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Posted by RicodJour on April 3, 2008, 7:05 pm
wrote:
>
>
> > wrote:
>
>
> >> > wrote:
>
> >> >> > The smaller dormer could easily experience more turbulence and be
> >> >> > subjected to greater forces, and since code requires that certain
> >> >> > areas (end zones) be designed with a greater wind load for a given
> >> >> > wind speed, you're right in not skimping on the dormer.
>
> >> >> Pardon,
>
> >> >> How could a smaller dormer experience MORE turbulence?
>
> >> > More turbulence than a roof without a dormer?
>
> >> Okay...maybe I'm missing something here: the point was not a dormer
> >> versus
> >> NONE, it was a smaller one versus a BIGGER ONE.
>
> > Roofs are designed with loads that are attributed to zones. Eaves,
> > edges and ridges are subjected to greater stress and the design loads
> > and nailing pattern requirements are in acknowledgment of the
> > increased stress on those areas. Since a smaller dormer is
> > essentially all end zone the requirements are actually more stringent
> > than in the middle of the roof field or on a larger dormer.
>
> >> > Easy. You're putting
> >> > an object in the way of the air stream => turbulence and quite
> >> > possibly increased localized wind speed.
>
> >> Okay...you've totally lost me.
>
> > A certain volume of air is moving at a certain speed across a roof,
> > that creates a certain pressure and a certain load. When the wind
> > encounters an obstacle it doesn't just stop or change direction with
> > no change in pressure. Whether you approach it as a Venturi effect,
> > an airfoil or simply compressing the air, the net effect is the same -
> > the wind pressure/load is increased locally.
>
> Gotcha!!
>
> Thanks.
I can usually explain something in three or four
attempts...unfortunately people wander off after two or three. ;)
R
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