How Strong Winds from Tornadoes and Hurricanes Can Lift off Roofs with Overhangs
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- Опубликовано: 23 авг 2024
- www.homebuildin... Click on this link if you looking for more information about building design, architecture and new-home construction. This video will provide you with a few examples about how strong winds from tornadoes and hurricanes can create enough air pressure to raise or lift a roof off of the home or building that has a long enough fascia board or eave overhang.
Ok so firstly, this is not an accurate view of the dynamics of a low speed flow (and yes, to an aerospace engineer, hurricanes and tornadoes are low speed flows). Modeling would be needed to give detailed answers but remember that the wind acts everywhere, not in a single jet. In practice you’ll have a region of high static pressure on the upwind side and relatively low flow speeds. As free stream winds pass over the house, the streamlines will curve over the roof of the building indicating an area of lower static pressure. Finally, at the back of the house, expect a region of separated flow and low static pressure. The details will depend on roof/house shape, but the overall effect will be a combination of a vertical lift and lateral drag force on the building. The vertical lift force is what “peels” the roof off the house, or overturns the entire structure if not well anchored, while the lateral loads can lead to shear failures in walls, or shift the entire structure off the foundation if anchoring is inadequate. IMPORTANTLY: these forces exist regardless of overhangs. A house with bigger overhangs does have a bit more roof surface area and thus may have a bit more uplift force all other things being equal, (there will also be an interesting effect at the overhang due to the high static pressure air below it, but the leading edge overhang is a small fraction of the total roof area), but eliminating the overhangs will not eliminate the uplift force or even remove the primary cause. Even a flat roof will experience an uplift force as the air passes over the house. Merely eliminating overhangs is unlikely to save a structure. A second issue is that eliminating overhangs greatly increases the rate of wall failure due to water intrusion, and associated rot and mold (flat roofs also have comparatively high failure rates for water intrusion). It would be better to have the structure properly engineered to resist the expected uplift force with proper overhangs for long-term durability, rather than attempt to limit the aerodynamic forces (largely ineffectually) by eliminating the overhangs.
Think you could help with my homework? Both True/False questions 1)Negative pressures occur on both sides of a pitched roof no matter how large the slope. 2) Negative design wind pressures occur on the side walls of a rectangular building. Thanks!
Just shut up n make your own video
It's not completely correct..... read if are a student 🇮🇳🇺🇸🇮🇱🇷🇺
The reason is that.... high wind blowing over the roof creates a low pressure in accordance with BERNOULLI'S principle, the pressure below the roof is equal to the atmospheric pressure which is now larger than pressure above the roof, this difference of pressure causes an upward thrust and the roof is lifted up....✌✌
"properly engineered" HOW? all that yapping and you concluded into having no actual specific solution.
@@SlimTK the reason people like this guy, who yap but provide no actual solution, is because they want you to hire them. Otherwise, all the time and money spent on their degrees would go to waste.
Hip roofs are better for high wind areas. Also 30 degree slope is optimum to prevent wind blown rain issues, any more and the roof acts like a sail less slope and you increase the chance of wind blown rain entering the roof structure. Our home has a hip roof with a slope of 27 degrees.
I have 3ft overhang and 4ft in another section... skillion roof design. And the building is also uphill 😅.
What I'll be doing is installing a thicker metal roofing sheet and also fastening the rafters and purlins with angle clamps/storm metal brackets... it's an L-shape metal screw to hold wood with additional holding power. Will also bolt the roof tie beam against the concrete block wall and plant coconut tree on the front side of the building to shield a bit from the wind. The tree will help reduce wind pressure during a rain storm.
A long overhang will shield the building against hot sunshine here, help shade my top-to-bottom windows a bit, and it complements the skillion roof facade...look really nice.
Two questions, please. First, Metal roofing vs. Asphalt shingles? Which would you recommend in the high wind area of Colorado/Wyoming? Secondly, if winds are blowing into the house from the West, how would you position the house to avoid it getting pounded by the winds? I ask these questions since I will be meeting with the builder in the next few weeks. The house will also have a front porch running about 16 feet in length. Your answer to the second question will help in deciding house positioning. Thank you so much! Anyone else with ideas, please feel free to jump in as well!
