Moisture in basements: causes and solutions
Moisture in basements: causes and solutions
By John Carmody; Brent Anderson; and Richard Stone, Extension educator University of MinnesotaThis page briefly describes moisture sources, moisture movement mechanisms and typical basement moisture problems. Then, a step-by-step process for addressing each problem is presented along with several detailed approaches to solving the problem.
A problem that can damage your health and home
Moisture problems in existing basements are very common, but often are not understood or properly treated. In a basement that is seldom used and separate from the living spaces above, this may not present a great problem. However, most basements in Minnesota are connected to the rest of the house through ductwork or other openings. In addition, basements are increasingly used as finished living and bedroom spaces. In these cases, moisture problems are not only annoying and uncomfortable, but can lead to significant health problems. Molds and mildew can grow in damp carpets and beneath wall coverings. Finishing a basement without first dealing with the moisture problems can result in making health conditions worse and lead to significant damage as well. Basement water problems are solvable, but there is a cost to doing it right.Understanding the problem
To correct basement moisture problems, it's necessary to understand where the water is coming from and what mechanisms permit it to enter the basement. There are just three sources of moisture:- Liquid water from rain or ground-water.
- Interior moisture sources such as humidifiers, unvented clothes dryers, bathrooms and cooking, as well as the moisture in concrete after construction.
- Exterior humid air that enters the basement and condenses on cooler surfaces.
- Liquid water flow.
- Capillary suction.
- Vapor diffusion.
- Air movement.
Symptoms
- Water trickling out of walls.
- Standing water on floor.
- Saturated base of concrete block walls; a ring of dampness.
- Damp, humid air.
- Condensation on cold walls and floor in summer.
- Odor, mold and mildew.
- Deterioration of carpet or wood.
- Rot and decay of wood headers, joists, sill plates and columns.
- Staining and blistering of wall covering.
- Efflorescence, spalling of concrete or masonry.
Basement moisture sources
Rain and groundwater
In a 1-inch rain, 1,250 gallons of water fall on the roof of a 2,000-square-foot house. Without proper grading, gutters and downspouts, some of this water flows into the basement. The below-grade water table can also rise due to flooding or seasonal site conditions. This is why drain tile systems are recommended around basement walls even in sandy or gravel soils.
Interior moisture sources
Moisture is generated inside of basements from people and their activities. Common sources are humidifiers, unvented clothes dryers, showering and cooking. When basements are finished, these activities increase.Another source that can be thought of as internal is the moisture contained in new concrete after construction. In a typical house, this can amount to 0.2 gallons per square foot of wall, and 0.1 gallons per square foot of floor. It may take many months or even years for a new house to come into equilibrium with its environment.
Ventilation with humid outside air
In the summertime, basement windows may be opened for fresh air. If the outside air is warm and humid, it will condense on the cool basement wall and floor surfaces. Many homeowners see this moisture and believe they are experiencing basement wall leakage, when in fact the accumulated moisture is from condensation.Moisture movement mechanisms
Capillary suction
Capillary suction moves moisture through porous materials. The water can be drawn upward through small pores in the concrete footing and slab and laterally through walls. This effect creates the ring of dampness seen at the base of many basement walls. This is very common at cold joints. Water can rise by capillary draw significantly as shown below:Soil type and amount of capillary rise:- Gravel - Less than a few inches.
- Sand - 1 to 8 feet.
- Silt - 12 to 16 feet.
- Clay - 12 to 20 feet.
Air leakage through walls and floor
In most houses, a stack effect is created because warm air rises. This induces a negative pressure on the basement and draws moist air in through any cracks or openings in the foundation including open sump pits. For this reason, sumps should have an airtight cover. With a concrete block foundation, moist air is drawn through the block cores, especially if they are left open at the top course.
Vapor diffusion through foundation walls
Vapor diffusion is the movement of moisture in the vapor state through a material. It's dependent on the permeability of the material and the driving force of vapor pressure differential. In a basement, vapor can diffuse from the wetter ground through concrete walls and floors toward the dryer basement interior. Vapor retarders such as foundation waterproofing and polyethylene slow down this process.Typical causes of basement moisture problems
Inadequate grading
PROBLEM: If the ground around a foundation is level or slopes toward the house, water is directed into the basement. The soil next to the house is often backfilled without proper compaction and later settles. This is especially true under stoops where water can collect next to the basement wall.SOLUTION: Place earth around the house so that it slopes away from the foundation wall a minimum of 1 inch per foot for at least 6 feet.
Defective or missing gutters and downspouts
PROBLEM: Missing gutters and downspouts cause rainwater to be directed toward the foundation perimeter. A downspout without an extender or splashblock is worse than no downspout at all. It is depositing the huge volume of rainwater from the roof in a single concentrated location near the basement.SOLUTION: Place a minimum of one downspout per 50 linear feet of roof eave. Extensions should discharge water at least 4 feet beyond the wall. Sloped concrete sidewalks around basements are very effective in directing rain runoff.
