Smashing Greenhouse!

Hi, Dave, just have a whizz through my last post about air pressure and see if it's any help.

 

Hi Dave, do you know I missed the fact that your Greenhouse was on wooden decking!! Actually, when I think about it, I think, unfortunately, that it adds to the problem. Some of the air being pumped through the decking by wind will go straight through the decking under the Greenhouse but a lot will be sucked and deflected up into the Greenhouse. That will happen because the lower pressure area in the Greenhouse will give way to the higher wind pressure until it equalizes. I've been digging into the past and found a couple a my service reference books covering the subject - which reminds me how much I've forgotten!! Anyway, back to the problem. The air being forced in gives a higher pressure inside the Greenhouse while outside the wind pressure is not constant and that will cause the glass to pop. I've got my Greenhouse on a concrete paving base and I have sealed between the base of the Greenhouse and the concrete base with silicone to stop the air getting through. While you've got little glass in your Greenhouse it might pay you to take it off the decking and put it on a harder base that you can seal, just don't forget to anchor it down!! Lukeanotts has said he has used more clips than he was given to retain his plastic windows and I have done the same, putting blobs of silicone on the "'legs" of the clips and where the head of the clip rests on the glass. I think putting up a temporary fence as a shield might work. We had to protect 18 ton aircraft from being blown over in the wind where ever we were and at 1 -2 millions pounds each in value we didn't want any red faces! We found that hard surfaces used as a shield didn't work as well as a soft fence of fine mesh nets. The net allowed the wind through but slowed it down. A hard fence pushed the wind up and then at a distance of one to two heights of the fence it hit the ground again! I think that, unconsciously, when I was building my Greenhouse I was applying the science I'd been taught in the RAF - very strange!! I hope my wanderings on will be of some help to you.

 

Some excellent advice from Armandii there I think..

BTW.. I have 4 "W" clips to one pane on my G/houses...

 

Thanks Pete, I think you're right, a hard base is part of the solution. In Dave's case the wind was coming from the Southwest which meant his Greenhouse wasn't on the lee [sheltered] side and it was getting jolted and shook by a blustering wind. The Air Force taught me about "cause and effect" and I've taken that thinking with me through business and private life. It also taught me to look for the worst scenarios and think long term, which is why I don't think Dave should continue with the decking base. Wood is relatively soft and even when pressure treated will weaken and deteriorate over time, especially if it's being stressed. The stress will come from the wind on the Greenhouse pushing at which ever side it's blowing on. This happens on all Greenhouses which is why they're are anchored to the ground. My point is that Dave's Greenhouse is already in a position where wind is being channeled and funneled, when it's coming from the Southwest, onto it. If Dave's Greenhouse base is screwed into the decking then, within a few seasons, I wouldn't trust it viability. You're right again about the twisting of a Greenhouse frame being a danger, and if the Greenhouse base did become
suspect in part, that would lead to twisting. If I appear to be a "belt and braces" person then let me assure you I'm not! I had to several tests when in certain jobs which analysed me as a "high risk taker" - who me!?
But when carrying out modifications on an aircraft you had not just to do the modification but analyse what effects that mod would do. We had one or two technical mod's that although approved by the MOD got rejected on the "front line" servicing because somebody didn't take things for granted and saw that instead of improving performance and safety it did the opposite. The "hands on Techie" was often more far seeing than the "Boffin" who dreamed up the mod because he had to be - he wanted the pilot to land again and buy him a beer!

 

Back again! The confusion wasn't your fault, Lukenotts, it was mine. I'd just returned from a family emergency which had me driving from Cheshire to Northeast Yorkshire and back in a day, followed by a call from the last company I'd worked for on help with a problem they'd got [I don't think they've ever understood the meaning of retired} Anyway it was a bad day, so when I got onto Gardeners Corner I was tired and didn't read the posts correctly - so my apologies all round! Having said that my opinion, for what it's worth, regarding wooden bases still stands. In answer to your questions, Dave, I think the trellis idea is a good one as it will break up the air flow and slow it down. But, if your budget will run to it, I would still advise using the net in conjunction with the trellis. One last thing about where your Greenhouse is sited and the air flow from the funneling effect. Take a soft ball and stand centrally about 20' from your Greenhouse and your house with your back to the direction of the wind [bear with me!]. Throw the ball at the corner brickwork of your house and I think you'll find it'll ricochet towards your Greenhouse - my point being that's what the wind will do - get bounced off the wall in that direction if it's coming from the Southwest at speed. Aerodynamics is all all about cause and effect. Wind hitting a brick wall head on or, in your case, at an angle has to go somewhere!! Your second question about the clips and would the alternative clip fit and I think the answer is no but I'm sure a talk with Greenhouse supplier or somebody more knowledgeable than me will confirm that.

 

Hi Dave, yes thank you, the family problem has been sorted. A close relative had been in a major accident and was having an operation to repair some internal injuries so I went to the hospital in support of the family. It went extremely well and her being only 5 years old but tough helped her through. It was 33 hours without any sleep - but worth it.
We experimented with the size of mesh for the net using different sizes and also layers of net. There's a Service Trials Reference Manual and Report on it somewhere in the depths of Strike Command! Fruit netting should be fine. If you have enough of it to fold it into layers that would be better and have more of the desired effect of slowing the air flow down but also letting it through. I said that you could use it in conjunction with the trellis because the trellis would act as a frame. but if you think you could suspend the net another easier way then why not? You'd have to secure the net extremely well to combat the pressure of the wind even though it will be passing the the layers of mesh. Despite the holes the net will behave partially like a sail giving way in the direction of the air flow as it absorbs the energy of the wind and slows it down.

I know Bridgemere and used to visit it in the early days when it was just a couple of sheds in a field! I also
used to work with the brother of John Ravenscroft who bought it and made it such a success. I think his brother has now gone to Spain to renovate a old farm house that had no electricity or running water! To be quite honest I find Bridgemere very expensive now it has been taken over by a national company and has lost the original purpose of selling good quality stock at a fair price with knowledgeable staff. Why not have a look on-line to see if you can get whatever you're looking for cheaper

 

Dave, I use the Greenhouse People for all my needs and they're really friendly and helpful. They're just outside Stoke at a village called Cresswell. You can get them on the blower [0800 093 3297], ask them and you should get the answer!