Many professional home inspection associations set standards and rules for home inspectors. National Association of Certified Home Inspectors (NACHI) has its own Standards of Practice covering:

1. Definitions and Scope.
2. Standards of Practice
2.1. Roof
2.2. Exterior
2.3. Basement, Foundation, Crawlspace & Structure
2.4. Heating
2.5. Cooling
2.6. Plumbing
2.7. Electrical
2.8. Fireplace
2.9. Attic & Insulation
2.10. Doors, Windows & Interior
3. Limitations, Exceptions & Exclusions
4. Glossary of Terms

NACHI has also Code of Ethics observed by its members.

Home inspection rules (standards of Practice) by ASHI

American Society of Home Inspectors (ASHI) has been working on the standards in home inspection industry for years. Its Standards of Practice covers:

Introduction
Purpose & Scope
Structural System
Exterior
Roof System
Plumbing System
Electrical System
Heating System
Air Conditioning Systems
Interior
Insulation and Ventilation
Fireplaces and Solid Fuel Burning Appliances
General Limitations and Exclusions