It is hard to talk to three people in the same room that all agree on what makes high tunnels and greenhouses different.
In this post we go into A TON of detail as to what makes a High Tunnel a High Tunnel, how Greenhouses differ, which structure might be easiest to get a permit for, and...which structure type is right for you.
In short, High Tunnels are un-heated plastic covered growing spaces most often configured with manual ventilation and without concrete anchors while greenhouses are glass or plastic covered protected growing spaces often including permanent utility hook-ups, heating, exhaust systems, Horizontal Air Flow (HAF) fans, and with concrete anchors and sometimes a concrete pad.
While, I provide a quick answer to what each structure is above... in recent years the lines between the two structures have become much blurrier.
This is mainly due to High Tunnels being more economical EVEN when decked out to include all the defining features of a Greenhouse.
Keep scrolling to get a better understanding of:
- What really makes a high tunnel a high tunnel
- What really makes a greenhouse a greenhouse
- How the uses of each structure differ
- Which structure is BEST FOR YOU
- More on how growers are blending both into one structure
Defining High Tunnels vs Greenhouses is Important
If you're reading this, you likely are wanting a little guidance as to whether a High Tunnel or Greenhouse would best fit your needs. In order to get to the bottom of that the first step should be to provide a little more detail about what each really is.
Defining each sounds like an easy enough task, but...
The lines between these two growing structures have often blurred, especially as small farmers have done their best to squeeze everything possible from their structure(s).
Even though some "line blurring" has occurred, it is still important for YOU to set the parameters by which YOU want to define the structures. This way you can better compare them and decide which is right for you.
Two Primary Ways High Tunnels and Greenhouses are Defined
You can define either structure by:
- How they are being used, or
- By its structural features
Which of the above ways to classify a structure is correct?
That can be up for debate, but if you read on we feel we've made some compelling reasons why setting boundaries based on architectural features makes most sense.
The above is especially true when your money or time could potentially be on the line if there are ever issues with your municipality regarding permitting, usage, occupancy, and more.
Defining High Tunnels and Greenhouses by How They're Used
If we're defining structures based on what they are ACTUALLY used for, here are what greenhouses are often used for:
- Seed propagation
- Potting and re-potting plants, and
- Commercial retail sales
Alternatively, one could define a high tunnel or hoop house as a structure where in-ground planting is the primary activity.
While, the above sounds cut-and-dry, it isn't; High Tunnels and Hoop Houses have increasingly been utilized for starting seeds, potting plants, AND retail sales.
Defining a High Tunnel and Greenhouse by Structural Features
Here is how we would take on defining each structure if going by structural features.
Traditionally, greenhouses include the following structural elements:
- Concrete footers as anchors, or more often than not, a complete concrete pad.
- Complete utility hook-ups in the form of water, gas, and electricity.
- Propane or Natural Gas Heater(s) for temperature control
- Thermostatically controlled exhaust fans
- Thermostatically controlled power intake shutters
- Interior HAF fans
- 8 mm Polycarbonate Sheeting / Hard End-Wall Coverings
From that same traditional point of view, a high tunnel hoop house would not come with the above structural configurations.
But, as we have increasingly seen, high tunnel hoop houses can indeed be anchored with concrete footers, can come with heaters, and sophisticated ventilation systems.
For a dollars stand-point, it is good news for farmers that High Tunnels can be retrofitted to work as a greenhouse system. It maximizes the investment and provides a structure with a lower initial price point.
High Tunnels and Greenhouses Can Be Propagation Houses
If you are planning to start seeds in a structure with supplemental heat and ventilation, you would likely want to call the structure a Propagation House.
Propagation Houses are exactly as they sound. They're used to start seeds, and function as a greenhouse.
While there are benefits to starting seeds over covered soil (to reduce humidity) it doesn't necessarily matter for the defining of the structure... when you are using a structure primarily for starting seeds you are growing in a propagation house.
