Residential Building Inspector B1Footings and FoundationsHard
A builder is constructing a residential foundation in an area with a high water table. The plans specify a full basement. According to the 2021 IRC, which of the following is the MOST appropriate method for preventing water intrusion into the basement?
- AApplying a 6-mil polyethylene vapor retarder to the interior face of the basement walls.
- BInstalling dampproofing on the exterior of the foundation walls and a perimeter drain at the footing.
- CImplementing a full waterproofing system, including a drainage system and a sump pump, in addition to dampproofing.
- DUtilizing a capillary break beneath the slab and a continuous Class A vapor retarder.
Show answer & explanationAnswer & explanation
Correct answer: C. Implementing a full waterproofing system, including a drainage system and a sump pump, in addition to dampproofing.
In areas with a high water table, hydrostatic pressure can force water through foundation walls and slabs. A full waterproofing system (membrane, drainage, and sump pump) is essential, as dampproofing alone is insufficient to resist hydrostatic pressure. The IRC (R406.1) mandates waterproofing where a high water table is present.
Why the other options are wrong
- A. An interior vapor retarder does not prevent water intrusion from the exterior; it only slows vapor diffusion.
- B. Dampproofing resists soil moisture but is not designed for hydrostatic pressure from a high water table. A perimeter drain helps, but without true waterproofing, it's often inadequate.
- D. A capillary break and vapor retarder are primarily for moisture vapor, not liquid water under hydrostatic pressure.
High Water Table Waterproofing
In areas with a high water table, comprehensive waterproofing (membranes, drainage, sump pumps) is required to prevent hydrostatic pressure from forcing liquid water into basements.
- Dampproofing is for soil moisture, not hydrostatic pressure.
- Waterproofing systems are designed for liquid water resistance.
- IRC R406.1 mandates waterproofing where groundwater conditions exist.
Memory trick: Water's rise needs a strong defense.