos-generate-config may generate "subvol=/" instead of "subvol=@"
+    for mount_point, correct_subvol in subvol_map.items():
+        # Match any "subvol=<something>" and replace with correct subvolume
+        # This handles cases like "subvol=/" or "subvol=/home"
+        pattern = r'(fileSystems\."{}"[^;]*"subvol=)[^"]*"'.format(re.escape(mount_point))
+        replacement = r'\g<1>{}"'.format(correct_subvol)
+        hardware_config = re.sub(pattern, replacement, hardware_config, flags=re.DOTALL)
+
+    return hardware_config
+
+
 def run():
     """NixOS Configuration."""
 
@@ -388,11 +437,22 @@ def run():
 
     # Pick config parts and prepare substitution
 
+    # Check if root filesystem is btrfs
+    root_is_btrfs = False
+    for part in gs.value("partitions"):
+        if part.get("mountPoint") == "/" and part.get("fs") == "btrfs":
+            root_is_btrfs = True
+            break
+
     # Check bootloader
     if fw_type == "efi":
         cfg += cfgbootefi
     elif bootdev != "nodev":
-        cfg += cfgbootbios
+        # Use btrfs-specific config to avoid blkid issues with subvolumes
+        if root_is_btrfs:
+            cfg += cfgbootbiosbtrfs
+        else:
+            cfg += cfgbootbios
         catenate(variables, "bootdev", bootdev)
     else:
         cfg += cfgbootnone
@@ -734,9 +794,20 @@ def run():
             libcalamares.utils.error(e.output.decode("utf8"))
         return (_("nixos-generate-config failed"), _(e.output.decode("utf8")))
 
-    # Check for unfree stuff in hardware-configuration.nix
+    # Read and fix hardware-configuration.nix
     hf = open(root_mount_point + "/etc/nixos/hardware-configuration.nix", "r")
     htxt = hf.read()
+    hf.close()
+
+    hardware_modified = False
+
+    # Fix btrfs subvolume configuration if needed
+    htxt_fixed = fix_btrfs_subvolumes(htxt, gs.value("partitions"))
+    if htxt_fixed != htxt:
+        htxt = htxt_fixed
+        hardware_modified = True
+
+    # Check for unfree stuff in hardware-configuration.nix
     search = re.search(r"boot\.extraModulePackages = \[ (.*) \];", htxt)
 
     # Check if any extraModulePackages are defined, and remove if only free packages are allowed
@@ -765,14 +836,17 @@ def run():
                     )
                 )
                 expkgs.remove(pkg)
-        hardwareout = re.sub(
+        htxt = re.sub(
             r"boot\.extraModulePackages = \[ (.*) \];",
             "boot.extraModulePackages = [ {}];".format(
                 "".join(map(lambda x: x + " ", expkgs))
             ),
             htxt,
         )
-        # Write the hardware-configuration.nix file
+        hardware_modified = True
+
+    # Write the hardware-configuration.nix file if modified
+    if hardware_modified:
         libcalamares.utils.host_env_process_output(
             [
                 "cp",
@@ -780,7 +854,7 @@ def run():
                 root_mount_point + "/etc/nixos/hardware-configuration.nix",
             ],
             None,
-            hardwareout,
+            htxt,
         )
 
     # Write the configuration.nix file
@@ -789,6 +863,14 @@ def run():
     status = _("Installing NixOS")
     libcalamares.job.setprogress(0.3)
 
+    try:
+        subprocess.check_output(
+            ["pkexec", "chmod", "755", root_mount_point],
+            stderr=subprocess.STDOUT,
+        )
+    except subprocess.CalledProcessError as e:
+        libcalamares.utils.warning("Failed to set permissions on {}: {}".format(root_mount_point, e.output))
+
     # build nixos-install command
     nixosInstallCmd = [ "pkexec" ]
     nixosInstallCmd.extend(generateProxyStrings())