Wet basement prevention: this article discusses methods for preventing wet basements by attention to multiple best construction practices, including the basics of foundation d & roofing, poor site drainage, bentonite clay for basement waterproofing, foundation membranes to prevent leakage, foundation drain tiles, proper backfill, and proper finish grading.
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. A case study of a flooding basement, a rotted piano, and clogged gutters describes how home buyers were fooled into thinking they were buying a home built over a stream.
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How to Prevent a Wet Basement - causes and cures for basement water entry may be more basic and easy than you think
Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
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:
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 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.
The epitome of the "make it work" approach that I find troubling is wet basements.
People will install a $15,000. internal trench and drain system to "dry out" their chronically wet basement before first noticing that outside the gutters and downspouts spill right by the foundation wall, and inside we see water stains originating high on the basement wall, confirming that source of moisture. Instead we install a "fix" that first lets the water come into the building (where secondary problems of moisture will continue), then drain it away.
One of our clients (DJF) lived for thirty years in a house that flooded repeatedly in wet weather.
Many years ago I was hired to inspect a house for sale. The owners were told by their realtor they really ought to look into fixing their flooding basement before putting the home on the market. The basement had been chronically wet, flooding to several inches each time it rained, since before the owners bought the home 25 years before.
At my inspection the basement was full of 30 years of accumulated stuff, most of which was soaked and rotted. There was an upright piano that whose legs had rotted off - the piano had gradually settled down to the floor and just its top two feet remained.
"I'm Just Washing the Basement Walls" the home seller said.
When Mr. owner was looking at the home and liked it his wife wanted to come up from New York City to see it. They called the owner the next day. It was raining. "Today is not a very good day" the owner said. "I'm kind of busy". They insisted. Owner acquiesced. On their arrival, in pouring rain, the buyers, naive city dwellers who'd never owned a house, found the owner, in the basement, standing in 24" of water. He was wearing hip boots, and with a garden hose hooked up he was "spraying" the basement walls.
"What are you doing? " they asked. --- I would have asked "What the hell are you doing???"
"I'm washing down my basement walls" was his explanation."I do this once in a while. Today seemed like a good time."
The buyers were not the least suspicious. They didn't think this was an odd rainy-day activity. They bought the house with the very clean basement walls.
The house is built over an old stream bed, he explained
Soon however, the new owners complained to the old owner that every time it rained their house had a basement flood. He explained that well the house was "... built over an old stream bed, and when it rains the stream rises into the basement - there's really nothing to be done about it."
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.
Inside the basement I saw huge water streak stains running down the rear basement wall at each of three basement grade-level windows.
Outside I found a solid concrete patio that had been poured against the foundation wall and that sloped in towards the house.
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 basement windows and inside, down the foundation wall onto the floor. Interestingly I did not see other water entry marks elsewhere on the basement walls.
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.
Fixing the in-slope patio was also needed to handle the heavy rainfall case.
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.
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.
As Carson Dunlop Associates' sketch (above) 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: D & roofing 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.
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.
Details about water barrier coverings for foundations are at WATER BARRIERS, EXTERIOR BUILDING
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.
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.
Details about foundation drains or footing drains are found at FOOTING & FOUNDATION DRAINS
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.
More details about foundation drains or footing drains are found at FOOTING & FOUNDATION DRAINS
Details about eliminating exterior sources of foundation leaks and building water entry are at EXTERIOR WATER SOURCE ELIMINATION . Check and correct these sources of building water entry:
Details about proper site grading to handle surface runoff and groundwater, including swales (shown below) are at GRADING, DRAINAGE & SITE WORK. Excerpts are below.
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.
Find and Clear Clogged Footing Drains
Details about installing, finding, and repairing foundation drainage systems are at FOOTING & 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.
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.
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
Readers needing more extensive guidance on preventing or fixing basement leaks and moisture should see BASEMENT LEAKS, INSPECT FOR, or if your building includes areas over crawl spaces, see CRAWL SPACE DRYOUT - home.
If your building has been flooded, see FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
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. The original wet basement prevention article (linked-to below) has been adapted and expanded in this document.
The article above paraphrases, quotes-from, updates, expands and comments on an original article original article (see links just above)"The Almost-Too-Tight-House" by Steven Bliss.
Keeping Basements Dry: Wet Basement Prevention - part 1 [PDF form], use your browser's back button to return to this page &
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Frequently Asked Questions (FAQs)
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
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.
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.
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;
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.
Also see FOUNDATION WATERPROOFING
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.
Question: I get water in the basement when it rains hard and it is windy. I have a front patio made of cement, ...
I get water in the basement when it rains hard and it is windy. I have a front patio made of cement, and it seems like the water is going through my brick, and is not getting to the weeping hole, since that specific area I do not have a weeping hole. I can not put a weeping hole in that area, because I believe under the brick the rubber membrane was damaged when the masons put the brick. I had to close the area where the weeping hole was with a silicone mortar fix. I then sealed the brick walls in the area, I still have water. Any suggestions for me? If you need pictures let me know please.- Water in Basement 4/24/12
Indeed some sharp photos would help us comment. Use the CONTACT US link found at the top or bottom of any InspectAPedia page to find an email address. Patios collect a lot of water when it rains, and few are waterproof. If your patio does not slope away from the building, that's likely to remain a problem, independent of what you do with a brick veneer on the building walls.
