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Is A Vapor Barrier Good For A Greenhouse?

A greenhouse can be constructed from all different types of materials. Some structures are big and expensive, while others are smaller and more cost-effective. However, the one thing that they all have in common is a vapor barrier or a vapor retarder. Without one, moisture could seep into the walls, roof, and structure causing mold and mildew to grow or causing the structure to rot.

A vapor barrier is good for a greenhouse as it controls moisture caused by high humidity, keeping the greenhouse free from mold and mildew. Installing a vapor barrier on the ground and walls prevents moisture entering from the outside, giving you better control over the internal environment.

A vapor barrier helps to prevent moisture from spreading and can prevent water damage to your greenhouse. By ensuring that your greenhouse is safe from mold, mildew, rot, and water damage, the plants you grow inside your greenhouse will be healthy, strong, and disease-free. First, let’s look at why a vapor barrier is a good idea for your greenhouse.

Why Is A Vapor Barrier Good For A Greenhouse?

A vapor barrier is a necessity for any greenhouse under certain conditions. A vapor barrier is a low-permeable material that controls or regulates the movement of moisture in your greenhouse.

The correct term for a vapor barrier is a vapor diffusion retarder (VDR). The goal of a VDR is to prevent moisture from collecting and corrupting your greenhouse structure. True VDR’s allow a small amount of permeability while still protecting the structure from moisture.

Vapor barriers are recommended in certain situations and can be tailored to suit your climate and region. For example, as a greenhouse is a contained growing system, it will have high humidity levels, and a vapor barrier will control moisture inside the greenhouse.

Moisture is a great heat conductor, but moisture from inside the building can contribute to the deterioration of the structure and the covering of the greenhouse. Therefore, six mil plastic sheeting is the best material to use as a vapor barrier for the roof and walls of a greenhouse.

Fiberglass should not be used as a connecting wall on an attached greenhouse. Even if a layer of plastic is used together with fiberglass as a vapor barrier, the moisture inside the greenhouse will affect the insulation because of the humidity and high temperatures.

  • Many greenhouse growers install a vapor barrier on the ground underneath their greenhouse structure as a preventative measure to stop moisture from seeping up from the ground and into the greenhouse.
  • Not only does a vapor barrier on the ground prevent heat loss, but depending on which materials you use, it can help to conserve soil moisture and prevent the spread of soil-borne diseases.

Here’s a quick video where this greenhouse builder explains that you really only need lumber and vapor barrier to build a greenhouse:

Which Materials Are Used As A Vapor Barrier In A Greenhouse?

Any greenhouse structure can be made from galvanized steel, aluminum, wood, plastic, or glass. Steel or plastic are great options to use for your structure if you are on a budget. Choosing the ground cover all depends on what type of greenhouse you are building and where it will be situated in your garden.

The choice of materials for the greenhouse covering, which will go over the structure, is essential as it will affect how much light your plants will receive. Too much light and heat and your plants could die, too little heat and too much shade and your plants could die.

  • Any material can cover a greenhouse as long as it can keep moisture out and allow sunlight in.
  • The size and shape of the structure should determine which material the walls and the roof should be covered in.
  • The choice of materials could also be decided by whether the structure will be permanent, semi-permanent, or mobile.

Using a lightweight material like plastic on a semi-permanent or mobile greenhouse structure would make more sense than heavy fiberglass or glass. However, using fiberglass or glass on a permanent structure will be a more cost-effective and a better solution in the long run.

Vapor Barrier Materials To Cover The Greenhouse

Greenhouse plastic is the perfect solution to use as a vapor barrier covering your greenhouse. There are four recommended types of plastic to use on a greenhouse. Most will last for three years or more before they need to be replaced unless they are damaged by extreme weather conditions or for any other reason.

Polyethylene Plastic – Utility-grade polyethylene plastic is mainly used in small to medium-sized greenhouses. Purchase a poly repair kit to repair small tears in the plastic. If well maintained, the plastic will last about three years.

Polycarbonate Plastic – This plastic is considered the best for use on a greenhouse. Because of its double-wall design, it has excellent heat and humidity-retaining features. In addition, it could last for ten years or more if well looked after.

Copolymer Plastic – Copolymer plastic is stronger than polyethylene and can last for three years if regularly maintained.

Polyvinyl Plastic – This is an expensive plastic, but the hardiness justifies the price. It will last for five years if well maintained.

Vapor Barrier Materials To Use On The Floor Of A Greenhouse

If you are growing plants directly into the ground in your greenhouse, flooring can be installed first to create a weed-free, vapor-tight environment. There are various types of ground cover to suit your needs. Be careful when using gravel or a dirt floor as they do not protect your plants from pests, and they don’t retain heat.

Weed Guard Ground Cover – This standard black polyethylene ground cover will suppress weed growth while conserving soil moisture.

Polymax Reflective Flooring – Reflective greenhouse flooring is an excellent choice as a floor covering in your greenhouse. It will keep the environment warm by distributing heat while reducing your energy costs and can prevent the spread of soil-borne diseases. In addition, by installing this 14 mil material with the white side up, the light will be reflected at the plants, providing better lighting and growing conditions.

Black Or White Silage Film – This five mil sheeting works well as a reflective cover in a greenhouse. It works well as a weed and moisture barrier and is tear and puncture-resistant. Place the film on the floor over the existing ground covering and secure.

Concrete – Concrete is porous and allows water to drain while retaining heat. Concrete creates an impenetrable barrier, protecting your plants from pests.


While a vapor barrier is highly recommended for use in a greenhouse to maintain heat and control moisture in your greenhouse, when and why you should use it depends on your growing conditions and budget.

Not all vapor barriers are designed for use in a greenhouse. However, a greenhouse does have specific requirements to control the moisture in the structure to prevent mold, mildew, and rot.

There are various wall, roof, and floor coverings available to suit your particular climate. Ensure that you do your research first before buying to obtain the best materials to suit your needs and growing conditions.

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