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Does Your Crawl Space Really Need A Vapor Barrier?

Sam Smith Foundation Repair Consultant

Crawl space under the house

Are you wondering whether your crawl space needs a vapor barrier? You’ve come to the right place!

Regional Foundation Repair is here for you. This guide answers all the common vapor barrier questions you may have including:

  • What Are The Benefits Of A Vapor Barrier?
  • How Do You Prepare Your Crawl Space for Vapor Barrier Installation?
  • How Do You Install a Crawl Space Step by Step DIY?
  • How much Will Your DIY Vapor Barrier Cost?
  • What Are Some Maintenance Practices For Your Vapor Barrier?
  • What Can You Do to Keep Your Vapor Barrier Installation Costs Low?

For a quick pricing quote on vapor barrier installation, tell us more about your crawl space in the form and one of our foundation repair experts will reach out to you, or continue reading to learn more about how you can keep your crawl space moisture-free.

If you are like most normal people, you probably don’t spend too much time in your crawl space. So, should you care if it is damp or smelly?

The answer is a big YES.  Although you and your family members may not regularly interact with your crawl space, it is still a significant part of your home ecosystem that will affect the quality of life above.

The ventilation in most crawl spaces is usually pretty basic. It’s just enough to facilitate air exchange with the outdoors. The problem is, this doesn’t remove the moisture content from the air, meaning that most of the water vapor trapped under your house will remain there.

The moisture will settle on pipes, walls, and the subflooring, where it could result in serious problems. Some of the signs that should alert you to moisture issues in your crawl space include:

  • White, chalky mineral deposits on your foundation wall
  • Peeling or discolored paint
  • Visible mildew, mold, or a musty odor
  • Rust on interior metal fixtures or appliances
  • Rotting on wood on cabinets, trim, or exposed framing
  • Discolored or damp areas on floors or walls
  • Damaged insulation like fiberglass on the crawlspace floor

Fortunately, installing a moisture barrier is a simple and cost-effective solution that will go a long way in keeping your home’s crawl space dry.

Vapor barriers are made of polyethylene plastic or foil that prevents moisture from entering your crawl space. These simple-to-install fixtures will help keep your space moisture-free and save you from numerous costs and inconveniences.

What Are The Benefits Of A Vapor Barrier?

Although inexpensive and relatively easy to install (with just a few DIY tips), a moisture barrier adds numerous advantages to your crawl space and home.

Improved Temperature Control And Energy Efficiency

Temperature is a major contributor to your home’s comfort level. While there could be several reasons for abnormal or fluctuating indoor temperatures, moisture in your crawl space could be the main culprit.

When the moisture from your crawlspace seeps into the floor and walls, they will act as temperature disruptors, exaggerating the conditions in your home. During cold seasons, the walls and floor will be colder than the room temperature, absorbing what little warmth is left. In the warmer seasons, the moisture will prevent the heat from escaping, making it unbearably hot.

These fluctuations in temperatures will also take a toll on your HVAC system as it will have to work harder (and for longer) to keep your home comfortable. The result is massive energy inefficiencies which will translate to higher energy bills – often more than 15% higher than homes with sealed crawl spaces.

A vapor barrier keeps moisture away from your floors and walls, which allows you to enjoy normal, consistent temperatures in your home.

Prevention of Dampness and Odor

Hidden moisture in your floors and walls will not just alter your home’s internal temperature, it also leads to general dampness and unwanted odors. When the dampness spreads to your furniture and other household items, it makes them susceptible to rot.

When the textiles in your home are unable to dry out completely, they can be susceptible to bacteria growth which causes them to release odors and even mold spores which will impact the air quality in your home.

If you notice a lingering odor, even after giving the whole house a thorough cleaning, you might want to check your crawl space. A puddle of dirty, smelly water could be creating issues from below.

moisture and mold on the wall

Staving Off Mold and Mildew Growth

Molds, mildew, and other fungi are big fans of damp, dark environments, making your crawlspace the perfect target for these organisms. If left unchecked, they could attract other creatures like ants, termites, rats, and even snakes.

Even worse, molds can affect you and your family’s health by causing eye irritation, coughing or wheezing, skin irritation, nasal stuffiness, and throat irritation in sensitive people.

Since eliminating molds and treating mold-related problems is difficult and expensive, it is wiser to prevent their growth in the first place.

Preserving Your Home’s Structural Integrity

Most homes have wood as part of their foundation and frame. When the moisture in your crawl space seeps into the joists and other areas, it will cause wood rot and compromise the structural integrity of your home. As every homeowner knows, repairing structural damage can be very costly, which makes prevention a wiser alternative.

