How to Stop or Prevent Basement Leaks & Water Entry InspectAPedia® -
Steps to prevent a wet basement and offers a few simple cures for existing wet basements
Multiple defenses are the best guard against basement leaks
Foundation dampproofing & correcting poor site drainage to stop basement leaks
Using bentonite clay for basement waterproofing
Using foundation membranes to prevent basement or foundation leakage
Using foundation drain tiles, proper backfill, proper finish grading are discussed as basic steps towards a dry basement
Case report of foundation collapse due to settlement & wet soils
Photographs of basement waterproofing methods & procedures
Simple cures for wet basements without major work - steps that might work
Questions & answers about wet basement cures and wet basement prevention
Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
This article discusses methods for preventing wet basements by attention to multiple best construction practices, including the basics of foundation dampproofing, poor site drainage, bentonite clay for basement waterproofing, foundation membranes to prevent leakage, foundation drain tiles, proper backfill, and proper finish grading.
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A case study of a foundation collapse is described and we offer a few simple steps that might cure a wet basement without major work. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
How to Prevent a Wet Basement - causes and cures for basement water entry may be more basic and easy than you think
The original wet basement prevention article (linked-to below) has been adapted and expanded in this document. The text below paraphrases, quotes-from, updates, and comments an original article original article (see links just above)"The Almost-Too-Tight-House" by Steven Bliss.
Wet Conditions Lead to Building Foundation Collapse
This article begins with a pair of foundation collapse case studies, describing poor site drainage and wet soils that led to the foundation bursting into the home. Our photo (left) shows an example of severe foundation damage and ultimate collapse due to water and wet soils outside the foundation wall. Mr. Bliss points out several factors that led to two foundation catastrophes that he investigated:
The site was sloped, and each foundation collapse was on the uphill side of the building
The land was sloped so that water collected behind the foundation and soaked into the ground
While original site grading might have sloped away from the foundation it was inadequate, so as excavated soils settled around the building ground sloped in towards the foundation wall
Surface or perhaps roof runoff collecting close to the foundation saturated the soils, increasing the soil's mass and ultimately bursting in the foundation wall
No sub-surface foundation drainage system was installed, or if there had been one, it was no longer working
In-house basement wall waterproofing, if present, might actually have contributed to the foundation wall collapse by failing to provide another possible path for water (and its pressure) to escape from outside the foundation wall
Bliss notes that foundation leaks are said to cause more callbacks than any other problem in new home construction. Some building sites with good natural drainage are unlikely to result in a leaky basement even if the builder does not follow all of the best foundation water entry prevention steps during construction and site work. But others are a catastrophe waiting to happen - or as above, a catastrophe that has already happened.
Living With a Basement that Floods is Unnecessary and It's a Bad Idea
Living with periodic basement flooding - which some people manage, is not a great strategy, risking moisture-related damage such as toxic mold contamination (photo at left), building rot, termite damage, or even shorter roof shingle life.
One of our clients (DJF) lived for thirty years in a house that flooded repeatedly in wet weather.
The owners told me (DJF) that as city people, they didn't think anything was amiss when on first visiting the home on a rainy day, the original owner was standing in the basement in hip boots with a garden hose spraying down the basement walls. "I'm washing out the basement" he told them - a creative cover up for serious basement flooding. When I saw the house it had been flooding for 30 years. A wooden upright piano that had been stored in the basement had so badly rotted that it was only two feet tall.
The owners had later been told that "nothing could be done" because the basement was built over an underground stream that flooded in wet weather.
Starting by noticing that basement leak stains originated high on the foundation walls I was sure that even if there was an underground stream, basement water was also coming off of the roof or from bad surface drainage. Outside I found that a concrete patio had been poured against the foundation wall, later settling and tipping towards the home.
Tall pines near the home made sure that the house gutters were constantly clogged with pine needles and clogged, overflowing onto that patio at every rainfall. Water ran across the patio and down through the foundation wall. A simple experiment of cleaning the gutters and temporarily routing the downspouts well away from the home using above-ground flexible extensions was enough to immediately stop the basement water entry.
Steps to Prevent Basement Water Entry - the Basics
Soil Testing Predicts Soil Drainage Ability
For new construction, start with a few soil tests to understand what the house is being built upon. Any civil engineering manual will include a soil guide describing soil types and their drainage characteristics. Watch out for clay soils and silts that are unstable and expand when wet or frozen.
