As an avid reader of Passivhaus books (actually any books on a variety of subjects); below are two I would heartily recommend to get you started on Passivhaus theory and onto more advance topics.

1. The Passivhaus Handbook by Janet Cotterell and Adam Dadeby

A great primer in everything Passivhaus. Chapters include:

Part One: The how and why of Passivhaus
• What is Passivhaus
• The economics of Passivhaus
• Passivhaus Certification
• Challenges of meeting the Passivhaus standard
• Natural materials,zero carbon and resilience
• Setting up a Passivhaus project

Part Two: Passivhaus projects: a practical guide
• Using PHPP
• Thermal bridges
• Airtightness and sequencing
• Moisture
• Windows
• Ventilation
• Living in a Passivhaus
• Policy change in the UK

The book is extensively Appendixed with a great glossary of terms/units plus notes and resources.

I used this book as part of my revision before…