\showframe \showgrid

% \enabletrackers[columnsets.*]

\setuplayout
  [grid=yes,
   lines=40]

\setupwhitespace
  [none]

\definecolumnset
  [parallel]
  [n=1,
   align={lesswidows,lessclubs,lessbroken,lessorphans}]

\definesubcolumnset[parallel][L][1]
\definesubcolumnset[parallel][R][2]

\startsetups balance:example
    \balancetopskip    \strutht
    \balancebottomskip \strutdp
\stopsetups

\setuphead
  [chapter]
  [before=\blank[2*line]\testcolumn[5],
   after=\blank[line,samepage],
   page=]

\setuppagenumbering
  [alternative=doublesided]

\starttext

    \page[left]

    \startcolumnset[parallel]

        \dorecurse{20}{
            \startsubcolumnset[L]
                \title{Knuth #1}
                \input{knuth}
            \stopsubcolumnset
            \startsubcolumnset[R]
                \title{Zapf #1}
                \input{zapf}
            \stopsubcolumnset
            \flushsubcolumnsets[spread]
        }

    \stopcolumnset

\stoptext