Look it up
Humidity chart
Every number this site uses, on one page: by season, by outdoor temperature, by room and by climate.
How to measure it
A cheap hygrometer in the wrong place, read at the wrong time, produces a number that means nothing. Four rules fix that.
Glossary
Plain definitions, in the sense the terms are actually used when someone is trying to fix a damp house.
Where the water comes from
The full accounting: what each activity releases per day, ranked. Most damp problems are on this list.
When to call a pro
The lines worth knowing before you spend money: what is yours to fix, what is not, and who to call for which.