Conduct a soil percolation test to get an accurate idea of how soils drain around the home. If a septic system is to be installed you're going to need soil perc tests anyway. See Septic Soil PERC TESTS and PERC HOLE SPECIFICATIONS. Remember that if your perc tests are performed in the dry season you may get over-optimistic results. And if living space in the home is going to include below-grade areas, consulting with a soils engineer may be good insurance.
Water Entry Prevention Priorities
Keep water away from the foundation. This means proper site drainage that assures that surface runoff and roof spillage are conducted away from the building.
Most of the wet basements that we (DJF) have investigated were suffering from mis-handling of roof drainage. Between gutter defects that spill large volumes of water close to the foundation and improper site grading, we estimate that 80 percent or more of basement water entry problems can be explained. \
Our photo (left) shows a home with an in-slope grade facing the house wall. It would have been relatively easy to install a swale draining hillside water and roof spillage around the left side of the home in this picture. Instead the owners suffered decades of wet basements until the wet conditions made the home sills so attractive to termites that major structural damage had occurred.
Dampproofing: traditional dampproofing is a bituminous coating that is rolled, brushed, or sprayed (least effective) on the foundation wall. Dampproofing is not waterproofing, and water will leak through a coated foundation wall wherever there is the combination of cracks or other openings and water.
What dampproofing does is slow the flow of water vapor through the foundation wall by breaking the capillary flow of water through the masonry. Without dampproofing, water evaporating from the more dry indoor side of the wall actually pulls moisture through the foundation wall. But we're talking about moisture, not flowing water. If water never accumulates against the outside of the foundation wall, leaks and moisture won't be flowing through the wall.
Amateur foundation waterproofing: as extra insurance, some builders drape plastic against the dampproofing coated foundation wall. This is a very inexpensive step that certainly reduces foundation leaks, even if the plastic is somewhat damaged during backfill. However amateur waterproofing alone does nothing to prevent a foundation collapse if lots of saturated soil is pressing against the foundation exterior.
Effective Foundation Waterproofing Method Details
Foundation Drainage Mats & Geotextiles for Foundation Waterproofing
As Carson Dunlop Associates' sketch (left) and our photos (below) illustrate, proper installation of a combination of damp proofing, a drainage mat, and a geotextile to keep the drainage mat from becoming clogged by soil particles can be effective in keeping roof spillage and surface runoff from penetrating the building foundation walls.
Watch out: even this approach won't prevent basement or crawl space water entry if groundwater levels are so saturated that they are rising up beneath the basement floor slab.
Sealing Foundation Walls: Damproofing vs Waterproofing
True foundation waterproofing: for poorly drained soils, investigate true foundation waterproofing, such as heavy textured plastic or rubber membranes that are placed against the foundation wall to form a drainage layer to conduct roof spillage or ground water down the exterior of the foundation wall and into a foundation drain system to carry water safely away from the building.
Our foundation waterproofing system photographs above show (photo above right) and also Carson Dunlop Associates' sketch (left) show the use of a plastic membrane, protected by a geotextile to combine good water drainage down the foundation wall (and into the footing drains) with gravel backfill to nearly the top of grade (photo above left).
This basement waterproofing system was installed on a home that had suffered recurrent basement flooding due to a combination of in-slope grade at the rear and right side of the home combined with improperly installed and non-working footing drains, aggravated by wet soils in the area.
Bentonite clay waterproofing: bentonite clay can be pumped into soils around the building foundation wall - an old basement waterproofing method that in some installations works quite well to slow or stop foundation leaks. Watch out - by leaving water in soils near the foundation wall, the risk of foundation collapse may remain.
Use a basement waterproofing paint on the interior (or a dampproofing on the exterior) of porous masonry block foundation walls - we have had excellent results with Thoroseal™ but don't expect an indoor foundation waterproofing paint to hold back a flood. See BASEMENT WATERPROOFING for details.
See BASEMENT HEAT LOSS for a discussion of foundation and basement insulation methods. See POLYSTYRENE FOAM INSULATION for a guide to using this material in below-grade applications. See TERMITE SHIELDS vs TERMITICIDE for a discussion of avoiding insect damage when foam insulating board is used below or at ground level.
Foundation Footing Drain Details to Prevent Basement Water Entry
Foundation drainage - drain tiles also called footing drains and by some folks "French drains" (a mistake - see FRENCH DRAINS for DOWNSPOUTS),: water flows in the path of least resistance. Perforated 4-inch PVC or flexible ABS are the least costly and most foolproof foundation drainage conduits. Foundation drains should pitch at least 4 inches in every 100 feet of length.
