Install Sub-Slab Drainage Network (Horizontal)

Definition: Install sub-slab drainage network (horizontal) checklist guides contractors and inspectors through verifying internal drain layout, slopes, outlets, and cleanouts beneath slabs, excluding perimeter drains, to achieve dry, durable foundations.

Confirm internal layout, slopes, outlets, and cleanouts match approved drawings.
Use laser levels, slope logs, and photos to verify compliance.
Prevent slab moisture issues by ensuring free-draining under-slab laterals.
Interactive, commentable checklist with export and QR code verification.

Start Interactive
Checklist

Install sub-slab drainage network (horizontal) is a focused scope for building interiors that ensures under-slab drainage laterals, collectors, outlets, and cleanouts are accurately placed and sloped to move water away from the slab. This checklist targets under-slab drainage, sub-slab dewatering lines, and horizontal drainage laterals beneath slabs-on-grade or mat foundations, while explicitly excluding perimeter drains outside the foundation line. By validating design layout, slope continuity, connection integrity, and accessibility of cleanouts, you prevent water accumulation, slab heave, and moisture-related defects. The outcome is a dry, durable base ready for reinforcement and vapor retarder installation without conflict or rework. You will confirm materials (perforated pipe, washed aggregate, and geotextile), verify trench grades with laser controls, and document outlets to sumps or internal collectors per approved project specifications and authority requirements. Launch interactive mode to tick items, add comments, attach photos, and export the signed record to PDF or Excel via QR-secured sharing.

Ensure internal sub-slab drainage lines are accurately staked, consistently sloped, wrapped, and connected to sumps or internal collectors. This prevents standing water, slab curling, moisture ingress, and mold risks while supporting durable, code-aligned floor performance.
Interactive online checklist with tick, comment, and export features secured by QR code.
Capture decisive evidence: laser grade readings, invert elevation logs, materials certificates, photo and video of flow tests, and as-built plans with grid references. Reduce rework by clarifying scope boundaries and excluding perimeter drains from this workflow.

Pre-Installation & Layout

1. Confirm latest approved drawings, shop details, and drainage schedule are issued for construction; mark planned laterals and collectors on grid-referenced plans; obtain superintendent sign-off and upload dated markup.
2. Verify the scope excludes perimeter drains; highlight the building line on the plan and confirm all runs remain internal; capture photo evidence and notation “per approved project specifications and authority requirements.”
3. Establish benchmark and transfer control to subgrade; check subgrade elevation at 10 m grid intervals with laser level; tolerance ±5 mm; record readings in the checklist table.
4. Stake lateral and collector alignments with paint and flags at 2 m spacing; label chainage and run ID; upload overview photos covering at least two gridlines per image.
5. Clash-check trench routes against footings, conduits, sumps, and reinforcement zones; adjust alignments as needed; attach coordination sketch and foreman approval.

Materials & Components

6. Verify pipe type and size per submittal (e.g., 100 mm perforated HDPE, slot pattern per spec); capture delivery tickets, batch/lot numbers, and photos showing markings.
7. Confirm non-woven geotextile filter class per approved project specifications; record roll numbers and manufacturer certificates; photograph labels before installation.
8. Check washed aggregate grading 10–20 mm with fines ≤1%; attach supplier certification and a clear photo of material cleanliness at point of use.
9. Inspect cleanout assemblies, threaded caps, boxes/sleeves, and identifiers; confirm compatibility with slab embedment and load class; attach approved submittal and packaging photos.

Trenching & Bedding

10. Excavate trenches to width ≥3× pipe OD (minimum 300 mm) with smooth bottoms; verify depth allows design slope; upload tape/rod measurements and trench photos.
11. Install 100 mm bedding of compacted sand or fine aggregate; achieve uniform support along full pipe length; compaction to 95% MDD; attach compaction log or density test.
12. Grade trench to achieve designed slope; tolerance ±0.1%; confirm with laser receiver every 2 m; record start/end invert elevations and intermediate checks.
13. Stabilize soft or wet subgrade with working platform or additional bedding; prevent pumping/rutting; add before/after photos and note remedial thickness used.

