Underneath the Basement Floor

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We never think about it. What is underneath the basement floor? We are too busy enjoying the rest of the house to ponder on that thought. Our basements may be unfinished and occupied by the usual suspects; a furnace, oil tank, water heater, water treatment tanks, washer, dryer, forced-air heating system, and storage. There is no reason to be down there besides using the washer and dryer.

On the other hand, you may have a finished basement with tile, wood, or carpeted floors. You may be using it as a playroom, TV entertainment room, or a workout area. You will never think about; “what is underneath the basement floor?” It should not be a concern, finished or unfinished. One day, it may become a serious concern if a heavy downpour or super soaker floods your basement.

Beneath Your Basement Floor

Whatever is underneath your basement floor is very important because it will determine your house’s structural integrity. In most new homes, a basement floor or concrete slab sits on top of a concrete footing. The space underneath the floor and between the footing is taken up by 12 to 16-inches of backfill or loose soil repurposed from the excavation site of the home. 4 to 6-inches of coarse aggregate (usually sand, gravel, and crushed stone) is the next layer before another 4 to 6-inches of concrete is poured on top to make the slab floor.

In older homes, the building code requirements are not too strict, so the amount of backfill, aggregate, and thickness of the slab is not predictable. That is not to say that modern home builders will not cut corners to make an extra buck. Hopefully, the building inspectors are fast enough to catch a problem before allowing a crew to proceed with the foundation construction.

Water Problems

A basement will have many years of problem-free comfort as long as there are mechanisms to divert natural water sources away from the house. Here are some places water or moisture come from:

  1. Moisture comes from the humid air that condensates on cold pipes or surfaces.
  2. Bathrooms without an exhaust fan, clothes dryers with poor ventilation, and concrete still curing after construction.
  3. Water penetration from rain or groundwater.

We can correct numbers one and two immediately, but three will take a bigger intervention. Here are several things that minimize lateral pressure (the pressure produced by groundwater in your backfill area) to build upon your basement walls:

  • Roof gutters with extended downspouts to take rainwater away from the backfill area of the house.
  • The ground around the house should slope away from the house.
  • Properly waterproofed basement drainage to a sump pump.
  • A sump pump setup with a discharge pipe takes water a safe distance away from the house to avoid recycling the water back towards the basement.

Basement Waterproofing Solution

If you finish your basement without waterproofing it first, you could find yourself dealing with unforeseeable problems, such as:

  • The odor is produced by mold and mildew.
  • Buckling tile, damp wood, or carpet.
  • A sticky feeling generated by humidity in the air.
  • Condensation forming on surfaces.
  • Exposed concrete will show efflorescence or red staining from the breakdown of lime in concrete.
  • Standing water on the floor.
  • Decaying wood molding around doors and windows.
  • The problems stack on top of one another, creating a structural issue and a health hazard with growing mold and mildew added to the mix. So, as long as you keep water away from the house, you will also keep water from coming under your floor.

That area under your basement floor will have water making its way up after every rainstorm. Bear in mind that only one-inch of rain equals over 1,200 gallons of water falling on the roof of a 2,000 square foot home. That rain will also travel through underground capillaries, adding more to the backfill area around your home; it will eventually pass the hydrostatic line and create lateral pressure on the basement walls.

At this point, water begins to rise under your basement floor. Every time there is a big rainstorm that goes on for a few days or torrential super soaker hits in late August, the area under the slab will become damp and displace the aggregate and soil underneath the slab flooring. Repeating this action, year after year, will eventually create a big enough pocket of space to comprise the integrity of the floor, and it will crack.

American Dry Basement Systems will make sure it never gets to that point if you call them before the problem happens. Moreover, if it does happen, we will be there to make it better than it ever was before and keep it dry for a lifetime. We understand basements, crawl spaces, and foundations like no one else. Contact us for a free, no-obligation inspection and quote; you will be glad you did.

What are Basement Engineering Tabs?

Basements should have engineering tabs made during basement waterproofing for a strong foundation. Leaving sections of your floor on the footer is vital.

backhoe making foundation clay bowl

Wet Basement Problem: False Water Table

A false water table is the primary cause of wet basements, deteriorating foundation walls, and cracking floors. It is “false” because it is temporary.


6 Ways to Prevent Basement Flooding

Basement flooding usually occurs when groundwater finds the path of least resistance. There are six things you can do to prevent flooding inside your basement.

monolithic slab foundation with poured concrete walls

What is a Monolithic Slab Foundation?

A monolithic slab foundation is created by pouring a single layer of concrete to form a slab and footing. The construction process is faster and low cost.

Useful guide: General Permit for the Discharge of Stormwater