Photo courtesy of Adobe Stock/Veronika

A hoop house (also called a "high tunnel") is a hoop frame covered with plastic, high enough to walk underneath, and used to extend the growing season of vegetables, flowers, and fruits. They are also called "unheated greenhouses", "polytunnels" and "cold frames". They can be used to grow seasonal crops throughout the year. Although the indoor temperature is not much higher than outdoors when the sun is not sufficient, the hoop house manages to promote an impressive growth rate and high-quality crops. The hoop house generally does not have supplementary heating, and the crops are directly planted in the ground. Hoop houses are usually double-layered, which means they have two layers of plastic film, and a small blower is used to keep the space between the two layers inflated. This provides enhanced insulation and strength against wind and snow or ice loads, and extends the life of the plastic by preventing slapping and abrasion. If the wind is not strong, the winter overnight temperature of the double-layer hoop house may be about 8 degrees Fahrenheit higher than the outdoor temperature. In zone 7a, the soil temperature of the hoop house is rarely lower than 50 degrees.

If you want to build your own hoop house, you need to consider the following factors before you invest time and effort and the final return.

Sunlight exposure is the first important factor to be considered when choosing a location for a hoop house. Walk around your farm in the middle of winter, pace and mark several potential locations. At this time of the year, the sun will be at its lowest angle and the shadows of obstacles will be the longest. The hoop house is a solar planting area, so your site needs as much sunlight as possible in winter. Make sure you don’t choose a shaded location. We looked at three or four possible locations in the Twin Oaks Intentional Community where I live and work, and evaluated them based on all the criteria described here. We chose the best location for the winter sun, but at the last minute we had an idea to move the structure 100 feet east for better drainage. It worked, but we underestimated the shadow of a group of nine loblolly pine trees about 100 feet to the southeast. In winter, after about 2:30 pm, one-third of our hoop house was in the shade. During the two winters, we felled these trees. 

A double-storey hoop house sloping down to the west end, with no shadow to the south. Photo by Pam Dowling

Brandy Macdonald's chart

The orientation of the hoop house is usually east and west at both ends, and the longer side faces south and north to get the most light. Some books suggest that the greenhouse in the south faces the opposite direction, with the long sides facing east and west, and the ends pointing north and south. (See the picture below.) I think this is not a good idea for hoop houses where winter crops are the most important and sunlight is very precious. If tall vine crops will be your focus, then the north-south rows will provide the most uniform lighting.

Good fertile soil will be your goal. Of course, you can improve the soil when you use it. Just don't start with boulders, gravel pits, clay plates-you know.

Ideally, your site has a 1% vertical gradient from east to west or west to east. Single-story temporary structures in the warm season, such as the Highgrove Tunnel, can accommodate steeper slopes, but permanent hoop houses cannot. You can adjust the slope of your website by one or two feet within a range of more than 100 feet, but not too much.

The site needs to be fairly level from side to side. If you need to move a lot of soil to meet ideal conditions, be sure to keep the topsoil. Search for "Growth in Four Seasons: High Tunnels" on the Natural Resources Conservation Service website. The federal agency also provides grants for certain types of hoop houses through its High Tunnel System program.

Your site needs to be well drained, and you also need to accommodate rainwater runoff from the roof. There is a horseshoe-shaped V-shaped moat around our hoop house. Some growers cover the plastic roof too long and use it to divert water away from the hoop house; some growers with the hoop house have rolled up or down side walls choose to install plastic drains on the butt wall timber required for these structures , And then collect rainwater for irrigation. The collection bucket will be very low, so the water needs to be pumped or soaked and dragged to be useful.

In addition, look for locations that are not affected by wind (at non-shaded distances). Choose a location with good frost drainage, not at the bottom of the slope. 

You also need to consider road accessibility and proximity to water and electricity. If connecting to the grid is relatively easy, then do so. You can decide later whether it is worthwhile to provide an alternative power source. The inflatable blower will use very little electricity, so the financial cost will be worth it. You might want your hoop house to be close to your house, barn, or main work area, where you can pay close attention to it and suddenly show up during the strange half-hour work. For winter harvesting, please make sure your packing shed is nearby, because you don't want your crops to freeze during transportation. Most growers do not heat their hoop houses, but if you want to use wood for heating, you need to plan to obtain firewood or to lay underground pipes from furnaces elsewhere.

After seeing the benefits of the hoop house, it will be difficult to resist building another one! Or, you can build a relatively short wide hoop house. After that, you can buy more hoops and larger plastics and double the size of the original house. Leave at least 10 feet between side-by-side hoop houses; if the snow in your area is deep, more. For readers in the north, they must build a building twice the height of the building in the south.

