Moisture In Crawl Space – How To Prevent and Fix The Problem

If your home has a crawl space, it is very important that you make sure that it stays dry and free from moisture.  A damp crawl space could lead to a variety of health and safety problems in your home. These could include mold and mildew growth, as well as rotted floor joists and support beams. Furthermore, a damp crawl space will welcome unwanted pests such as termites, snakes, rats, spiders, and other vermin that seek out damp, dark spaces.

Homes built on top of crawlspaces are more common in areas where the water table is often high; the reason for this is because if you were building an underground basement in these areas then you would constantly find yourself dealing with water problems.

Before I get ahead of myself, I should quickly point out that the water table refers to the point between two zones at which the ground starts to become completely saturated with water in the soil.

A high water table will increase hydrostatic pressure on the basement walls and floor, which could cause leaks and structural cracks in the foundation.

The problem with having excessive moisture in your crawl space is that it could have just as much of an impact on your home as a flooded crawlspace would have. Not to mention that all of the damp, moist air will seep up through the floorboards and negatively affect the air you breathe on the first floor of your house.

What Causes Moisture In Crawl Space?

Different sources could contribute to moisture in the crawl space. Let’s take a look at some of the more common reasons below.

Condensation – One of the biggest contributors to condensation in the crawl space is because of venting. Venting allows the outside air to enter the crawl space and come in contact with the inside air. Most often during the summer months, the crawl space becomes a breeding ground for mold and other harmful bacteria. The best way to combat condensation is to seal any vents or loose doors to prevent the outside air from being able to get in.

Water Seepage – After heavy rainfall or when the snow begins to melt, all of that water-saturated in the soil will begin to seep up through the ground and come up into the crawl space. The best way to stop this from happening is to lay strips of heavy-duty plastic over the ground to act as a barrier, better known as crawl space encapsulation.

Gutters and Downspouts – One of the biggest causes for a damp crawl space is one that could have easily been prevented, and that is by making sure that the gutters are clean and clear of debris and that the downspouts are properly directing water away from the foundation.

Leaking Pipes – Plumbing pipes under your crawl space are another culprit that tends to get overlooked. Keep an eye on your utility bill and make sure there are no sudden spikes in usage.

What is an Acceptable Level of Moisture in a Crawl Space?

Ideally, the level of relative humidity in your crawl space should be 55% on the high end. You can measure relative humidity using a hygrometer (analog or digital). Typically, however, you can tell just by entering the space if the humidity feels high – if the air feels “wet,” that’s your sign. It’s vital to keep the relative humidity at this level since mold can grow at 70% relative humidity or sometimes even lower based on other external factors. The lower the humidity in your crawl space, the better.

Is it Normal to Have Moisture in a Crawl Space?

Moisture and pooling water is a common problem in crawl spaces and something that happens naturally. However, crawl spaces with excessive moisture are problematic and can lead to detrimental problems that impact your health, as well as the structure of the home, not to mention it could decrease property value.

Keeping your crawlspace dry is essential in avoiding the following issues:

Wood Rot: The water vapor found in the air of your crawl space will keep wood damp and cause floor joists and support beams to decay, which could cause the foundation of your house to sag.

Insect Infestation: Cockroaches, spiders, and termites are just a few types of insects that are attracted to humid environments and the darkness of a crawlspace. While bugs may seem harmless when left alone, some could carry diseases while others wreak havoc on a homes structure and foundation.

Mold: Same as insects, mold spores, which are little particles of fungi that usually float around in harmless amounts, are attracted to humid environments where they can grow. Mold also feeds off of dead organic materials, such as the rotting wood. If allowed to thrive, the mold can be lethal to your health.

How to Get Rid of Moisture in Crawl Space

Moisture in a crawl space is a common problem and one that you can find in any area of the country. Here are some simple tips that you can follow to get rid of what could be causing moisture in your crawl space.

  1. Check Gutters and Drainage – The first thing that you should do before you start tackling the crawl space is to inspect your gutters to make sure they are draining properly and not contributing to the dampness in your crawlspace. Look at the foundation and make sure it slopes away from your home so that rainwater doesn’t collect next to your foundation.

  2. Inspect Foundation – Inspect the surrounding foundation of the crawl space for cracks or other sources of where water might be seeping in. If you do notice any foundation cracks, you should look at having them repaired by a professional or if they are not too severe you could repair them yourself.

  3. Inspect Plumbing Pipes – Take a look at any plumbing pipes found in your crawl space to make sure they are not leaking. Have them repaired right away if you find any.

  4. Seal Gaps and Any Openings – Take a look around the crawl space for any gaps or openings, and fill them in with spray foam, or a caulking gun. Take a look around pipes that might be coming out of the crawl space and seal around those opens where it exits the wall. This is also a good way to help keep critters out.

