Is interior or exterior basement waterproofing better?
Interior drainage manages water inside the foundation; exterior wall protection addresses the outside face. The entry path and access determine which scope to compare. Our recorded interior drain reference is $40–$85 per ft and typically includes a sump.
Membrane-only work is $4–$7 per ft² of wall, with excavation assessed separately. Start with runoff corrections when those solve the cause; compare complete system scopes when leakage persists.
Key facts as of Oct 30, 2026. Sources and recorded dates.
SIGNS
What should you observe before choosing a side?
Note whether water follows rainfall, collects along the slab edge or appears as droplets on cool surfaces. These observations help the inspector separate leakage from humidity. Keep a record of any previous drains and where they discharge.
Guidance: University of Minnesota Extension: Moisture in basements, causes and solutions.
CAUSES
Why can the same damp basement need different repairs?
Bulk water, moisture moving through porous materials and condensation are different mechanisms. A wall coating cannot substitute for a working drainage path. A pump also needs a way to collect water before it can remove it.
Guidance: University of Minnesota Extension: Moisture in basements, causes and solutions; PNNL Building America: Foundation wall water/damp-proofing.
FIXES
How do you compare interior and exterior offers?
Interior work may require opening the floor edge and reinstating concrete. Exterior work needs access to the buried wall and a plan for surface restoration. Have the contractor explain why the proposed system addresses the observed entry point.
- Interior: identify collection channel, sump provision and discharge.
- Exterior: identify wall preparation, barrier, drainage and excavation.
- Both: confirm exclusions, access, testing and restoration in writing.
Guidance: PNNL Building America: Foundation wall water/damp-proofing; PNNL Building America: Pre-retrofit assessment of crawlspaces and basements.
Which costs belong in this scope?
| Work | Planning range |
|---|---|
| Interior drain tile / sump system | $40–$85 / ft |
| Exterior membrane only | $4–$7 / ft² of wall |
| Exterior foundation drain only | $30–$90 / ft |
The interior reference typically includes a sump; avoid a second pump allowance. The exterior drain price excludes membrane. These different units cannot be compared as complete system totals.
Read the basement waterproofing cost guide for the worked example and price factors, or calculate an estimate for your measured scope.
Sources and dates
Public guidance checked Oct 30, 2026. Cost references retain the recorded Oct 24, 2026 retrieval date; this guide adds no new price observations.
- University of Minnesota Extension: Moisture in basements, causes and solutions
- PNNL Building America: Foundation wall water/damp-proofing
- PNNL Building America: Pre-retrofit assessment of crawlspaces and basements
- HomeGuide: french drain cost — recorded Oct 24, 2026.
- HomeGuide: basement waterproofing cost — recorded Oct 24, 2026.
Read how the calculator works and the source inventory for calculation limits.