5 Questions with Billy Tesh

1. What is the purpose of using polyethylene (poly) vapor barriers in a crawlspace and how should it be installed?

Polyethylene vapor barriers, also called poly liners or poly, have long been the go-to option for helping reduce crawlspace moisture. They act as a shield to reduce moisture that originates in the ground or that moves hydrostatically through the walls. Placing this liner between the ground/wall and the crawlspace, along with the use of other control methods (e.g., sealing vents or mechanical drying), will help reduce and maintain appropriate moisture levels within the crawlspace. This reduced humidity helps to prevent unhealthy conditions, mold and wood rot, as well as the parameters conducive to various insects.

A basic installation will ensure that 100 percent of the ground is covered with the seams overlapped by at least 12 inches and taped. Additionally, the liner should extend up the wall, stopping 3-4 inches short of the sill plate (for termite inspection), and be used to wrap the piers. Always check your local building code to ensure there are no other requirements or limitations. 

2. What are the different types of poly used in crawlspaces (reinforced, non-reinforced and woven-coated) and what are the pros and cons of each?

There are many different varieties of poly liners available to encapsulate crawlspaces, and while there are some physical differences, the vapor transmission rates are very similar. Here are some of the most common materials:

Reinforced: String reinforced liner has been a popular choice for a long time. It is comprised of multiple layers of polyethylene and string reinforcement which is then fused together with a molten layer of polyethylene. The string pattern improves tear resistance and increases the longevity of the product.

Non-Reinforced: Many are familiar with the standard, non-reinforced liners that have been on the market for years. This tried-and-true product has long been an excellent choice as a moisture barrier and is more flexible than the other options.

Woven-Coated: Another popular material is the tightly woven liner which is then coated in a layer of polyethylene. This product has a slightly lighter weight than other options but still offers great moisture protection and tear resistance.

3. Why are there different thicknesses of poly and what does the “mil” in 12 mil mean?

Polyethylene liner is manufactured in many different thicknesses. It is most commonly produced in thicknesses between 4 mil and 20 mil. The biggest benefits as the thickness increases are puncture resistance, durability and longevity. In a crawlspace with rocky surfaces or in one that has a lot of traffic, a thicker liner is much less likely to be punctured. Vapor transmission through the liner is reduced as the thickness increases. However, even a good quality Class A 6 mil vapor barrier will provide great protection as long as it remains intact. Class A is defined as having a permeability of less than 0.1 perm.

So, what does the “mil” in 8 mil stand for? A mil is a unit of measurement but should not be confused with a millimeter. A single mil is defined as 1/1000th of an inch. That means that in the example of an 8 mil liner, it is on average 8/1000ths of an inch. A couple things to keep in mind when selecting the thickness is getting an appropriate balance. If the conditions don’t dictate a very thick liner, an 8 mil or 12 mil will still perform exceptionally well. As you go thicker, you start to see diminishing returns when looking at the cost and the weight of the material.

4. Poly comes in black, white and translucent. What are the benefits of the different colors?

Another option to look at when it comes to selecting poly is the color. The most common colors are black, white and translucent. While the color does not have any effect on the performance of the vapor barrier in a crawlspace, there can be benefits to selecting one over the other.

Black has long been associated with the traditional crawlspace vapor barrier and you can still find it under many homes today. With the growing popularity of closed/encapsulated crawlspaces over the past 20 years, other colors have now become the norm.

These days, the most popular choice of color belongs to the white polyethylene vapor barrier. Let’s face it: white poly brightens the crawlspace and makes it look nice and clean. So much so that the tape used on the seams is also white. It creates that “wow factor” when a homeowner gets their first look into their complete crawlspace job.

Of all the color options, translucent has a true utility, especially when used on the walls or piers. As any PMP will tell you, having more visibility for termite inspections is always a plus. That is why when conditions permit, we recommend using a translucent liner on the walls and piers. It still provides the same performance as the other options, and a clear liner is usually a little more cost effective too.

5. What are the benefits of buying poly liner from Crawlspace Depot?

Crawlspace Depot has a wide selection of liner that fits almost any need. We currently carry 23 variations of liner which span many different types, thicknesses, roll sizes and colors. Plus, most orders ship out the same day if ordered before 2 p.m.

We also work with the manufacturers to ensure we are receiving a quality product that will meet or exceed specifications. That “above and beyond” mindset is one that we bring to all elements of our operations, especially our customer service — our team of representatives are here to answer any questions you may have about our products or about best installation practices.