Small Passive Houses: Efficient Design Under 1500 sq ft A small passive house under 1500 sq ft offers a clear path to very low energy bills, simplified mechanical systems, and an achievable DIY self-build scope. This guide explains how to design a compact passive house that meets common Passive House benchmarks—heating demand near ~15 kWh/m²·yr and airtightness around ≤0.6 ACH50—so readers can plan a 1,200–1,500 sq ft home that performs like a larger certified build but costs less to run and to maintain. Expect concrete choices for form, envelope, MVHR sizing, solar and foundation strategies plus practical trade-offs for budget-conscious DIYers. TL;DR: - A compact small passive house can hit Passive House heating demand (~15 kWh/m²·yr) and airtightness (≤0.6 ACH50) with a simple rectangular form, 1–2 south windows for passive solar design, and continuous exterior insulation. - Prioritize airtightness, right-sized MVHR (heat recovery >70%), and high-performance triple-glazed windows; sa...