Wet Basement Solutions for New Home

Missy writes: I am in the process of building a new home in Michigan and when the foundation was poured last fall there was water sitting in the basement throughout the whole process. Now three months later as they are finishing the house, the sump pump has continued to run. We have a mix of clay and sand soil on the property. We want to know if this is just a temporary problem because the ground still needs to settle or is this a sign of water problems?

Steve Bliss, Editor of BuildingAdvisor.com, responds: It sounds like you have a serious water problem. Basement water problems can be complicated and difficult to solve. The best time to solve them is before the house is built, no longer an option in your case. Assuming that you have not paid in full for the house, you should still have some leverage at this point. I would recommend withholding enough money at the end of the job to repair the problem, in the event that your contractor/developer is unable or unwilling to do so.

I don’t have enough information to say what is the cause of your specific problem and its solution. In general, however, water in your basement comes from one of two sources, or possibly a combination of the two. The two sources are surface water and groundwater. A responsible builder provides the necessary grading and drainage systems to keep your site and home free of water problems.

Groundwater is the permanent water table below the ground surface. The water table often rises and falls with the seasons — higher in the rainy season or when the snow melts (and drains under the ground) and lower in the dry seasons. If the water table is above the level of your basement floor for part of the year, you will have water in your basement during that time. Only a sump pump, like you have, can keep the basement dry during that time. No basement is 100% leak proof so the water will get in. In some cases, it is possible to manage groundwater using special “dewatering” techniques that use drainage systems below and around the foundation to keep it out of the basement, but this is much easier to accomplish before construction begins.

Surface water, also called “runoff,” is water from rain and snow on the ground surface, including rain from your roof. If this water is not managed properly, it can run down the walls of your foundation and into your basement.

Surface water problems are generally easier to deal with than groundwater problems. Sometimes they can be fixed by a simple improvement in the gutter/downspout system such as adding horizontal leaders at the bottom of the downspouts to direct water away from the foundation. Splash blocks can also help. Also, it’s important to slope the finish grade around your house away from the foundation to help move water and snow melt away. If the backfill is not properly compacted, it may slope away from the house at first, but slope toward the house a couple of years later and need new soil and re-grading.

Foundation drains at the base of your foundation are a secondary defense. They are designed to catch any water that accumulates around the foundation and to conduct it, via buried drain pipe, away from the basement . On a sloping lot, the best place to discharge the water is to “daylight” on the ground surface. On a flat site, you may be able to discharge to a storm sewer, if allowed by local codes. If neither is an option, you will need to discharge the footing drains to a sump pump inside the basement. This requires a solid pipe run though the footing when the concrete is placed.

swale with culvert

CLICK TO ENLARGE              Swale with culvert. Also note green “daylight” pipe from foundation drains.

Swales. On sites with extensive surface water, for example, at the bottom of a hill, surface water can be directed away from the house by shallow ditches, called “swales”. These are often located between house lots or along roads and drain toward the front or rear of the lot or into a storm sewer.

Swales are usually planted in grass, but can also hold water-tolerant plants, or be lined with rock.

 

 

 

Curtain drain, French drains can help protect a building site from water problem

CLICK TO ENLARGE             On very wet sites, properly placed curtain drains can intercept water before it reaches your foundation. Courtesy of Wikipedia.

Curtain drains. Where swales are not practical, curtain drains (also called “French drains”) are sometimes used.  These are gravel-filled trenches that intercept the flow before it reaches your foundation and lead the water away from your house. Their location and depth depend on the specific drainage patterns of the building site.

If you’ve had standing water in your basement all fall and winter, there’s a good chance that groundwater is the main problem. If this has not been an usually wet winter in your area, the sump pump may be running much of the year. Surface water may also be contributing to the problem.

Given the difficultly of figuring out the source of the problem and possible   solutions, I strongly recommend that you get the advice of an independent specialist — in this case a civil, geotechnical, or soils engineer with experience in residential construction.

If you don’t have any names of engineers, check with your local building department or local architectural firms, who work with engineers regularly. The causes and solutions of water problems are very site-specific, so you need to have someone come out and look at your building site and project. There’s a good chance that they can offer some options beyond running a sump pump all the time.

