Experience with additions/loft extensions & energy-efficient renovation (EFH, NRW) – financing without equity?

**Hello everyone,** I'm facing a big challenge and I'm hoping for honest reports, tips and warnings from the community! **Initial situation:** * We are a family of 5 and are expecting twins (so soon 7 people). * Home: Bungalow (EFH, built in 1970) with gable roof (NRW). * Currently only 2 bedrooms, 1 living room, hallway, kitchen, bathroom. * Goal: Increase the floor (raise knee, new roof) for 3 additional rooms + bathroom on the upper floor. * Heating: Old oil heater (Buderus G115,