Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.
Sweating walls, or wall condensation, is a sign of water damage that is often unnoticed by homeowners. If left untended, it can lead to mold in your basement, which can then lead to other health risks. Fixing and preventing the problem can help save your basement.
Why do basement walls sweat? Basement walls can begin to sweat when there is a buildup of water or when warm, moist air reaches the cold walls. The most common causes of sweating basement walls are:
- Inadequate grading
- Problem with gutters and downspouts
- Improperly designed window wells
- Structural cracks
- Improper drainage with under slab ducts
Poordrain tile or sump pit
- Home not adequately ventilated or insulated
- Interior water leak
When you begin to notice your basement walls sweating, you should immediately fix the problem to prevent further damage, mold, and health conditions. Understanding the causes of basement sweat can help you prevent the problem from arising. Here we will discuss the causes of sweating basement walls, how to fix them, and how to prevent it in the future.
Why do Basement Walls Sweat?
Basement sweat typically occurs when warm, moist air hits the cool walls of the foundation. That is why you’ll see the walls sweat in the basement but not in your home – because basements are typically cool.
Basement wall sweat can also be caused by indoor and outside sources that cause an excess of moisture:
- Rain or groundwater that makes its way inside
- Cooking appliances
- Letting outside, humid air into the basement
Signs of Your Basement is Sweating
There are different ways basement sweat can make itself present. But it is most commonly seen as water droplets on your basement walls and floors, especially where the wall and floor meet.
Other signs that your basement walls are sweating include:
- Standing water on the floor
- Humid air in the home
- Deterioration of wood or carpet
- Wall staining
- Ring of dampness on the wall
Why Your Basement Walls Sweat
There are many reasons why your basement walls sweat. Luckily, most of the reasons have relatively easy fixes. The following sections discuss the most common reasons that basement walls sweat and how to remedy them.
1. Inadequate Grading
When there is unsatisfactory grading, rain and groundwater can easily make its way into your basement. Grading is the level of the ground around the house. If the ground is level or sloped more towards the house, the rainwater will sit and accumulate against the foundation and then eventually leak into the basement.
This can also be caused if the fill dirt around the house is not properly compacted. After the rainwater soaks into the dirt, the dirt settles in a different way causing the slope to change. You want your house to be at the high point of your property so that water flows away from it.
How to Fix
The best thing to do to fix a grading problem is by creating a slope that goes away from the house.
To do this, you will:
- Find the low and high points, – This will be where the water starts draining and where it ends up.
- Figure out the rise and the run of your property, – The run is how far apart your high point and low point are. The rise is the inches or feet the ground slopes from the high point to the low point.
- Get some soil.
- Pour the soil at the lowest point to turn it into the highest point.
- Smooth the dirt.
- Pack the dirt.
- Plant new grass.
2. Problem with Gutters and Downspouts
Gutters and downspouts are designed to direct rainwater away from your house. So, when they are damaged, or there is buildup, they work ineffectively. The buildup of leaves and twigs causes the rainwater not to drain and be directed toward your house. When water is being directed toward your house, the water will begin to accumulate and eventually seep into the basement.
Not having an extender in conjunction with your downspout can sometimes be a worse result than not having a downspout at all. The extender is an attachment to your downspout that extends further away from your house. Without this, the rainwater leaves the downspout in high volumes and continuously hits the same spot near the basement.
How to Fix
To fix an issue with your downspouts or gutters, you can:
- Purchase a downspout with an extender. It is beneficial to have one downspout placed every 50 feet. You’ll want the downspout to be able to transfer the water at least 4 feet away from the foundation of your home.
- Check for any leaks or damages in your gutters and downspouts.
- Clean the gutters and downspouts regularly. Buildup debris in your downspouts can make them ineffective at properly dispersing the water.
