Few qualities are more vital to your home's health than its ability to stay dry, even in the wettest of conditions. When the home has a basement, those needs are ratcheted up even more due to the basement's below-grade level and its proximity to the water table.
A reliably dry basement expands your living space, often doubling it. A finished basement—or even an unfinished but dry basement—increases your home's value and guarantees that the home's structure and upper floors will remain in good condition.
Why Your Basement Needs to Be Dry
Your basement should stay dry in case you want to renovate it into a habitable space. Minus vital services located in the basement such as the water heater, furnace, and washer and dryer, a finished basement can mirror the square footage of the floor directly above. A 1,000 square foot home can transform into a nearly 2,000 square foot home with a smart, well-planned basement finishing project.
With this, the stakes are high to create a dry space for those renovations. Few surfaces in the finished basement tolerate moisture well: drywall, carpeting, paint, and even hard flooring such as laminate or engineered wood flooring.
If you do not plan to remodel the basement, you'll still want to keep your basement as dry as possible. Moisture can rot away building materials, including elements vital to your home's structural integrity, and mold and mildew can develop. While not all molds are toxic, some molds can produce harmful mycotoxins.
Basics of Basement Waterproofing
Basement waterproofing is not a single project. Common quick fixes like coating the inside of your basement wall or clearing gutters alone will not solve wet basement issues. Instead, waterproofing is a group of interlocking projects that coordinate to bring your basement to its driest possible condition.
Think of your house as having three concentric rings or zones—outermost, middle, and inner— that work together to keep your home's basement dry.
The outermost ring is the space outside of the home but not connected to the house itself. This includes improperly graded earth that sends water toward your house. Your goal in this area is to stop the water before it can even reach your home.
The middle ring is your home's exterior envelope. This is the exterior house itself: foundation wall, gutters, drainpipes, windows, window well covers. Here, you'll want to make sure that water-elimination systems are doing their job and that the water protection systems keep water from entering your home.
Finally, the inner ring or zone is everything inside of the basement, including the interior side of the foundation wall, flooring, and sump pump (if you have one).
Causes of a Wet Basement
- Poorly Graded Soil: Earth next to your house that is level or which slopes back to the house can send water alongside the foundation, where it can seep into the house.
- Missing or Improperly Draining Gutters and Downspouts: Gutters that are blocked can cascade water over the sides and next to the foundation. Downspouts may be missing pieces designed to send water away from the house.
- Poorly Designed Window Wells: Window wells are the pockets in the earth around basement windows. Wells can pool up with water.
- Poorly Installed Window Well Covers: Window well covers are designed to prevent debris and water from reaching basement windows. If covers are loose or missing, water may reach and infiltrate basement windows.
- Ineffective Drain Tile: Drain tile is a buried drainage system close around the outer perimeter of a house. Tile is a misnomer since it's not actually tile but pipe. This pipe may become blocked or crushed.
- Blocked French Drains: French drains are buried drain systems that can become blocked with soil or roots.
- Sump Pump Not Draining: Inside the basement, an inoperable or poorly operating sump pump cannot drain rising water.
- Water Up Through the Sump: In flood conditions, water can sometimes come into the basement up through the sump pit.
- Structural Cracks: Cracks in the foundation wall can permit water to flow into the basement.
Exterior Yard Methods of Stopping Water
Grade the Soil Away From the Home
Use a shovel, wheelbarrow, and rake to create a slope that extends downward and away from the foundation wall. A 5-percent slope is considered sufficient (about 6 inches of drop per 10 feet). Make sure that the slope extends at least 10 feet to prevent water from draining back to the house. Keep the soil away from the siding.
Develop a Robust Drainage System
Create a drainage system of catch basins that receive downspout water and move the water far away from the house along buried 4-inch sewer pipes. Bring the ends of the pipes to daylight, if possible. If not, the water can exit through pop-up drains located in the yard. Ideally, all downspout water should drain to the property line or as close to it as possible.
If it's not possible or practicable to create this system of catch basins and buried pipes, attach downspout extenders to the ends of the downspouts.
Build or Fix French Drains
Identify areas of your yard where water collects or where it moves back toward the house. Dig a trench and install a French drain. This is a perforated pipe covered with dirt-inhibiting cloth, then a layer of gravel, and then refilled with earth and sod.