Leave at least 10 feet between two side-by-side hoop houses. Photo by Pam Dowling

When determining the size of the hoop house, ask yourself the following questions: How much food do I want to grow? Do I already have a market? I have never met a grower who complained that their hoop house was too big. The peak height varies from 6 feet to 17 feet, the width varies from 10 feet to 30 feet, and the length can reach 100 feet, which is the most common size of plastic film.

Consider the surface-to-volume ratio. You can get more volume without increasing the surface area too much. The cost of the material is related to the surface area. In other words, it pays to be as big as possible. But 20-foot-wide structures require less support than 30-foot structures, so even if they cover the same area, the price of narrower and longer hoop frames may end up being lower than wider and shorter frames. One hundred feet may be the maximum length to work without forced airflow. Having plenty of fresh air will help your plants stay healthy. The tall windows on the end walls will help release old, warm air without cooling the plants on the ground.

On sunny days in cold weather, soil and air act as heat reservoirs. At night, heat is released, which is beneficial to plants. Therefore, to a certain extent, the more air and soil in your house, the better. The small structure does not store much heat. In addition, edge beds are usually colder, so the more center beds you have, the more comfortable the plants will be. High tunnel pioneer Steve Moore calculated that a hoop house of 28 or 30 x 96 feet is the optimal size for thermal efficiency.

If you have a preferred bed width, please choose a hoop width that fits that width. We have a 30-foot-wide hoop house with five 4-foot-wide beds in the middle, two 2-foot-wide edge beds and a 1-foot-wide path. Don't make the bed wider than you can comfortably cultivate. If you plan to drive a tillage tractor through, install the bed in the axle space.

After the hoop house is in place, make sure that no new buildings will obscure it. Photo by Bridget Alehir

Is DIY worth it? Although some people advocate the use of PVC piping instead of galvanized steel, I do not recommend it. PVC is not strong enough to accommodate large hoop houses; it degrades rapidly in the sun; it reacts with polyethylene sheets and degrades both; the manufacture, burning and final dumping of PVC will release dioxins, causing various health problems.

Some people like to buy and bend steel pipes themselves, but this is a large-scale hard work. For most of us, the price of pre-formed galvanized steel pipe is worth paying. You may be considering making 25 hoops out of 25-foot-long pipe. If you are a good grower and own a market, your basketball court can pay for itself after the first year. The advantages of commercial spectacle frames are that they have the same curve, fit together, and are of the right length.

Consider the snow load and wind force you may encounter. A 6-foot pitch hoop is sufficient to withstand snow loads up to about 9 inches. With only 4 feet between the hoops, I sleep more easily. If you are unlikely to get more than 9 inches of snow, use a 6-foot separation. If you prefer to prepare for climate change and more extreme precipitation, choose a 4-foot separation. We studied the past extreme weather in Twin Oaks prior to construction and learned that there are 32 inches of snow and a maximum sustained speed of 60 mph wind speed, as well as higher wind gusts. It was thought-provoking, but we continued. Fifteen years later, the hoop house is still standing. Other growers told me that wind speeds in the range of 75 to 80 mph would destroy a hoop house.

Hoop houses come in different shapes, and each has its own advantages. Photo courtesy of Adobe Stock/Serge Touch

The shape of the hoop house is important, especially when considering its function in your environment. Gothic shapes are easier to sprinkle snow than round Quonset shapes. Gothic provides more headroom in more areas and better sun angles. If you bend the tube yourself, it may be easier to round it.

How much side wall height do you need? You may want to be able to stand the work edge bed upright, so make sure you need 2 feet of standing space from the side wall.

The transportation cost of heavy materials can be quite high, so please check with local suppliers. Some brands are stronger than others. Check not only the cross supports and end supports provided, but also the specifications of the steel pipes. The more snow, ice, and wind you get, the stronger the structure you need. The Gothic arch structure is stronger than the Quonset shape, and the 4-foot hoop spacing is stronger than the 6-foot spacing. Double-layer plastic is stronger than single-layer. Weigh all these factors, as well as your budget and willingness to take risks. Not only should you consider the possibility of your site collapsing, but also another aspect of the risk: the impact of the collapse. If the tunnel collapses, the grower will usually rebuild it. You are at risk of losing your crops, but as long as you stay sane in the storm, you will not lose your life or limbs.

Are you considering a movable hoop house? Remember, you need to completely secure the hoop house. The movable hoop house is easily blown away by strong winds. I heard that several growers have built hoop houses and plan to move them several times a year to grow a series of crops; however, due to inconvenience, they can only move once a year.

Are you going to hang things from the rafters, or tie the plants to the rafters with rope or wire? If so, consult the manufacturer and purchase a hoop house with strong rafters. Most frames are not designed to support the additional weight of the crop. Another method is to install a separate support frame underground.

