diff --git a/modules/grub.nix b/modules/grub.nix
index 092ff21..5f5c4e2 100644
--- a/modules/grub.nix
+++ b/modules/grub.nix
@@ -1,10 +1,20 @@
-{
+{ lib, ... }: {
+  # Use the GRUB 2 boot loader
   den.aspects.grub = {
-    nixos = {
-      # Use the GRUB 2 boot loader
-      boot.loader.grub.enable = true;
-      boot.loader.grub.efiSupport = true;
-      boot.loader.grub.efiInstallAsRemovable = true;
+    settings = {
+      device = lib.mkOption {
+        type = lib.types.str;
+        description = "The drive on which to install Grub";
+      };
+    };
+
+    nixos = { host, ... }: {
+      boot.loader.grub = {
+        enable = true;
+        efiSupport = true;
+        efiInstallAsRemovable = true;
+        device = host.settings.grub.device;
+      };
     };
   };
 }
diff --git a/modules/host.nix b/modules/host.nix
new file mode 100644
index 0000000..47c8975
--- /dev/null
+++ b/modules/host.nix
@@ -0,0 +1,103 @@
+{ lib, den, ... }:
+let
+  inherit (lib) mkOption types;
+
+  settingsType =
+    let
+      # Keys that are NOT children of an aspect: structural keys (includes, nixos, ...)
+      inherit (den.lib.aspects.fx.keyClassification) structuralKeysSet;
+      classKeys = den.classes or { };
+      quirkKeys = den.quirks or { };
+      skipKey = k: structuralKeysSet ? ${k} || classKeys ? ${k} || quirkKeys ? ${k};
+
+      # settings can be a plain options-attrset ({ foo = mkOption {...}; })
+      # OR module-shaped ({ imports; config; options; }). Normalize both to one shape.
+      reshapeSettings =
+        raw:
+        let
+          imports' = raw.imports or [ ];
+          config' = raw.config or { };
+        in
+        {
+          imports = imports';
+          config = config';
+          options = removeAttrs raw [
+            "imports"
+            "config"
+          ];
+        };
+
+      # True if this place, or anything below it, declares settings.
+      hasSettingsDeep =
+        node:
+        builtins.isAttrs node
+        && (
+          (node ? settings)
+          || lib.any (k: !(skipKey k) && hasSettingsDeep (node.${k} or null)) (builtins.attrNames node)
+        );
+
+      # Build the submodule for one place (node) in the aspect tree, mirroring
+      # the tree. Merge this place's own settings with its children's settings.
+      nodeModule =
+        node:
+        let
+          ownSettings =
+            if node ? settings then
+              reshapeSettings node.settings
+            else
+              {
+                imports = [ ];
+                config = { };
+                options = { };
+              };
+
+          settingChildren = lib.filterAttrs (
+            k: v: !(skipKey k) && builtins.isAttrs v && hasSettingsDeep v
+          ) node;
+
+          childOptions = lib.mapAttrs (
+            name: child:
+            mkOption {
+              type = types.submodule (nodeModule child); # recursion (calling itself)
+              default = { };
+              description = "Settings under ${name}";
+            }
+          ) settingChildren;
+
+          ownImports = ownSettings.imports or [ ];
+          ownConfig = ownSettings.config or { };
+        in
+        {
+          imports = ownImports;
+          config = ownConfig;
+          options = (ownSettings.options or { }) // childOptions;
+        };
+    in
+    types.submodule (nodeModule (den.aspects or { })); # ← reads the aspect tree
+in
+{
+  flake.den = den;
+  den.schema.host.isEntity = true;
+  den.reservedKeys = [ "settings" ];
+
+  den.schema.host.imports = [
+    (
+      { ... }:
+      {
+        options = {
+          # auto-generated settings namespace
+          settings =
+            mkOption {
+              type = settingsType;
+              default = { };
+              description = "Per-aspect typed settings";
+            }
+            # Keep settings out of the entity's identity (see Gotchas).
+            // {
+              identity = false;
+            };
+        };
+      }
+    )
+  ];
+}
diff --git a/modules/hosts/roost/roost.nix b/modules/hosts/roost/roost.nix
index 41afe17..7cdec77 100644
--- a/modules/hosts/roost/roost.nix
+++ b/modules/hosts/roost/roost.nix
@@ -9,18 +9,14 @@
       grub
     ];
 
+    settings = {
+      grub.device = "dev/sda";
+    };
+
     nixos = {
       imports = [ ./_hardware-configuration.nix ];
       system.stateVersion = "25.11";
 
-      # Use the GRUB 2 boot loader
-      boot.loader.grub.enable = true;
-      boot.loader.grub.efiSupport = true;
-      boot.loader.grub.efiInstallAsRemovable = true;
-      # boot.loader.efi.efiSysMountPoint = "/boot/efi";
-      # Define on which hard drive you want to install Grub.
-      boot.loader.grub.device = "/dev/sda"; # or "nodev" for efi only
-
       # todo: openssh aspect
       services.openssh.enable = true;
       users.users.root.openssh.authorizedKeys.keys = [