hayloft (n.)

"grass mown," Old English heg (Anglian), hieg, hig (West Saxon) "grass cut or mown for fodder," from Proto-Germanic *haujam (source also of Old Norse hey, Old Frisian ha, Middle Dutch hoy, German Heu, Gothic hawi "hay"), literally "that which is cut," or "that which can be mowed" (from PIE *kau- "to hew, strike;" source also of Old English heawan "to cut;" see hew).

Slang phrase hit the hay (pre-1880) was originally "to sleep in a barn;" hay in the general figurative sense of "bedding" is from 1903; roll in the hay (n.) is from 1941.

"an upper chamber," c. 1300, an extended sense from late Old English loft "the sky; the sphere of the air," from Old Norse lopt (Scandinavian -pt- pronounced like -ft-) "air, sky," originally "upper story, loft, attic," from Proto-Germanic *luftuz "air, sky" (source also of Old English lyft, Dutch lucht, Old High German luft, German Luft, Gothic luftus "air").

If this is correct, the sense development would be from "loft, ceiling" to "sky, air." Buck suggests a further connection with Old High German louft "bark," louba "roof, attic," etc., with development from "bark" to "roof made of bark" to "ceiling," though this did not directly inform the meaning "air, sky" (compare lodge (n.)). But Watkins says this is "probably a separate Germanic root." Meaning "gallery in a church" first attested c. 1500. From 1520s as "apartment over a stable" used for hay storage, etc.