Zero-Threshold Glazing: Engineering Flush Indoor-Outdoor Transitions

1. The Infiltration Challenge of Flush Sills

Traditional building codes require a 50mm to 100mm raised door step to prevent rainwater from being blown beneath exterior doors. Eliminating this step to create a single continuous floor plane creates serious water management challenges if poorly detailed.

Achieving a true zero-threshold requires treating the transition zone not as a simple door frame, but as a sophisticated hydraulic drainage structure.

2. Concealed Trench Drains & Hydraulic Capacity

Directly adjacent to the exterior track, we install a continuous stainless steel linear trench drain fitted with a removable architectural grate or narrow 8mm stone-slotted intake. This drain catches sheets of surface rainwater and evacuates it before it ever contacts the door gasket.

Sub-trench drainage piping is engineered with positive 2% slopes connected to dedicated storm catch basins, ensuring zero water backup during torrential downpours.

3. Dual-Layer Waterproofing Membranes

Beneath the door sub-sill, we apply continuous hot-applied rubberized asphalt or multi-ply elastomeric sheet membranes that turn up 150mm on adjacent structural jambs, forming an impermeable watertight pan.

4. Motorized Pocketing Systems & Track Tolerances

For glass panels exceeding 3.5 meters in height and 400kg in weight, motorized track systems must be set on perfectly leveled structural steel beams with zero deflection. Hidden wall pockets are lined with acoustic seals and exterior weather flaps to prevent drafts.

5. Eliminating Thermal Bridging at the Threshold

A continuous concrete slab extending from the heated interior to the cold exterior acts as a giant thermal radiator, causing interior condensation and mold. We detail structural thermal isolators that structurally bridge the threshold while breaking the thermal conductivity path.