An update from administrator FRP Advisory revealed the scale of debts after the firm went under in March.
Total debts at the business were £4.5m including more than £2m owed to HMRC in VAT payments.
Unsecured creditors including subcontractors and suppliers are unlikely to see any cash following the administration process.
Latest accounts for Castlehouse for the year to March 31 2022 showed a turnover of £23.5m generating a pre-tax loss of £158,000.