How To Flood-Proof Your Basement

Table Stack

The First Law of Basements is “Basements Flood”.
The Second Law of Basements is “Basements Flood”.
I think the Third Law says something about spiders.

I learned the trade of home-improvement around Washington D.C., where flooding is much more common. Here in Boulder Colorado I’ve worked in many basements, which pretty much all of them were unprepared for a flood. Pointing this out, I am told that they never had flooding in their basement, and they’re not concerned about it. If the house has any age at all, there are old stains and water-damage which say otherwise. And of course, it’s a basement (see above).

Any basement can be flood-proofed, although that may not be what one thinks it is. Floods will still happen, but with less damage and a quick recovery.

Basement Rule of Thumb: Live like at any time there can be 1/2 inch of water on the basement floor for 24 hours.

BRoT Method: Look around, see what would be ruined, and throw it out. Because it might as well be trash already.

If you can follow that rule of thumb to its logical conclusions, there is no need to read the rest of this post. Also I probably miss some things below, so you should consult the rule of thumb anyway.

There are four aspects to flood-proofing (interior construction, habits, plumbing, and exterior construction), follow them and your next flood will be a minor inconvenience:

  1. Interior Construction. Floors: No painted concrete, wood, carpet or linoleum. They all get ruined by persistent moisture. Use porcelain tile, which is cheaper and easier to maintain than stone tile. You could use stone, which can be prettier, but it’s a freakin’ basement. And it’s gonna flood.
    Walls have more options. Stucco is ideal. Drywall is usually fine, if it is done right. There must be a gap between the drywall and the floor. This prevents the paper-lining of the drywall from wicking moisture off the floor and allows water to drain down the wall and evaporate in the air at the suspended bottom. It is best to use water-resistant drywall, and the woods studs should be treated or better yet aluminum-frame studs. Trim should be real wood not particle board, which is destroyed by moisture. Trim covers the gap, keeps pests out, makes it pretty. Concerning repairs, moldy drywall needs to be replaced, but mold on wood can be sanded off and painted over with Killz or other anti-microbial base paint. I attach trim with counter-sunk deck screws so they won’t rust and the trim can easily be removed and reattached to let the walls dry out. Brad-nails look better, but it’s a freakin’ basement. And it’s gonna flood.
  2. Habits: (furniture, lifestyle and storage) When placing items on the floor of your basement, imagine you are placing them in half an inch of water. Maybe you don’t want to do that. Maybe you want to build shelves, or buy plastic tubs. Perhaps what you’re saving is worth saving right.
    Furniture should be solid wood or metal, and cloth coverings should be well above the floor. Again, no particle board should be present in the basement. Papers and books should not be placed on the floor, put them on a shelf or in plastic totes. Clothing can go on the floor since it can be washed, if you get to it soon enough after flooding. Rugs are a good way to warm up your cold tile floors. If they are expensive spend a couple hundred to have them dry-cleaned after a flood, and if they are cheap spend a couple hundred to replace them.
  3. Plumbing: Municipal water enters the house through pressurized pipes, and is the cause of most minor basement flooding. In Boulder the water pressure runs high, over 100psi to every house I’ve checked, and is subject to pressure spikes (especially over holidays and when you’re on vacation). Consider shutting the water off when on vacation. Most pressurized plumbing components(copper pipes, faucets, toilet fill valve) are designed for about 40-60psi, and will fail at a much higher rate when the pressure is consistently over 80psi. A pressure regulator at the input will take care of that, unless it is old and worn out, in which case it isn’t working and should be repaired or replaced. A pressure regulator will also make your pipes less noisy.
    Sewer lines are not under pressure, are gravity-driven, and require air intake vents (those pipes on your roof) for proper drainage. U-joints exist at every drain to prevent sewer gases from backing into the house (the gas goes out the air-intakes). Most sewage back-ups are caused by blocked drainage lines rather than pressure from the street. Common causes of blockage are roots getting in the ceramic junction between the house line and the street line, cooking oil poured down the drain, children’s activities, tampons, powdered detergent, or all of the above. As in all things, prevention is the best cure. Roots can sometimes be prevented by pouring rootkill (copper sulfate) down the line in the Fall when tree roots are most active. Enzye/microbe solutions will help break down debris in the sewer line. Not flushing debris is also a good way to prevent debris. Draino is useful for killing microbes and melting holes in the pipes.
    The basement floor drain has an anti-siphon (floating plastic ball) which will prevent sewer backups as long as it is clean and in good working order. When is the last time you cleaned your basement floor drain?
    Remodels which added a bathroom to the basement also added new points of sewer back-up which lack an anti-siphon (toilet and shower). A backflow preventer (flap) or manual shutoff can prevent sewer back-ups from the street.
    A sump pump is a great all-purpose last-ditch defense against basement flooding. Most installs I’ve seen drain right outside the house and back in the window. Don’t do that. I would suggest sending the (buried) drain line all the way to the street.
  4. Exterior Construction: (gutters, roofing and landscaping) The purpose of gutters is to direct water away from the house. Without them the water just drips off the roof and surrounds the house in a moat which seeps into the basement. Gutters don’t work if they’re full of debris, but you knew that. When mine are blocked I just go clear them in the rain. There’s probably a safer, more convenient time to do that. If the water makes it to the downspout, it still is at the base of the house and draining into the basement. That water needs to be directed away from the house, which can be done with plastic tubing (can get plugged with gutter leaves), or my favorite solution: gravel-filled ditches. The gravel will prevent roots from filling in the ditch, and a heavy rain will wash out the dirt that settled in.
    The roof requires the least maintenance in this list. Regular roof repairs will greatly postpone the need to replace the whole thing, which is expensive. Boulder County experiences 100F temperatures in the Summer, 100mph winds, and daily thawing and freezing in the Winter. Architectural asphalt shingles are the most popular, durable and cost-effective roofing material used here.
    Landscaping does require some maintenance, as it shifts over time. The ground needs to slope away from the house (especially basement window) and allow water to drain around and past the base of the house. You don’t want water pooling near your house, or soon enough it will be coming in through the foundation.
    One big lesson from the Boulder flood of 2013 was that while primary creeks and runoffs were well-maintained, they were under-utilized because secondary community ditches were blocked. This led to excessive urban flooding. So landscaping concerns may need to be addressed beyond your property line.



4 thoughts on “How To Flood-Proof Your Basement

  1. asnat

    Thanks so much for the post. Where would I see this plastic floating ball in the basement floor drain? If I remove the cover, all I see is water. Because, while we were lucky and had no flood damage, I do worry about backflow and future flooding.


    1. Toby Fernsler Post author

      You shouldn’t see water. I’d guess it’s just not draining and is full of debris. Use some rags to ring out the water to a bucket so you can see what is there, probably loose rust which I pull out with a magnet on a stick. If you don’t find the ball or can’t clear it the whole drain may need to be jack-hammered out and replaced, they do have a lifespan.



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