Poor Drainage -
Don't Get Soaked!
Of all the problems discovered during a home inspection, one of the most common, and most disconcerting, is poor surface drainage. Poor drainage is a problem that may exist from the start (original grading deficiencies), or it may develop over time. Frequently it is the result of an action taken by the property owner (or a neighbor), sometimes out of complete ignorance of the potential problems it can cause. It may be limited to the area immediately adjacent to the foundation, or it may involve the entire property and beyond.
Since an inspection will discover numerous problems with a given property, a home inspector must be able to put things into perspective with regard to priority and magnitude. But when it comes to drainage, extra attention and education of the client is frequently needed. Why? Because water can have a DEVASTATING effect on a structure, either directly (moisture damage/wood rot/fungus) or consequentially (soil related settlement/upheaval/lateral pressures/slip planes, etc.) The tricky thing for the inspector, is that the potential for damage may actually exist, but with no current evidence of damage to observe and report! Many homes with persistent water intrusion problems will show no physical evidence of the ongoing problem, due to cleanup efforts of the owners. Therefore the inspector needs to be alert for conditions that COULD present a problem, and address them with the intensity as if they ARE a problem.
In my years of experience inspecting homes, the following cases stand out in my memory as classic examples of poor drainage and its effects:
1. Basements with 8 feet of water in them - In a brand new subdivision, poor compaction of the backfill soils created depressions around the foundations of several homes. The homes backed up to a large undeveloped property that generally sloped toward the homes in question. The undeveloped property had a small diversion berm to route the drainage away from the new homes. However, during the first heavy rainstorm, the drainage overflowed the berm and entered the back yards. The sudden inundation of water caused rapid collapse of the loosely compacted backfill soils, and water penetration through the basement window wells. The windows broke and you can guess the rest. This was an extreme case, but I have seen many others where water has penetrated the basement causing thousands of dollars in damage to finished surfaces, mechanical equipment, etc. In all cases depressions around the foundation, and/or poor slope in drainage swales were at the source of the problem.
2. Backfill soil settlement - When a foundation is constructed, the excavation must extend beyond the limits of the foundation (typically 3 to 5 feet) to accomodate the forming of the foundation walls. This area outside the walls must then be "backfilled" after the walls are complete. Ideally the backfill soils should be compacted to prevent settlement, but frequently they are either not compacted or poorly compacted. The soils settle over time, under their own weight, and more quickly if they become wet. This results in depressions around the foundation that trap water and cause additional soil settlement. This is a real problem as drainage cannot escape these areas and water can impact the foundation and the bearing soils. If the original backfill was uncompacted or very poorly compacted, the results can be dramatic and sudden with large depressions forming literally overnight. If the backfill was moderately compacted the settlement can take years, but gradually goes from positive drainage to flat slope, to reverse slope. In this scenario a homeowner may be unaware of this process (like watching your hair grow) till the first time there is water in the basement or crawlspace, or foundation movement begins.
3. Foundation settlement and/or upheaval - Poor drainage can result in wetting of the foundation bearing soils, which then consolidate under the weight of the foundation as the moisture leaves the soil. This is especially evident if the foundation (or a portion thereof) was placed on fill material. I have seen 100 year old homes with no history of movement suddenly settle after the drainage was changed, so the "test of time" only applies when environmental conditions are consistent. In some cases the simple condition of a blocked roof downspout can trigger a dorment condition. If expansive soils are present, the reverse can occur, with the soils swelling and exerting upward pressure on the foundation.
4. Foundation wall lateral displacement - When backfill soils become saturated, due to poor drainage or other moisture intrusion, they exert considerably greater pressure on the foundation walls than when they are dry. This excess pressure can cause buckling or overturning of the foundation wall. Good foundation design will accomodate this pressure, but not all foundations are well designed! I have seen many walls displaced 3 to 4 inches with severe cracking. In one case I observed a foundation wall completely collapsed by poor drainage!
