From UMass Extension web site- by John Bartok, UConn ag engineer emeritus
Although you have no control over the force or direction of severe winds, here are a few tips to help minimize storm damage:
•Check the area for loose objects. Anything that can be picked up and hurled through the glazing should be secured or moved indoors. Metal chimney (stove pipe) sections should be secured with sheet metal screws.
•Inspect for dry or weak tree limbs that could fall on the greenhouse.
•Close all openings including vents, louvers and doors. The effective force of the wind is doubled when it is allowed inside the building. The wind on the outside puts a pressure or lifting force on the structure. The wind inside tries to force the walls and roof off.
•On air inflated greenhouses, increase the inflation pressure slightly by opening the blower’s intake valve. This will reduce the rippling effect. Check to see that the plastic is attached securely and that any holes are taped.
•Disconnect the arm to the motor on all ventilation – intake shutters and tape the shutters closed. Then turn on enough exhaust fans to create a vacuum in the greenhouse. This will suck the plastic tight against the frame.
From Ed Person, Ledgewood GH frames:
I’d like to share a couple of thoughts about protecting greenhouses and high tunnels from high wind events. The most important thing to do is close the tunnels completely. Roll down sides, close and secure doors and vents so the wind can’t get inside and apply lift on the frame and poly. If your poly is off the tunnel make sure you secure the doors against wind pressure from the inside blowing outward. I have seen cases where the end wall is torn apart by a flailing door. Also, pick up and/or secure all items that could fly around and puncture the poly. A sheet of plywood for example makes a very good flying object!
Also, I have seen many tunnels with very weak or non-existent ropes securing the roll ups in place. If the ropes break or come loose the side will start flapping and in the worst case scenario it can put enough torque on the hip board bolts that they actually snap off and the entire piece of poly will tear off the tunnel. Then you have a piece of pipe with poly attached possibly flying to your next tunnel and ripping through the roof.
From Skip Paul, farmer on RI coast with a lot of hurricane experience:
Check all your connections and structural members. Like a weak link in a chain, if a nut vibrates off a critical connection you will start a cascade of other failures. Clean the bugs out of your inflation fans. Keeping the two sheets of plastic a bit over-inflated during a storm is a good thing. This requires patching the small holes and nicks. We just open up the inflation fan air intake (all the way) and get that plastic extra tight. Don’t forget to readjust the inflation fan intake slide vent after the storm you don’t want to over-stretch your plastic. It will shorten its life over time. Clean up junk around the farm that can get going in the wind and rip a hole in the plastic. If we know we will loose power, we will duct tape the intake shutters to keep the air out. Keep your large doors securely closed by putting something in front of them. Most greenhouses don’t have good door latches for their doors; if they vibrate loose or fail the wind will get in. An important decision is whether to cut or take off the plastic. If we know we are getting 100+ mph winds then we take the plastic off; the structural damage to the greenhouse doesn’t warrant trying to make it through the storm. Plus you probably will loose your power and there is another reason you will be glad you took the plastic off. Uninflated greenhouses especially are like a large sail and can be dangerous and just beat on the structure. If you do take the plastic off; try to do it in two separate pieces and put it away somewhere dry. If you let it slump off the greenhouse and fill with water between the sheets it will be impossible to recover the house till they are separated and dry. People with Haygroves (that includes us): don’t even think about trying to make it through winds over 65 mph. Your manual will tell you it isn’t made for that kind of wind. Especially, since their solution to lower wind speeds is to open the structure up! That can work up to 55 mph but above 65 it will act like a wing on an airplane and you will be sorry. Our Haygrove had one end crushed in a sudden wind gust last season; it can happen. Those with Rimol moveable houses (or greenhouses on skids a la Elliot Coleman) you should heed the same warning: small pipes driven in here and there will do you no good when the wind gets over 75 mph. It better to take the plastic off than to see your greenhouse rolling over your neighbors hayfield. Probably the most important thing is respect the peak of the storm. Don’t switch plans and try to do any of this in the midst of the storm; the wind is dangerous and adding heavy rain to that can be catastrop