Is That Flip Hiding Issues? Foundation & Drainage Checks for Homebuyers
Deniz Kahramaner
Aug 25
Introduction
Winning your dream home on the first offer would be a lucky break. In the Bay Area, most first‑time buyers need to tour and evaluate numerous properties before they can confidently write offers—especially in a market where polished cosmetics can distract from costly system issues such as persistent moisture in the crawlspace.
That was the case for our clients, two busy healthcare professionals in the Palo Alto VA Medical and Stanford Medical networks. They preferred a move‑in‑ready home but were open to light projects at the right price. Striking that balance requires disciplined due diligence.
The “Almost” Home
Their favorite contender was a nicely renovated single‑family home in Redwood City’s Central Park neighborhood—a convenient, family‑friendly area with access to schools, shops, and restaurants. The kitchen and baths were beautifully updated, new hardwood floors and light fixtures were newly installed, and fresh paint and landscaping delivered strong curb appeal. To many buyers, it would read as “new.”
Home buyers need to understand that sellers often prioritize cosmetic upgrades over infrastructure (foundation, drainage, plumbing, roof, windows, HVAC) because cosmetics produce faster, more visible ROI. That isn’t automatically a deal‑breaker—it simply means the buyer must dig deeper.
Quick Foundation & Moisture Facts (Bay Area Context)
- What foundations must handle: Vertical loads, seismic and wind forces, and soil moisture cycles that cause expansion and contraction.
- Where moisture appears: Foundation walls in crawlspaces commonly exhibit efflorescence (a white, powdery salt deposit on concrete) and wet soils, particularly after storms or in areas with higher groundwater. In areas where moisture has no path to drain, deterioration may appear on foundation surfaces.
- Why this matters locally: Sea‑level rise can also elevate groundwater tables in bayside communities, increasing the potential for below‑grade moisture and nuisance flooding even away from the shoreline. Redwood City and San Mateo County agencies flag rising groundwater as a growing risk in the coming decades. (KQED, Redwood City, ArcGIS)
What the Seller Inspections Missed—and Our Site Findings
The seller's home inspection mentioned surface-level details on efflorescence and damp soils. We conducted our own crawlspace inspection and documented more extensive, persistent moisture:
Photo 1. Footings on the harder‑to‑access side showed accelerated surface deterioration and dark waterlines climbing high up the concrete—evidence of periodic high water under the home.
Photo 2. Newer replacement footings on the opposite side also displayed high moisture stains, suggesting prior deterioration and spot fixes rather than system‑wide remediation.
Photo 3. Crawlspace stem walls exhibited high tide‑line staining; soils were wet to the touch, indicating the crawlspace likely becomes very wet during heavy rains.
What Moisture in the Crawlspace Can Do
After this on-site observation, our team noted the following concerns:
- Moisture & wood increase risk for termites and wood‑decay fungi (dry rot). Subterranean termites require moist conditions and often travel through soil and damp wood. (UC IPM)
- Indoor air quality risks: Older or unreplaced ducting can have small leaks; if a crawlspace develops mold, those spores can be drawn into the supply/return path. Some species of mold can release mycotoxins that are neurotoxic at high doses; in typical homes, the clearest risks for infants are respiratory (wheeze/asthma). Moisture control—not bleach—is the core of mold prevention. (US EPA, CDC)
- Soil movement & recent footing replacements: Chronic water in or around footings can undermine bearing soils over time, especially in poorly drained or high‑groundwater zones. Evidence of several footings replaced means the prior ones were structurally compromised by water damage. (See local sea‑level‑and‑groundwater guidance.) (Redwood City, ArcGIS)
Can Moisture Issues be Alleviated? Yes—But Scope Matters
There are proven ways to manage below‑grade water. The right plan depends on source (surface vs. groundwater), volume, and pathways:
- Keep water away from the foundation (first line of defense): Clean/extend gutters and downspouts; correct grading so water moves away from the structure.
- Intercept & divert subsurface water: Perimeter (French) drains with proper filter fabric and daylight or pumped discharge can lower water levels around footings. Pair with exterior waterproofing where feasible.
- Collect & remove water that gets in: An interior sump pit + pump with battery backup and an airtight lid is standard best practice for managing periodic inflows; it prevents soil gases and humid air from entering the home. (Building Science, Building America Solution Center)
- Control vapor & condition the crawlspace: Install a durable vapor barrier (10–20 mil) sealed to walls and piers; consider a sealed/conditioned crawlspace approach when compatible with local codes and seismic detailing. (Building America Solution Center)
- Concrete “rat slab” (optional): A thin, non‑structural slab can improve access and cleanliness, but does not solve groundwater by itself; it must be integrated with drainage and vapor control.
Reality check on costs: In high-water-table areas, fixes for homes that need multiple drainage and moisture control solutions tend to be expensive. Based on similar projects, we estimated $100K+ for drainage and moisture control alone, with any additional seismic and structural work. Final costs require site-specific engineering and competitive bids, and even with these upgrades, future moisture problems aren’t guaranteed to be eliminated.
Additionally, our team was concerned that other key systems in the home had not been updated during the remodel, such as the windows, the plumbing system, the roof/siding, and the HVAC system. These were eventual cost considerations for our client.
Decision Time For The “Almost” Home
We advised our clients against pursuing this property. Competing offers would likely underprice the true remediation scope, pushing the sale price beyond what made sense once the total cost of ownership—including near‑term drainage, moisture control, and probable system upgrades (windows, plumbing, roof/siding, HVAC/ducting)—was considered.
Our clients ultimately made the smart decision and decided not to write an offer on the property. The right home is not only one you love—it’s one whose systems and risk profile you understand and accept.
Stay tuned for part two of this story, where we’ll cover how we assessed and fiercely negotiated on their dream home, complete with all the aforementioned system upgrades.
Redwood City Real Estate
Redwood City Homes
Flipped Home Red Flags
Home Inspection Checklist
Best Real Estate Practices
Buyer Due Diligence Checklist
Foundation Issues
Real Estate Case Study
Bay Area Housing
Questions? Ask our team of experts
Deniz Kahramaner is the Founder & CEO of the data-driven Real Estate Brokerage Atlasa. His mission is to help home buyers understand the tradeoffs of different home options using big data and analytics. Feel free to contact Deniz if you need help with the home buying or selling process at deniz@atlasa.com.