The top of the foundation drain, should be below the top of the finished basement or crawl space slab. From the low corner of the building, the foundation drain should continue to daylight or, if permitted by local codes, to a storm sewer, so that water will drain away from the building without relying on an electrical sump pump or other magic.
Bury the footing drains in gravel, both under and above the drain tiles. Extend the gravel backfill at least two-thirds of the way to the top of finished grade.
Gravel helps water flow easily into the drain system instead of seeking a way into the building, and the removal of water outside the foundation wall also avoids foundation collapse later. The gravel size needs to be larger than the holes in the drain tiles.
Our sketch (left) shows a less than optimum footing drain installation because the artist placed soil too close to the drain pipe.
Eliminate Exterior Sources of Water that Cause Building Leaks, Water Entry, Flooding
Details about eliminating exterior sources of foundation leaks and building water entry are atEXTERIOR WATER SOURCE ELIMINATION . Check and correct these sources of building water entry:
Roof gutters and downspouts - check to see that roof runoff is effectively disposed of away from the building, and that it is actually working - see GUTTERS & DOWNSPOUTS Also see FRENCH DRAINS.
Site grading and control of surface runoff - see Finish Grading [below]
Footing drains / foundation drains - check for presence of and check that water is flowing out of footing drains if water is in the basement. If the basement is wet and the footing drains are dry, they are not working. Details are at FOOTING & FOUNDATION DRAINS.
Storm drains - nearby storm drains should be un-blocked and not backing up onto the property.
Sump pumps - also check that if they are installed, the sump pump(s) are working and that water is pumped to a location that does not drain back into the building. Some properties use an outdoor catch basin and sump pump to dispose of roof runoff or surface runoff. See SUMP PUMPS GUIDE
Finish Grading to Prevent Foundation Leaks & Water Entry
Details about proper site grading to handle surface runoff and groundwater, including swales (shown below) are atGRADING & SITE WORK, EXTERIOR. Excerpts are below.
At grade, the main object is to get water away from the foundation as quickly as possible. Finish grade should slope away from the building for at least 10 to 15 feet, and should not contain low spots that will make water ponds.
Swales: if one or more sides of the building face an upwards sloping hill, slope the finish grade away from the building for at least 10-15 feet, and then shape the finish grade at that point into a swale that itself continues to carry water around to the downhill side of the building.
A swale, illustrated by Carson Dunlop Associates' sketch at left, is a nice word for a "gentle ditch" - it does not have to be deep.
If the building roof system includes gutters and downspouts, do not tie the downspouts into the footing drains - you will simply overload the footing drain system and risk future basement water entry. We want to see gutters extended to release roof drainage no less than 10 feet from the home, more is better, and even more important, from the point at which water leaves the downspout end, it should continue to flow away from the building, not back towards it.
Simple Retrofit Repairs Can Cure Basement Leaks
First identify where water is entering the basement or crawl space. See BASEMENT LEAKS, INSPECT FOR for examples of common leak points that might be hidden behind finish walls or paneling. Our photo (left) shows a previously-hidden foundation wall crack that was sending water into a finished basement and under the raised wood basement floor from the time the home had been built until severe flooding in the basement motivated the owners to remove wet walls and find this leak.
Patch leaky foundation wall penetrations or holes: Mr. Bliss reports stopping a substantial basement water leak (a couple of gallons per rainstorm) by chipping out around a waste pipe where it passed through the foundation wall, and patching that area with hydraulic cement.
Find and Clear Clogged Footing Drains
Details about installing, finding, and repairing foundation drainage systems are atFOOTING & FOUNDATION DRAINS. Excerpts are below.
Find the end of the footing drain system that used to drain to daylight - it may have become buried with mud or covered by backfill. Clear it open and check the end for water flow in wet weather. Our photo (above left) shows the footing drain that was excavated and removed at the home of a client whose house suffered recurrent flooding. The old footing drain was totally impacted with mud.
The photo at above right shows the ends of three new footing drains that were installed and carried to daylight. We remained a little nervous about just what the builder used for backfill - notice that silty mud coming out of the new drains? They may not have a long life
Use an Intercept Drain at In-Sloping Driveways and Walks
Add an intercept drain at the entry of garages into which a paved driveway is sending water whenever it rains.
If you are planning to re-pave a driveway, that's a great time to go to the trouble of cutting in and installing a drain that prevents water from flowing into the garage.
Connect the intercept drain to a storm drain or to a new buried drain line that slopes to daylight well away from the building.
