Sliding door gear must be chosen at design stage because the track type, door weight and pocket depth dictate the structural opening, the wall build-up and the floor finish. Specifying sliding door gear at design stage costs almost nothing extra. Trying to add it at first fix almost always forces a compromise: a lower door height, an exposed surface-mounted track, or a switch back to hinged doors.
This guide explains why sliding door system planning belongs early in a UK build, and what needs to be coordinated at that point.
Structural implications of sliding door gear
Top-hung sliding door gear transfers the entire weight of the door into a header above the opening. The header must be structural or must be reinforced back to structure. On a stud wall, this means specifying the header before the wall is plasterboarded.
Bottom-rolling systems transfer weight into the floor. This affects the floor finish and any underfloor heating layout. Pocket door systems require a stud cavity built to a specific finished wall thickness, which needs to be agreed before framing begins.
Door weight versus track rating
Sliding tracks are rated by maximum door weight, typically 40 kg, 50 kg, 70 kg, 90 kg or higher. Rated capacity should exceed the door weight by a comfortable margin, because a door dragging near the top of the track rating wears faster and runs less smoothly.
Solid timber internal doors, especially those over standard height, can easily exceed 40 kg. Glass doors and acoustic doors can be heavier again. On any door over standard mass, choosing sliding door gear for timber doors with correct headroom clearance is a design-stage decision, not a first-fix one.
Pocket doors: the design-stage decision that cannot be reversed
Pocket doors run into a cavity built inside a stud wall. The cavity depth, height and finished wall thickness are all set when the wall is framed. Adding a pocket door to an existing wall after plaster is almost always a rebuild of that wall.
Sliding pocket door kits are specified to a finished wall thickness. This is the thickness after plaster, not the stud dimension. Confusing the two is the most common cause of pocket door problems on UK builds.
Soft close and low-headroom variants
Soft close mechanisms and low-headroom track variants both add specification requirements at design stage. Soft close needs a small amount of extra runoff at the closing edge. Low-headroom variants need the ceiling void or bulkhead to be planned for the specific track profile. Neither is easy to retrofit.
Coordinating with joinery: door thickness, edge profile and handle centres
Sliding doors have specific requirements that hinged doors do not. Door thickness must fall within the track manufacturer's range. Edge profile affects how the door meets the jamb and how any soft close hook engages. Handle centres, flush pulls and edge pulls need to be positioned so the door can retract fully without the handle catching on the frame or on the pocket entry.
On larger builds, using the SDS scheduling service at design stage prevents these coordination issues from surfacing on site.
Frequently Asked Questions
When should sliding door gear be specified in a build?
Sliding door gear should be specified at design stage, before framing begins. The track type, door weight and pocket depth all affect structural decisions in the wall build-up, floor build-up and ceiling void. Waiting until first fix usually means accepting a compromise on door height, headroom or track visibility. On a design-stage decision, none of these compromises are needed.
Can pocket doors be added after the walls are built?
Pocket doors can technically be added after walls are built, but the process almost always means rebuilding the wall in question. The pocket needs a specific stud cavity depth and a controlled finished wall thickness. Retrofit is possible on a stud wall by dismantling and rebuilding that section. On a masonry wall, the cost is usually prohibitive and hinged or surface-mounted sliding doors are chosen instead.
How heavy can a sliding internal door be?
Sliding internal doors can be very heavy when the track is rated for the load. Common track ratings include 40 kg, 50 kg, 70 kg and 90 kg systems. Doors above 90 kg are supported by heavier-duty industrial and architectural gear. The important rule is that door weight should sit comfortably below the track rating, not at the top of it, so the mechanism runs smoothly and wears evenly.
Do sliding doors need a bottom track?
Sliding doors do not always need a bottom track. Top-hung systems carry the full weight in a top track and use a floor guide rather than a continuous bottom rail. This suits internal doors and keeps the floor line clean. Bottom-rolling systems transfer weight into the floor and are more common on heavier commercial and external doors. The choice affects floor finish planning.
Next Steps
SDS London has supplied architectural ironmongery to the trade and public for over thirty five years. Speak to the team on 020 7228 1185 for advice on sliding door specification, or use the SDS scheduling service for larger projects.