For windows or other basement openings that extend below-grade in flood-prone areas, water-tight barriers can be constructed that act as dams to hold back water. FEMA, the Federal Emergency Management Agency, recommends watertight masonry barriers or earth berms in areas that experience flooding.
Exterior House Methods of Basement Waterproofing
Add or Fix Window Well Covers
Galvanized steel or molded plastic pieces called windows wells are attached to the home's exterior foundation. Window wells can also be fitted with window well covers.
Though window wells are chiefly designed to prevent soil collapse and to keep your window clear of debris, they can help with moisture infiltration, too. Enclosing the window wells with well covers prevents water and snow from reaching the window.
Window wells scoop out a section of the earth around the window to permit light and air to reach basements and to aid with egress. As with grading the soil away from the foundation, make sure that window wells do not direct water toward the basement window.
Waterproof or Damp-proof Seal the Foundation Wall
Damp-proofing is a common method where an asphalt-based material is brushed, rolled, or sometimes sprayed onto the outer foundation wall.
Waterproofing is a more involved project where thick rolls of impermeable material are bonded to the outside of the foundation. All seams are lapped to prevent water leakage.
Some foundation waterproofing methods use a sprayed-on material comparable to the thickness of the solid materials. The product is a liquid-rubber, elastomeric coating that must be applied multiple times to achieve the proper thickness.
Fix or Add Gutters and Downspouts
While fixing gutters and downspouts might seem like one of the more prosaic ways to waterproof a basement, it's actually one of the most efficient methods—especially when the cost-to-benefit ratio is considered.
Downspouts lacking extensions drive water directly against the foundation with potentially devastating effects. So, for the minimal cost of an extension, you can save thousands of dollars in damage to your foundation.
- Fix sagging gutters so that they have a proper slope.
- Fix loose downspouts and add extensions.
- Seal gutters to prevent leaks.
- Clear out clogged gutters and downspouts.
Interior Methods of Basement Waterproofing
The best-case scenario is that you should not have to employ any interior methods of waterproofing your basement if exterior methods can do the job. But the reality of basements is that you'll often need to extend your attention to the inside.
Interior Foundation Coatings
Waterproofing coatings roll or brush onto the inside of concrete block, poured concrete, or other types of masonry foundation walls. These ready-mix products usually come in white or neutral colors but can be tinted. Application is easy and usually fairly quick, depending on the scale of the project. Most waterproofing coatings drying in about three hours to allow for additional coats.
Waterproof coatings are the last line of defense for damp or leaky walls. Most coatings have a 10 to 15 psi water pressure rating. These coatings are effective at managing damp basement foundation walls.
Sump pumps are a common feature in basements that have problems with groundwater intrusion. They can, however, also clear flooding from within the basement.
Install a sump (the basin or pit portion) plus a sump pump if your basement has water issues. If you already have a sump pump, keep it well-maintained.
Sump Backflow Valves
Make sure that your sump pump discharge line has a backflow or check valve. This prevents water in the pipe from flowing back into the sump (pit) after the pump has stopped pumping.
If your basement humidity level is more than 50-percent, likely it's too high. A better basement humidity range is between 30- and 50-percent.
You can remove excess moisture in the air with dehumidifiers. Most dehumidifiers can pull between 30 to 60 pints of water from the air per day. In cold climates, one residual benefit of dehumidifying your basement is that drier air will feel warmer than moist air.
Cost of Basement Waterproofing
The cost of waterproofing your basement ranges dramatically. If your waterproofing plan is complete except for just one element such as a dehumidifier, interior waterproofing, or gutter extensions, expect to spend $50 to $200 to bring the plan to completion.
Self-installing a window well and window well cover will cost between $75 and $200.
Hiring a professional to install French drains costs between $20 and $30 per linear foot.
Re-grading the soil by yourself requires no materials. So, the only cost would be the cost of tools.
Gutter and downspout materials are inexpensive. Ten feet of PVC or metal gutters cost between $10 and $20, with downspouts in the $10 to $15 range. Downspout extensions cost between $5 and $20.
A Brief Guide to Mold, Moisture and Your Home. United States Environmental Protection Agency.