Don't connect the intercept drain to the building footing drain system - you may overload the footing drains and cause basement leaks.
Add a splashblock to route surface runoff around a chimney whose side formed a water trap against the foundation wall
Basement Perimeter Drain Systems for Basement De-Watering: Installing & Inspecting "French Drains"
Details about interior perimeter drain systems such as B-Dri™ and Beaver Basement™ are found at PERIMETER DRAIN SYSTEMS. Excerpts are below.
Some people call an interior perimeter drain used for basement or crawl space de-watering a "French Drain". Whatever you want to call it, an interior perimeter drainage system cut into the basement or crawl space floor can effectively stop basement or crawl space flooding - or can it?
An interior drainage system can indeed work to keep water off of the floors, and properly installed it can also resist sending problematic high moisture levels into the building as well.
But first you should check and repair obvious outdoor water entry sources that send water through the building foundation walls.
Carson Dunlop Associates' sketch (left) shows t approaches to installing an interior drainage system
Key building water entry diagnosis and cure articles:
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
Frequently Asked Questions (FAQs) about the cure or prevention of wet basements or crawl spaces
Question: my beach property crawl space floods during heavy rains. What's the best cure?
I live about .25 miles from the beach and my crawlspace gets flooded during very heavy rains due to a high water table. My crawlspace is the footprint of the whole house (2100 sq. Ft.) about 4 feet high with a concrete floor. The water comes up from the floor by the footings were the concrete has broken away and it appears that the floor is just a skim coating of concrete about 1.5 inches thick. I have gotten several conflicting opinions/estimates about installing sump pumps (French drains are just too cost prohibitive, approximately $20,000) and I am hoping you can help.
Some companies have suggested that I not install sumps due to the high water table they would constantly be running and that it will possibly make the flooding worse by creating another opening for the water to enter the basement if the dumps fail or cannot keep up with the flow of water rising. These companies suggest just using surface pumps when needed. This option would not stop the basement floor from getting wet and then i still have to deal with a wet vac for the puddles. Some companies have suggested shallow sump pits, just the height of the pump itself, others have suggested larger pits with two pumps in each, along with battery backup pumps. Some suggest holes on the sides of the sump liner, others not.
Needless to say I am confused. I would like to keep the water out before the floor floods, but I certainly do not want to make the problem worse. I have lived in the house for 6 years and we have flooded 3 times during a couple of Nor' easters and Hurricane Irene, so it is not a constant problem, but i would like to be better prepared for the next event.
Any suggestions would be greatly appreciated. Thanks! - Nina K
Reply:
Nina, If your area regularly floods, a gravity drainage system "French drains" won't work in your area; in very wet weather or storms it's more likely, unless you live on a hilltop, that the entire drainage system will flood or be under water. Similarly, drywells or seepage pits don't work well in areas that seasonally or periodically flood.
If you're going to have to rely on sump pumps you'll probably want a duplex system and for more reliability you'll need sufficient battery backup to survive the maximum likely time that you may have lost electrical power during a storm. Also the crawl space will need to be as waterproof as you can make it, and the sumps will have to be capable of handling the maximum anticipated in-flow rate; and finally the sumps will have to pump to a destination that does not simply send water draining back into the crawl area.
If you're using a sump system you want water to run under poly or other floor covering and into the sump - otherwise you're pumping water and moisture into the home and asking for a mold problem.
And I agree with the installers who want the sump pit liner to have holes in it. The holes allow water from under the basement/crawl space floor to flow into the pit, thus dropping the water level and drying out the floor. Installers who leave out the holes are installing a design that requires that water first enter higher in the structure, run across the floor, and then enter the sump pit.
Having water leak into a basement or crawl space and run across the floor to a sump pit is, as you suggested, unacceptable and just bad practice. The problem is that even if you prevent actual flooding, the wet floor acts as a pump sending moisture up through the entire structure, risking mold growth and contamination anywhere from basement or crawl area all the way up through the attic or roof space.
The advice to keep sump pits shallow is contrary to my experience. I found that making a sump pit deeper under the basement or crawl space floor eventually lowered the water table under the floor and stopped water entry on the floor.
Since your questions are about a periodically flooding crawl space (CRAWL SPACES) rather than basements (discussed in the article above), please take a look at CRAWL SPACE DRYOUT PROCEDURES for details on how to proceed to keep the crawl space dry.
More about sump pumps and their selection, backup systems, and installation, can be read at SUMP PUMPS GUIDE
Question: When it rains, water leaks into my basement around the sewer pipe. How should I fix this and what sealant should I use.
