How much does it cost to build a greenhouse?

A greenhouse is a structure that is designed to help plants grow year-round. It affords protection from the elements while allowing sunlight to flow through its confines. Greenhouses are always constructed of a transparent material such as glass or plastic. These include polyethylene ¹, corrugated fiberglass ², PMMA acrylic glass, and polycarbonate ³ sheets. Structures range in size from small garden sheds to large, industrial greenhouses.

Building a greenhouse costs on average $13,000 to $20,000, with the average homeowner spending around $16,500 on building a greenhouse measuring 12'x12' that is constructed from polycarbonate sheets and a cedar wood frame.

Pros and cons

Before you decide to build a greenhouse, you must weigh out the pros and cons. If you genuinely enjoy gardening and desire a space where you can indulge your hobby year-round then a greenhouse might be a superb investment. However, if you are simply building a greenhouse to save money instead of buying vegetables at the local store then you will want to carefully consider the costs involved before making a final decision. Without a doubt, there are pros and cons involved in constructing a greenhouse.

Things to consider before building a greenhouse

If you have decided to build a greenhouse then there are many things that you need to take into consideration, such as what will you be growing? Will you be starting seeds or overwintering plants? If you will have full-grown potted plants, then you will need a greenhouse that is at least 10’x10’ so that you have enough room for plants on either side, with a walkway that is at least a foot wide in the center. If you have an interest in hanging plants, then you will want a greenhouse with cross-beams so you can effectively hang the plants. Some plants, such as orchids, must have light-diffusing glazing to protect them from direct sunlight. Remember, in the winter the sun’s position is further from the Earth and the days are shorter, so plants often require artificial grow lights in the greenhouse.

Most greenhouses are positioned north-south. However, some people opt for an east/west position. You’ll need to make sure no trees or shrubs inadvertently shade the greenhouse. You can choose from a rounded, peaked, double-sloped, or lean-to design.

You must determine the type of flooring in the greenhouse, such as concrete, rubber flooring, interlocking tiles, gravel, or soil. When constructing the greenhouse frame, never use pressure-treated pine to build a greenhouse because the chemicals can leach into the soil and kill or damage the plants. Use cedar, PVC piping, or galvanized steel ⁴ to frame your greenhouse. The covering on the greenhouse, referred to as glazing, can be made of polyethylene ¹ film, polycarbonate ³ sheets, corrugated fiberglass ² sheets, or glass.

Freestanding vs attached

You will have to decide between a freestanding or attached greenhouse. Both types have their pros and cons. A freestanding structure stands alone, but an attached structure can be incorporated into the side of a shed, garage, house, or some other structure. Here is a brief outline of freestanding vs attached greenhouses.

Heated vs unheated greenhouse

Technically, a greenhouse is only heated by the sun and a hothouse is heated using artificial sources. However, many people with a greenhouse want to heat their greenhouse using an artificial heat source if they live in a region that suffers from particularly cold winters.

A heated greenhouse lets you grow year-round. However, some only want to use their greenhouse seasonally so do not bother to heat in the winter months.

Another consideration in choosing between a heated versus unheated greenhouse is the type of plants you will be growing. Some rooted and leafy vegetables will live in an unheated greenhouse if they are protected from the snow. However, if you grow tropical or warm-season vegetables then you will need a heated greenhouse.

Types/Style

One of the most important considerations when building a greenhouse is the type and style. You will want the greenhouse you choose to effectively utilize the light for its position. If you live in an area that experiences considerable snowfall, then you will want to pick a style that won’t be damaged by it.

A-Frame greenhouse

An A-frame is a common greenhouse structure. It is simple and requires only minimal building materials. In areas with snowfall, the snow often slides off the roof without causing damage. Air circulation within an A-frame greenhouse is often not ideal because of the corners. Situate the A-frame greenhouse so it faces south for best plant growth results. Average costs are about $25 per sq.ft.

Gothic arch greenhouse

The Gothic Arch greenhouse design is a form of the Quonset design, with a semicircular frame. The greenhouse is typically constructed using galvanized pipe. The total frame is circular in design. Plastic sheeting is usually used for such the Gothic Arch style. The simple design is ideal for shedding snow and rain. The only drawback is the low sidewall, which can limit grow space and restrict headroom. Average costs are about $25 per sq.ft.

Lean-to greenhouse

A lean-to greenhouse shares the wall of a shed, garage, or house. In many cases, a lean-to greenhouse is an addition to the home and formed of all glass. The lean-to greenhouse shares a wall with another structure, so the cost of construction is less than a stand-alone greenhouse. The temperature within a lean-to greenhouse is hard to regulate because the wall of the structure absorbs heat, but the greenhouse loses heat. A lean-to greenhouse should be built so it is south-facing. Average costs are around $10-$25 per sq.ft.

