- Rainwater standing against or under the sill
- A cold floor edge by the door due to missing insulation
- A beam above the door that deflects too much, making the door jam
- A terrace that falls towards the house
Building detail · Window frame
Sliding door in an extension: threshold, drainage and insulation
A wide sliding door connects house and garden. A low or level threshold does need a careful detail: water must be able to drain away, and the floor by the door must not turn cold.
- A low threshold without water problems
- Drainage with a channel drain and a falling terrace
- Insulation under the sill against thermal bridges
Principle sketch
Build-up of the detail
Vertical section through the sill of a sliding door in an extension. The numbers in the sketch refer to these parts:
- Sliding door with insulating glass
- Low sill
- Channel drain with grating
- Terrace, slightly lower than the floor inside
- Watertight connection under the sill
- Insulation under the sill against thermal bridges
- Screed with floor finish
- Floor insulation
- Concrete floor of the extension
Common mistakes
Where it often goes wrong
Leaks, condensation and cracks usually start at the junctions, not in the middle of a wall or roof.
In the drawing
What we look out for
We work out the detail for your home, based on a site survey and the chosen materials.
- The level difference between the floor inside and the terrace outside
- Drainage: channel drain, fall and outlet
- The watertight connection under the sill
- Insulation under and around the sill
- The beam above the door and the deflection the supplier allows
A sliding door often goes into a new opening in the facade. We calculate the beam and its bearings. Structural calculations
Detail FAQ
Frequently asked questions about this detail
Can a sliding door be completely level?
Often yes, but then drainage in front of the door, a watertight connection and the right level difference with the terrace become even more important. What is feasible depends on the system and the situation.
Why does the beam above the door matter?
A sliding door tolerates very little deflection. The beam above it must be stiff enough, otherwise the door can start to jam.
What does a channel drain in front of the door do?
A channel drain catches rainwater flowing towards the door and carries it away, so it does not stand against or under the sill.
Can I use this principle sketch for my own home?
The principle sketch shows the build-up, but it is not a working drawing. Dimensions, materials and fixings depend on your home. We work out the detail for your situation.
Detail library