Metal roof is better for high wind areas.
I have friends in the Philippines and they just had a super typhoon. Common problem is that the corrugated roofs blow off. However, it seems that there are opposing design criteria. For example, normal tropical rains are heavy and this would tend to favour wider eaves. Similarly, the sun's heat in the tropics would also favour wider eaves to shelter the walls of the house. Cost is another constraint as poor people can't afford expensive building materials. Not sure what the answer is in these cases.
Thanks for sharing and great points about home design.
I live in Ph and the answer is to build houses from cheaper materials such as plywood and nipa (for roofing). It's less expensive to build a house again and again.
With the 2 inch overhang, the little gap thats still there, you could finish it of nicely by putting something like a Ceiling plinth against it
This is not the main reason for blowing off the roofs
During windy storm when the wind blows over the roof it creates a low preesure area over the roof realtively lower than inside of the house so due to this inequality in preesure the roofs usually blows off .
I’m not so sure ...
Then it should be the same with airplanes ✈️
But airplanes can fly upside down too 🙃
So there is a problem with this logic...
And the same problem applies for house roofs and winds 💨
@@thanosgr5984 yeah it is same with the aeroplanes too . They don't rely at all on wing shape for lift. To fly upside down, a stunt plane just tilts its wings in the right direction.
They are shaped so that that air flows faster over the top of the wing and slower underneath. ... The high air pressure underneath the wings will therefore push the aircraft up through the lower air pressure.
Airplanes use that low pressure for lift, wings follow low pressure - they're not tied down to the ground...think....
Ha! The inset at 0:34 looks like my house with a 2 foot overhang on all sides. Working on retrofitting ideas now. It’s too big for the ladder type reinforcement so will probably need to add outriggers somehow. Has anyone seen reinforcing this area with steel?
what about a rounded roof, no peaks at all,with 2 inch overhang?
Thanks for pointing me to this video and this other channel (Do you have more than two?). I have subscribed!
You're welcome and Yes, if you go to our website and then click on the home link, it should take you to our index page and on it you should find the rest of our channels dealing with construction.
It's not completely correct..... read if are a student 🇮🇳.........🇺🇸🇮🇱🇷🇺
The reason is that.... high wind blowing over the roof creates a low pressure in accordance with BERNOULLI'S principle, the pressure below the roof is equal to the atmospheric pressure which is now larger than pressure above the roof, this difference of pressure causes an upward thrust and the roof is lifted up....✌✌
I came here after my roof blew due to cyclone nisarga in India mumbai. I have a village house in Maharashtra and now tommorow going to fix cement roof sheets.
Read BERNOULLI'S principle
I calculated that 100km/h of wind causes 50kg per square meter (60mph does 10lbs/square foot) of force. If your roof doesn't weigh much, it'll just get lifted up. If the speed is double, the force is quadruple!!! I did DIY something that didn't budge at 50mph, but at 60mph it was almost like a piece of paper in the wind.
Bernuli's principal, fast moving fluid creates low pressure.
Good to know 👍
Any way to install a curved flashing in the wedge of the wall and overhang to divert the wind up and over the roof?
I've seen them built out of stucco and wood framing, but don't have any videos on how it's done.
Good day sir. May i ask what is the maximum safest overhang of a roofing? What if i want to build a 3rd extension using a single slope roofing? Thanks
Thank you for this video! I live in south Louisiana and have been hit with 4 hurricanes in the last few months. Actually the 4th one right now tonight.
Great information!
I wonder what is the best attic ventilation for high wind areas ? Not so much worried about cost savings on energy bills, more worried about not contributing my roof coming off due to venting the attic poorly.
I would look around at new homes being built and see what they are doing for better ideas.
i've installed the continuous soffit vents and 2 solar roof vent rates for over 180mph, do you think that might help in relieving some of the pressure the roof gets?
thank you... makes me confirm something I was fearing. I have like 4 foot overhangs. Crap..
just put some piles of bricks on the roof to weigh it down.
C C 😂😂
Not scientificl
I came here for my engineering class 💀😭
Keep learning future engineer.