Room's upper surface (7)
I believe the answer is:
ceiling
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">room's upper surface</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ceiling that I've seen before include "Room's upper surface" , "Overhead surface" , "likely to get plastered" , "upper limit on wages" .)