There is water seeping around waste pipe where in enters foundation during rainstorms. I have read conflicting suggestions about what type of sealant to use to prevent this. - Anna M.
Reply: Diagnose the cause of water leakage at the sewer pipe; seal the wall and pipe on the outside of the foundation or install an intercept trench or sump pit if necessary;
Anna M:
Often when we find water entering a building around the waste pipe there are one of two causes:
1. the trench for the waste pipe acts as a natural catchment that traps surface runoff or ground water and directs it back towards the foundation just where the pipe penetrates the foundation wall. That's because the backfill soil in the pipe trench is less dense than the original soil around the area and because the trench leads towards the building. This problem is worst if the waste pipe trench slopes upwards from the building and worse still if the trench is long and crosses a hill down which surface and subsurface runoff pass during wet weather.
2. there can be a leak in the waste pipe itself, just outside the building, causing water entry at the wall penetration.
The best fixes for case #1 (waste line trench directs water towards the building) are
Seal the foundation wall on the building exterior. Hydraulic cement works well on rough masonry surfaces; if there are clean visible cracks they can be sealed with any of several caulks or sealants intended for underground or exterior exposure such as polyurethane injection sealants or foams (Seal Cracks by Polyurethane Foam Injection) or caulks and sealants intended for use in radon mitigation of masonry wall and slab cracks. Sealing on the wall interior is easier, won't involve digging, and is less reliable This is particularly so with masonry block walls as water from outside can enter and travel inside the wall, coming out at other basement or crawl area spots. Also see Seal Cracks in Concrete, How To.
If the waste pipe trench slopes towards the building we cut an intersecting trench close to the building exterior wall and slope it downwards away from the building to a suitable location. I'd not connect it to the footing drains as they may thus be overloaded and fail. If there is no easy way to slope the interception trench away from the building we might install a sump pit that pumps to a suitable destination well away from the building.
For case #2, (leaky sewer line) which does not sound like your home, if the leak is due to a damaged waste pipe the line is excavated and repaired outside the home.
Question: We think our sump pump and pit has begun to draw water from more distant soils and properties - is this possible?
This was the most informative article I've read during my extensive online research on the topic of "Basement Flooding". Ground water/high water table has been determined the cause of water entry into my basement "pit" area underneath my main sewer trap. We have a Basement Watch Dog Dual Sump Pump with battery backup installed however the constant presence of groundwater in our pit continues to worry us.
Our Staten Island, NY home location is situated where the properties behind, to the left and right of us are elevated. PVC fencing with sealed bottom molding prevents rain water from cascading over the concrete/paver surfaces; however it is our belief that the groundwater underneath from all three directions have found a hydrostatic relief in OUR PIT!
What recourse do we have? Any advice you can give us would greatly be appreciated. - Joe Apap, Staten Island NY
Reply: Yes, over time water flow into a sump pit increases the flow rate of ground water in that direction; in some cases foundations can be undermined.
Thanks for the nice note, Joe; we've been working hard on wet basement and wet crawl space information, particularly since recent hurricanes and tropical storms have led to so much flooding.
The question you raise about the effects of a sump pump on soils, water flows, and by implication even the building foundation is an important one.
Indeed sump pumps as basement de-watering systems work better over time precisely because the ultra fine soil particles pumped away open improved water drainage passages towards the sump pit. I have not been able to find data, and I doubt there is reliable data, about the "reach" of sump pump water movement past the building where it is installed.
Surely sump pump water movement reach will be a function of local soil characteristics including particle size, density, water and ground water sources, and frequency of sump operation.
And water tables underground can fool you - they are not level flat but indeed follow terrain contours. Still I would not be surprised if being surrounded by higher properties means you are receiving their surface as well as subsurface runoff.
If it's cost justified you could consider a curtain drain around your property. Such a drain, a ditch to an adequate depth and filled with No4 crushed stone and perforated piping led to an outdoor pumping station could intercept water from neighbors and keep it away from your home. Your outdoor pumping station will need to be deep enough to be frost proof and it will need to discharge to an approved destination such as a local storm drain.
Earlier I thought of advising you to ask neighbors to be sure their roof drainage is not aimed at your property, but given the vagaries of people and inconsistent property maintenance, I suspect that's a waste of time.
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Questions & answers about wet basement cures and wet basement prevention.
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[1] Scott Anderson, The Journal of Light Construction, December 2005 [1]. Mr. Anderson is owner of Tri-State Basement Systems in Berlin VT
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in buildings, and other topics.
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