Dome greenhouse

A dome greenhouse has excellent structural strength that can easily withstand all four seasons. Of all the greenhouse styles, the dome greenhouse has the greatest snowload capabilities. In addition, the design maximizes light for optimal plant growth. The style is usually made from polycarbonate ³ panels or sheets of glass. The average price is $33 per sq.ft.

Hoop greenhouse

Hoop greenhouses are shaped like a hoop lying across the ground. The design is very inexpensive and easy to construct, which makes it popular with DIYers. However, if you want a permanent hoop greenhouse then you should have a contractor undertake the construction. The hoop house is usually covered with plastic sheeting. The shape of the hoop structure lets snow and water easily slide from the top, however, the design is not as sturdy as an A-frame. The price averages $5-$10 per sq.ft.

Pit greenhouse

A pit greenhouse is constructed by digging a hole in the dirt and then building a greenhouse roof over the top. The benefit of a pit greenhouse is that the earthy floor can help the space maintain a 50-degree temperature year-round. The pit greenhouse always stays about 10 degrees warmer than that of an above-ground greenhouse. Average cost is $6-$12 per sq.ft.

Barn-style greenhouse

A barn-style greenhouse is often favored in areas where it gets hot during the summer months because the design features ground-level vents to keep plants cool and improve air circulation. With a barn-style greenhouse, there is an edge where the roof connects with the sidewalls, which are often slanted or vertical. The roof is sturdy and strong. Also, there is a lot more headroom in a barn-style greenhouse than an A-frame. Average costs are $25 per sq.ft.

Solar style greenhouse

Solar style greenhouses are often called Chinese designs. The structure always faces south and has supported walls ⁵. The solid north wall helps to maintain the consistent temperature within the greenhouse structure and provide strength. Such a greenhouse is always made from building materials that exceed 30 inches in thickness. The south wall is arch-shaped to absorb the sun’s rays. The peak is 12 to 18 inches tall. The material of the south side wall can always be rolled up to provide ventilation. Insulation pads ⁶ constructed of straw are placed on the south side during the winter to help hold in heat. This style can easily cost up to $30,000 depending on size, frame type, insulation, HVAC, and water system.

Conventional (post and rafter) greenhouse

The conventional style is extremely common. It is very strong because it has rafters which lend strength to the entire structure. The design is top-heavy so the base will have to be anchored or footed ⁷. This is a very straightforward and simple design that is easy to construct. The long side walls maximize space for growing. Average price of $25 per sq.ft.

Framing

Greenhouse frames are made of PVC, metal, or wood. Each one has its pros and cons. Cost and appearance are always a factor when choosing a type of framing material.

Glazing

Glazing is a term that refers to the material used to cover a greenhouse. It lets sunlight into the structure, while protecting the plants it houses. Glazing also helps control temperature and humidity. The type of glazing that you choose will depend on the location of the greenhouse and the crops you will be cultivating. Another factor to consider is the longevity of the glazing material. Some forms of glazing will last a lifetime and others only a season or two. Many people want opaque glass for privacy in the greenhouse and others like translucent material so they can see out and in.

Insulation

When winter arrives, it is time to insulate your greenhouse. You can line the interior with plastic to create a double-glazing effect. It will also help seal off any air gaps. Bubble wrap is another insulation option. Big bubbles offer the greatest insulation value while continuing to allow light through. The price of bubble wrap averages $67 for one 24”x125’ roll. Thermal insulation foil is used in the far north where the temperature gets exceedingly cold. Ideally, bubble wrap insulative material should be used on the whole structure for best results. However, thermal insulation must only be used on the sides so that the plants continue to receive light. A roll of thermal insulation that measures 16”x25’ averages $16. If you live in an area that experiences extensive snowfall, then do not dig the snow away from the greenhouse because it is highly insulative.

Heating, cooling, and ventilation

You can use a simple space heater that is vented or unvented to warm the interior of your greenhouse. Natural gas or propane ⁸ units are typically used. If you choose a vented heater then you will have four types to choose from: condensing units which are high efficiency, gravity vented, power vented, and separated combustion, which offers a thermal efficiency of at least 80 percent or higher. Unvented heaters can increase the CO2 in the air for better plant growth. They are also almost 100 percent efficient, which saves on energy. Many unvented units require oxygen to be pumped into the greenhouse to replace the oxygen the unit uses. By pulling in colder outside air, the heater must run longer to warm the space. The cost of a greenhouse heater ranges from $54-$2,000 or more, depending on the type, size, and efficiency rating.

Keeping a greenhouse from overheating in summer requires using vents in the greenhouse, if available. Also, shade covers help. Always have fans within the greenhouse to circulate the air and keep the plants cool. Dampening the greenhouse also cools the space. Greenhouse cooling pads ⁶ affixed to the walls will help.

