DRIP…DRIP…DRIP… A Guide to Leaky Basements

Posted by on Mar 14, 2017 in Housing | No Comments

No, that’s not the sound of that old leaky faucet, it’s the water leaking into your basement. Basements are great; while they’re the perfect space for extra rooms or storage, basements are notorious for leaking during wet weather. There are all kinds of reasons why water might be coming into your basement, and we will be exploring all kinds of ways water tries to find its way into yours.

Concrete Foundation Walls

First of all, all concrete cracks. There is no concrete foundation wall without some cracks even if just hairline. This is because concrete is installed as a wet paste, and as it cures, it shrinks some and cracks to relieve internal tensions. These are called shrinkage cracks. For the most part, these types of cracks are benign, but they do sometimes leak. I’ve seen them go anywhere from just a wet spot on the wall to water barely leaking through the crack to water squirting out like a water fountain. In most cases if the water leakage is small, the crack can be sealed from the inside by either epoxy or urethane injection techniques. A licensed installer drills a series of holes along the length of the crack and inserts small tubes that look like straws. The length of the crack is then covered with a heavy caulking-type material that seals the surface of the crack. The epoxy or urethane is then injected into the tubes until the full length of the crack has been sealed. This method provides very good coverage to the cracks and typically seals most of the depth of the crack. In my experience, this type of sealing performs really well and keeps the majority of water from leaking through. If you go the epoxy route and do not like the appearance of the epoxy and straws sticking out of your wall, you can have them ground flush with the face of the concrete. If you choose urethane you can’t grind it down; it is softer, so it doesn’t work well when it’s exposed.

Concrete Block Foundations

Concrete block foundations by nature have large open cores in the middle. They have a thin concrete face on both sides and thin webs that connect the faces together to form the block. Because the cores are hollow, they typically allow water that seeps through the exterior to drain to the base where the water can leak into the interior. Because of this, there are no easy ways to seal concrete block. There are many systems on the market that cut out the floor slab on the interior side of the foundation wall and install a drainage system and a slot drain at the base of the wall that captures water coming through the wall and lets it drain to a sump pump. The sump then pumps the water away from the house. Some of these systems work and others don’t. For small amounts of water, having a slot drain at the bottom of the wall allows any water draining through the wall to weep into the gravel bed below the floor slab so it doesn’t drain onto the floor slab. Larger amounts of water draining into the basement will get captured in the drain system and be ejected by the sump pump. There are several things a homeowner should watch for with this type of system:

  • The sump pump outlet should be extended far enough away from the house and should outlet to a drainage system to keep the water from cycling back into the basement. I have seen professionally installed systems where the sump pump outlet is so close to the house that the water just seeps back into the basement.
  • Some systems attach a plastic panel to the wall to provide a channel to direct any water coming through the wall to flow into the slot drain at the bottom of the wall. Make sure you are okay with the look of this system before you sign the contract.
  • Drilling holes through the bottom of the wall helps allow water to weep into the drainage system. There are different types of concrete block, so the contractor should make sure to drill all the cells along the walls that are being treated.
  • Removing the concrete slab at the base of the wall can allow the foundation wall to push inward due to the pressure from the soil at the exterior of the wall. A well thought out system will allow the replacement slab to have some contact with the foundation wall at points along its length to hold the base of the wall in place and keep it from sliding inward.

Old Stone Foundation Cracks

Most foundations have cracks. Old stone foundations have cracks all over and are typically very porous. If you have a 19th century or earlier house with a stone foundation, you should expect your foundation to leak. If it doesn’t, count your lucky stars. Since stone foundations were constructed before the introduction of Portland Cement, the mortar holding stone foundations together was made of sand and lime. This porous material loses strength over time. Stone, as a natural product, is also very rough on the surface; this combined with the soft mortar joints make stone foundations very hard to waterproof from the inside or outside. Consequently, they are notoriously leaky. Drainage boards (dimpled boards or plastic matrix sheets that lay against the exterior face of foundation walls and provide a channel for water to drain) can be an effective way to divert water away from the foundation, but water can still sometimes get hung up on rock ledges as it’s working its way to the foundation drain. Of course, none of this retrofitting comes cheap. In order to install drainage boards and a foundation drain, the full perimeter of the foundation needs to be excavated to its base (remember that most stone foundations only extend to just a couple inches below the basement slab, so don’t over-dig for your foundation drain and undercut your foundation wall). Backfilling with free draining gravel is generally the best choice, and only fill to 2 ft below the ground surface. Cover the gravel with a filter fabric and fill the last 2 ft with soil. Be sure to slope the top of the ground 6 in over 10 ft away from the foundation wall to help water drain away from the foundation.

I once owned a house built into a hillside in 1906 with a stone foundation wall. It leaked terribly; rain water would work its way down the sloping hill in my backyard, and my foundation wall acted like a dam to keep it from flowing further. Well my dam leaked, and water would weep through the wall in all kinds of locations. I eventually installed a French drain (a deep trench with a drain pipe in the bottom that is filled with free draining gravel) out from the foundation wall. This was effective most of the time, but heavy rains still caused some leakage. Old house owners with a stone foundation usually just learn to live with some level of leakage in the basement.