Even if the moisture does not create an obvious problem for you right now, its presence will reduce the value of your home and make it difficult to sell. Vapor proofing your crawl space is therefore a home improvement measure that will make your home safer and also more valuable.

Protecting Pipes and Other Fixtures

Most of your home’s utilities, including your gas, water, sewer line, and electricity probably pass through your crawl space. While this design is neat and makes efficient use of space, it leaves them susceptible to the elements.

When moisture settles on metallic pipes, it will cause them to rust and lose their integrity, and they may end up bursting. Leaky water pipes will not only increase your water bills, but will also increase the level of moisture in your crawlspace, accelerating and enhancing the problems we mentioned above.

You can avoid all these safety hazards and overhead costs of repair by installing a vapor barrier to keep your crawl space moisture-free.

What Needs To Be Done Before Installing A Vapor Barrier?

Before installing a vapor barrier in your crawl space, there are some steps you should take to solve any pre-existing moisture problems and prepare the area for encapsulation.

Waterproofing Your Crawl Space

The chief aim of installing a moisture barrier is to prevent water vapor from entering your crawl space, either through the vents or from the ground. For this to be effective, you should first ensure no water is leaking into the area from other sources.

First off, identify and repair any faulty pipes and taps leaking to the area. You should also insulate water pipes to prevent them from altering the surrounding air temperature, as they could lead to the formation of water droplets from condensation.

The next step is repairing and redirecting any downspouts and gutters that direct water to your foundation. Some simple landscaping works like creating a slope of soil around your foundation and creating drainage trenches around your house will prevent run-off water from finding its way into your crawlspace.

To prevent moisture from seeping in from the surrounding soil, it’s important to apply a sealant to the foundation walls to fully encapsulate the crawl space.

Remove Existing Water and Dry Out Excess Moisture

After ensuring no water will force its way into your crawl space from the outside, the next step is to remove any moisture that may have already accumulated. If you are lucky, you will only be dealing with slight dampness, or at worst, you could be facing a puddle of stagnant, smelly water.

If all you are facing are a few puddles, you could use a wet vacuum cleaner (wet vac) to suck up the water and dump it outside, far from your home’s foundation. For widespread flooding, less than an inch deep, sweeping the water out with a broom will do the job.

If your crawl space is severely flooded or difficult to access, a pump may be the only practical option. Position the pump’s suction hose in the flooded space, directing the drainage pipe far enough so the water doesn’t flow back to your crawlspace.

After getting rid of all the standing water, the next step is to thoroughly dry the space, including the wood framing, the crawl space floor, and the subflooring above the crawlspace. For this, you will need a dehumidifier. Let your dehumidifier run between 30 to 45 percent for several hours, checking on it regularly and emptying it as required.

It could take up to 10 hours for a wet crawl space to dry out completely. To speed up the process, position a low heat source like a light bulb inside your crawl space and use electric fans to blow the warm air across damp surfaces.

Clean and Clear Out The Crawl Space

This step should come after removing any stagnant water but before drying out the area with a dehumidifier. Start by removing any post-construction material and debris, especially sharp objects that could puncture the plastic barrier.

The next step is clearing out mold and mildew from the space. Also, if there were other pests like insects and rodents in the crawlspace, clean out their droppings and destroy their shelters.

DIY: How To Install A Crawl Space Vapor Barrier

As mentioned earlier, installing a crawl space vapor barrier is an easy process that most owners can DIY with the right tools and skillset.

For the tools and equipment, you will need:

  • 6-mil polyethylene plastic
  • 1-½ inch rigid foam insulation
  • Landscape fabric stakes
  • Caulk
  • A caulk gun
  • Water-resistant sealing tape
  • Double-sided butyl tape
  • Utility knife
  • Tape measure

Step 1: Level the crawl space

It will be easier to install your polyethylene barrier if your crawl space floor is level. Use a garden rake to dig out any mounds to keep your space as even as possible.

Step 2: Line the ground with plastic

Once your space is clear and as level as possible, it is now time to lay your 6-mil polyethylene plastic on the ground inside. Six millimeters is the minimum advisable thickness of plastic you should use, but you can go for thicker ones if you wish (at a higher cost, of course).

Ensure the sheet of polyethylene plastic covers all the ground and leaves an extra six inches to run up the side walls. Tape it there using water-resistance tape. You should also overlap the seams and tape them.

