Building your Foundation
To protect the ground beneath, and to ensure a stable foundation, wood, concrete, and even brick can be used to create an underlayment for a healthy, happy greenhouse. A strong foundation ensures structural stability within the greenhouse, a clean interior, and opportunities to install various systems for drainage, electrical connections, and more.
Wood
- Wood is a popular choice for greenhouse foundations due to its relative low-cost and ease of installation. A simple wooden frame can be placed over a ground cover, like landscaping fabric, to allow water to pass through without allowing weeds to sprout. From there, it can either be filled with gravel or mulch, sealed with wooden boards, or made solid with masonry. Sturdy, rot-resistant wood like cedar is a good option when building your greenhouse. Additional boards can be used to raise the foundation, and therefore increase the vertical space within the building. However, the more room inside, the more air will need to be heated, and the further air will have to travel in order to adjust temperatures.
- Due to humidity and weathering, cedar and even pressure treated wood will begin to decay and require investment in replacement. Plastic decking material won’t rot with moisture and may last longer before being vulnerable to damage.
Concrete
- Concrete is a heavier, and therefore more durable option when it comes to the foundation of your greenhouse. Some cities may require a concrete foundation, depending on your location and the size of your designs. The larger the greenhouse, the more essential it is to ensure the base is strong and sturdy (like in the case of heavy glazed windows). If it’s an attached greenhouse, the new foundation is often level to or only a few inches below the original foundation. A drain will need to be installed within the concrete to allow water to pass through into the ground below, rather than collecting at the bottom
The Supporting Structure
Framing is the basic supportive skeleton within your greenhouse; the most popular materials include aluminum, steel, and wood. Rigid PVC pipes or rebar are excellent options for simple forms of hoop-house construction.
Aluminum is a durable and affordable option and is commonly found in pre-made ‘greenhouse kits’. Aluminum is lightweight without sacrificing strength and won’t rust like steel frames. Heavy gauge aluminum is ideal for a stronger greenhouse.
Wood warps and rots quickly in a humid greenhouse environment, and while some types of pressure treated lumber can perform fairly well, certain types have been found to give off fumes that can harm plants.
Steel is much heavier than aluminum, making it more expensive to ship and less suited for certain structural components that need support over long spans. Additionally, steel is susceptible to rust.
Covering your Greenhouse
The covering you choose for your greenhouse is just as essential as its bones. This will determine the amount of light that’s able to enter your greenhouse, as well as be a major factor in the overall durability and aesthetics of your creation.
Glass
- This is the most traditional form of covering greenhouses. Made popular in the industrial period with the rise of 19th century conservatories, the heavy and permanent glass panes were prized for their aesthetic appeal. However, glass is not very efficient when it comes to containing heat. Glass transmits heat and cold very quickly. In order to truly trap heat, as well as prevent breakage, any glass used must be at least double or triple strength.
- Due to glass’ weight, it requires much heavier and stronger framing in order to support it. Glass also focuses light, rather than diffusing it. A sharp, focused ray of light can burn plants, like using a magnifying glass to set grass alight. Glass is much easier to break than plastic, and even a small crack can ultimately result in a shattered mess.
Plastic
- Plastic greenhouse covers can refer to several different kinds of material. This includes fiberglass, polycarbonate, etc. All plastics are incredibly durable, and can resist breakage from rogue baseballs, hail, and the like. Plastics can be rigid, or flexible enough to bend over a curved surface.
- Fiberglass: This is a popular choice for backyard greenhouses. Fiberglass is flexible and retains heat much better than glass. Fiberglass also diffuses the light, removing any particularly bright or dark spots within the greenhouse. Fiberglass is typically UV protected through a thin gel coat that prevents dirt from sticking. Once this wears off however, the fiberglass can appear very dirty.
- Polycarbonate: UV resistant polycarbonate provides much of the clarity and of glass. However, it is much more durable against impact, fire, and damage. Like other materials, polycarbonate is available in varying levels of stacked layers. While single wall polycarbonate is less expensive than other options, it also lacks the strength and heat-retention that can come with a multiple-walled solution. Most polycarbonate sheets can last over 15 years if well maintained, and no significant damage occurs, yet can be expensive.
- Polyethylene Film: This form of plastic doesn’t last quite as long as polycarbonate, but it is much cheaper to purchase and install. It is typically the best and most cost effective choice, if you are careful to select a high quality product.
BTL’s ArmorClear is a powerful and long-lasting option when it comes to greenhouse covers. Most greenhouse films are expected to last between two to six years. ArmorClear is a reinforced blend of high-density polyethylene (HDPE) and low-density polyethylene (LDPE). A woven inner layer resists punctures and tears, giving the cover an expected lifetime of over ten years. This kind of poly film is durable against UV radiation, while still allowing nearly 90% of light to pass through the material. A greenhouse film offers much higher rates of light diffusion, scattering light particles so that they reach even the underside of exposed leaves and foliage.
