A few thoughts on cornices: Buildings divert wind so well that the wind
speed "near" the facade is practically nothing, and this dead zone may
extend outward by a matter of feet, less at corners. Rain is carried to the
facade not by wind but by momentum, through air that has already been
stilled by proximity to the building. So wind can carry only large
raindrops onto a building facade; small drops, drizzle, and drips off the
cornice have practically no horizontal momentum and only "dead" air to fall
through. One effect of the cornice is to fatten the dead air cushion around
the building.

The biggest EIFS failures are in Vancouver condos, where the zoning code
penalized cornices, so there were none. The EIFS buildings there with
cornices have done well.

At 06:31 PM 6/23/99 -0400, you wrote:
>Re: Evidence of a rain-shielding function by a cornice
>
>It has been my experience that aside from the peculiar effects of a driving
>rain which can blow moisture into, under and up any possible fissure, the
>most damage is from  the long persitent drizzle that goes well beyond the
>"rain" itself.  The wetness just doesn't stop and little leaks and cracks
>just keep leaking in.  Therefore the lower the building, the deeper the
>overhang (or cornice) and the gentler the breeze (pushing the moisture
>against the wall), the better the protection and less the potential for
>damage.  The same goes for roofs.  Except for drains backing up, the
>persistent wetting of the surface is probably more damaging that one short
>intense wetting.
>
>When I look around structures with overhangs (no gutters), the drip line
>generally is found away from the wall, indicating that the water is falling
>relatively straight down, enough to form a pattern on the ground.  Then,
>splash-back becomes a problem...in cases a big problem if weak masonry or
>wood is near the ground.
>
>Also observe the condition of paint on a frame building...best near the top
>of the wall, under the eaves, and worse on the bottom, on anything which
>projects, and varying according to exposure to wind and sun.
>
>So, below the top story or two, I doubt a cornice will protect the wall of
>a taller building very much.  Problem with some cornices is that they
>deteriorate from exposure too.  That's why so many of them are torn down by
>Local Law chickens.
>
>And I'm very much a believer in microenvironments effecitng the direction
>and scouring effect of wind in the city.  Dominant wind direction three
>seasons of the year is from the northwest (shifting to south in the
>summer).  But just walk around the city with an umbrella on a windy day and
>watch where the winds come from: whether you're on an avenue, on a side
>street or near a park.  I've seen some spectacular eddies during snowstorms
>near Central Park (By the GM tower on 58 Street!), and the scoured stone on
>south and east cornices and facades when the wind curls across.  I think
>the eddies can be worse than the simple pressure of direct wind due to
>turbulence.
>
>I guess I straddle between the one who says yes and the five who say no to
>cornice protection.  I say, sometimes.  --Jim
>
>