Category Archives: structure information

Adding a Softcover Structure to Another Building

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There are two ways of adding a structure to the side of a building. It can be done as a lean-to (half structure) that goes parallel to the building and up to the eave, or it can be a complete building at 90 degrees to the existing building. This article applies to the latter option.

When considering attaching an MSS structure at 90 degrees to another building, there are some important considerations to be mindful of before the purchase.

The first is that these buildings are almost always considered high humidity (especially when it is a greenhouse). This means that you will be subjecting that wall to a higher level of moisture. Extra waterproofing should be considered. This high level of humidity should be an extra concern if the intent is to use the warm air as a source of heat for the solid building.

The other thing to bear in mind is the potential snow shedding patterns from the bigger building roof. If the height difference is more than 2’, measures should be implemented to slow the process of shedding snow. Without slowing the rate that the snow comes off the taller building, the force of the impact could be triple or quadruple the weight of the actual snow.

If there is a likelihood of significant snow levels being shed, we recommend reducing the rib spacing of the first 12’ of the building. Going from 4’ to 3’ spacing will increase the strength by 1/3. Going from 3’ to 2’ is a 50% increase in strength. This will give your building the added strength for the impact of shedding snow and the volume that would potentially be on the roof.

The third thing that needs to be considered is how the cover will be fastened to your shelter at the wall. For a stand-alone building, you would be on a ladder or platform off the end but this is not possible if the end hoop is right against the wall.

One option is to have the first hoop about 2’ from the wall and then cover that section with something solid (plywood, sheet metal, Lexan, etc.). This will give you a place to crawl up and secure the cover into the wirelock.

Another option would have you put the first hoop about ½” to 1” from the wall. The wirelock channel would be installed on the underside of that hoop. During the cover installation, you would slide the cover through the gap and then wrap the cover around to the bottom. The wire inserts would be installed from the underside. This option is a little more tricky when doing the double plastic cover. After the cover is installed, the gap can be filled with square foam strips which are available at the building centers. Extra care must be exercised to protect the cover from bolt heads and nuts.

The third option would be to install the structure as per normal but about 1’ from the wall. The covering would be done as usual and once this is complete, the building would be slid up against the wall. This process is a bit risky since the building is not secured to the anchors for a short period. The longer the building is, the more challenging this option is.

The last challenge which needs some attention has to do with the method of ventilation which will be used. Typical ventilation flows through the building. In this scenario, ventilating though the building would also mean that you have to go through the attached building. It can be done, but you would be best to get some additional advice on the process.

If roll-up sides are going to be used, it must be noted that the attached building will interfere with proper airflow.

The challenge with using forced ventilation is “where does the air get into the building. It would be best to create a sketch of the building with thoughts as to what you intend to do. We will use our experience to advise you.

It is important to understand and work through these challenges before you purchase. We are here to advise.

Aerodynamics Considerations on Greenhouses

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Aerodynamics is a very complex concept in how it applies to greenhouses and similarly constructed buildings. The better that you understand these dynamics and how to deal with them, the better your chances of having long-term success with the structural integrity of your building.

In many of Norm’s presentations, he has compared the similar shape of a greenhouse to that of an airplane wing. The basic challenge is that you want the opposite result. An airplane needs to efficiently get off the ground while a greenhouse needs to stay where it is.

The greater the distance over a surface is (wing or building), the greater that the lift is. When height is combined with distance, there is a multiplier effect. That is why a pilot will extend the flaps on a wing when taking off and landing.

It is the vacuum on the backside of a structure or a wing that causes the lift. The upward force of the vacuum on the backside is actually double what the leading edge force is.

This effect happens exponentially even when a small change is made. Many people have suggested, “I am only lifting the building two feet (or some other relatively small amount)”. They do not realize that doing that small lift is sometimes adding 50% or even doubling the wind load on the building.

These forces must especially be considered when a structure is oriented so that the prevailing winds hit the sides of the building. Structurally, it is preferable to have the structure facing into the prevailing winds. If the lay of the land or the logistics of how you work in the structure do not allow this, there are ways that the stress on the building can be minimized.

The least expensive way to stiffen a building is to add crossties (also known as collar ties). Crossties tie the left and right sides of the structure together so that the load is more balanced in how it affects the structure. Reducing the hoop spacing will automatically make the structure stronger with a greater ability to resist the effects of external forces.

Ultimately, however, a structure’s ability to deal with the aerodynamics of a situation is only as good as the anchoring provided. Anchors provide stability for resisting up, down and lateral forces. There is no such thing as too many anchors.

These things add to the structural ability to handle things but it does not help the cover. Extra steps must be implemented to secure the sides of the cover. This includes but is not limited to adding extra and longer screws for the cover fastening system.