3. Improperly Designed Window Wells
A window well is a U-shaped hole that surrounds a basement window. They are typically used as an emergency exit. Not having a properly designed window well can lead to many problems such as flooding from rain or snow. An improperly designed window well will be built in a way that makes water go towards the window, rather than away.
It’s common for some homebuilders to take shortcuts when it comes to window wells and not create them with proper drainage. Additionally, some drains are placed in the ground in front of the window, and homeowners don’t think to unclog them.
To see if you have an improperly designed window well or if it needs to be cleaned, you must check the wall underneath the window after a rainfall. If water is trickling down the wall, then water is not being adequately drained from the well. You will want to fix this problem immediately, so it doesn’t cause damage to your basement walls or window.
How to Fix
If you know your window well has a drain and is just now beginning to have leakage, then most likely, the drain is clogged. You should:
- Unclog the drain to allow it to do its job correctly.
- Get a window well cover to help prevent future clogs.
- Fill the window well 3/8 to ¾ inches deep with gravel or course rocks. This will help with drainage and also help prevent frost in the winter.
4. Structural Cracks
Concrete foundations eventually develop cracks for several reasons – foundation settlement, storms, extreme heat, too much moisture, and flooding are just some of them. When cracks appear in the foundation, you most likely will run into the problem of water seeping through. Too much water around the foundation can even cause the cracks.
Water causing cracks in the foundation is caused by its accumulation against the foundation walls. The pressure from the water, also known as hydrostatic pressure, can help push the water into the foundation and form cracks.
Cracks in foundations are more severe when the floor joists are not appropriately connected to the foundation walls. Floor joists are used to support a floor in an open space, so the disconnect allows the wall to move.
How to Fix
It is possible to drain water from the cracks, but the problem will reoccur and eventually get worse. So, it is best to take care of the problem in the right way. Depending on what is causing the cracks, how to fix the issue varies.
If hydrostatic pressure is the issue, then:
- The exterior drainage should be repaired
- You should have proper gutters, downspouts, and grading.
- You want the water to flow away from your house.
If the cracking is caused by a structural problem, then you should call a professional to look at the foundation to see if any significant repairs are needed. In the meantime, you can seal any cracks that have formed in the foundation, depending on what kind of material it is made of.
A concrete foundation can be filled with an injection of:
- An expanding urethane sealant
However, foundations made from stone or brick cannot be injected. These types of foundations need to be repaired using a flexible, trowel-on elastomeric membrane. If you are not able to repair the cracks outside, you can install a tear-resistant liner to protect the inside of your basement.
5. Improper Drainage with Under Slab Ducts
When there is an accumulation of standing water in the ducts, this can cause mold to form, which leads to serious health concerns. Water can also block the airflow and can transmit the growing mold as the air moves through the duct.
How to Fix
It is essential to check any heating ducts that are placed beneath the basement floor. You want them to be insulated, watertight, and sloped towards areas for proper cleaning and draining. If this is not the case in your basement, a drain tile can be installed. This is a piping drain system placed along the sides of your basement under the floors.
If the duct develops mold, you will want to clean it out to prevent moving the mold through the air. You can do this by first making a mold removing solution made from:
- 1 cup of water
- ½ tablespoon of baking soda
- One tablespoon of household detergent
Once you have made a solution for removing mold, you can remove the mold by:
- Shutting off the heating/cooling air vents
- Putting on gloves
- Using a wet rag or brush, scrubbing the areas where there is mold
- Repeat scrubbing until the mold is gone
- Placing the rags in garbage bags, tying them tightly, and throw away
6. Poor Drain Tile and Sump Pit
A drain tile is a system that makes sure groundwater does not enter your basement. The sump pit is a hole in your basement that collects any water and uses a pump to move it away from the house through piping.
If you have an old home, you most likely don’t have these systems because older homes were not intended to be habitable spaces. If your house does have these systems, they can become ineffective due to clogging, a collapsed pipe, or a broken connection.
