Planks and slats are ceiling covers that generally only attach along, and perpendicular to, the main profile joists of the ceiling grid. There are an endless variety of these but they may all employs similar methods of attachment.
Plank ceilings use planks largely similar to that of hardwood flooring, except that they are often designed to enhance their seams as an architectural detail instead of creating a perfectly smooth surface and may employ either independent planks or interlocking dovetail planks. They often employ continuous spans across a ceiling or an interleaved pattern. When relatively light and thin planks are used, attachment by simple ‘U’ channel snap-lock strips fitting in the facing joist slots is sufficient, the panels spaced so that any plank end fits completely over a slot. Spring alloy side lock angles can also be used. Heavier or wider planking, however, may employ alloy angles to bolt them to the joist profile sides. This requires the planks to be installed in a series, so that access to the joists is maintained until the last plank row, which may snap in place between a stop-strip (using dovetail joinery) or employ snap-locks in the last planks. Jacks and battens are used to support the planks during assembly. Plank ceilings are often used in combination with pelmets, which can also be used to conceal the gap of a last plank row.
Slats come in a great variety of forms, materials, and arrangements. They are typically arrayed in parallel series relative to the framing but occasionally employ a diagonal arrangement, though this requires many different sized pieces across a large span room. Interleaved patterns are also common, and are one of the lightest and easiest to install forms. They are often used without spacer frame pieces in the ceiling and in combination with a screen material to conceal the ceiling volume, held in place by being clamped between ceiling joists and slats as they’re installed. Slats generally attach in exactly the same way as planks, though their lightness generally favors the use of snap-locks.