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Below-Grade Waterproofing Services

Our below-grade waterproofing services protect basements and foundations from leaks, mold, and costly water damage. Get expert design and QA.

Our below-grade waterproofing services protect foundations, basements, and other below-ground spaces from water intrusion. When these systems fail, they can cause mold, corrosion, and structural damage. We help you make sure everything stays watertight—from the ground up.

What is Below-Grade Waterproofing?

Below-grade waterproofing means using systems that stop water from entering underground spaces. For example, we assess membranes, drainage mats, and sealants. Additionally, we check tie-ins and joints to prevent weak spots that lead to future problems.

Why Waterproof Foundations?

  • Keep basements and parking garages dry
  • Protect concrete and rebar from long-term damage
  • Meet local code and warranty requirements
  • Prevent mold, humidity, and indoor air quality issues
  • Avoid costly excavation or retrofits later

As a result, below-grade waterproofing services reduce long-term costs and increase the reliability of your foundation system.

Case Study: Transit Station Foundation

Problem: Water was leaking into mechanical rooms at platform level.

Solution: Our team coordinated the design details, installed a drainage mat, and improved flashing tie-ins. We also verified each layer during QA inspection.

Result: No leaks post-construction and full warranty approval.

Learn more about below-grade design at the WBDG Envelope Watershed Guide.

Our Below-Grade Waterproofing Services Include:

  • Construction drawing and detail review
  • On-site QA/QC waterproofing inspections
  • System evaluations and diagnostics
  • Tie-in support for curtain walls, pits, and podium decks
  • Leak testing and remediation planning

If you're planning or repairing a foundation, our below-grade waterproofing services deliver reliable, code-compliant solutions you can build on.

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Further reading

From the technical library

Common questions

Can below-grade waterproofing be repaired without excavating?
Sometimes. Injection grouts, gels and interior negative-side systems can address certain conditions, particularly isolated cracks and joints. Whether they are appropriate depends on hydrostatic pressure, substrate condition and the leak mechanism. Excavation gives access to the positive side and the drainage layer, but is far more disruptive. We evaluate both paths and explain the trade-offs before you commit.
Does Inspec install below-grade waterproofing?
No. Inspec is a consulting engineering and architecture firm. We investigate leaks, design and specify systems, review submittals and observe installation, but the work itself is performed by contractors you hire. That separation means our findings and specifications are not influenced by a product line or by the scope of a construction contract.
When should a consultant get involved on a new below-grade project?
Ideally during design, while foundation details, drainage and the grade-line transition to the above-grade wall are still being drawn. Involvement before backfill is the practical deadline for meaningful review, because buried assemblies cannot be inspected afterward without excavation. Later involvement is still useful, but the options narrow and the cost of correction rises.
Why does water appear in a basement far from where it enters?
Below-grade water follows the path of least resistance along cold joints, between the membrane and the substrate, through slab-edge gaps and along conduit or pipe penetrations. Interior staining marks the exit point, not the entry. Identifying the actual source requires reviewing construction details, groundwater conditions and drainage performance rather than treating the visible wet spot.
What is the difference between dampproofing and below-grade waterproofing?
Dampproofing resists moisture vapor and incidental damp soil; it is not designed to hold back standing water. Waterproofing is intended to resist hydrostatic pressure. Buildings with occupied or finished space below grade, a high water table, or poor drainage frequently receive dampproofing where waterproofing was warranted, and the difference only becomes apparent after backfill.
Should waterproofing go on the positive side, the negative side, or blindside?
Positive side means the soil face, which is where waterproofing performs best because water is stopped before it reaches the concrete. Negative-side treatments are applied from the interior and are usually a remedial choice. Blindside systems are installed against sheeting or a neighboring structure before the wall is poured. Site constraints, groundwater and schedule drive the selection.
Do you review plaza decks and podium slabs over occupied space?
Yes. A landscaped plaza or podium slab over parking or occupied rooms carries many of the same risks as a buried wall: the membrane is covered by overburden, defects are expensive to reach, and drainage at the membrane level governs performance. We review the assembly, the drainage layer, and the transitions at planters, curbs and penetrations.
What should we gather before your first site visit?
Original foundation and waterproofing drawings and specifications if they exist, any product data or warranty documents, records of previous repairs, and a simple log of where and when water appears relative to rainfall or snowmelt. Photographs taken while water is active are especially useful, since many below-grade symptoms dry out between visits.