bwright_gw

Windbreak for HFGH

bwright
14 years ago

I have really appreciated the input from this forum. I just picked up our first GH based largely on this forum... a 10'x12' HFGH and am trying my best to preplan construction. We get hit with a very strong wind from the north west that among other things reaks havac with our 27' pool cover... thats certainly a post for another day. This has, however, made me very aware of the power of wind. We are going to have to construct our new GH in an area that will be exposed to a very potent wind during stormy weather. Given the mods from all of the great folks on this sight I still feel that a wind screen of some kind will need to be assembled. I was considering a couple of pre-fabed 6'x 8' vinyl panels along the wind side wall. I question the distance the panels should be erected from the GH to slow down or disrupt the wind?

Again thank for all of the great recommendations for this GH!

Comments (16)

  • nathanhurst
    14 years ago

    Solid walls actually increase the wind speed (bernoulli effect I think). You want trees.

  • bwright
    Original Author
    14 years ago

    OK, what type of trees/shrubs would you recommend, would arbevita fit the bill?

  • nathanhurst
    14 years ago

    I live in Australia, so what I would recommend would probably not be available there. lilypillies, wattles and mallees are good choices.

  • oakhill (zone 9A, Calif.)
    14 years ago

    Perhaps this link will give you some starting points.

    Here is a link that might be useful: windbreaks

  • jimmydo2
    14 years ago

    When constructing Natural windbreaks, you actual need to plan alternating trees and shrubs.

    Evergreens are recomended, especialy since winter months can be stormier.

    However, it takes years to esablish. Mine is three years old, and not even near established.

    For a Quick artificial windbreak you would want to mimick nature, and disperse, as opposed to block the wind.

    A wall built of alternating inside and outside planks, or with lattice, will help

  • gardenerwantabe
    14 years ago

    Posted by nathanhurst VIC Aust (My Page) on Wed, Dec 27, 06 at 20:27

    Solid walls actually increase the wind speed (bernoulli effect I think). You want trees.

    Nathan can you please elaborate on this a little. This makes no sense to me. When the wind is blowing hard and you walk behind a wall a car a dumpster or whatever and it is nearly calm. Some theory's don't always work. They say that a bumble bee can't fly but they forgot to tell him that.
    I have a lot of arborvitae trees but it took about 20 years for them to get big enough to really make good wind break.
    If I was faced with this problem I would buy 12 ft, 4x4 treated timbers-and put 4 foot in the ground and then build a 8 foot wall to protect the GH. You could plant evergreen trees and when they get big enough you can remove the wall. The one thing that I'm sure of is if you don't make a wind break you will lose your GH

  • laserfan
    14 years ago

    Our 10x12GH site is on the back-side of our very tall garage/guest house, which in theory protects it from our severe NW winds. In reality we found (immediately!) that under difficult conditions the wind swirls and the GH is still at risk.

    bwright build the windbreak if you want but my idea would be to spend the $ instead on structural enhancements to the HFGH.

  • gardenerwantabe
    14 years ago

    Posted by laserfan
    How far in feet is your GH from the building that you use for a windbreak. Is it longer than the GH and if so by how much.This kind of info could prove valuable to those that build in the future. My 10x12 is 3ft away from a 24 foot structure and it is on the west side of the GH because here all are hard winds are from the west. A west wind hardly does anything at that location but it will cause a slight swirling effect but only a small percentage of what the accrual wind speed is. Maybe that the distance is important.

  • nathanhurst
    14 years ago

    wantabe: the wind speed increases after a short distance down/up wind. I think the reasons for this is the bernoulli effect due to the local space for the air being restricted, and the momentum being transfered down the face of the wall by the coanda effect, perhaps google can tell you? The theory is sound.

    Solid objects will reduce the wind speed up close, but then the wind will travel faster further downstream. A porous screen on the other hand will have a large area of reduced wind with a gradual return to original speed.