A discussion on aerodynamics is not complete without discussing windbreaks. The only effective windbreak is trees. Trees restrict the speed of the wind coming through and therefore minimize aerodynamic stresses on a building. There is an optimal distance from a windbreak. This is determined by the size, density and texture of the trees involved. Since this is something that changes with age and season, there is not a perfect formula.

One last note on windbreaks. Another building, especially a bigger building is not an effective barrier. If anything, this building will significantly increase the aerodynamic stresses on your building. Wind will be swirling in one direction and then a slight shift in wind direction will reverse the direction of the swirling.

Please note: We are not engineers and as such can not give structural opinions. The above points are simply items that should be considered and come from 40+ years of experience of watching what wind does to buildings.

Mitigating Climate Change with a Greenhouse

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In a tongue-in-cheek manner, Norm has often declared that if it weren’t for crappy weather we would not have a business.

The plain reality of the fact is, people, use greenhouses to mitigate the negative impact of weather, and nature in general, on their food and plant production.

Greenhouses allow a person to control the local environment. The more efficient they are at that process, the more profitable they can potentially be.

The main areas of this control are heating, cooling, irrigation, disease and insect and weed control. When all of these areas are exercised efficiently, production can be significantly increased and the timing of production can be better controlled.

Heating is typically the number 1 expense in operating a greenhouse in colder climates in the wintertime. Numerous covers will reduce heat loss but it is often at the expense of light transmission. The cost of certain covers may not be justified in light of the heat savings they would create. There are creative ways that the area which needs to be heated can be reduced. Growers will often choose crops with lower heat requirements to reduce the expense. Even though the heating is usually associated with cold weather, heating can also be used when dew is present to reduce the risk of fungus diseases.

Cooling a greenhouse to acceptable levels is critical during warmer seasons. During warm times, this requires a minimum of one air change per minute. If the temperature goes about a plant’s high threshold, it will stop growing for up to two weeks. There is a wide range of options for cooling a greenhouse. Many of the passive methods are more economical to install but harder to control and fine-tune. Items like roof vents are extremely effective, and have a low operating cost but are costly to install and even more costly to automate. In addition to creating uniform air changes, it is equally important to have uniformly even moving air. Stagnant air fosters diseases.

Having an area covered with a greenhouse, allows the grower to control the water to the plants. Irrigation requires the proper timing and volume of water to the plants and also proper location. Many plants perform much better when the foliage remains dry.

Greenhouses can also protect plants from excessive rain during wet seasons. One often overlooked area of irrigation is existing groundwater. When there is a high water table, care must be taken not to over water plants.

Greenhouses provide management opportunities for disease and pest control. Especially with a proper irrigation protocol, the risk of diseases can be minimized. If insecticides or fungicides are being used, it is much more controlled in the controlled environment of the greenhouse. Systems of netting can be installed over the ventilation openings to prevent the entry of airborne pests. It is important to bear in mind that this netting does restrict airflow as well.

A greenhouse also allows for more control of the weed population. Weed seeds can be allowed to germinate in the beds and then rototill them under. In the protected environment of a greenhouse, it is easy to put down black plastic for a short period of time to kill off weeds and weed seeds. It is also important to remember that if netting is used over the roll-up side openings, this will restrict airflow. Proper airflow takes priority over weed control.

When all of the above points are worked together efficiently, the grower will be able to significantly increase his or her yields. There will also be the opportunity to control the timing of the harvest to take advantage of increased pricing. i.e having a crop ready 2-3 weeks ahead of field-grown crops will easily cover the added expenses of growing in a greenhouse.

Disclaimer: we are not professional growers. The above information should only be used to draw attention to the importance of certain concepts. It is critical to seek out the advice of a professional grower to work through issues.

If you’d like to read more about these topics, let us know. We hope to have a book about this put together in time for Christmas and Winter Planning!

Modified Hanley Tunnel

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One of our most popular structures is the Hanley tunnel because it is the cheapest way of covering an area for season extension.

As a way of addressing some of the challenges and limiting factors with the tunnels, we have come up with a modified Hanley.

The two areas where it significantly improves on the regular tunnel are the side clearance and the peak for snow shedding. Instead of using 24’ of steel to make 17’ wide and 7’6” high, we are using 26’ of material to make 16’ wide and 9’ high. It still uses 28’ wide plastic with extra at the ends to make the same kind of “tails”.

Sliding the plastic up on the sides is still the way that the tunnel is ventilated and you will still have the same challenges as far as creating access.

