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From our recent Winter Q&A
Segment #1: How to Prepare Your structure for Winter
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The main attraction of roll-up sides, as a method of ventilation, is that it is economical. There is not a significant investment and can be added to virtually any structure. Regardless of structure length, nowhere is very far from open air.
It is only by properly understanding the limitations and drawbacks that one can maximize the benefit. Just because something is inexpensive does not mean that it won’t end up being costly if it does not fulfil its purpose.
Roll-up sides should always be done in pairs (both sides). Even if you have a really high percentage of prevailing wind from one direction, there will be times when you need to ventilate into the prevailing wind.
Any time you have wind going in without opportunity of escaping,
there can be damage to the building.
The average vertical opening of roll-up sides is usually about 4’. If your greenhouse is in an extremely exposed area without any protection or wind breaks, quite often 2’ of vertical opening will be sufficient.
On the contrary, if the building is extremely sheltered, 6’ of vertical opening will be required.
One thing to remember on the height of opening is that if you have a low profile structure with a high opening, a sizeable area could get wet inside when it rains.
Regardless of the size of opening, if there is not a breeze, you will not have air movement.
It is based on this potential problem, that we recommend having end wall openings as high as possible. These openings will trigger a “chimney effect” air movement that will get rid of hot air that is trapped in the greenhouse. These openings will double as your first stage of ventilation since they would be opened when it is too cold outside to start rolling up the sides.
A drawback of roll-up sides is the amount of exposure they create for airborne weed seeds and pests. It is important to remember that when you use shade cloth to minimize this drawback, you are also significantly restricting incoming air.
The biggest drawback of roll-up sides is that there is no practical way to automate them. In other words, you have to be there to open and close them. This can be challenging on the cool, sunny days that have sporadic cloud cover. The sun goes behind a cloud and the temperature plummets and then soars when the sun reappears.
The best way to minimize this challenge is to add a small exhaust fan to the set up. This way you will have something to handle the borderline situations and then open the roll up sides once there is a more predictable need.
In the next article we will explore forced ventilation in greater detail. We also have many resources on our website, as well as videos if you want to explore the topic of roll-up sides further.
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
Ventilation, excess heat, making sure roll up sides are critter proof
One of the critically important things that each gardener/grower needs to know is the temperature threshold of each plant.
This is the temperature at which a plant will stop growing and an even higher temperature at which a plant will die.
When a plant has passed the threshold where it stops growing, it will take some time to recover and start growing again.
This is why proper ventilation is so vitally important. On a sunny day, proper ventilation is defined as one air change per minute. You must know the volume of air in your greenhouse and have your ventilation method capable of moving that much air.
A forced ventilation system is the simplest to set up and control since it is thermostatically controlled. The up front and operating cost are significant. Each exhaust fan has a cubic feet per minute (cfm) rating which must be equal or greater than the air volume of the building. A forced ventilation system also has a motorized louvre which will open each time the fan turns on.
On a shorter structure that is facing into the wind, there is the option of ventilating through the doors and windows. This is an economical system but the hardest to control.
Adding roll up sides to a structure has the capacity of moving a lot of air as long as there is air movement around the greenhouse.
This is why it is a good idea to install a window as high on each end as possible. Since warm air rises, this will create a “chimney” effect on a calm day. The down side of roll up sides is the potential for draft across the floor and the fact that you have to be there to open and close the system. You may need to put up mesh to deter uninvited guests.
In addition to changing the air in the greenhouse, it is also important to circulate the air horizontally. Stagnant air pockets invite disease problems. There is not a prescribed rate to move the air, it is just important to keep it moving.
A proper watering system would not be considered as a part of making a greenhouse more efficient but it must be remembered that a greenhouse will increase the water needs of all of the plants.
A final consideration for growing over the summer is the potential need for shade. Most vegetables are good for full sun, all the time, but it is important to remember that this does not apply to all plants.
Wishing you a productive growing season!
Ventilation can either be done passively through openings or mechanically with fans. Roll up sides are an economical way of getting lots of air movement since no electricity is required. Roll up sides become even more effective when used on longer buildings. Roll up sidewalls are often used in combination with a small exhaust fan for early and late season ventilation when opening the sides is not practical.
If a structure is very exposed, it is best not to open more then 3’ in height due to potential of wind damage. If a structure is extremely sheltered, it is best to go even up to 6’ to create maximum opening. Roll up sidewalls are most effective when used in combination with peak end wall vents to create a “chimney effect” to draw warm air out of the building, especially when it is very calm. These vents are effective for air movement when outside temperature does not allow opening of the sides.
When a structure has a low profile, you will need to be careful during rainy periods due to moisture getting into the structure area. High profile structures (with straighter walls) usually work better with roll up sidewalls. When preventing a floor draft is an issue, the roll up mechanism can be raised and then the structure is lined with a skirt for the bottom 2’-3’. When using this method of ventilation, it should always be done on both sides. An effective use of this method includes opening the “downwind side totally and the opposite side on marginally.
Download our Roll up Side Wall Installation information sheet for more information
We made some tutorial videos regarding our roll up sides options. Please enjoy and let us know any comments you may have. You can also watch them all on our YouTube channel here: https://www.youtube.com/playlist?list=PLBUPJhbi2DLs0UYSo0FRwwi0pMo51PV80
As always, we are available for any questions that come up, so feel free to email multisheltersales@gmail.com or call our office 1-866-838-6729 Thanks!
You can also see more at our Roll Up Sidewall Considerations article (also below videos)
Multi Shelter Solutions 