AngularJS not listening to all my fields

I'm using AngularJS with Rails and creating dynamic nested form items which are not registering in the AngularJS scope. They are assigned the 'ng-dirty' class.

I have an investor which has three houses, in my Angular controller I only assign the first 2 as I really want to set these through Rails instead.

$ (event) ->
  app = angular.module "investor", []

  app.controller("InvestorCtrl", ["$scope", ($scope) ->
    $scope.houses = [
      { cost: "295000", value: "450000" },
      { cost: "600000", value: "620000"  }    
    ]
    $scope.calc_totals = ->
      # Initialise variables
      cost = 0
      value = 0

      # Go through each house and calculate the total cost
      for h in $scope.houses
        cost = parseInt(cost) + parseInt(h.cost)
        value = parseInt(value) + parseInt(h.value)

      # Set the total
      $scope.total_cost = cost
      $scope.total_value = value  

    # Run the calculation at the start  
    # $scope.calc_totals()
  ])

  angular.bootstrap document, ['investor']

Here is my form

%div{"ng-controller" => "InvestorCtrl"}
    = form_for(@investor) do |f|
        - if @investor.errors.any?
            #error_explanation
                %h2
                    = pluralize(@investor.errors.count, "error")
                    prohibited this investor from being saved:
                %ul
                    - @investor.errors.full_messages.each do |msg|
                        %li= msg
        .field
            = f.label :name
            = f.text_field :name, "ng-model" => "name"

        - i = 0
        = f.fields_for :houses do |builder|
            .field
                = render :partial => "house", :locals => {:f => builder, :i => i}
                - i = i + 1

        .field
            = f.label :total_cost
            = f.number_field :total_cost, "ng-model" => "total_cost"
        .field
            = f.label :total_value
            = f.number_field :total_value, "ng-model" => "total_value"
        .actions
            = f.submit

If I type in the first or second house 'cost' or 'value' then it updates the total_cost, but if I update the third house it will not update the total_cost.

Is there a way to dynamically tell angularjs to listen to these elements without assigning them in the controller?