useLayout.js

// Defining the application router, you can attach sub routers here.
var Router = Backbone.Router.extend({
  routes: {
    "": "index"
  },

  index: function() {
    this.useLayout("main").setViews({
      header: new UI.Views.Toolbar()
    }).render();
  },

  // Helper for specific layouts.
  useLayout: function(name) {
    // If already using this Layout, then don't re-inject into the DOM.
    if (this.layout && this.layout.options.template === name) {
      return this.layout;
    }

    // Ensure previous layouts are completely removed.
    if (this.layout) {
      this.layout.remove();
    }

    // Create a new Layout.
    var layout = new Backbone.Layout({
      template: name,
      className: "layout " + name,
      id: "layout"
    });

    // Insert into the DOM.
    $("#main").empty().append(layout.el);

    // Render the layout.
    layout.render();

    // Cache the reference on the Router.
    this.layout = layout;

    // Return the reference, for later usage.
    return layout;
  }
});