Type of Greenhouses

There’s nothing more satisfying than eating fruit and vegetables you’ve grown yourself.
Yet, in most climates, it’s too cold for plants to grow outdoors for much of the year.
Luckily for gardeners, nowadays many greenhouses are quite affordable and easy to assemble. Some gardening stores have pre-fabricated greenhouses in stock with experts on hand to help with installation. Many companies specialize in the construction and maintenance of greenhouses, and some will ship standard or custom greenhouses and glass conservatories worldwide.

While greenhouse kits are an easier option for most homeowners, a custom greenhouse build is an excellent project for an experienced DIYer.For larger projects, it may be best to defer to an experienced installer or contractor. Keep in mind that, depending on its size and your local by-laws, you may need to obtain a permit to build your greenhouse.

It’s also important that before beginning construction, you first assess your needs, and decide on the perfect location, materials and style. You may need to prepare the space by levelling and compacting the dirt, or even digging out the footprint, installing proper drainage, and pouring a concrete pad.

Greenhouse structures

While the shape and style may vary, certain structural elements are common to most – if not all – greenhouses. Posts or columns will form the vertical supports and determine the height of the greenhouse wall.

These are topped by the rafters; they might be trusses, or curved arches and are generally placed between 2’-4’ apart. Purlins are horizontal supports connecting the rafters, and are usually spaced 4’-8’ apart, depending on the overall size of the greenhouse.

Purlins can be connected by cross-ties for additional support – this is required by some local by-laws, especially where high winds are frequent.
If building a custom greenhouse, so long as the basic structural elements are respected, the design and size options are virtually unlimited.

Though less varied, there are still several types of prefabricated greenhouse, and kits are available in many sizes.

Whether starting from a kit, or building from the ground up, the most typical greenhouse styles are free-standing greenhouses, lean-tos, hoop houses, and ridge and furrow (or gutter-connected) greenhouses.

Free standing greenhouses

The most common greenhouses are freestanding structures – they also tend to be the largest. When building a freestanding greenhouse, you can choose the shape, size and materials that best meet your needs.Generally, free-standing greenhouses have post and rafter construction with a peaked and sloping roof, but they can be built in many different shapes: A-frame, domed, skillion, or unevenly gabled.

Though most commonly made of metal supports with tempered glass panels, it’s possible to construct a free-standing greenhouse of wood as well. The wood could even extend partially up the walls, with glass between the upper timbering.

Given the finished weight of a traditional wooden or metal greenhouse, it’s important to install it on a prepared and compacted pad, which will increase the construction time and costs.

An inexpensive option is to cover a lightweight prefabricated metal structure with plastic sheeting or polycarbonate sheets. They are, however, less durable options and may require frequent repairs or periodic replacement.

A free-standing structure can be built as large as needed (providing that proper construction permits are obtained and local by-laws are respected) and might even include a planting bench or central table as well as wall shelves.

It’s possible to add heating and other climate-control measures such as humidifiers, or window and roof venting to a free-standing greenhouse to adapt the growing environment as needed. Any electricity, water, or gas required for heating would need to be redirected to the greenhouse, which can increase construction costs and might require additional permits and inspections.

Lean to Greenhouses

As the name implies, a lean-to is a structure attached to – or leaning on – a larger building. Many older homes have lean-to porches, and a solarium is an example of a more modern lean-to. This type of structure is an excellent option for the smaller yards found in urban and suburban areas and could even be installed on a large apartment balcony.

As they’re attached to the home, it is much easier to redirect electricity, water and heat to a lean-to greenhouse, though it’s best to verify local by-laws and obtain any necessary permits or inspections during the construction process.

Installing a lean-to greenhouse is usually best left to a professional contractor, as it may impact the original structure. They are generally either curved at the eave, or have a straight eave, and can be inset with glass or polycarbonate panels from the ground to the roof, or can have a base wall, which is usually made of brick or masonry.

If installed against a brick exterior wall, the bricks will help retain heat within the greenhouse.

There are a variety of pre-fabricated sizes available ranging from slightly less than a 6’ projection and going up to nearly 16’; the structure width also varies based on how many panels are installed and the width of each panel. The greenhouse height is dependent upon that of the shared wall.

There is usually sufficient space within even the smallest lean-to greenhouse for a narrow planting bench or plant shelf. The wall can be used for climbing plants or to train fruiting vines or small espaliered trees. In a smaller lean-to, there may be limited floor space for a stove or other heating or climate-control systems, but the windows and roof panel could still be designed for venting.

The larger lean-to could have a significantly higher footprint, and allow space for climate-control equipment as well as a larger central table or planting bench and still have a narrower plant shelf on the glass wall.
Because of the way it adjoins an existing structure, lean-to greenhouse can also be a less expensive option – with the structure wall connecting at the peak of the roof, technically, they’re only half of a greenhouse!

A variation of the lean-to, the even-span greenhouse is a larger, full-size structure that backs up to a building. Maintaining the advantage of proximity to utility hookups, as well as the potential heat retention of the exterior structure wall, an even-span greenhouse provides a larger interior space than a traditional lean-to, and allows for better air circulation within the greenhouse.

Hoop Houses

For gardeners on a budget, a hoop house can be an excellent option – overall construction costs can often be less than $1 per square foot. The materials used in hoop houses can be obtained at any home improvement or garden supply store, and the greenhouse is easy to build and maintain. A 2015 article by Tim O’Neill for Natural Living Ideas describes his DIY hoop house construction in detail, and gives tips for anyone considering their own project.