5. Foundation degradation - Soils with sulfates or other naturally occuring chemicals can attack a concrete foundation, with water acting as the catalyst or transport medium. I have seen crawlspace foundations where the footings were severely degraded, with piles of powder laying where the footing used to be! These were homes built in the 1940's when no soils report was generated prior to construction. A soils report would have identified the problem and specified Type II cement for the foundation to resist attack.
6. Slide conditions - Hillside construction with poor drainage is potentially a recipe for disaster. Excessive moisture can lubricate slip planes causing the all too familiar videos seen on TV as the home slides off the hill. Even if a slip plane is not present, the home may undergo "creep" as the wet soils slowly move downslope. Poor drainage on the uphill side of homes with walkout basements can also exert overturning pressures on the home, causing rotation or lateral displacement.
7. Extreme mold - Water penetration, from poor drainage, into a crawlspace or basement is the usual cause of mold in these areas. Wet soils create elevated humidity conditions that mold thrives in. Areas with mold may not always be visible, so one needs to suspect its presence when poor drainage is observed.
8. Home set too low on the lot - Some homes are set too low on the lot, with no way to add soil to improve drainage while maintaining clearance between the ground and wood framing (most codes require at least 6" clearance). In these cases there are basically two choices - raise the house, or regrade the yard. Raising the house can be done but is very expensive and therefore rarely done. Regrading can be accomplished by cutting the soil down and away from the foundation at the required slope, and creating a swale system to carry the drainage to a low spot on the lot. If the low spot is below the natural drainage discharge point, a "sump" condition with pump may be needed to "lift" the water to the discharge point. This solution has its obvious drawbacks, but is better than allowing the drainage to affect the foundation. Another possible solution, that I would not recommend unless special attention is given to waterproofing the existing structure, would be to install a retaining wall adjacent to the house, thus allowing the grade to be raised at the house. This solution is frequently seen, poorly performed, when landscape ties are laid up against the home and soil is added to improve the slope. This can result in wood rot to the siding and/or framing as moisture can penetrate the tie joints, and become trapped between the house and the ties. Any moisture accumulation in the wall cavity (from any source) will have difficulty escaping with this "solution" as well. Hence, this "solution" to one problem creates other problems, and should be avoided unless professionally designed and approved by the local building department.
HOMEOWNER TIPS: Do not do anything to create poor drainage. Resist the temptation to install solid landscape barriers around the foundation that can trap drainage. Add soil to settled areas to maintain flow away from the foundation. Discharge your roof drainage beyond the limits of the backfill soils (3 to 5 feet from the foundation) with splash blocks or downspout extenders. Clean you gutters regularly as clogged gutters/downspouts can overspill water adjacent to the foundation. Resist the temptation to install sprinlkers adjacent to the foundation (unless you live in an area with shallow/slab foundations and expansive soils, where moisture stabilization via wetting is the norm).
INSPECTOR TIPS: Look at the ground adjacent to the foundation by sighting along the foundation from each corner. There should be positive slope away from the foundation, preferably on the order of 5% (3" fall in the first 5 feet) as a minimum. Here in Denver with our expansive we like to see 10% in the first 10 feet (12" in 10 feet). If flat slope or reverse slope exists, you have to suspect that infiltration could be an issue even if there is no interior evidence. Report on it as having "the potential to cause infiltration and/or structural damage if not corrected". Also, scan the site for non draining conditions. Make a note if there appears to be large offsite flow contributions. Keep in mind that grass areas need 2% slope (2 feet in 100 feet, or approximately 1/4" per foot) as a minimum in order to drain. To the eye a 2% slope will appear quite flat (use a 4 foot level when in doubt). Landscape swales need 2% slope along the flow-line as a minimum. Less than 2% slope can be accomodated with a french drain. Look for soggy flow-lines and/or fungus growth in the swales that would indicate non-draining or slow draining conditions.
REALTOR TIPS: Listing Agents - make sure your seller discloses any water infiltration problems. I have testified in court cases where disclosure was not made and in one case the Realtor was also named in the suit! Buyer's Agents - be nosey and ask direct questions of the seller and listing agent. Obtain and provide a copy of the Seller's Disclosure statement to the inspector so he/she can follow up on any historical issues.