It’s not too late to do the work necessary to improve your site’s drainage. If foundation drains were not installed, the builder may need to re-excavate around the foundation. Much better to do this now than after the house, walkways, lawn, and plantings are in place around the foundation.

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Terri writes: We want to build a 1800 sq ft Ranch with a basement and a three-car garage on a flat parcel of land that has water at 4 ½ feet below grade. We are being told that in order to achieve this, we will only be able to have 2 ft of foundation below grade with 6 ft above grade. Any ideas on how to grade the yard without having a ton of fill dirt brought in and it looking like we are living on a hill top? Thanks

Steve Bliss, of BuildingAdvisor.com, responds:  On a lot like this, most people would forget about the full foundation, and go with a slab-on-grade or crawlspace foundation – with a minimum 6-mil vapor barrier protecting the slab or crawlspace from moisture in the soil, which can work its way into the house. Water vapor from the soil can move pretty readily though solid concrete!

I would also be concerned about the seasonal high water table. A soils engineer or septic system designer can identify the approximate high water table by examining the soil in a “deep hole” test, or get precise measurements with monitoring well. You don’t want you basement to be a swimming pool part of the year.

On a flat site you also have the issue of where to direct runoff from the roof and foundation perimeter, and where to dispose of water from the sump pump you may need. It’s best if you can drain to daylight on a sloped site. Other options are a drywell located away from the house or a storm sewer where this is allowed.  Ideally, you want the ground to slope downward about 6 in. over the the first 10 ft around the foundation.

If you are set on building a full foundation, you have little choice other than to bring in a lot of fill. You could potentially have a walk-out on one side of the house requiring less fill, but need to make sure that the footings on all sides of the house extend to below the frost line. You also need to make sure the fill is properly compacted or you will have excessive settling around the house, potentially lowering stairs, walkways, driveway and other paved and unpaved areas around the foundation.

You will need to get creative to make the grading look natural and fit in with the surrounding landscape. A good landscape designer or landscape architect might be a valuable resource for coming up with a cost-effective and attractive solution. Best of luck with your project!

Terry responds: Thanks for the prompt reply!  We had a soil boring test done on the property and it indicated that signs of seasonal high water table had been at 28 inches and 36 inches below grade. Would you consider this to be ” higher than average”? We live in Southwest Michigan.

We really like this property and the location is perfect for us- we just want to be sure that if we build our dream home on it we dontt end up with water in the basement or any moisture / mold issues.  There are three other homes on the street- plus two more being built.  Two have full basements (8 ft) and one has what looks like a daylight basement…

Steve Bliss, of BuildingAdvisor.com, responds:  This is definitely a higher than average water table – good if you want to make a pond; not so good if you want a full basement (or a septic system).

Any time the water table is above the level of your basement floor, you will have water in your basement unless it is built waterproof like a boat, which is very expensive and difficult to achieve. And even boats have bilge pumps!

You may end up running one or more sump pumps continuously during the springtime and that still may not keep up with the inflow of water. You also have the problem of where to dispose of the water from the sump.

It’s possible to build a dry house on a wet site, but it takes extra effort and money and a knowledgeable builder. Well-designed  drainage around and under the foundation are essential, along with a high quality vapor barrier under the slab.

Foundation drainage should include footing drains around the foundation and a thick layer of compacted granular fill below the slab. Drain pipes under the slab are also advisable on very wet sites. All foundation drainage pipes must lead the water safely away from the foundation or they will simply create a catch basin that will fill up and leak into your basement.

But good foundation drains may not be enough on a very wet site. Foundation drains are a secondary defense. The primary defense is managing water before it reaches the foundation.

Surface water can usually be managed by good grading around the house, but on a flat site like this that typically requires a lot of fill to raise the grade around the house.

Sometimes the water table can be controlled around the house by using curtain drains (also called “French drains” or “trench drains” — see photo above.) Engineers call these “dewatering” techniques. The effectiveness depends on a number of factors such as soil type, amount of surface and ground water, and size and slope of the trenches. These techniques are also challenging on a flat building site.

Basement waterproofing, as opposed to the typical “dampproofing” can also help. However these systems can get expensive and are rarely 100% effective at keeping out water.

You might want to get the opinion of a professional engineer (civil or geotech) experienced with residential foundations. High water-table problems can be quite complex and difficult to solve.

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