Pipe Installation & Slope

14. Lay perforated pipe with slot orientation per approved project specifications (commonly down or lateral); keep orientation consistent; take close-up orientation photo per run.
15. Join pipes using approved couplers/gaskets; ensure full insertion to witness marks; verify straightness; document with a photo of each joint type and count.
16. Achieve run slope per design (typ. 0.5–1.0%); acceptance ±0.1%; measure invert at start/end and at 5 m intervals; upload slope calculation sheet.
17. Connect laterals to collectors with 45° wyes; avoid 90° bends; verify minimum 1× pipe diameter straight approach; photo each connection with tape for scale.
18. Restrain pipes against floatation or displacement using stakes/sandbags at ≤2 m spacing; record locations and provide overview photos before cover.

Cleanouts & Outlets

19. Install cleanouts at lateral ends and direction changes >45°; fit threaded caps; record a plan showing each cleanout ID and grid reference.
20. Set cleanout risers vertical in sleeves; top 50–75 mm below finished slab; position tolerance ±10 mm; upload level check and elevation note.
21. Connect collectors to internal sump/collector with required backflow prevention; provide air gap if specified; verify outlet invert prevents reverse flow; log RLs and attach photo.
22. Label all outlets and cleanouts; update as-built plan with run IDs, chainage, and gridlines; attach PDF and native file export.

Encasement, Cover & Protection

23. Place washed aggregate to 150 mm above pipe crown; hand-tamp around haunches; avoid displacing slope; upload cross-section photo with measuring staff.
24. Wrap pipe and aggregate with geotextile; overlap seams ≥300 mm; secure to prevent gaps; provide close-up photos of overlaps and ties.
25. Coordinate vapor retarder placement per approved project specifications; avoid puncturing; seal any penetrations; photo each penetration before cover is placed.
26. Protect network during reinforcement installation with walkway boards and barriers; perform daily condition checks; log and repair any damage with photos.

Testing, Commissioning & Handover

27. Flush each lateral using a hose ≥20 L/min for 2 minutes; confirm free flow at outlet without backup; record video or photo of discharge.
28. CCTV or borescope each run end-to-end; verify continuity and no obstructions; save footage with chainage notes and run ID.
29. Spot-verify elevations every 5 m post-backfill; reconcile with initial slope logs; document any corrections and re-test evidence.
30. Compile as-builts, materials certificates, test logs, and photo index; obtain superintendent and inspector digital signatures; archive package with QR-secured link.

Plan the Internal Network for Slope and Access

A reliable sub-slab drainage network starts with precise internal layout and control. Stake the laterals and collectors on grid, confirm there are no clashes with footings, sleeves, or reinforcement, and verify that the entire network remains inside the foundation line. Establish accurate benchmarks and transfer elevations to the subgrade so trench grades deliver continuous fall to the internal sump or collector. Aim for a design slope of 0.5–1.0%, and enforce a construction tolerance of ±0.1% using a laser level and documented invert checks. Avoid sharp bends; specify 45° wyes for lateral tie-ins to maintain hydraulic performance and camera access. Early attention to cleanout placement and riser sleeves ensures tools can reach the entire system for maintenance. By building a complete evidence trail—marked-up drawings, elevation logs, and overview photos—you reduce risk of rework and safeguard the slab from moisture-driven failures. Keep perimeter drains out of scope to maintain clarity and avoid mixing standards.

Keep all drains inside the foundation footprint.
Set slope targets early and measure with lasers.
Use 45° wyes for smooth hydraulic transitions.
Locate cleanouts for full-length camera access.
Record grid-referenced markups and invert logs.

Select Materials and Build for Durability

Material choices determine whether the sub-slab network stays free-flowing. Use perforated HDPE or equivalent pipe sized per design, with consistent slot orientation and secure couplers. Bed the pipe evenly on 100 mm compacted fine aggregate to 95% MDD, shape haunches, and confirm no point loading. Surround the pipe with washed 10–20 mm aggregate and wrap the envelope in a non-woven geotextile filter, overlapping seams by at least 300 mm to prevent fines migration. Keep the trench clean and stable; if the subgrade pumps, introduce a working platform or additional bedding. Install cleanouts at the ends of laterals and at direction changes to enable flushing and inspection. Set cleanout risers vertical in sleeves so final caps sit just beneath the finished slab for later access. Protect the network during reinforcement placement with boards and barriers, and coordinate vapor retarder placement without punctures.

