Protecting homes from water infiltration

Across the northeast, many thousands of basements and crawlspaces have taken on water. I’m sure this will cost tens or hundreds millions of dollars to fix. A sizable number of these instances could have been easily avoided. Here are some quick thoughts from someone who diagnoses and fixes buildings for a living. Comments here are limited to rural and suburban homes not located in a flood plain.

First an anecdote regarding one of the houses I was in last night. Late in the evening one of my neighbors knocked on my door to help another neighbor who she said had around 2″ of water in their basement. I grabbed boots and a headlamp and headed over. Once in the basement I found the owner and 2 other neighbors pushing water towards a sump pump in the rear corner. The water problem was so serious that they noted a nearby basement window well was full of water, which was running down the wall and back into the sump. 

<This might sound strange, but water infiltration is actually a window into the centuries old feud between religion and science, except that we currently live in something resembling the 1600s. Consequently, a great majority of people adhere to a religious perspective, which stipulates that the gods put water in basements, and there is nothing you can do to stop the basement water gods, aside from being a good person generally. Conversely, the profoundly unpopular scientific view stipulates that water in basements actually originates somewhere other than the basement, and remediation of water infiltration should see considerable effort devoted toward the prevention of water entry. Back to the story.>

Being an adherent to the scientific camp, I proceeded outside to investigate potential sources of water infiltration. Once there I discover that the sump outlet was directing most of its water into the window well. So three dudes pushing water into a sump that pushes water into a window well that leaks back into the house in an infinite loop, while Yakety Sax loudly plays in the background (maybe the music is just in my head). 

My purpose here isn’t to ridicule my neighbors. It’s simply a window into the shortcomings of the nearly universal approach to this problem. In my experience the great majority of basement water infiltration is due to very remedial problems compounded by homeowners’ and technicians’ lack of sophistication, buttressed by their deeply held conviction that they’re a lot smarter than they are.

For every 1.5″ of rainfall, each horizontal square foot of your home will manage roughly 1 gallon of water. The footprint of most single family homes is probably over 1500 sq ft (think overhang, garages, porches, etc), which means that a lot of houses last night saw 6000 gallons. In a heavy rain, a single downspout and the ground around it might see over 1000 gallons of water. So this system has to have high integrity. What are some common problem areas? 

  • The roof  deposits the water into a gutter via a flashing connection (drip edge) which directs water from the roof into the gutter. This drip edge has to be over the gutters. Gutters are often placed over the drip edge, which can direct water behind the gutter.
  • The gutters must be sloped to downspouts (not aggressively 1/16″ per foot is fine) or they will overflow.
  • The gutters must be free from debris or they will overflow.
  • The gutter connection to the downspout must be robust, and the cutout from the gutter must be adequate (read that carefully – a large number of gutters simply have a hole to the downspout that’s too small). 
  • The downspouts and sump outlets should deposit water at least 10′ from the foundation where the grade slopes away from the house. (A corollary to this that I may cover later is that we usually don’t go over 20′ and we avoid tying multiple downspouts/sumps together!)
  • I prefer to use 4″ PVC sub-grade to daylight wherever I can. Horizontal downspout extensions get stepped on by people with lawnmowers. Corrugated pipe extensions get knocked loose. 
  • Houses where the ground slopes toward the house may need to use grading and landscaping to direct water to the sides. 
  • Downspouts are often located in intractably stupid places, i.e. where water simply can’t be managed from the ground. Look up! Can you eliminate that downspout and pitch the gutter towards a different downspout? Can you redirect a substantial amount of water from an upper roof to an alternate downspout? At least half the homes I see have a significant opportunity to redirect water before it hits the ground.

One of the most effective ways to evaluate your drainage system is to walk around your house during a torrential rain. Look at every part of the system from the roof-flashing-gutter-downspout-drainage system. Does water pond against the house? Can you redirect it? 

For advanced diagnosticians, here are some handy tips for interpreting symptoms and the nomenclature of homeowners or techs: 

  • Efflorescence is characterized by salt deposits on the inside of masonry walls. This will form in areas with longstanding moisture problems, meaning the foundation is staying wet for a very long time. Check for water sources on the outside. I play a fun guessing game from inside the basement called ‘where are your downspouts? Oh, there they are!’ 
  • “My house has high water table.” = Water is getting into my basement and I don’t know why.
  • “This whole neighborhood has high water table.” = My neighbors are idiots too. 
  • “The water is coming in through the floor.” = I don’t know where the water is entering and I’ve confused the low point in my basement slab with the point of entry.

Hope someone finds this helpful!


  • Comments (12)

    • 2

      With our soil around here and the large storms that come thru, basements are very rare in our area.  

      • 2

        That’s fair, and not installing a basement is a good way to prevent basement water infiltration. However, basements tend increase in popularity the further north you go, probably due to code provisions around increased depth below frost line for foundations. Once you’re required to put your footings 4′-6′ below grade (and de facto extend the foundation nearly a foot above grade), the marginal cost of making a full basement is pretty low, so a lot of people are going to choose to have one. 

        I’m somewhat surprised frost-protected shallow foundations haven’t become more popular in cold climates, as they give pretty good access to slab foundations in cold climates at low cost. See https://www.homeinnovation.com/~/media/Files/Reports/Revised-Builders-Guide-to-Frost-Protected-Shallow-Foundations.pdf

    • 2

      Good afternoon JEsse,

      Now if only (“If” is a famous word !) the Feds would stop subsidizing houses ON a flood plain.