The re-bar anchors, base plates, clasps and rope are the same on the modified Hanley as they are for the regular tunnel. We supply 5’ more of extra plastic for the tails since the building is taller.

The peak on the end hoops are very hard on the plastic, so we have designed a more rounded hoop at each end. It is strongly recommended to have 3 guides ropes at each end to brace back to the anchoring posts of the plastic.

Any structure with ends is not considered a Hanley Tunnel. We are more than willing to discuss the differences and benefits/drawbacks between tunnels and cold frames should you wish to know more.

The main thing which is critical to understand before going with a modified Hanley is the extra wind load which the structure will be subjected to. Going from 7’6” to 9’ high, results in a 40% increase in the wind load. This issue is what makes the correct tightness of the ropes an even more critical consideration.

It is also the reason why we strongly urge customers who
do not have any tunnel experience to start with a regular tunnel.

Season Extension: Ventilation & Heating

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To make your greenhouse more of a year round functioning entity, there are two main areas in which you have to make the structure more efficient-Heating and Ventilation.

1. Heating is your biggest expense for the winter so retaining heat is a priority.

The easiest way to retain heat in your greenhouse is to install a double poly cover with air in between. A small squirrel cage blower attached to the inside layer of plastic aids in maintaining air between layers.

The more dead air space between these layers you can create, the closer you will be to achieving a 30% reduction in heat loss. Holes will result in air movement and therefore less efficiency. 3″-5″ consistent space is ideal. It is a given that you would have less than that around the edges and over the ridge.

Double plastic will have a considerably longer life span. It is important to realize that as plastic gets older, the light transmission will be reduced which will reduce production.

Infrared plastic (IR poly) does further reduce heat loss and increase light diffusion so it can also be a consideration when looking for ways to reduce heating costs.

2. Ventilation is also one of your biggest considerations for the warmer times of the year. Ventilation can be done through forced or mechanical methods or passive through vents or roll up sides.

Vents are extremely effective since they can be placed higher up where the heat needs to be expelled. Mechanical ventilation is more costly both up front and to operate but it is easier to control since it is attached to a thermostat. For mechanical ventilation to be effective, it needs to be sized and located properly.

Roll up sides are less costly and simpler to install but are restricted by the fact that you have to be there to open and to close.

Climate control is especially challenging in the spring and the fall since most days you will have the need for both ventilating and heating.

One area that you need to be especially aware of is stagnant air. Without proper air movement, circulation and exchanging, stagnant air can cause many different types of diseases. It is important to understand what your plants require

Season Extension: Hanley Caterpillar Tunnels

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The first area to discuss regarding season extension are those structures that are simple enough to disassemble and relocate to another spot-primarily referring to Hanley Caterpillar Tunnels.

The real lure of these buildings is their low cost and simplicity to move. Generally the area is prepared in advance and then the tunnel is moved over the area when the planting is to be done.

Since the original design specified 6′ hoop spacing, the intent was always to remove the cover before risk of heavier snow fall. More often now, growers are going to 5′ spacing (and sometimes 4′) to allow the covers to remain on longer or even permanently.

By having a smaller hoop spacing, it allows the cover to stay on permanently, which allows for a much earlier start in the spring.

The key to the concept of the Hanley working is in the rope.

  • The back and forth pattern of the rope resembles the way a person would lace up a boot.
  • Typically there is a spring loaded clip at the base where the rope passes through.
  • Once the rope is fully installed, it is important to tighten it through three passes from end to end.
  • If the rope is not tight enough, the wind will create wiggle and movement sideways.
  • When the plastic is tight enough, it also allows the grower to slide the plastic up the hoop to allow ventilation.

Generally the plastic is about 25′ longer then the tunnel.
This allows the installer to bunch up (pig tail style) the extra poly at both ends between a pair of posts.
It is important to get the plastic as tight as possible lengthwise first.
There must also be a rope from the top of the last hoop to the tie off post.

There are a couple of challenges to consider with the hanley tunnels.

  1. One of these challenges is to create a proper entrance. Typically entrance is achieved by slightly lifting the plastic and ducking underneath.
  2. The other are of challenge is the low shoulder height of the structure. This restricts the use to a couple rows of taller items in the middle and a couple rows of shorter plants along the side. The width of the tunnel does lend itself to three regular size beds.

Once you have learned about the nuances of the hanley tunnels, and asked any questions that come up, you will be better prepared to have these efficient season extenders work for you and your application.

Feel free to look at our Hanley Application page for more information and photos, and give us a call with anything else you require.

We are pleased to have many happy customers these structures are working for, and look forward to you being next!

Check out our new book if you want to know more “So You Want to Buy a Greenhouse…Your Guide to Planning a Greenhouse Purchase”