Confirm pipe size, slots, and couplers match submittals.
Compact bedding and shape haunches for full support.
Use washed aggregate and wrap with geotextile.
Install cleanouts at ends and direction changes.
Protect drains before steel and vapor retarder.

Test Performance and Document Handover

Commissioning verifies the network drains as designed. Flush each lateral with a constant flow and confirm discharge at the outlet without backup or crossflow. Push a borescope or CCTV through every run to confirm continuity, joint integrity, and clean interiors. After backfill, re-check representative elevations to confirm slopes remain within tolerance, then reconcile with initial logs. Label and record every cleanout and outlet on an as-built plan with grid references and chainage. Package test videos, photos, material certificates, and slope tables for sign-off. Obtain digital signatures from the superintendent and inspector, and archive the bundle with a QR-secured link for future maintenance. This record simplifies warranty claims, enables quick troubleshooting, and provides clear evidence that only the internal system—excluding perimeter drains—was constructed and verified per approved project specifications and authority requirements.

Flush flows and verify clear, continuous discharge.
CCTV runs to check joints and obstructions.
Spot-check slopes post-backfill for tolerance.
Label cleanouts and outlets on as-builts.
Archive a QR-secured, signed dossier.

How to Use This Interactive Checklist

Preparation: Gather approved drawings, slope design, submittals, laser level, tape/rod, compaction tools, washed aggregate, geotextile, perforated pipe, PPE, borescope, and a hose. Confirm site access, sump readiness, and safe, dry subgrade conditions.
Using the Interactive Checklist: Start interactive mode, assign runs to team members, tick each item as verified, attach photos/videos and elevation logs, add comments for deviations, and export progress snapshots to PDF/Excel for coordination.
Sign-Off: Compile evidence, finalize as-builts, and obtain digital signatures from responsible parties. Distribute the QR-authenticated export to stakeholders and archive with project records for traceability and maintenance planning.

Call to Action

Start Checklist Tick off tasks, leave comments on items or the whole form, and export your completed report to PDF or Excel—with a built-in QR code for authenticity.

License: CC-BY 4.0. Please credit: “Sub-Slab Drainage Network Installation (Horizontal) by Quollnet” with a link to this source page.

Download Excel - Sub-Slab Drainage Network Installation (Horizontal)
Download PDF - Sub-Slab Drainage Network Installation (Horizontal)
View Image - Sub-Slab Drainage Network Installation (Horizontal)

Lila Gonzalez Lila Gonzalez

Mar 14, 2026

130

FAQ

Question: What slope should I use for sub-slab drainage laterals under a slab-on-grade?

Most designs target 0.5–1.0% slope to maintain positive flow without excessive excavation. Use a laser level to set trench grades, check inverts every 2–5 m, and hold construction tolerance within ±0.1%. Always follow approved project specifications and authority requirements.

Question: Where should cleanouts be located for effective maintenance and inspection?

Provide cleanouts at the ends of all laterals and at direction changes greater than 45 degrees. Extend risers vertically in sleeves to sit just below the finished slab. This placement enables flushing and full-length borescope inspection after handover and during future maintenance.

Question: How do I prevent fines from clogging the sub-slab drainage network over time?

Use washed 10–20 mm aggregate and wrap the pipe and aggregate envelope with a non-woven geotextile filter. Overlap seams at least 300 mm and secure them. Maintain clean trench operations to avoid soil contamination before wrapping and covering the system.

Question: What tests prove the network is unobstructed before pouring the slab?

Perform a flushing test on each lateral using a steady hose flow and confirm visible discharge at outlets without backup. Then complete a CCTV or borescope pass for every run to verify continuity and joint integrity. Save videos, photos, and logs in the checklist record.