The question might be considered a duplicate of thisthis question, but for clarity I will show how by adapting the answer given there.
barHatched[gap_, h_, seg_][{{xmin_, xmax_}, {ymin_, ymax_}}, ___] := Module[{width, line, yt, yb, lend}, {yb, yt} = Sort[{ymin, ymax}]; width = xmax - xmin; line = Table[{{xmin, i}, {xmax, i + width}}, {i, yb, yt - width, h/seg}]; lend = line[[-1, 1, 2]]; line = { Line[line], Line[Table[{{xmin + i, yb}, {xmax, yb + width - i}}, {i, h/seg, width, h/seg}]], Line[Table[{{xmin, lend + i}, {xmax - (lend + width - yt) - i, yt}}, {i, h/seg, width + h/seg, h/seg}]] }; {{Opacity[.2], EdgeForm[], Rectangle[{xmin, ymin}, {xmax + gap, ymax}]}, {CapForm["Butt"], line}, {FaceForm[], Rectangle[{xmin, ymin}, {xmax, ymax}]}} ] barSolid[{{xmin_, xmax_}, {ymin_, ymax_}}, ___] := Rectangle[{xmin, ymin}, {xmax, ymax}] mixedBar[args : {{xmin_, xmax_}, {ymin_, ymax_}}, ___] := If[xmax < 3, barHatched[0, 5, 35][args], barSolid[args]] BarChart[ Transpose[{ {2, -1, 1.5, -3, 3, 2.5}, {2, -1, 1.5, -3, 3, 2.5} }], ChartElementFunction -> { mixedBar, barSolid } ] 
The idea is to build custom CharElementFunctions for the bar appearances. To have variation with a set we need to make a ChartElementFunction which depends on the position of the bar. This is what the mixedBar function is for.
