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Question DetailsAsked on 1/23/2015

best fence designs to withstand high winds

fence subjected to infrequent but strong winds that may blow over part of fence

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1) the less surface area it has, the less wind force - so a three strand electric or barbed wire fence will withstand highest winds (ignoring effects of blowing debris), probably chain link next, a split rail or three-rail fence and common wrought iron post fence probably next most, on up to full coverage board privacy fences that have to absorb the most force. Peek a boo or shadow box fencing, where the board alternate on opposite sides, restrict the airflow so much that the wind force is not significantly different from a single-sided fence with same number of boards.


2) to prevent board blowoff, use screws rather than nails or staples and install the board on the positive side - the side the wind is blowing against.


3) to prevent panel blowout, use Simpson metal brackets with #10 or #12 versus the usual #8 screws to mount the supporting cross supports to the posts - this provides a stronger connection and also increases the rigidity of the entire fence. Using a flat top with cap fence (has a top support board across the top too) can also help with this. Also, putting the supporting members on the windy side of the fence will greatly reduce panel blowout type damage.


4) wood will generally take higher winds than comparable vinyl construction


5) if post failure is the worry, close up the post spacing. Wind load goes up with the square of the wind speed (roughly), so a 120 mph wind, while 50% higher than an 80 mph wind, exerts about 125% more force on the fence, so you would have to have about 1-1/4 times as many posts (cut spacing to 45%) as a fence designed to handle 80 mph. Another alternative, if panel blowout is not a problem, is to use heavier posts at the normal spacing - like 4x6 with the 6" dimension perpendicular to the fence rather than usual 4x4 post. If using steel posts, you can go to a larger diameter pipe or use a structural steel member like a channel o rtubing for the post or fill the pipe with grout or concrete to increase its strength significantly. With wood posts, blowover commonly occurs due to post rot not sound wood breakage, so use treated timber for posts and support beams (always a good idea anyway). Also, embedding posts in concrete provides protection against post blowover that can occur without post breakage at the post just pushes the soil away and pries out of the ground.


6) for existing fence, simplest solution is probably to add another post in the middle of each span, backing up the support beams.


7) in areas with strong winds from several directions, increase the strength of the fasteners holding the fence to metal posts.

Answered 2 years ago by LCD




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