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Crawl Space Waterproofing - Fixing Groundwater Leaks

You can repair your crawl space yourself if

  • You have the time and motivation
  • You aren't claustrophobic
  • You don't mind getting very dirty
  • You have the tools required
  • You can get the right materials
  • You aren't afraid of any bugs being on you
  • You are physically fit.

Otherwise, find a contractor who is trustworthy, reliable, and an experienced expert in crawl space repair. 

There are three steps to totally eliminating the dirt crawl space from having any negative effects on the rest of the house.

Some crawl spaces don't leak when it rains hard. If this is you, go to step two. If your crawl space does leak when it rains hard, even if it's only once in a while, then you have to do something to control the groundwater, before you isolate your home from the earth by putting a plastic liner or a concrete floor in your crawl space.

If you don't know if your crawl space leaks, do a careful inspection to look for signs of water pooling in the low areas. Most crawl spaces have a lowest spot, or perhaps even several areas that are lower than the rest. Look in these areas carefully with a good light. When water ponds there, even if it's only once every few years when it gets really wet outside, you will see signs of that happening. Look for waterlines, rings of silt and fine soil particles that washed down to the low areas, or erosion patterns in the soil where the water made its way from its entry point to the low spot.

The first thing that must be done is the installation of a sump pump. To install one, you first need a hole to put it in. A sump liner must be installed to keep the sump out of the mud, and to collect the water from the ground. sump pump linerA hole must be dug at the low spot of the crawl space that is 22" deep and at least as wide. The soil can be removed or spread around in the crawl space to fill other low areas, or to crown the middle a bit. The idea is to have the crawl space floor pitch down, even if only slightly, towards the sump hole, and not have low areas where water can puddle before it gets to the sump hole.

Next install a sump liner in the hole to keep the mud out and provide a nice housing for the pump. In crawl spaces that are very low, the liner may have to be cut in half to even fit in there to begin with, and can be reassembled once in place.

Some crawl spaces exist because there is rock ledge that the builder did not have the means or desire to remove to dig a basement. In these crawl spaces you can poke around in any dirt that is there for the spot where you can dig the deepest without hitting this rock, usually farthest away from the highest part of the rock. In some cases with rock ledge you cannot get a sump hole 22" deep and have to settle for as deep as you can get; 10" being an absolute minimum.

The sump liner should be sturdy, and have lots of holes in it to allow water from the ground to enter and be pumped out. It should also accept an airtight lid. There many products designed precisely for this purpose. 

A sump lid that is sturdy and airtight is very important because you are trying to dry the crawl space out completely. You don't want an open hole with water sitting in it, to evaporate up into your crawl space environment.

The sump pump is next. I recommend a pump that is 1/3 hp, cast iron, and that has a mechanical float switch. Pumps with pressure switches or "ball on a wire switches" should be avoided. A check valve should be installed on the discharge line very close to the pump. The discharge pipe should be 11/2" PVC pipe and run to the exterior of the house.

A proper sump discharge line location will vary from property to property. The idea is to get the water to run to a place in the yard where it will continue its flow downhill and away from the house once it comes out of the discharge line. If you have good pitch away from your house then you may not need to run it very far. If your yard is relatively flat, then you may have to run it farther. We have run discharge lines from 3 to 103 feet away from a foundation.

Some pumps don't run very often and it's not a big issue, and others run quite often. The good news is that you can always extend or move the sump discharge location later if the first location proves to be unsuitable.

There are a few other important elements to a proper sump pump installation in your crawl space. First, an alarm to tell you if the pump is not running. There could be a circuit breaker tripped, the pump may be unplugged, or the pump could fail for some reason all things you want an alarm to tell you before your crawl space floods.

Also, plumbing leaks must be accounted for. Sump installation is only part of the solution to the problem and will be installed along with a heavy plastic lining in your whole crawl space. If there is a plumbing leak, you don't want your plastic-lined crawl space to fill with water, but you want it to go down into the sump hole instead. But the sump pump has an airtight lid on it. The solution? a floor drain in the airtight lid that lets water go down but damp air cannot come up.

If you don't need a sump pump in your crawl space, an alarm that will alert you to plumbing leaks should be installed on top of the plastic crawl space liner in the low spot.

Another important feature you want to include in your sump is a stand for the pump to sit on that allows silt that washed into the sump hole to go to the bottom without getting sucked up by the pump. Many pumps can pump muddy water, but this only clogs the discharge line at the check valve, so it's not a good practice. Besides, you don't want to be pumping soil out from under your house, which could possibly cause voids and settling.

SuperSump has all the components specifically designed to meet all the important criteria detailed here.

Once the sump liner is installed, the space between the sump liner and the hole you dug in the ground should be filled to the top with clean stone, such as crushed stone or river rock. This stone zone will allow water from the surface of the dirt (under your crawl space liner which is the next step) to drain down into it and through the holes in the sump liner to be pumped out by the pump.

Unless you have an automatic generator for back-up power in your home, a battery back-up sump pump system such as the UltraSump System is recommended. This system includes a second DC operated pump, a second switch, a special long term stand-by battery, and a matched smart charging system and control unit. If the water rises above the point where the primary pump should turn on for any reason including a power outage, then the secondary pumping system will automatically operate to pump the water out. In addition, there is an alarm that alerts you that the pump is running on battery power, so if there is a malfunction with the primary pump, or there is no power to the primary pump, you have time to get the primary pump going again before the battery goes dead.

In many crawl spaces, the sump pump will be all the drainage needed before moving to step two, the installation of a crawl space liner. This depends on the grade in your crawl space. Remember that the water comes in at the perimeter of the crawl space. We don't need to keep the dirt floor dry, like we would need to keep a basement floor dry if we were waterproofing a basement. We just need to keep the water from pooling, and allow it to run to the sump location. If we can regrade with a small rake or hoe to make paths for the water to flow to the sump location, then that's fine.

Another option is to dig a shallow trench at the perimeter to make the water flow to the sump location. In extreme cases you can dig a deeper trench and install a perforated PVC drainage pipe, and even add stone around it but in most cases this is a waste of resources and not necessary to accomplish what you need to.

Once the groundwater leakage situation is under control, check a few things outside. First extend all the down spouts away from the foundation if they aren't already. Sometimes extending them 5 or 6 feet away can cut down the amount of water going into your crawl space quite a bit. Also, look for holes along the foundation, or a grade that pitches towards the foundation. Obviously, you'll want to fill these in. The gutters should also be kept clean to prevent roof water from dropping right down along the outside of the crawl space walls.

If you have an occasional crawl space water problem, do not extend a downspout or two and call it fixed. Even in cases where it makes a big difference, it will almost never prevent your crawl space from leaking completely all of the time.

The downspouts from the gutters should never be connected to a perimeter footing drain around the outside of your crawl space. Instead, either run separate below-grade pipes for the downspouts away from the house, or direct the water from each downspout to the surface but away from the foundation.

International Residential Code - available for purchase from the International Code Council

US Department of Energy - Crawl Space Moisture Control