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I'm working on a test for a solution. Since it was windy again, I had plenty of non-sleeping time to ponder it, and I now think I understand the problem.
First - the blind fasteners have nothing to do with it other than providing "good" spacing that will cause the whistle. Think valve instrument, not woodwinds. The gap is held constant by the fasteners.
Now, for the flow of air: Think airfoil. The underside of your deck is somewhat obstructed by joists and skirts etc. the upper portion of your deck is smoother and generally unobstructed, e.g. air will flow over it more freely. In airfoils, the underside of a wing is the high pressure area, cause by the lower pressure area on the upper surface of a wing. This is due to air flowing faster over the upper surface causing the lower pressure. So, essentially, the air is being sucked from the lower surface (underside of deck) through the seams, and out the upper side.
Skirts and whatnot may not work and will depend on how high off the ground your deck is. We know that regular decking doesn't cause the problem. The difference is that Trex has a slightly greater radius than cedar or other decking - although I had some pressure treat decking in WI some years ago, that had a similar radius on the upper surface. What is markedly different is the grooves on each side of a deck board. If those can be filled with whatever, I think the noise will stop.
My question whether or not both sides of an opposing pair of grooves need to be filled. Is the dual concave groove/recess on each opposing side enabling the noise, or would filling one of them do the trick?
What to fill it with. I dunno. I'm looking at extruded vinyl tubing or solids from the weatherseal industry. However, some of this stuff will not be UV stable. Silicon is an option, but that will require a very specialized nozzle. But, at least you could get some colored stuff to match. Getting the grooves clean will be an issue.
Another method could be dual pre-form at ... 14 inches long each. Two pieces of extruded shape similar to the grooves separated and connected by a flat spring. Insert one side at an angle, compress the other into the other slot, and slots/grooves filled.
Houston: I think the mesh idea that may indeed work. The mesh would break up the uniform flow of air between the deck boards. However, as stated previously, my deck is 22 feet AGL. I gotta do this from the topside of the deck. Also, we're coastal - salt.
My local Trex dealer may collaborate on a test. Dig up a few scrap slabs of Trex, build a box, put the Trex in the middle, and suck air through it with a big fan. Then fill the grooves and repeat.
Fiberglass mesh ?
I actually believe that deckbuilder111's and Houston's idea of an underdeck mesh fabric can work.
I don't think it will work- here's why. The sound is caused by the differential airflow pressure over the top. All it needs to resonate is air coming from underneath which is still going to happen. If you broke up the airflow on top them maybe, but otherwise as long as the bottom is open it will admit air and that's all it will take for it to be sucked through and howl.
I joined to bump this thread to see if there were any resolutions....
My wife and I recently built a house with a 575 square foot Trex Transcend deck with hidden fasteners that is having this problem. Below is a link to a YouTube video with the noise.
The sound is definitely caused by vibration of the boards. You can feel it when it's howling. As someone else mentioned, I believe it to be much like an airfoil. As wind moves over the boards, it creates a differential pressure that causes airflow to oscillate between the top and bottom of the deck, which causes the vibration and noise - much like blowing on top of a bottle.
I think installing a dense wire mesh directly to the bottom of the boards would fix this - something that restricts airflow, but allows drainage. Ideally, it would be installed to the bottom of the joists to make installation simple, but I think it would have to be on the boards.
Has anyone tried a fix for this? What were your results?
I had same issue. Here is what i found that works. Cut several pieces of window screen material in 6 inch by 2 inch pieces. Roll them up lengthwise and place them between the boards spaced between the joists. The concave shape of the decking holds them inplace and the screen disrupts the air flow so it won't whistle. They are also pretty invisible down in the cracks. Hope this helps.
We have experienced the same noise for about a year and a half....in fact the deck is howling as I write this! In our case the deck belongs to a neighbor. Their Trex deck is built over a canyon and anytime the wind blows above 9 or 10 mph, the deck howls. We hired an acoustic consultant to determine the source of the noise and to recommend a solution to fix it, as it's driving us nuts. The consultant did a noise study during the day & night and at numerous times it registered around 100 decibels . During a one hour period in the middle of the night the deck made noise 99 times! If you Google "Trex Howling Deck" or something similar, you'll find many You Tube videos demonstrating the noise. Our consultant contacted one of the guys who posted one of the Trex deck noise videos to see if he was able to find a solution. And bingo! Turns out Trex has had a lot of complaints about this issue and they ended up manufacturing a rubber gasket to fill the groove between boards. It is considered a warranty issue and they supply the gaskets for free, but as the homeowner, you have to pay for the labor to install them. They send a detailed installation guide and it looks relatively simple. Our consultant followed up again with the guy who posted the video to see if the gasket solved the problem and he said that he was doubtful during install, as the noise didn't stop until he installed every single gasket. And now his deck is silent. Hope this helps.