Question: Which is best for basement water proofing: bentonite clay injection outside or crack sealing inside?
I am getting mixed recommendations from local contractors here in the Chicaoland area. Some contractors want to stop my basement seepage by using a Bentonite clay injection rom the outside and some contractors want to use epoxy/ urethane foam to repair the crack. Which procedure will last longer and what is the normal price to fix one crack using bentonite and the price to fix one crack using epoxy/ urethane. - Jillian 5/11/12
Before choosing a solution to a wet basement or crawl space, it is very important and useful to get an accurate and honest diagnosis of the cause of water entry in the first place.
The nature of the waterproofing measures or repair as well as repair cost to correct water entry due to a misplaced downspout or roof gutter overflows is very different from water entry due to in-slope grade outside of a building or (more rare) construction of a building placed too deep into soils with a high seasonal water table. [Photo at left of the Little Dutch Boy placing his finger on a hole in the dyke, Wikipedia creative commons]
The best method for stopping basement water entry is neither of the options you gave: our first choice is always to divert outside water away from the building. Usually, and especially if the outside water source is roof runoff or downspout drainage, this best method is also the least costly.
The second best method for stopping basement water entry, in terms of effectiveness in my OPINION, is to seal the exterior of the foundation by any of a variety of methods, of which the bentonite clay approach has a long history of use and usually of effectiveness.
It's also usually a more costly approach than sealing a single crack indoors. Because building foundations are not constructed to function as a waterproof boat hull, making a foundation really waterproof can be a challenge, and expensive.
The Procedure & Effectiveness of Bentonite Clay Injection for Waterproofing Foundations
Bentonite clay injection into soils around a home is one of many foundation waterproofing methods. Bentonite, a clay dominated by the mineral montmorillonite (synonym "smectite") is a naturally-occurring geological deposit that occurs worldwide, but bentonite mined in the U.S. in northeastern Wyoming and southeastern Montana is recognized world-wide as the purest sodium montmorillonite that is commercially available from a natural source.
In the bentonite clay waterproofing procedure, using a truck containing a thick colloidal mixture of bentonite and water, and using a high pressure pump, bentonite clay is injected into the soil at appropriate depths (from the foundation footing up) and intervals around the building foundation. The bentonite clay, injected through a hollow one-inch diameter drilled or driven rod, is pumped into soils quite close to the building foundation wall, forms a water resistive barrier. The injected bentonite expands in all directions for about 12-inches (varying by soil conditions) from its pumping location and requires about 45-minutes to an hour to cure to a putty-like stable state that leaves the material in place..
Bentonite clay waterproofing companies point out that by injecting the bentonite close to the foundation wall, you may see some of the clay mixture seeping into the building through existing foundation cracks where it forms a sealant in the crack from outside the foundation wall and through the wall thickness as well.
The appeal of the bentonite clay injection approach to waterproofing a leaky basement below a building is that it may be effective, and injecting clay into the soils around a building is far less disruptive than excavation to apply waterproof mats and a buried drainage system. How well the bentonite clay approach will work depends on more variables including soil and site conditions. 
The Effectiveness of Epoxy Crack Sealing in Foundation Walls
The third approach to basement waterproofing by interior surface crack sealing can be effective and cost-effective on a poured concrete foundation that is leaking only at one or a few very specific locations.
For concrete block foundations, for a foundation with many cracks, for a basement that has many water entry points, for a basement in which water enters at the bottom of the wall around a footing or interior floor slab, this approach, while least costly, is also likely to be least effective.
Details about sealing cracks in concrete walls or floors using epoxy or epoxy grouts are at Seal Cracks in Concrete, How To and at Polyurethane Foam Injection where we give details for using polyurethane foam to seal foundation cracks.
Durability of basement waterproofing methods
Properly applied, both bentonite clay and epoxy crack sealing are very durable in the location where they are placed. Of course if you have a lot of water outside your foundation and you simply rely on the little Dutch Boy at the dyke who placed his thumb over the first crack that appeared, the risk is that the water simply finds another entry point.... then another.
The moral of the Little Dutch Boy story was that quick action and bravery averted a catastrophe. But it was the workers who came later to actually repair the dyke who were able to perform a lasting repair.
Question: how do I diagnose & fix a damp patch on my wall?
For some time now I have had a strange damp patch in my party wall. On closer inspection, the plaster has broken down to reveal sand, and mud ? in the wall. There is also what appears to be copper wire about 3 to 4 mm thick which I believe to be the old damp proof; it is here where the damp/water is prominent which suggests failure of the damp proof.
My house is of stone construction and the front room where the main problem is, is of wooden floor construction with a 2/to 3 ft gap underneath where electric cables and pipes travel. Could you please advise.
I don't know enough from just your email to offer much advice except
1. I'm unaware of instances in which copper wire provides dampproofing; you might be looking at steel reinforcing mesh or something else.
2. It makes sense to look for the source of moisture and fix that; the problem may be above the samp spot you see or in the building on the opposing side of the wall.
3. You describe a very tight crawl space area below the main problem room - someone needs to inspect that interior for problems of moisture, insect damage, mold, etc.
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