Floor/Foundation

You must determine the type of flooring in the greenhouse. Some people to choose to leave a simple dirt floor where they can plant directly in the soil. However, others use flooring such as rolled rubber flooring with an anti-grip design which averages for $1.95 per square foot for 8mm-thick. Interlocking plastic tiles with drain holes are another option. The interlocking tiles measure 22”x22” and are sold in boxes of 12 for $163.99. The tiles offer excellent drainage. For permanent flooring, you can choose textured concrete with a trench drain ⁹. Concrete layers charge $35-$85 per hour to grade ¹⁰ the soil and compact the site, place concrete forms, and pour, finish and pattern concrete. You can also opt to lay a pea gravel walkway in the greenhouse which affords excellent drainage and good traction. The price of 5 yards of pea gravel averages $430.

Doors

You can have sliding doors, roll up doors, or a hinged ¹¹ door for your greenhouse. Some people choose one entrance door and others choose two. The size of the door will depend on if you are pushing machinery into the greenhouse which might require a sliding door, rollup door or dual-hinged doors. A prehung hinged door averages $500. A roll up door averages $1,000. A single sliding door for a greenhouse averages $1,000.

Electricity and water supply

You can choose simple hand watering for your greenhouse, but many people opt to have piping water, a plant drip system, or an automated water system installed. Landscapers typically charge $45-$75 per hour and can install a water system in the greenhouse. Electricians charge $65-$85 per hour to install electricity for lights, extension cords, and power tools in the greenhouse.

Labor

If the site where the greenhouse will be located requires excavation to level ¹⁰ the area or remove underbrush, then you will have to hire an excavator. The cost of excavations depends on the land. Flat to moderately sloped land with light to medium vegetation normally costs $3-$6 per sq.ft. Sloped or hilly land with heavy vegetation averages $15 or more per sq.ft.

The price to hire a landscaping contractor to construct the greenhouse will average $45-$75 per hour for labor to frame the greenhouse and apply the glazing. Landscaping contractors might charge by the hour or by the project.

Many people opt to hire a handyman to construct the structure and apply the glazing. A handyman charges $60-$90 per hour or they charge by the job.

Enhancement and improvement costs

Shelving and benches

You can place shelving in your greenhouse to hold potted plants and supplies. Some people also use them for potting. The average price of shelving is $75. Benches are nice to sit on and pot plants. The average price of a greenhouse bench is $69.

Watering/misting system

A watering/misting system can be installed by a landscaper. Landscapers charge $45-$75 per hour for labor. The system keeps the soil moist without flooding it. The average cost to install a water/mist system in a greenhouse is $500-$1,000.

Rainwater guttering

A rainwater guttering system can catch the water that you can reuse to irrigate. The gutter system also keeps water from running down the sides of your greenhouse and saturating the soil. A 10’ gutter that is 5” rounded averages $28.50. You can have a landscaper install the system. Landscapers charge $45-$75 per hour for labor. A handyman can also install guttering. A handyman charges $60-$90 per hour or they charge by the job.

CTT and security lights

You might want to have CTT and security lights installed around your greenhouse because some crops and are valuable. They can easily be stolen without the protection of a security system. Electricians charge $65-$85 per hour to install lighting.

Additional considerations and costs

• Depending on where you live, you might be required to purchase a zoning permit and building permit. The cost of permits averages $250-$500.
• Building a greenhouse can be a DIY project. Kits are sold that provide instructions on how to build the greenhouse. You can also design your own greenhouse if you have a basic understanding of carpentry. However, for a greenhouse that is made to last for years, it is advised that you hire a skilled landscaping contractor that specializes in greenhouses. A 6’-12’ greenhouse kit with polycarbonate ³ panels and a wood frame averages $2,000.
• When hiring a contractor you should always research the company on the internet, ask for references, verify their license and insurance, request a written permit, and check the contractor with the Better Business Bureau. Also, obtain more than one quote from various contractors. You should never choose the lowest or the highest, but instead opt for the middle-priced quote.

Remodeling Terms Cheat Sheet

² Fiberglass: Plastic that is reinforced with glass fibers. The fibers may be mixed randomly throughout the plastic, or come in the form of a flat sheet, or be woven into a fabric

⁴ Galvanized steel: Steel that has had a protective zinc coating applied to it to make it resistant to rusting

⁶ Pads: A cushion placed under a carpet to absorb impact, thus extending the life of the carpet

⁷ Footed: A support for the foundation of a house that also helps prevent settling. It is typically made of concrete reinforced with rebar, but can also be made of masonry or brick. It is usually built under a heavier part of the house like a wall or column, to distribute the weight of the house over a larger area.

⁸ Propane: A hydrocarbon gas used as a common fuel source

⁹ Trench drain: An outdoor buried drain line that leads water away from the house. Water runs through a trench filled with gravel into a perforated pipe underneath, which leads the water downhill to a safe area

¹¹ Hinged: A type of joint that attaches two items together but allows one of them to swing back and forth, such as a door attached to a door frame