Checklist
Tiny house ventilation and moisture checklist
Cooking, showering and breathing all put water into the air, and a small sealed house has little air to absorb it. Use this list once when you move in, then again each season. Allow about 30 minutes plus the time to read a humidity meter.
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Why this order
Measuring comes first because moisture problems are easier to fix when you know where the air is wet. The bathroom and kitchen come next, since they make most of the moisture. Storage and leaks follow, because a hidden damp spot often shows up behind things pushed against a cold wall. Safety is last on the list but not least important: a tight house also holds combustion gases if anything burns fuel.
The numbers behind it
US Environmental Protection Agency guidance on mold says to keep indoor humidity below 60 percent, ideally between 30 and 50 percent, and to dry wet materials within 24 to 48 hours. The 20-minute fan run time is the figure the Home Ventilating Institute gives for bathroom fans. Everything else on the list is common-sense practice, not a measured threshold.
Limits
A checklist cannot tell you if you already have mold or a structural leak. If you see widespread mold, smell a strong musty odor you cannot trace, or find soft wood, get help from a qualified building or remediation professional. If anyone in the home has breathing problems, talk with a doctor about the home environment. If a carbon monoxide alarm sounds, go outside and call your local emergency number. Ventilation rules and equipment requirements vary by place and by build type, so check your local requirements.
Where this comes from
We checked EPA mold and moisture guidance for the humidity range and the 24 to 48 hour drying window, and the Home Ventilating Institute bathroom ventilation page for the fan run time. This is general information, not a home inspection or professional advice.