Improperly designed window wells
PROBLEM: Window wells are like a drain right next to the basement wall. Often they are improperly built so that any water is directed toward, rather than away from the foundation.SOLUTION: Window wells should be filled from the footing to the window sill with 3/8- to 3/4-inch coarse aggregate. A supplemental drain tile extension should extend from the footing to the base of the window well.
Ineffective drain tile and sump pit
PROBLEM: Many existing houses simply have no subsurface drainage system. This comes from a time when basements were not used as habitable space. In other cases, the systems don't work for a variety of reasons, such as collapse of the pipe, clogging of the pipe with silt and/or tree roots or a broken connection to the sump. The sump pit usually contains a pump designed to lift the water to the ground surface outside the foundation wall. This pump can fail.SOLUTION: See approaches 2 through 5 that follow.
Improper drainage with underslab ducts
PROBLEM: If heating ducts are installed beneath a basement floor slab, the drainage system may be inappropriately left at a level higher than the duct. In effect, the duct becomes the drainage system. With standing water within the heating duct, there are potentially serious health consequences from mold contamination.SOLUTION: Heating ducts placed beneath the basement floor must be insulated, watertight and sloped to collection points for drainage and cleaning. A drain tile and coarse aggregate can be placed under the ductwork.
Structural cracks
PROBLEM: Concrete and concrete block foundations usually develop some cracks. They can be severe if floor joists are not properly connected to the foundation wall, thus permitting the wall to move. Also, soil settling causes cracking. Places where walls meet rigid structures like the fireplace often crack as well. Usually, drainage removes the water from cracks, but repair may be necessary.SOLUTION: Proper footing design and proper connection between the foundation wall and the structure above are required (e.g. anchor bolts or straps at the sill plate and floor joists nailed to the sill plate).An overview of solutions to basement moisture problems
The best way to approach any building problem is to first do the things that are easy and low cost. Then proceed in a logical order doing the next least costly technique with the most positive likely result. With moisture problems, the best approach is almost always to remove or control the source of the moisture, not to try to stop it at the last line of defense.- First, the simplest and least costly techniques are to remove excessive internal moisture sources in the basement (humidifiers, cooking) and ventilate other sources (clothes dryer, bathroom).
- Second, if condensation in the summer is the problem, do not ventilate the basement directly with warm, humid air. Ventilation through an air conditioning system or with a dessicant-type heat exchanger is recommended.
Dehumidification is not a permanent solution
Dehumidification can be used as a means of reducing the symptoms of humidity and odor in a basement, but it is not a permanent or complete solution. In fact, if a dehumidifier is used in a basement with moisture problems, it may cause greater damage. By drying out the basement air, moisture is drawn into the basement more rapidly causing efflorescence and spalling of concrete and further damage to interior finishes.Interior membrane or coating is a temporary solution
It is appealing to solve a basement moisture problem with a membrane or coating on the inside. It's less expensive than a drainage system and seems to work for a time in some cases. The water is still there, however, and eventually these systems deteriorate or simply move the water to another pathway into the basement.Recommended approach
Evaluate gutters, downspouts and surface grading: The recommended approach after removing interior moisture sources is to evaluate the gutters, downspouts and surface grading around the house. These should be corrected first and may solve the problem.Interior or exterior drainage system: Then, if a moisture problem persists, proceed with an interior or exterior drainage system. All of these techniques are described below. If your goal is to finish a basement that has water problems, it is recommended to first deal with the water problem.Sub-slab depressurization system: An active sub-slab depressurization system including a washed-rock layer below the slab is recommended. This draws moist air from beneath the slab and may help to reduce the amount of moisture vapor that enters the home through openings in the slab. It also assists in controlling radon and other soil gases. Sumps and other open connections to the soil outside the foundation and below the slab should be blocked and sealed.More information on soil gas management can be found in "Building Radon Out," a booklet available in electronic format (PDF) from the Environmental Protection Agency.Step by step process
- Control interior moisture sources.
- If summertime, don't ventilate with outside air.
- Correct grading, gutter and downspout system.
- Provide an interior or exterior drainage system.
Notes
- A dehumidifier can help reduce the symptoms of humidity and odor, but doesn't solve the problem.
- A membrane or coating on the interior without providing drainage generally won't solve the problem in the long term.
- Walls must be dry before insulating. Slabs must be warm and dry before carpeting.
