There’s no attachment navigation in roots, is it, or am I missing something?
AFAIK, to build this feature, an image.php would be required. Unfortunately I couldn’t find much (up to date) information on doing this efficiently -let alone roots - unless looking it up in other themes.
As for roots, I would think the best start would be to copy single.php to image.php and go on from there.
Has anybody done similar yet?