The quality or state of being drafty; the degree to which a space has uncontrolled air currents flowing through it.
From 'drafty' plus the noun-forming suffix '-ness,' which creates abstract nouns describing qualities or states. 'Drafty' derives from 'draft' meaning air current.
Complaining about 'draftiness' is oddly modern—medieval people lived with it constantly, but by the 1800s as homes became warmer, people suddenly discovered this as a problem worth naming and solving.
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