Withdrawal resistance, building orientation, exposure; what does it all mean in relation to your greenhouse? That your greenhouse can act like a sail and pull the structure right from the ground if not secured and braced properly. (See: here and here)
For example, an 80 mph gust of wind can produce a pressure of 16 pounds per square foot (psf) on your structure. That means a 28’ by 100’ hoophouse withstanding these winds would be exposed to 220 pounds per square of length – or 22,000 psf on the entire structure. This is why building inspectors, to the dismay of many anxious growers, often require that ground posts be embedded in concrete. That is, dismayed until that first big storm hits and the greenhouse is still there with all the crops safe and sound inside.
5 Tips for Wind Loading
• Close up the all openings, including vents, louvers, and the doors. Whatever outside force is applied to the high tunnel is doubled when allowed inside the building. In essence, the wind entering the structure will attempt to force the walls and roof outwards and upwards.
• Research the typical wind patterns on your property. The building orientation can reduce the friction and pressure on your tunnel when set up correctly. You want your tunnel to provide the least resistance possible.
• For air inflated greenhouses, increase the pressure on the inside to reduce rippling effect of the poly. Double down and make sure any slits or openings are taped with film repair tape.
• Use windbreaks to reduce the wind speed or deflect wind over the greenhouse. Typical windbreaks are conifer trees such as hemlock, spruce, or pine at least 50’ upwind from the greenhouse – far enough that falling limbs will not come into contact with the structure. Wood or plastic fencing can also be used as a buffer.
• If you have a metal chimney, stove pipe, or any exterior ventilation susceptible to high winds, secure them with sheet metal screws.
Snow can be light and fluffy. It can also be wet, heavy, and destructive. For example, just 1 inch of rain is often equivalent to over 10 inches of snow. For anyone that has shoveled after a snow storm, 10 inches of snow – especially the heavy, wet stuff – is no small task to clear away. Without being removed, that weight is being applied directly to your greenhouse.
5 Tips for Snow Loading
• Leave at least 10 to 12 feet between individual greenhouses so that snow can accumulate. This will also prevent sidewalls from being crushed in as pressure builds from added snowfall over the winter.
• If you have a heating system, it should be equipped to maintain a temperature of 60 degrees Fahrenheit to melt snow and ice and preventing excessive build up. Make sure the heat is turned on at least a couple hours before the storm begins.
• Pull energy screens aside to allow heat to get to the glazing and melt snow and ice.
• Make sure you have diagonal bracing to keep the greenhouse from racking from the weight of snow and ice. If you don’t already have this installed, consider retrofitting your structure. It will add years to your investment.
• Keep the following three items on hand:
1. Durable lumber to brace your structure and complete temporary repairs.
2. Brooms to help push snow off of poly structures without damaging the cladding.
3. Backup poly for temporary repairs and to ensure heat is retained to protect crops.
A little preparation can go a long way to minimize damage from severe weather events such as blizzards, windstorms, and ice storms. First, make sure that your environmental controls are working properly to heat snow and ice from the inside. And just as important, have a well-stocked generator in the case you lose power.
Being a New England-based company with a focus on four-season farming, we have dealt with some of the most formidable weather in the country. That's why we created unique product options such as our truss support system - as seen on our Nor’Easter Series – to make sure the devastation we’ve encountered in the past never happens to you. Because remember, it only takes a short time of below-freezing temperatures to destroy an entire season of work.