Why stairs need a different carpet
Stairs experience significantly more concentrated wear than flat floor areas — every step involves bending, friction and compression in exactly the same spot. The carpet needs a higher density, a shorter pile and a higher twist rating than you would use in a bedroom. A twist pile with a rating of 5 or above is recommended for stairs.
Full width vs stair runner
Full width carpet covers the entire stair from wall to wall. A runner leaves a border of bare or painted wood either side — this can look stylish in the right setting but requires a neat, even staircase to carry it off. Runners require stair rods to hold them in place and are typically fitted to a fixed central position.
Underlay on stairs
Stair underlay is fitted differently to flat floor underlay — it wraps over each nose (the front edge of the step) and is stapled or glued. This is a specialist job and a key reason why DIY stair carpeting often fails prematurely.
Landing carpet
The landing is typically fitted as a continuation of the stair carpet for a seamless look. The join between landing and stairs is hidden under the nosing strip on the top step. Getting both done together by the same fitter ensures a matching result.