Next, push the landscaping stakes through the plastic and into the floor every couple of feet to hold it firmly in place. The holes left by the landscaping stakes are too tiny to compromise the integrity of the barrier and will allow any water that gets into the crawl space to drain away.

The landscaping stakes will also prevent the plastic from bunching or tearing, making it easy to maneuver within the crawl space.

Step 3: Cover the walls with insulation

Next, you need to insulate the walls to prevent dampness from seeping into the crawl space through the foundation. Here you can use the 1½ rigid foam insulation to cover the walls and ceiling of your crawl space.

Attaching rigid foam insulation to a concrete wall

Step 4: Insulate the rim, floor joists, beams, and other fixtures

Cut the insulation to fit the rim, joists, beams, columns and other exposed fixtures like pipes. Fill any spaces left with spray foam, and whenever possible, use siliconized caulk to seal any air cracks.

Step 5: Cover the insulation with plastic

The final step is running the six mil plastic vapor barrier to cover all the insulation on the crawl space wall, ceiling, joists, and other fixtures. Use waterproof tape to hold the polyethylene plastic in place.

For DIY enthusiasts, installing a vapor barrier will be an easy process, but it could prove daunting if you are not much of a handyman. If this is the case, consider seeking the help of our crawl space professionals who have handled thousands of similar projects before.

How Much Will A DIY Vapor Barrier Cost?

We have repeatedly mentioned that vapor barriers are a cost-effective method for keeping your crawl space moisture-free. But just how cost-effective are they?

If you already have all the other tools and equipment, you will only need to buy polyethylene plastic and sealing tape. The cost of the vapor barrier ranges from $0.15 to $0.50 per square foot depending on the thickness of the plastic (from 6 mils to 20 mils).

The cost of vapor barrier sealing tape averages around $120 to $200.

Therefore, if you are using a 6 mil barrier for a 2000 square feet crawl space, you will spend about $300 on the plastic and $150 on the sealing tapes, bringing your total costs to around $450.

Add this to the cost of other tools and material – say $500 – and the total costs of DIY vapor barrier installation comes to just around $950.

This is a very small price to pay considering the numerous benefits of a vapor barrier.

How To Maintain A Crawl Space Vapor Barrier

When properly installed, your crawl space vapor barrier should serve you for more than 10 years. However, since the barrier is basically plastic sheeting, there are some maintenance measures you could take to increase its lifespan.

Avoid Storing Heavy or Rugged Items in the Crawl Space

Do not treat your crawl space as a tool shed if you have a vapor barrier installed. Heavy and rugged items could easily tear holes into the plastic barrier, decreasing its efficiency.

Seal Off the Vents

In the past, air vents were thought to provide the required ventilation to keep moisture away from crawl spaces, but this was later discovered to be misguided as they pose a higher risk of radon getting into your home. Sealing your air vent will prevent moisture-laden air from entering your crawl space and damaging your vapor barrier.

You should, therefore, seal all the air vents to prevent them from carrying humid air into your crawl space.

Install a Dehumidifier

If you live in a high-humidity area, installing a vapor barrier might not be enough to solve your moisture problem. Consider installing a dehumidifier to periodically remove any water vapor that finds its way into your crawl space.

For areas prone to flooding, you will need to go the extra mile and install a sump pump. This will pump out any water that settles in your crawl space, preserving your plastic sheeting in the best condition for as long as possible.

How To Save Money When Installing A Vapor Barrier

The best way to keep your vapor barrier installation costs low is to do it yourself. Labor costs are the most expensive part of the installation process, costing an average of $1.50 to $3.00 per square foot. Therefore, for the 2000 square foot crawl space, you could end up spending from $3000 to $6000 extra depending on the condition of your space.

However, it is better to spend more on labor if it will get the job done right. A properly installed vapor barrier is more efficient than a poorly fitted one, making it the cheaper option in the long run.This is why you should always let the pros handle it if you are in doubt.

At Regional Foundation Repair, our experts will carefully examine your crawlspace, clear out any dirt, mold and water, and install a vapor barrier that will serve you well for years. Contact us today and our specialists will guide you through the process of keeping your crawl space moisture-free for a safer, healthier, and more comfortable home.

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Sam Smith Foundation Repair Consultant
SHORT BIO: Hey, I'm Sam Smith. I'm one of our service techs here at Regional Foundation Repair. I'm here to help you learn more about your home's foundation. I've been doing this for a while, so I have a few insider tips and tricks to share!

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