How to Fix
If you believe the sump pump, or the lack of one, is the cause of your water problem, then this is most likely a situation you should hand over to a professional. Repairing or building these drainage systems is a difficult task. It’s a process that involves digging up the floors and fixing or adding in a whole new system.
If you have an old home, it is recommended to find out if there is a drainage system and call a professional to see if they think one will be needed for your home.
7. Your Home is Not Adequately Ventilated or Insulated
Because basement sweat occurs when warm air comes in contact with the cool walls, the issue is often caused by you and what you do in your home. Showering, cooking, and doing laundry are some activities that can cause heat to reach your basement if your home is not adequately ventilated and insulated.
Some newer homes are required to be ventilated just above the frost line, which is only the upper part of the walls that are the most exposed to exterior temperature changes. This, however, does not create a complete thermal break, and moisture can still form on the surface.
How to Fix
To check if your house is adequately ventilated or insulated, you should:
- Make sure that anything that can create condensation is insulated correctly. This would be your cold-water pipes and ductwork.
- If you have a finished basement, the floors and walls should also be insulated entirely.
- When you shower, there should be a fan running, or a window opened to help decrease the buildup of steam in your bathroom.
- If your laundry room is in your basement, or above your basement, make sure the dryer is properly ventilated to the exterior of your home.
- Make sure the vent isn’t clogged so that the hot air can expel outside and not come in contact with the cool walls.
8. An Interior Water Leak
This cause is a very obvious but common problem. When you notice wet basement walls, you should first check for indoor leaks. This could be a leak from a washer, sink, shower, toilet, dishwasher, or damaged piping. If there is a leak within your interior, it will most likely make its way down to your basement.
How to Fix
When you have an interior leak, all you need to do is repair that leak. Leaks can be temporarily fixed with epoxy putty.
To fix your leak, follow these steps:
- Identify where the leak is coming from. Water leaks typically have to do with a problem in the plumbing.
- Shut off the water supply and allow for water to fully drain
- Make sure the area is clean and dry
- Figure out how much epoxy putty is needed for the leak
- Soften the epoxy putty between your hands
- Use epoxy putty to cover the area of the leak
If it is a simple leak, you may be able to fix it yourself. However, if it is beyond your control, you should call a professional for help. The wall most likely will need to be cut for the repair to happen. Then, the wall can be patched and painted.
How to Reduce Basement Condensation
Having condensation in your basement walls not only can create mold and mildew, but it can also damage any belongings you have stored down there. Anything paper like books and pictures will absorb the moisture, and anything with metal will begin to rust. These are things you want to avoid.
Luckily, along with taking the steps needed to draw water away from your basement, there are steps you can take to protect your basement walls in case water does get through.
Seal the Ducts
We’ve discussed that improperly installed ducts can be a cause of too much moisture in the basement. But there is more you can do to these to help reduce the condensation in your basement, as well.
Once you have the proper drainage set up within the ducts, the next thing to do is to seal all the joints and holes in the ductwork. When you seal the ductwork, it should be done with duct mastic tape or metal duct tape. If you use regular duct tape, it will dry up quickly and easily peel off, which will cause you to need to replace the tape more often.
If there is an abundance of warm air getting into your basement and causing condensation on your walls, the best thing to do is to add insulation to those cold surfaces.
Adding insulation will:
- Make the cool surfaces warmer. This will significantly reduce the condensation when the warm, moist air makes its way inside.
- Prevent cold air from getting inside, which will help keep the basement warmer.
- Create a thermal barrier between cool temperatures and warm temperatures.
The most effective areas you should air-seal are the mudsills and rim joists. The mudsills are the lowest sill of a structure, in or on the ground. Rim joists provide lateral support for the joists. Insulating these will not only keep air out, but it’ll also keep any unwanted bugs out.
After air-sealing the mudsills and rim joists, you can:
- Insulate using rigid foam insulation board or fiberglass.