      Harris County / Houston was not an adverse weather problem.  It was a sand castle built at the low water mark and builders thought it would remain there.

      Like Redneck’s Mississippi, only a rare basement found around the Chesapeake Bay. 

      Good info above I will be mentioning to a few colleagues here.

      Have a happy and safe Labor Day weekend celebration.

      • 3

        I figured I’d annoy enough people with the original post without getting into that, but yeah. And just generally inhabiting areas where humans shouldn’t live is an interesting topic. 

    • 2

      Thank you for this very good information Jesse Smith, it is very helpful for me in my current circumstances of looking for a house to buy right now. 

      I have seen many houses over the past few months of looking and almost all of them have no gutters, totally useless and broken gutters, ones that deposit the water right next to the house, or ones where the roof overhangs the gutters completely. I’m blown away that all of these home owners don’t have any sort of water removal ability. 

      One house had the basement actually flooded when we were there looking at it!

      Because of all this incompetence/laziness in water runoff that I’ve been seeing while house hunting, I have been studying about different remediation steps and techniques to prevent further issues from occurring. And I saw many people recommending the same techniques that you do here. 

      So you say my down spouts should be pouring the water at least 10 feet away from the foundation? Do you have any pictures of your ideal setup of this? You say using 4″ PVC to daylight. That must be a pain to mow around and is an eye sore if it’s what I’m thinking about. To get that water 10 feet from the house, I think I will want to invest in trenching an underground pop up emitter like this or a dry well that leaches the water into surrounding dirt.

      I’m hoping to add some rain catchment system into my downspouts to help aid in watering our garden when we want it.

      Thanks for your help, and yes I did find your post very helpful indeed. Especially the efflorescence. That was a tip I didn’t know about.

      • 2


        Looking for houses can definitely be frustrating! 

        I prefer to connect the downspout to an adapter for 4″ PVC, then use a 90 degree elbow below ground. I generally don’t glue the adapter just in case I need to pop it in the future to snake a clog (rare but not inconceivable) I don’t like any horizontal drainage components above ground if I can avoid it, because stuff tends to get knocked loose or damaged. Pop-ups are fine as long as they’re not excessively restrictive. I’m more apprehensive about dry wells because of the sheer volume of water that an individual downspout might see (>1000 gallons being fairly common over the course of a few hours). 

        The presence of efflorescence can be a useful indicator of moisture, but it gets a bit tricky for new home purchases. In cases where efflorescence is present, someone may have resolved a longstanding moisture issue and just not cleaned the wall. Alternatively, infrequent but severe flooding won’t generally result in efflorescence. However, where present you definitely know that at some point there was a longstanding moisture issue. Also, the correlation between interior location and improperly managed downspouts is probably like .8 or something. 

      • 2

        Thank you for your answer and advice on the pop-ups and dry wells. Can I ask a follow up for more clarification? 

        It sounds like you do that adapter (thanks for that link), then 90 degree elbow it below ground, but what do you do on your house and recommend others do beyond that? Do you pipe it to the street, have a pop-up, or a dry well?

      • 1

        In general, I’m way less conservative with my own house, so sometimes answers to that question can be misleading. However, in this case my place is pretty normal. PVC to daylight on the front of the house where there’s aggressive sloping away from the house. Rear yard has a problematic downspout that goes to a pop-up in a natural depression on the side yard. 

        I generally avoid using a dry well due to the capacity problem. Street can be OK, depending on proximity of the house to the street (long runs of pipe are susceptible to clogging) and whether or not local authorities will allow you to do so. Environmentally, it’s better to buffer your groundwater across the site as much as you can, although there are many instances where this isn’t viable. 

    • 2

      Great topic and post, Jesse. As a new homeowner, I’ve been dealing with water infiltration issues. The majority of the problems ended when the leaf guard style gutter covers were removed and the gutters were cleaned. Debris from trees mixed with asphalt shingle particles created a mat over the openings to the downspouts. Water was bouncing off the roof and ricocheting back toward the garage foundation and flowing down the foundation through gaps onto the garage floor. The previous owner (and I) thought that the leaf guard style gutter covers would have prevented such a problem, but no.

      A previous owner had remodeled the home decades ago, adding rooms and a garage, yet keeping the same number of downspouts, just relocating them. Too many square feet of impervious area and downspouts too small. I’m told that replacing 4″ downspouts with 6″ ones in the problem areas would help.

      I am having a “rain garden” installed when some grass is being torn up in one corner of the yard. That will guide some drain spout water farther away from the house. My area had the first or second wettest August since records have been kept over 100 years ago. Extreme weather events are changing how water drainage needs to be handled.

      Best regards to you.

      • 2

        I’m sort of ambivalent on leaf guards. Seems like sometimes OK, consistently awful in valleys or other areas that deposit large quantities of water into gutters. 

        Large gutters can be part of the problem too, but make certain to check for some of the specific problems I mention, especially drip edge connection and gutter to downspout transition! 

    • 2

      Oooh, good stuff. Using the helpful translation guide at the end of your post, I’ve concluded that my partner and I and everyone in the neighborhood where we own our house are idiots. Fortunately, we’re idiots without a basement, and when we lived in that house we managed water on our property very actively*, but when we move back I’ll dig into this post and see if it points us to new insights and solutions. Thank you!

      * Perhaps someday I’ll provide a translation, but to be totally fair to us, our house came with some incredibly stupid attributes and that have necessitated some incredibly creative workarounds.

      • 2

        Ha! Please don’t take that part personally! Creative workarounds are the best!