Installation Precautions for Same-Floor Drainage Systems

Combining HDPE drainage pipes with the mainstream construction method of sunken-slab caisson-type in-floor drainage, this guide is divided into five major sections: preliminary design, pipe installation, caisson backfilling, waterproofing, and acceptance and commissioning.

Combining HDPE drainage pipes with the mainstream construction method of sunken-slab caisson-type in-floor drainage, this guide is divided into five major sections: preliminary design, pipe installation, caisson backfilling, waterproofing, and acceptance and commissioning. It can be directly used for engineering technical briefings and product detail documentation.
I. Key Points of Preliminary Design
Properly Plan Pipe Gradient
HDPE horizontal branch pipes must maintain the standard drainage slope (general sewage pipe slope ≥2%); reverse slopes and horizontal runs are strictly prohibited to prevent water accumulation and blockages.
Control Pipe Length and Number of Elbows
Minimize the use of 90° right-angle elbows; prioritize using two 45° elbows as a substitute. Avoid long horizontal runs without venting to prevent the water seal from breaking and odors from backing up.
Provision for Secondary Drainage Points
A secondary drainage floor drain must be installed at the bottom of the sump to serve as a collection channel for seepage, thereby preventing water accumulation inside the sump that could cause long-term saturation of the pipes and waterproofing layer.
Simultaneous Design of Ventilation Systems
When there are numerous sanitary fixtures, design corresponding vent risers and looped vent pipes to balance air pressure in the piping system, preventing the suction of floor drain water seals and the backflow of odors.
Finalize Sanitary Fixture Locations in Advance
The positions of wall-hung toilets, floor drains, and washbasins must be determined in advance to minimize the need for extensive piping modifications during later stages.
II. Precautions for Pipe Laying and Installation
Pipe Connection Standards
HDPE drainage pipes must be connected using heat fusion butt welding or electrofusion. During the cooling period, joints must not be subjected to stress or tension to ensure a leak-free seal; direct application of open flame to heat the pipes is strictly prohibited.
Secure Pipe Brackets in Place
Add pipe clamps to support horizontal pipes, ensuring bracket spacing complies with specifications; pipes must not be left suspended or compressed to prevent deformation or joint cracking after backfilling.
Pipe Clearance and Protection
Pipes must not be placed directly against shear walls or rebar; using drain pipes as structural supports is prohibited; properly seal pipes during concrete pouring and backfilling to prevent cement slurry, sand, and gravel from entering and causing blockages.
P-Traps and Water Seal Depth Must Meet Standards
All floor drains and sinks must be equipped with P-traps, with a water seal depth of ≥50 mm to prevent the backflow of sewer odors.
Pipe Penetrations Through Walls and Slabs—Reserved Sleeves
Install sleeves where pipes pass through walls, and fill the gaps with flexible sealing material to prevent structural settlement from compressing the pipes.
III. Caisson Waterproofing Construction (Top Priority)
Level the Caisson Substrate First
Clean and level the caisson base slab, and grind down all sharp protrusions to prevent puncturing the waterproofing layer.
Double-Layer Waterproofing with Uplap on Walls
Apply the first coat of waterproofing to the base slab; apply the second coat after pipe installation is complete. The waterproofing on the walls must extend upward by ≥300 mm; create a reinforced rounded corner at inside and outside corners.
A Water Tightness Test Must Be Conducted After Waterproofing Is Complete
Once the waterproofing layer is installed, fill the caisson with water for 24–48 hours. Only proceed to the next step after confirming there are no leaks.
IV. Caisson Backfilling Requirements
Direct Backfilling with Construction Debris Is Strictly Prohibited
Do not use stones or broken bricks for backfilling, as they can puncture pipes and the waterproofing layer; lightweight expanded clay aggregate or foamed concrete is recommended.
Backfill in Layers and Lightly Compact
Backfill slowly in layers; do not use heavy machinery for vigorous compaction to prevent deformation of HDPE pipe joints due to compression.
Protect Secondary Drainage Floor Drains
Protect secondary drainage facilities during backfilling; ensure they are not blocked by expanded clay aggregate or mortar to guarantee smooth drainage of seepage.
Install a Leveling Layer on Top of the Backfill
After backfilling is complete, pour a fine-aggregate concrete leveling layer before proceeding with the installation of the surface floor tiles.
V. Temporary Sealing and Protection of Completed Work
Temporarily Seal Pipe Openings
During construction breaks, seal all open pipe ends with plugs to prevent debris from falling into the pipes.
Do Not Pile Heavy Objects Above Pipes
During the finishing phase, avoid piling heavy materials over the caissons for extended periods.