\version "2.16.2"

\score {
  \repeat volta 2 {
    \repeat unfold 16 g''4 \break
    \repeat unfold  8 g''4
  } \alternative {
   { % first ending
% decreasing the first number  increases the space BELOW the volta bracket
% increasing the second number increases the space ABOVE the volta bracket
    \once \override Score.VoltaBracket #'Y-extent = #'(-2.0 . 15.0)
    \repeat unfold  8 e''4
    \break
   }
   { % second ending
    \once \override Score.VoltaBracket #'Y-extent = #'(-15.0 . 2.0)
    \repeat unfold  8 c''4
   }
  } % alternative
} % score