Where's the moisture coming from?
Water or moisture in basements comes
from two sources. One source is indoor
humidity that condenses on cold surfaces,
much like water droplets form on
a cold drink on a humid day. The other
is water—or water vapor—that comes
from outside. Rainwater, melting snow
or groundwater can saturate the soil
around your foundation and leak in.
Water can leak through cracks, or it can
penetrate porous concrete or masonry
walls in the form of water vapor. And
basements can be wet from a combination
of indoor humidity and water from
outside. So your job is to figure out
what’s causing the problem and, starting
with the simplest fixes, work on
solutions. Photo 1 shows a simple test to
help diagnose your basement moisture
problem. But before you go to the trouble,
read the rest of this article for other
clues. The problem may be so obvious
that you can skip this test and get right
to solving the problem.
Get rid of excess humidity
When humid air in the basement
comes in contact with cool surfaces
like concrete or block walls, concrete
floors or cold water pipes, it condenses
into water. Then the condensation
drips off pipes and runs down walls,
leaving your basement wet and clammy.
The humid air that causes condensation
can come from outdoors, or
indoors from a leaking dryer vent, an
unvented shower or even a humidifier
left on by mistake. Water droplets forming
on cold water pipes or the outside
of your toilet are a clear indication that
at least part of your wet basement problem
is caused by condensation.
Eliminating the sources of humid air
will help dry out your basement.
Repair and seal your leaking dryer vent
(Photo 2). Add a vent fan to your basement
bathroom and make sure your
family turns it on during showers.
Keep your basement windows closed
during humid weather. And if you’re
still getting condensation on cool surfaces,
run a dehumidifier to lower the
indoor humidity. Air conditioning also
dehumidifies air, so if you have central
air conditioning, make sure the basement registers are open. Consider
adding air conditioning ducts to the
basement if you don’t have any.
Insulate cold surfaces to prevent condensation
Condensation dripping from cold pipes
or collecting on cool basement walls can
contribute to basement water problems.
Reducing the humidity level in the basement
is the first step, but in addition, try
insulating cool surfaces. Wrap cold
water pipes with foam insulation (Photo
3). Install a toilet tank insulating kit
(search online for “toilet insulating kit”)
or replace your toilet with one that has
an insulated tank. Reduce condensation
on exterior walls by insulating them
(Photo 4 shows one method). But don’t cover the
walls with insulation if water is leaking
in from outside; you’ll just create a
potential mold problem. Note: For more
information on insulating, search “insulate” on this site.
Keep water away from the foundation
If your basement leaks after heavy rains
or after snow melts, making sure water
is diverted away from your foundation
may solve the problem. It’s common for
the soil alongside your house to settle
over time, creating a moat that collects
runoff and directs it down your foundation
wall and into the basement.
Lawn edging and gravel along the foundation
can make things worse. The edging
acts like a dam, and the gravel can
hide the fact that the ground slopes
toward the house (Figure A). The fix isn’t
technically difficult; it’s just a lot of
Start by inspecting the ground
around your house to find areas that
are level or sloping toward the foundation.
If only one side of your basement
leaks, then start your inspection on that
side of the house. Figure B shows how to
slope the ground away from the foundation.
Unfortunately, this solution
may require you to dig up existing
foundation plantings, remove gravel
and landscape edging, and haul in
additional soil to raise the level next to
the house. But it’s worth the effort
because there’s a good chance this fix will prevent additional water problems
in your basement.
Start by creating a 6-ft.-wide slope
that drops about 4 in. away from the
foundation. For extra insurance, cover
the sloping soil with a layer of 6-mil
poly. Then hide the poly with mulch,
gravel or a layer of soil covered with
grass. This will keep water from soaking
in near the foundation.
Figure A: Basement Leak Problem
Figure B: Basement Leak Solution
Figures A and B: Basement Leak Problems and Solutions
As the soil settles around the foundation, water is channeled back towards the house instead of away from it. The solution (Figure B) is simple—add soil and create a slope away from the house.
Add gutters and extend downspouts
If your basement leaks after it rains and
you don’t have gutters, consider adding
them. Gutters catch the rain and channel
it to the downspouts, which direct
it away from the house. Whether you’re
installing new gutters or already have
them, be sure the downspouts have
4- to 6-ft. horizontal extensions to
move the water away from the house
The next time you get a heavy rain,
put on your raincoat and go outside to
see if your gutters are doing the job. If
water is gushing from your downspouts
and still overflowing the gutters,
you should install additional
downspouts or replace your standard
2 x 3-in. downspouts with larger, 3 x
4-in. downspouts to increase the capacity.
Also notice where the water is
going after it leaves the downspout. If it
looks like water is pooling in the yard,
one solution is to install drainage tubing
that leads to a dry well.
Plug holes and cracks in the foundation
Holes and cracks in your foundation
can let moisture and water seep into
your basement. Plugging them probably
won’t solve basement-leaking problems,
but along with the other solutions
we’ve suggested, it’ll help.
Hydraulic cement works great for
patching holes in a foundation because
it can set up even under water, and it
expands as it sets to seal the hole and
lock the plug in place. Use a cold chisel or an angle grinder fitted with a masonry-cutting
disc or diamond blade to
enlarge the hole or crack into an inverted
“V,” with the narrow part of the “V”
on the surface of the wall. Then follow
the package instructions for mixing and
using the hydraulic cement (Photo 6).
Coat the walls with masonry waterproofing
If your basement leaks periodically
after it rains or when snow melts, or if
the aluminum foil test (Photo 1) reveals
that water vapor is seeping in from outside,
waterproofing the walls on the
inside can help (Photo 7). Waterproofing
materials that go on like paint fill the
pores in the concrete or masonry walls
and prevent water from leaking in.
To be effective, these coatings
must be applied to bare concrete or
masonry walls. Start by removing loose
material with a wire brush. Then clean
off any white powdery “efflorescence”
masonry cleaner. Follow the safety and
application instructions carefully.
A common mistake when using
masonry waterproofing products is to
spread them too thin. The goal is to fill
every pinhole to create a continuous
Crystalline waterproofing material is
another type of waterproofing coating.
the surface and reacts with chemicals
in the concrete to form water-blocking
crystals. You’ll spend a little more for this option, depending on how porous the walls are. Check online for suppliers.
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Install a drainage system
If you’re still getting water in the basement
after sloping the ground away
from the house and adding gutters and
downspout extensions, then a drainage
system may be the only solution.
Drainage systems installed below the
basement floor level on the outside of
your foundation are very effective, but
this approach is only practical while
the house is under construction and
access to this area is easy.
There are two other options for existing
basements. You can buy a channeling
system that glues to the floor around
the perimeter of the basement. The
channel diverts water that leaks into the
basement into a sump pump. This system
is easier to install than one that’s
buried under the floor. The disadvantages
are that the channel is visible
above the floor, and the effectiveness of
the system relies on creating a waterproof
seal between the channel and the
basement floor. You’ll also have to
install a sump basket and sump pump.
The second option, drainage tubing
below the basement floor that’s connected
to a sump basket and pump
(Photo 8), is more expensive and difficult
to install, but it’s the best permanent fix
for chronic basement leaks. You can
install a system like this yourself, but
breaking out the concrete floor, burying
the tubing, and patching the floor are a
lot of backbreaking work. Materials to
do an average basement will cost $600
to $1,000. Expect to spend $3,000 to $8,000 for a professionally installed system in a standard-size basement.