Turning Your Existing High Tunnel Hoop House into a Propagation House
For many beginning small farmers, seed starting begins indoors. Literally, inside. As in... the inside of an actual house.
After all, it is much less costly to start trays of seeds indoors, and deal with the hassle of transporting them outdoors, than it is to run gas lines and install a heated greenhouse.
This presents logistical challenges though, even for the smallest operations.
While many farms don't have propagation houses, many do have a small High Tunnel or Hoop House that is used for in-ground planting / season extension. It is not uncommon for these structures to be converted into propagation houses.
To convert a High Tunnel Hoop House to a Propagation House you Should Consider:
- Laying 3.2 oz woven weed fabric to cover the earth
- Install a propane or natural gas heater with a thermostat
- Install an exhaust fan and a corresponding power intake shutter
- Have the fan and shutter hook up to a thermostat
- Installing HAF fans to keep air moving
The smaller the High Tunnel Hoop House being converted to a propagation house, the less it will cost to make the transition.
The heaters will need to be sized based on your structure volume, and desired temperature.
Your exhaust fans will need to be determined by your structure volume, and desired air transfer.
If you want help sizing the heater and fans you require for the structure size you have, you can shoot us a message at our Contact Us form. Just let us know your structure size, minimum desired interior temperature, what the lowest exterior temperature will be when the heater is operating, and your zip code.
Permitting for a Greenhouse vs a High Tunnel
The way you decide to set up your structure could have large implications for permitting.
Permits are issued based on different guidelines depending on what municipality you are building your structure in. The hoops you need to jump through (pun intended) to get a permit will vary widely depending on:
- Your municipality
- Your intended structure usage (will it be occupied vs not occupied)
- The zoning classification of your build site
- How your municipality views your structure (whether they view it as temporary or permanent)
Some states have what is called an agricultural exemption whereby structures being built for the use of agriculture have no need to get a permit. This agricultural exemption should cover the construction of high tunnels or greenhouses, BUT, not all municipalities honor it.
Some municipalities may even require your structure to not only get a permit, but have stamped engineered drawings that go along with the structure, and guarantee structural code compliance is being met.
If you need stamped engineer drawings with your High Tunnel or Greenhouse shoot us a message on our Contact Us page. This is something we have gone through multiple times before.
Is it easier to gain a permit for a High Tunnel or a Greenhouse?
High tunnels, in addition to being agricultural structures, can often qualify as temporary use structures due to the fact that they won't be anchored with concrete footers, and they won't have a concrete pad.
Municipalities may also require that heating elements not be used since those would require permanent utility hook ups.
For high tunnels, the fact that it might be considered a temporary use structure by the municipality will help the permitting process.
High tunnels are also less likely to require the need for engineer stamped drawings to accompany a permit application, which is a big deal due to the fact that engineer stamped greenhouse drawings are usually required on a per project basis, and usually add moderate to significant expense to the purchase of a structure.
If you have already done the research and know your municipality requires stamped drawings accompany your permit application, it is best to know this BEFORE requesting a structure quote. We go through this process a number of times each year, so feel free to drop us a line on our Contact Us page.
Which Structure is Right for My Farm?
As mentioned above, some of the defining qualities of a high tunnel and greenhouse can overlap.
For us though, if the intent of your structure is to focus 100% on seed starting and you are going to need to keep those seedlings warm in the beginning of the season, a greenhouse type of structure (Propagation House) would be appropriate for you.
If the intent of the structure is to focus on in-ground plantings that are planted based on seasonally appropriate crops (such as tomatoes in the summer and carrots or kale in the colder months) than a high tunnel is probably the structure you need.
Hopefully this post has helped clarify the differences between high tunnel hoop houses and greenhouses, even while many of the lines between the structures blur.
If you are interested in working through your own deliberations with one of our tunnel specialists please feel free to shoot us an email at email@example.com or give us a call at (833) 886-6351.