How to Install 6 Mil Greenhouse Poly Film onto a Steel Frame High Tunnel Greenhouse

by Chris Charlwood May 08, 2026

A quality greenhouse covering is one of the most important investments you can make for your growing season. At Grizzly Shelter, our steel-framed high tunnel greenhouses are designed to work with standard 6 mil greenhouse polyethylene, giving you the flexibility to choose either a single-layer or double-layer covering depending on your climate and growing goals.

Single-Layer Poly: Simple and Cost-Effective

A single layer of 6 mil UV-stabilized greenhouse poly is the most popular choice for seasonal growing. It provides excellent light transmission while protecting plants from wind, rain, and harmful UV exposure.

To install:

Unroll the poly on a warm, calm day (15°C or warmer is ideal).
Pull the plastic evenly over the arched frame without overstretching it.
Secure it using wiggle wire and lock channel for the strongest, most professional installation.
Keep the plastic tight to reduce flapping, which shortens its lifespan.

A properly installed single layer typically lasts 4–6 years, depending on weather conditions.

Double-Layer Poly for Better Insulation

If you're growing year-round or in colder climates, a double-layer system is an excellent upgrade.

The recommended configuration is:

Outer layer: 6 mil UV-stabilized greenhouse poly for maximum weather resistance.
Inner layer: 6 mil anti-drip greenhouse poly to reduce condensation dripping onto your plants.

An inflation blower continuously maintains a small cushion of air between the two layers. This insulating air space can reduce heat loss by up to 40%, helping lower heating costs while creating a more stable growing environment.

The blower operates continuously using very little electricity and also helps keep both layers tight during windy conditions.

Roll-Up Sidewall Options

Roll-up sides are one of the best upgrades for any high tunnel greenhouse. They provide excellent natural ventilation while helping control temperature and humidity.

Common options include:

Manual hand crank systems
Gearbox crank assemblies
Pipe-and-crank systems using galvanized steel tubing
Rope-and-pulley systems for smaller greenhouses
Electric roll-up motors for larger commercial installations

Most systems attach the greenhouse poly to a galvanized pipe running the full length of each sidewall. Turning the crank rolls the pipe upward, opening the sidewall for ventilation.

Many growers combine roll-up sides with screened end-wall vents or doors to maximize airflow during hot summer months.

Poly Installation Video

Built for Canadian Conditions

Grizzly Shelter high tunnel greenhouse frames are manufactured from heavy-duty galvanized steel and are designed to accommodate both single and double-layer greenhouse coverings. Whether you're extending your growing season, producing vegetables year-round, or starting seedlings, selecting the right covering and ventilation system will maximize your greenhouse's performance for years to come.

Need help choosing the right greenhouse poly or roll-up side kit? Contact the Grizzly Shelter team—we're happy to help you select the best option for your growing conditions.