    Regarding theories being wrong, science does not make incorrect theories so much as theories with low predictive accuracy. The classic bumblebee argument is discredited here:
    http://www.math.niu.edu/~rusin/known-math/98/bees

    We replace theories with more predictive ones as we get better. This does not mean the old theories are wrong, and often they are still used when precision is not requried (I use Newtonian mechanics when designing mechanisms rather than Einsteinian mechanics, because at everyday speeds the two have the same predictive power.

    Rather than building a wind break (which is a tricky art), a simple and effective solution would be to buy a taped shade sail large enough to cover the whole greenhouse and anchor that into the ground over the top to form a flatish tent. There are screw in soil anchors that would be quite adequate for this job, as long as the sail can't flap.

    http://www.shadesails.com/ready%20made.htm

  • bwright
    Original Author
    14 years ago

    Thanks for all of the input. I do plan to add as many structural mods as possible and deal with mother nature as I go. I will be assembling the GH over the next couple of weeks given time with the glazing going in at the very end, maybe even wait til March.

  • gardenerwantabe
    14 years ago

    Nathanhurst
    I had never heard of the bernoulli effect however after reading the link I will say that I do understand how the venturi in a carburetor works but as the air goes through the venturi the sides apply pressure and the speed increases. As the wind flows over the larger structure it then goes over my GH and it is rather calm where the GH is sitting. Since their are no sides like in a venturi maybe that is why it don't increase. Just for kicks I have a lot of survey flags that I can put out in the lawn in the open and around my GH and even attach some to the GH and see which direction the flags are blowing and where the air is calm and where it is blowing strong. But I already know that your theory is not working in my particular situation. It would be nice if I had several wind speed indicators to monitor the wind sped in the open and at the GH.

  • nathanhurst
    14 years ago

    10 seconds with google finds this:

    "A windbreak consists of any type of barrier designed to slow down the velocity and redirect the flow of wind. A good windbreak will not create excessive turbulence or wind eddies. Effective windbreaks do not stop the wind but break its forward movement, to slow it down. Solid barriers, such as walls and buildings, create unexpected wind currents and wind tunnels, often with increased velocity and unpredictable direction. Windbreaks composed of living plants allow some of the wind to slowly penetrate, making them more effective."
    http://aggie-horticulture.tamu.edu/southerngarden/coastplants.html

    "Research has shown that a porous windbreak
    allows some wind to filter through, providing better downwind
    protection than a solid windbreak of the same height. A
    windbreak with 20% porosity provides some wind protection as
    far as 12 times the fence height downwind, and very good
    shelter to about 6 fence heights downwind."

    http://www.cps.gov.on.ca/english/plans/E8000/8368/M-8368L.pdf

    The theory is sound, I question your methods :)

  • ronnywil
    14 years ago

    How about building a fence. You could use 4'x8' plastic lattice. This would slow the wind down some but you could also plant some type of fast growing vine to cover it.

  • doneover
    13 years ago

    I am in desperate need of a fast growing windbreak hedging suitable for the following conditions
    High Prevailing Easterly winds Bright Sunny conditions
    able to withstand drought after planting
    can anyone help ? Thought about the austree but dont know if it is a good investment

  • gardenerwantabe
    13 years ago

    We had 60 mph winds here yesterday and all I can say is Nathans Bernoulli effect don't work at my location.
    Maybe because my windbreak is so tall but the one thing that I'm sure of is it don't apply to my setup.
    In the last 30 days we have had a blizzard then a week later a Ice storm with 45 mph wind the Governor declared the area a disaster area due to all the damage then yesterday we had winds in excess of 60 mph.
    My cheap 10x12 HFGH is fine.
    After this winter and what we have had I don't think I need to worry about weather damaging my GH the Modifications that I did to it have proven to be adequate.

  • l_gettinger_yahoo_com
    9 years ago

    I'm new to this site. What is a HFGH and a GH?
    Thanks!
    Lorraine