Dryback construction
Dryback is the manufacturer's word for a plank with no locking edge and no backing, designed to be bedded in adhesive. Dryback boards run either 2 mm or 2.5 mm thick, which is a fraction of what a floating plank comes to.
The thinness is the point rather than a compromise. A floating floor has to be stiff enough to hold itself flat across a room, which is why it carries a rigid core several millimeters deep. A bonded floor does not: the subfloor underneath supplies all the stiffness, and the plank only has to carry the print and the wear layer. Take away the job of being rigid and the board can be thin, which is what makes it fit under a door that a thicker floor would foul.
Why dryback vinyl has no pad
Dryback boards never arrive with a cushion bonded to the back, and they should not. A plank that is going to be stuck down has to meet the adhesive directly, so a pad would sit between the floor and its bond and defeat the whole construction. That is a real difference from the floating ranges, where a pad on the back is common.
The consequence is that a glued floor takes its acoustic behavior from what it is stuck to, not from anything built into it. There is no air gap under a bonded floor, so it does not produce the hollow sound a floating floor makes over a hard subfloor, and footsteps read as solid, not as drumming.
Over radiant heat
Radiant heat compatibility runs right through this type, and the construction is the reason. Heat has to travel from the slab through the floor to the room, and each layer it crosses slows it down. A bonded 2 mm board sits directly on the heated surface with adhesive, not air between them, which is the shortest path a finished floor can offer.
A floating floor over the same slab has a pad, sometimes an underlay, and a much thicker core in the way. Both work, and the floating ranges are specified for heated slabs too, but a thin bonded floor reaches temperature faster and holds less of the heat back. Each manufacturer still sets its own maximum surface temperature for the slab.
On stairs
A staircase has to be fixed. A floating floor is designed to move as one sheet, and a sheet cannot turn a corner over a nosing and down a riser, which is why stairs are the awkward part of every floating floor job. A bonded plank has no such problem: it is fixed everywhere by definition, and many dryback lines include a matching stair piece.
That makes glue down the natural specification for a hall and staircase running together, and for any part of a house where the floor has to follow a shape, not lie in a field. Whether a particular floor is approved for stair use still comes from its manufacturer. Stair nose holds the nosings and flooring trim the rest of the profiles.
A glued vinyl floor is permanent
Two things, and neither is negotiable. The subfloor has to be flat, because a thin bonded board follows the surface underneath exactly and reproduces every dip and ridge in it. That is also why the boards here run narrower than the floating ranges, with 6 by 48 the largest group: a narrower board follows a surface more forgivingly than a wide one. And the floor is permanent in a way a floating one is not: it comes up destructively, so a glued floor is a decision for the life of the room instead of a surface that can be lifted and reused.
Water is the other honest caveat. Fewer dryback boards carry a waterproof description than the click lock range does, and the bond line matters as much as the plank. Wear layers here spread right across the range, from 6 mil at the light end through 12 and 20 to 22, and most of these floors quote a commercial rating, which is the market this construction was built for before it reached houses. The adhesive itself is specified by the flooring manufacturer instead of chosen separately, since the wrong one is the usual cause of a bonded floor failing.