Moist Basement Tips

All basements feel moist because they are below the ground and tend to have a higher relative humidity because of that. I have found that running a dehumidifier during the warmer weather months really helps the air quality in a basement. I usually start mine around late March or early April and run it through the end of October. The dehumidifier will strip water out of the air and collect it in a bucket that needs to be emptied every day. Another option is to locate the dehumidifier near a floor drain and to run a drain hose to the drain. I like to enhance the dehumidifier with an oscillating fan that runs constantly. This keeps the air circulating and allows for a more uniform removal of the humidity in the air. Moist areas in the basement can have a dedicated fan to keep the air moving.

Preferred Drainage Approach

For most structural engineers, we prefer to attack drainage issues from the source. This means that water should be captured on the exterior before it has an opportunity to get into the house. The following are several methods for alleviating water issues on the exterior.

Regrading

Storm water needs to stay away from the foundation of a house. If your yard slopes toward your house and storm water cannot go anywhere except to your foundation, then the water will find its way into the basement. Yards can be regraded to slope away from the foundation. The building code suggests 6 in of downward slope over 10 ft. This is achievable in many yards, but can be difficult in really flat situations. Grading a swale in the yard to direct water around and away from your house is helpful too. You want to make sure that you are not just putting the water on someone else’s property though. Storm water should be directed to flow to a place where it can safely drain away.

Downspouts

Downspouts carry the storm water collected in the gutters at the roof line to ground level. At that point, the water is either outletted to the ground or directed into conductor lines below grade and outletted at a place hopefully away from the house. If you have to outlet your downspouts on the ground, put a splash block at the outlet to direct water away from the house. Make sure that the water does not have an opportunity to pond at the face of the foundation – it will find its way into the basement. If there are conductor lines for the downspouts, that is the best thing, but make sure the conductor lines are free-draining and that they outlet away from the house.

French Drains

Some yards hold water and are soupy swampy feeling. Water in flat areas that cannot be drained other ways can have a French drain installed to carry water away. A French drain is a 12 in wide trench cut in the yard about 36 in deep or deeper. Some people make them shallower, but the deeper the trench the more effective it is. The trench can be lined with a filter fabric if you like. A 4 in diameter drain pipe should be installed in the bottom of the trench, and should be sloped to drain to the outlet. Fill the trench with free draining gravel and continue the gravel all the way to the surface, or hold it down 6 in, cover the top with filter fabric, and then cover it with soil and grass. French drains will draw water from several feet in each direction. If you have a large wet area, you might need to add several lines of French drains to dry out the whole area. Be sure to have a utility protection agency check your yard for underground utilities before doing any excavation.  You don’t want to hit any buried electric or gas lines.

Sump Pumps

With flat yards that need swales or French drains to manage storm water, exterior sump pumps are a good method for containing the water and pumping it to a location where it can drain safely away. We prefer sump pumps that are installed on the exterior rather than the interior, because it is not a good idea to bring exterior water into the house to try and pump it away. Exterior sump pumps will need a pit of some type and an electric feed from the house. We also recommend a decent battery backup system to help keep the pump running if the electricity goes off. A professional drainage company can help with the specifics of setting up an exterior sump pump system. Water from the sump pump should be outletted to a legal drainage location. Check with local officials for an approved outlet location.

Exterior Waterproofing

By far the best (and most expensive) way to alleviate water infiltration into a basement is to excavate around the exterior of the foundation wall, clean the foundation wall and waterproof with a high quality spray-on waterproofing membrane. This keeps any water from getting through the wall in the first place.  The membrane should extend over the top of the footing as well. Add a new 4 in diameter foundation drain at the bottom of the excavation and fill the trench with compacted free draining gravel. Hold the gravel 2 ft down from the surface, cover the top with filter fabric, and cover the final 2 ft with clayey soil and top soil. The clayey soil will keep water from just draining down from the surface unchecked. The surface should be sloped to drain away from the house 6 in over 10 ft. The foundation drain should be connected to a sump pump or other system to drain water away from the house.

New Construction Tip

One of my pet peeves is when foundation contractors put pipes through the footings at the bottom of the foundation wall. Their logic is that water that is inside the basement will drain to the outside. In practice, the exact opposite occurs – water from the outside weeps into the gravel below the basement slab and can cause all kinds of problems. I’ve seen water come up through the slab and cause flooding in the basement. I’ve also seen water from the exterior saturate the interior soil below the slab so much that it causes the soil to swell and actually lifts the posts up a couple of inches causing all kinds of cracking within the house. Here’s the tip: if you are building a new house, insist that the contractor DOES NOT put any drainage pipes through the concrete footings. If they do put them there and you see them, have the contractor fill the pipes solid with non-shrink grout to keep outside water out of your basement!

Managing water leakage in a basement is a difficult task that can take many tries before it is completely tackled. We recommend having a structural engineer who is well versed in residential water management look at your house to help you determine the best and most cost effective way to manage your leakage situation.

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