  5. Remove Standing Water and Wet Debris – Before we can begin the drying phase, we first need to get rid of any standing water and remove any junk or wet debris found under your crawl space. That includes pieces of wood, newspaper, boxes, and even insulation. If you suspect that the insulation is wet it is better to take it out and replace it once the crawl space is dry, and you’ve resolved the moisture problem.

  6. Get Rid Of Mold – Now, this job should be handled by a professional since many safety precautions are required to remove mold safely. If you do attempt to remove the mold yourself, please wear the proper safety equipment.
  1. Remove Moisture From The Air – If your crawl space has a lot of ventilation, you should be able to set up a large fan in the opening of the crawl space and leave it to run for 10 to 12 hours. Sometimes moving the air around is enough to remove moisture and dry surfaces.

    Alternatively, you could set up a crawl space dehumidifier and draw the moisture from the air that way. A lot of people have more success using a dehumidifier then simply using a fan.

    A crawl space dehumidifier is not a cheap investment; for example, on Amazon, a decent low costing unit such as AlorAir Dehumidifier will cost just under $900. I would suggest checking your local hardware stores to see if you could rent one for 24 to 48 hours.

    Before using a dehumidifier on your crawl space, make sure you seal up any ventilation, cracks, or gaps; otherwise, moisture will still be getting in, and you’ll be running the dehumidifier constantly.  
  1. Cover The Crawl Space Floor and Walls – A great way to help avoid moisture problems is to cover your crawl space walls and floor with a thick plastic heavy-duty moisture barrier. This process is referred to as a crawl space encapsulation.

    Don’t worry if you accidentally puncture or tear the plastic. It will still work as long as it doesn’t have any large holes or gaps. Do not cover the plastic barrier with dirt after because you still want to be able to see any new puddles that could be coming from a plumbing leak, or rainwater getting in someplace.

How to Keep Your Crawl Space Dry

The best method to reduce the amount of moisture in your crawl space is to perform a complete crawl space encapsulation. Encapsulation is an incredibly involved process, so you’ll want to hire a professional to do this. A hired professional, or a team, will create a barrier on the walls and floors with a heavy-duty plastic and drainage mats. Completely sealing off any vents or gaps between windows and door openings.

They will most likely suggest that you install a dehumidifier to lower the relative humidity in the air. A built-in dehumidifier is your best choice, especially if you never go into the crawlspace. You will want a dehumidifier that will turn itself on and off when the air reaches a certain humidity level.

You might also need a sump pump, which is usually installed by a professional as well. Because your crawl space might be close to or below ground level, it won’t be prone to just moisture build-up, but flooding and pooling water as well. A sump pit will be installed to catch the water, and the pump will direct it away from the house. If you’ve had your crawl space encapsulated, the drainage mat will assist the water into being directed towards the pit, though you can also lay down a drainage mat without needed to go through the entire process of encapsulation.

How Much Does It Cost To Install a Crawl Space Encapsulation System

Typically, on average, the homeowner could spend around $6,000 to install a crawl space encapsulation system. Of course, this depends on how big of a job you have, what materials get used, who you hire to do the work, how much cleaning and debris removal is required, and if there was any previous damage caused that would need repairing before the encapsulation could take place.

But to give you an idea, let’s take a look at some of the costs involved below:

Cleaning – Before the encapsulation can begin, you first need to remove any rocks, peddles, or any other type of debris to avoid causing damage to the vapor barrier. This is a job that the homeowner could do themselves to save money.

  • To hire a professional: Average cost: $1,200

Repair – Any rotted wood, such as floor beams and floor joists, should get repaired before you begin. Depending on what type of damage you have, you might want to hire an expert to handle this for you.

  • To hire a professional: Average cost: $2,500

Insulating Foundation Walls – Depending on the height of your crawl space, a non-water sensitive insulation foam board may be required.

  • To hire a professional: Average cost: 0.75 – $3 per board foot

Heavy-duty Plastic Vapor Barrier – A heavy-duty plastic vapor barrier will need to be laid out to cover both the foundation walls and crawl space floor. Different material is required to properly hold the vapor barrier in place.

  • To hire a professional: Average cost: $0.60 – $0.85 per square foot

    Material needed:
    • Vapor barrier – $140 (1000 sqft, True 10 Mil)
    • Vapor barrier seam tape – $42 (per roll, 4″ x 180′)
    • Double-sided construction tape – $18 (per roll, 1 inch x 36 yards)
    • Termination bars – $26 (1″ x 8′ long)
    • Concrete screws – $13 (box of 100 3.16 x 1-1/4 inch)
    • Tree Fasteners – $35 (box of 100)

Sump Pump – A sump pump might be required if your crawlspace is below ground level. Special drainage mats will be required to direct water towards a sump pit, where the sump pump is used to drain that water away from home.

  • Average Cost: $400

Dehumidifier – A dehumidifier might be required if the humidity level can not be reduced by sealing off the crawlspace.

  • Average Cost: $900


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