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What Is The Importance Of A Poly?

Jul 16, 2021

4 min read


There are so many things we life lessons we hope we could've learned earlier. Take out the importance of poly from them.

What is the importance of poly to your home? Yes, it is! Poly is a way to keep moisture from getting into the concrete and your home. But its benefit is more than just preventing moisture. Here’s why.

Poly or Vapor Barrier?

A vapor barrier or more commonly known as poly (short for Polyethylene plastic sheet), is a material that prevents moisture from entering your home. It is used in walls and the concrete floor separating the ground. But in this blog, we are going to focus on the latter. That being said, vapor barriers keep your concrete floor dry and then stay dry to avoid flooring problems.

Effects Of Moist Concrete Floor

Adhesives Problem

Too much moisture in concrete is a problem because it can cause pH changes that destroy adhesives. Here’s what happens. As moisture makes its way to the surface of a concrete slab, soluble alkalies come along for the ride and raise its surface pH above that of flooring adhesives. The problem is the adhesive between the vinyl floor tiles (for example) and the concrete. Most adhesives today are latex-based and very sensitive to alkaline environments–high pH–like concrete. Sticking stuff that does not breathe to wet concrete or gets wet with a latex-based adhesive does not work. The adhesive “re-emulsifies” (goes back to a soft and sticky state) in the wet alkaline environment. You will end up with an adhesive that doesn’t hold up!

Poor Indoor Air Quality

Moist and dark corners in your home are critical to mold growth. Mold exposure can cause several health issues such as; throat irritation, nasal stuffiness, eye irritation, cough, wheezing, and skin irritation in some cases. Mold exposure may also cause heightened sensitivity, depending on the time and nature of exposure.

Also, we already discussed how moisture re-emulsifies the adhesive from the floors. These broken-down adhesives can also impact your home's health with poor indoor air quality and create serious health issues for your family members.

Wood Floors Failures

Wooden floors finish in the basement seem to be a good idea. However, ignoring to put a vapor barrier under the slab can damage your wooden floors. If there is too much moisture in the concrete floor, you may end up with flooring failures such as swelling, bulging, or cupping.

More Work For Your HVAC

One of the critical ways many HVAC systems work is by removing moisture from the air and reducing the relative humidity in your home. By forgoing the installation of a below-slab vapor barrier, you ensure a greater amount of moisture entering the building from underneath your building’s foundation. This can mean more work for your HVAC system. The more your HVAC system is working, the more money you are paying for electricity costs. 

Moisture Behavior

Okay, let’s get technical here. There’s almost always water underneath any home. It may not be near the surface, but that doesn’t mean it’s not there. This water can move up through the soil and contact the bottom of a concrete floor via capillary action. A layer of crushed rock that goes between the ground and the concrete floor slab, known as a capillary break, can stop capillary action. A capillary break does a good job of stopping water in its liquid state from reaching a slab. However, they can’t stop water in vapor form from reaching and entering a concrete slab. Therefore, there needs to be something underneath the slab that prevents vapor moisture from entering.

Why Do You Need A Poly Or Vapor Barrier?

So we’ve learned that a capillary break is not enough to stop moisture from entering your home. This is where the importance of a poly or vapor barrier will come into play. 

In addition, you might also need a vapor barrier for liability reasons because most manufacturers of flooring include vapor barriers or retarders in their installation guidelines.

Lastly, the vapor barrier under your slab will also protect you from harmful ground pollutants like Radon gas. Radon (a radioactive, colorless, odorless, tasteless noble gas) can leech from the ground and into your house. According to studies, it is the second leading cause of lung cancer in the United States and the leading cause among non-smokers. If your family breathes in high Radon levels over long periods of time, this exposure can damage the sensitive cells of our lungs, increasing the risk of lung cancer.

How's the Poly in your Clearwater property? Is it working fine still? Make sure you do! In case, try to contact a trusted custom home builder in your area to help you with it.

How Will It Benefit You?

There are many benefits and importance of poly or vapor barriers under the slab. It prevents moisture and toxic gases from entering your home from the ground. Thus, improving your home’s indoor air quality. Moreover, it saves you tons of money from floor repairs and soaring electric bills. Finally, it gives you and your family peace of mind.

This article was last updated on Aug 8, 2022