For me trimming fixes the edges automatically.
The legacy mode only effects the roofs and associated skylights (and it seems it was version 15 that multi-plane roofs came into being).
I believe this option will automatically be set if you open a file created before version 15.
With legacy mode you don't see the double edge.
It has no effect on multi-plane roofs - only single planes.
Barry.
One of the forum moderators.
Versions 6.5 to 27
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