Although carbon monoxide is itself impossible to smell, hear or see, some 
Victims often cannot think clearly once poisoning has set in, which makes self-diagnosis challenging. One of the tell-tale signs is that pets and other people in the house will experience symptoms of poisoning at the same time.In the event of exposure, getting fresh air should be the first priority. Once outside, contact emergency services. Tell the authorities your assumed diagnosis so they can test you for exposure. Do not go back into your house until the air inside has cleared and the environment is safe. If you believe that your exposure is due to a problem with a gas-powered appliance, have your gas company inspect your house and gas line.If someone you love is exposed to carbon monoxide poisoning, call 9-1-1. Be aware that a rescue attempt in a carbon-monoxide rich environment could lead to a dangerous or even fatal level of exposure. Ask emergency responders for next steps before attempting to rescue a loved one yourself.
A simple reaction causes the alarm to sound. Carbon monoxide detectors come with sensors that measure the parts per million (PPM) of the carbon monoxide (CO) in the atmosphere. If the machine detects high amounts of carbon monoxide in the air, the alarm sounds. The higher the concentration, the faster the alarm will sound. 9 PPM is common in homes, but levels of 
There are multiple 
An array of things can cause carbon monoxide to buildup inside the house. Appliances must burn fuel efficiently or they could produce excessive amounts of carbon monoxide. You can protect yourself by inspecting your home's appliances for indications of a problem and by keeping your appliances in good condition.Gas-Burning FurnaceGas-burning furnaces use combustion to produce heat that keeps your home warm. Inspect your furnace on an annual basis and watch for signs of inefficiency. Take note of the following problems:
Under the right conditions, carbon monoxide poisoning can happen anywhere, in any home. Being aware of the potential danger can help you protect yourself, your loved ones and the people & pets in your household.If you and others in your household become mysteriously ill all at the same time, stop to ask yourself why. Keep carbon monoxide detectors on every floor of your house and in strategic locations. Replace batteries annually, check the expiration dates and replace as needed.If your carbon monoxide detector does go off, don't assume that it's a mistake. Get your family out of the house and work with the authorities to ensure that your house is safe.Many government agencies provide information about carbon monoxide poisoning.
Well, while it might not be the fastest task to accomplish, taking the time to pack up your belongings is, in fact, a fantastic opportunity. There is no better way to get rid of everything which has been left behind in the dusty corners of your wardrobe, the basement, or you name it.Instead of thinking of decluttering your home as a tedious obligation, why don’t you enjoy the ride? Below, we are sharing some contaminating cute ideas to help you on your quest. (Of course, don’t be shy to thank us later for the gulp of inspiration! Xo-xo).For starters, let’s discuss the different methods of decluttering.
Bathrooms are great to do next. This is because most people don't have much sentimental attachment to bathroom products making it less overwhelming to tackle. In regards to the rest of the house, the size of some rooms and amount of clutter will determine how you will tackle the remaining rooms. Approach such rooms’ one section at a time.Assuming you have one or two months before moving house, the one room at a time method is perfect as it will give you plenty of time to declutter.In this article, we’ll discuss in depth how to go about the One Room at a Time Method.
The main challenge here is discarding old and outdated stuff. Donate all the clothes that don’t fit and freebies you never wear. Again, start with the easy decisions such as the promotional tees from events and jeans that you outgrew way back in college.Once you've sorted each type of clothing, you will have four piles to deal with:
The kitchen is the storage for all kind of items. You should, therefore, declutter your kitchen by focusing on one category of an item at a time. This includes glassware, cutting boards, utensils, or cutlery. You can also do zonal decluttering of each part of the kitchen.Empty each space, analyze each item, and return everything back to its rightful space. First identify powerhouse storage areas, upper cabinets, and the pantry. Move onto the drawers, lower cabinets, and the space under the kitchen sink.For the most part, expired food needs to be thrown away. The exceptions are where there's a difference between "Use By" and "Best By" dates. Other foodstuffs to dispose of include freezer-burned food, expired or unused spices, old oils, stale crackers and snacks, and food you're never going to eat. Such food is better off with someone who will actually use it.While decluttering the countertops, move as many items as possible off of the countertops and into storage spaces. Keep only what you use on a daily basis on the countertops.Excess plastic grocery bags can easily build up and when you have more than you will use, they take up unnecessary space. Recycle them at your local grocery store or see if a neighbor can use them.Finally, take your put away box and return any item that doesn't belong to the kitchen to its rightful storage space in the house.
The key to decluttering the living room is to decide on permanent storage spaces for items you frequently use such as magazines, books, and remote controls.Start with side tables, consoles, and bookcases. Then move to the coffee table and entertainment unit. Empty them, evaluate the items they store, then return them to the proper storage area. Keep books out of sight, action your mail, fold blankets, prop pillows and the like.Next move to the electronics. Are you using every electronic item and do they work? Remove any gadget that is not connected to the television or home theater system. Store items such as gaming equipment and chargers where you use them.Finally, if you have kids, tackle the toys. Do all the toys work? Do your kids still play with them? Assess every toy for wear and tear. Donate the toys you don’t need or grab the put away box and return everything that belongs in another room to its rightful space.