The hoop house will extend the growing season of our crops. Photo courtesy of Adobe Stock/MaryViolet 

The single-layer plastic will not keep heat at night; the indoor temperature will be about the same as the outdoor temperature. The double-layer plastic provides a difference of 8 to 10 degrees. This is very important in areas where winter crops are grown. Whenever the temperature exceeds 40 degrees, spinach and kale will grow. This will happen more frequently in a two-layer structure. The extra cost is paid for by the extra income from the faster-growing crops.

The double-layer plastic is more resistant to the weight of wind and snow or ice, because the entire shape can resist the load and distribute the weight to the entire area of ​​the hoop house. In Iowa, the double-layer structure withstood wind speeds of 80 mph, because the "bubbles" prevented any ripple effect on the plastic. Double-layer plastic may also reduce the amount of light reaching the crop. Some growers may argue about single plastic or double plastic. A 1% decrease in light transmittance will result in a decrease of about 1% in yield. This must be balanced with the possible output loss of a single-storey hoop house that is cold at night.

Nick Calabro from Klerks Hyplast (the source of the plastic film for the hoop house) reports on the study of photosynthetically active radiation (PAR) light transmission through various film combinations. (See the table below.) At Twin Oaks, we use conventional 6 mil outer plastic and inner infrared (IR) plastic, and we are satisfied with our choice. The internal plastic also has a condensate control function, which means that condensate will not accumulate and "water bomb" us or our plants. Another option is Solarig from Robert Marvel, a woven polyethylene film advertised that its strength is 10 times that of ordinary polyethylene film. It will not tear in a storm, even if it is pierced. It comes with a 4-year or 6-year limited warranty, depending on the type. Compared with standard polyethylene, it transmits 88% of the light, and about 45% of the transmitted light is diffused, which reduces plant burning and evapotranspiration, and claims to increase photosynthesis and increase yield. I have not seen this material in use. It has condensate control and infrared additives and ultraviolet blockers. It can be used as a single layer with a strap on the top, or as a double layer, using the lighter version as the inner layer.

A newer possibility that is not inflated but still has the advantages of double layers is SolaWrap, a sturdy material that looks like a bubble wrap. It has reels that are 4 feet wide, 5 feet wide, and 6 feet wide, so special channels must be used to fix it to each bow. It provides 83% light transmittance and 83% light diffusion rate.

Shuangjiao generally requires an inflatable system. If the site is too remote for grid access, and other options are too expensive or too complex, then the second layer is not feasible. The three off-grid power options used to run the inflatable blower are solar with battery, air motor, and wind energy. Another option is to use a plastic foam block connected to the bow to maintain the air gap between the two layers without swelling. This will provide some expanded insulation value, but will not increase structural strength.

Planning and building a hoop house is accompanied by its share of research and decision-making, but a hoop house that has been properly planned will become a valuable asset for any farm enterprise in the next few years.

As the garden manager of the intended community of Double Oaks in Virginia, Pam Dawling has grown produce for 100 people on only 3-1/2 acres. This is an excerpt from her book "Hoop House All Year Round: Multiple Tunnels for All Seasons and All Climates" (New Society Press), which can be found below.

Light transmission of photosynthetically active radiation through polyethylene film

Single layer standard 4 years 6 mil (0.15 mm) polyethylene

Double-layer standard 4 years 6 mil (0.15 mm) polyethylene

Double layer: outer layer, standard polyethylene; inner layer, infrared thermal insulation (HR) polymer

Single layer infrared HR polymer

Double-layer infrared HR polymer

Similar to a cold frame or greenhouse, this multi-tunnel "super dome" provides the best protection from frost and extreme heat for your delicate seedlings. The shading material stitched to the multi-tunnel roof protects the seedlings from the midday sun and heat, while the openings on both sides allow for ventilation, easier plant care and watering. Its dimensions are 2.6 x 2.3 x 9.8 feet. This product can be obtained here or by calling 800-234-3368. Item #9941.

Join us for the long-awaited return of the Lone Star State! Early bird discounts are now available online.

In MOTHER EARTH NEWS for 50 years, we have been committed to protecting the natural resources of our planet and at the same time helping you protect your financial resources. You will find tips for cutting heating bills, growing fresh natural produce at home, etc. This is why we want you to save money and trees by subscribing to our earth-friendly auto-renewing savings plan. By paying with a credit card, you can save an additional $5 and get 6 issues of "Mother Earth News" for only $12.95 (US only).

You can also use the Bill Me option and pay $17.95 for 6 installments.

Canadian subscribers-click here for international subscribers-click here for Canadian subscribers: 1 year (including postage and GST).

Already a member? Log in with your online account.

Already a member but no online account?

Already a member but no online account?