- Insulate foundation walls with insulation board
- Install a framed and insulated wall in front of the foundation walls.
Note: When insulating basement walls is that it should not be done if moisture is getting through the walls. When you cover damp walls with insulation, you are at a higher risk of developing mold. You will need to discover why moisture is seeping through.
If you are noticing an increase of condensation in your basement, the easiest things you can do are:
- Open a window or door to let some air circulate. However, this should only be done if the air outside is cooler than the air that is in your basement. If it is warm and humid outside, that’ll only allow more moisture to enter.
- Clean out your basement. If your basement is packed full of things, there may be a problem with air being unable to circulate. You want space between different items. You also want air to be able to flow along the walls easily. Having less in your basement will allow the air to circulate.
- Run a circulating fan for a few hours each day. This allows for an extra flow of air.
Wrap the Pipes
It is common for homeowners to wrap insulation around their hot-water pipes to preserve the heat, but they ignore the cold-water pipes. Putting insulation around the cold-water pipes will help control the condensation.
For insulation around your pipes, you can purchase foam sleeves that slip over the pipes. These foam sleeves come with an adhesive strip that allows them to stay on. For even more protection, you can wrap the joints and gaps in a compatible tape.
Sources of Basement Moisture
There are different sources of basement moisture that may be causing the walls to sweat. Knowing these may help you understand how and why basement walls sweat sometimes.
- Interior moisture – The sources of interior moisture are from dryers, showers, cooking, etc. The moisture levels from these activities rise if you have a finished basement.
- Rain and groundwater – To help prevent water from leaking into your basement, you should have proper grading, gutters, and downspouts. If you don’t have the proper setup, much of that water can invade your basement.
- Humid outside air – In the summertime, the humid air reaches the cold basement walls creating condensation. If you are experiencing your basement walls sweating after a hot, humid day, then this is probably the cause.
Moisture Movement Systems
To correct a moisture problem within a basement, you should first understand how the moisture travels to the basement. There are different ways moisture can move through your basement.
- Capillary suction draws moisture upward through the pores in concrete flooring and slab. The moisture then moves laterally through the walls. This will cause a ring of moisture at the bottom of the basement wall.
- Vapor diffusion is the movement of water vapor molecules through solid materials. The vapor is dispersed when the ground is wet and moves towards the dry parts of the basement walls.
- Air leakage happens because warm air rises. The basement will draw in moist air through cracks in the foundation. A concrete block foundation has cores that allow the moist air to travel through.
Figuring Out if Moisture is Coming from Outside or Inside
Understanding if moisture is coming from the outside or inside of your house will help you solve and prevent the problem from happening. Moisture that is coming in from outside will be from melting snow or rain that is seeping its way to your walls. Moisture that is from the inside is caused by humidity.
An easy way to figure out where the moisture is coming from is to tape a piece of foil to the wall of the basement for two to three days. If there is high humidity in the basement, moisture will show up on the outside of the foil. If the moisture shows up behind the foil, it indicates that the moisture is coming through the walls.
Once you have figured out where the moisture is coming from, you can take the steps that fix the specific problem.
To help with removing moisture caused by indoor humidity you can:
- Seal dryer vents
- Keep windows and doors shut during humid weather
- Add a vent fan if you have a basement bathroom
- Insulate pipes
To help keep water from leaking in from outside, you should:
- Insulate your basement walls
- Repair any cracks with hydraulic cement
- Use a waterproof coating on the basement walls
To help with flooding in your basement, you can:
- Add a proper drainage system
- Install drainage mats on the floor
waterflowing away from the house
- Install a sump pump
Sweating basement walls is a sure sign that there is warm air coming in contact with the cold walls. Because this can cause mold and mildew to grow, it is an issue you want to take care of immediately to prevent any health problems, which frequently affect the respiratory system and cause sickness and allergies. There are several causes of basement walls sweating, and luckily, they can be easily discovered and fixed.
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