Posted: 10/21/2009 1:13:36 PM EDT
| Tin roof over a trailer to minimize sun baking and rain pounding the roof. Frame for roof should be adequate but anyone heard of spacing a few small holes in tin roof (top of arch of course) to relieve wind pressure under roof? |
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You can buy a pre-formed ridge vent that will look nicer and probably give you the same amount of ventilation. I've never actually heard of having vents to reduce uplift on the roof. From a common sense standpoint I get the concept. However, the structure and sheathing should be built and fastened to withstand the expected uplift. |
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Quoted: You can buy a pre-formed ridge vent that will look nicer and probably give you the same amount of ventilation. I've never actually heard of having vents to reduce uplift on the roof. From a common sense standpoint I get the concept. However, the structure and sheathing should be built and fastened to withstand the expected uplift. This. The limiting factor will be shear in the legs as there will be no siding so you will need adequate diagonal bracing. Unless you span from corner to corner, from ground to truss/rafter, the posts will need to be over-designed for this shear load and will be far over-sized for the wind loads. A ridge vent will not appreciably reduce the lift anyway. Design it properly. |
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A ridge vent will allow hot trapped air to escape. However holes or vents will not reduce wind loading.
Think about an aircraft wing. The flaps on an airliner have large gaps when fully deployed. Yet, they produce more lift. If you are serious about reducing lift, you can put spoilers on top. Basically, a vertical barrier mid span. It trips up the airflow. By the way, it's not the impact pressure of the air underneath that does the lifting. It's the low pressure on top. This is why roofs get ripped off of homes in hurricanes. I know that sticking your hand out the window of a car feels like impact air lifting your hand. If you were to instrument your hand, you would see that greatest differential is on top. |
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