  We revisit the "brick wall" model for black hole entropy taking into account
back-reaction effects on the horizon structure. We do so by adopting an
evaporating metric in the quasi-static approximation in which departures from
the standard Schwarzschild metric are governed by a small luminosity factor.
One of the effects of the back-reaction is to create an ergosphere-like region
which naturally tames the usual divergence in the calculation of the partition
function of the field. The black hole luminosity sets the width of such
"quantum ergosphere". We find a finite horizon contribution to the entropy
which, for the luminosity associated to the Hawking flux, agrees remarkably
well with the Bekenstein-Hawking relation.