Named for the curved wall shape, a hoop house is constructed of aluminum pipes or plastic PVC pipes covered with polymer plastic sheeting. Though generally only a single layer of plastic is used, a second layer can be added for extra insulation. A hoop house construction does not tolerate as many climate-control options as its glass-paneled cousins: it would be inconvenient to add electricity or heating systems. Therefore, the doors should be left open in warm weather and closed during the winter. A shade cloth can also be inserted between the plastic and the poles to help reduce overheating in mid-summer.

While the polyvinyl sheeting might not be as durable as glass or polycarbonate boards, if built well, a hoop house can withstand quite a bit of wind and rain with little damage; the sloped shape of the hoops will prevent snow and ice from building up on the plastic during the winter, and minimize any damage.

Though it’s not recommended to install a greenhouse near overhanging trees – as it’s best to avoid leaf buildup on the roof, or potential breakages should branches or limbs fall – it issuggested, if building in warmer climates, to situate a hoop house where it can be shaded by trees for part of every day.

It’s important that the long side of a hoop house be south-facing, so be sure to build east to west.Further North, less shade will be necessary, and it’s best to keep any structures on the north side of the greenhouse to block the wind and help retain the heat.

A hoop house design is adaptable to any size yard and budget, and prefabricated kits are available at many garden supply stores. It’s also easy to build a customized hoop house of any size – a project that can be completed by 2-3 people over a long weekend.

Hoop houses are an excellent choice for the gardener who isn’t certain they want a greenhouse, as they don’t require a concrete pad, and can be demolished easily; they can also be upgraded and extended with little effort.

Ridge and Furrow (or Gutter-connected) Greenhouses

For anyone planning a larger footprint, the gutter-connected greenhouse is an excellent choice. Though many styles of connected greenhouses exist, the most popular type is a ridge and furrow connection.

The greenhouse is built by joining even-span structures and will have multiple peaks (ridges) with gutters at the base of each adjoining slope for redirecting rain water.

The structures can have gabled roofs or curved arches; the arched house should be covered with lighter materials such as polyethylene or polycarbonates, while the gabled house can withstand heavier coverings such as glass or fibreglass.

Ridge and Furrow construction maximizes greenhouse efficiency by consolidating space and resources; it also simplifies greenhouse expansion as another unit can simply be added to the side of an existing greenhouse – or series of greenhouses.

Though the interior can be divided into contiguous units (for example, by plant type, or interior climate) a Ridge and Furrow greenhouse is generally left open throughout.

A consolidated interior is a good choice, as it’s easier to maintain the heat-level in a larger space where less heat is escaping through walls or doorways.

There is ample space within a gutter-connected greenhouse for heating systems, electrical connections and water hookups; the close proximity of the greenhouses means that expanding the climate-control system can be accomplished at little cost if the utilities are already present in one unit.

These greenhouses are effective in many environments, though it’s important in colder areas to consider the additional snow load on the structure when planning the construction.

Unlike a traditional sloped greenhouse which allows snow to slide off, the snow will remain within the furrow of a gutter-connected greenhouse unless it is removed, or until it melts.

If not installed properly, the gutters can allow water to build up in the furrows, which could damage the structure or cast shadow, prohibiting sunlight from reaching the plants below.

Greenhouse Materials

Greenhouses can be constructed from several materials, but the frame is usually made of aluminum, steel, or wood. Aluminum is the least expensive and most durable of the three, and can also be extruded in various shapes and thicknesses for forming the post or rafters.

Steel can be heavy, and is best used for framing glass panels. If using wood, it’s best to choose a pressure-treated lumber for resisting the decay that can happen all too quickly in the moist environment of a greenhouse; be sure to also choose a wood that is non-toxic to the plants you plan to grow.

A greenhouse covering should ideally be transparent – or as clear as possible so that natural light can penetrate into the greenhouse. It also needs to be durable, yet cost-effective.

Traditionally, glass was used in all greenhouses, though it can be quite pricey. Not only are the glass panels expensive, but the heavier structure required to support them also increases the construction cost.

Fibreglass is used on many commercial greenhouses, though it is easily damaged by UV light and may only last 5 years in certain areas.

Several polycarbonate or acrylic materials have been developed for use in greenhouses, including prefabricated panels designed to insert into pre-made frames.

The most economical option is double-layered plastic sheeting, inflated between with air. It can be installed on light structures easily and though not rigid, still provides enough weather resistance to be functional; however, it lasts only 2-3 years at most before requiring replacement, so is not the most eco-friendly option.

Greenhouse Positioning

A greenhouse should be situated to the south or southeast of any existing structures, and away from any overhanging trees or structures that could damage it. It should also be on level ground – or in an area where it will be easy to level the ground – and away from low-lying areas where water could build up.

Any greenhouse structure with a ridge roofline should be oriented so that the ridge runs east-west, allowing southern exposure on a long wall.
It’s important to also consider the distance any utilities will need to span from the nearest hookup.

Final Thoughts

If you’re thinking of building a greenhouse, take the time needed to plan the project thoroughly before beginning. Consider the angles ofsunlight and shadow for the entire year, as well as the interior and exterior environments. What plants will you grow? What conditions do they require?

Think of the durability of your materials and their future maintenance requirements, as well as the initial cost of construction.

How familiar are you with greenhouse gardening? If you’re uncertain if you’ll enjoy working in a greenhouse rather than outdoors, choose a lower-cost, less permanent option for a trial period.

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