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RE: Reroofing

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In San Jose we have a similar policy, however, not as liberal. Our criteria
is that if the total weight of the roof, including the existing and new
materials is less than 10 psf, we would not ask for calcs. The rationale for
this is that most likely the original calculations would have assumed
minimum 10 psf dead load. With most reroofing involving clay or concrete
tiles the dead load will most likely exceed 10 psf and therefore would
trigger a structural analysis.

Ben Yousefi
City of San Jose


	-----Original Message-----
	From:	Tom.Hunt(--nospam--at)fluordaniel.com [SMTP:Tom.Hunt(--nospam--at)fluordaniel.com]
	Sent:	Wednesday, April 14, 1999 8:35 AM
	To:	SEAINT(--nospam--at)seaint.org
	Subject:	Reroofing

	     Our homeowners association is planning on reroofing our entire
complex 
	     of 165 buildings (4 to 5 units per building).  They have
narrowed the 
	     options down to 5 roof coverings all of which are class A
concrete or 
	     clay tile.  The most likely choice will be "ClayMax" by US Tile
on 
	     plywood sheeting.  The existing 20+ year old roofs are cedar
shingles 
	     on what looks like 1/2 inch by 6 inch planks spaced about 12
inches 
	     o/c (you can see 4 to 6 inch of the black paper between the
planks).
	     
	     The new roof system is obviously heavier than the existing
system and 
	     therefore will generate more seismic load to the shear walls.
I was 
	     shocked to learn that the city of Irvine has a "city policy"
that if 
	     the clay tiles (EXCLLUDING the addition of plywood) are less
than 7.5 
	     psf then NO structural calculations are required.  The ClayMax
tiles 
	     weight 5.8 psf.
	     
	     The city official I talked to said that since the plywood would
add 
	     "extra seismic rigidity" they discount the added weight of the 
	     plywood.  I politely explained that with the 3 to 4 psf added
to the 
	     roofs from the new tiles and plywood the shear walls will be
taking 
	     more seismic load regardless of the roof rigidity.  His comment
was 
	     that since the buildings are 20+ years old they would never
"calc out" 
	     with the added weight and newer codes.  Duh!!
	     
	     For those with conventional construction and reroofing
experience (I 
	     am a concrete/steel guy) is it normal not to require structural

	     calculations when reroofing with a heavier system.  Without
structural 
	     calculations I would think as a minimum this could void our
earthquake 
	     insurance.
	     
	     Every time we have a good shaker I get cracks around the door
openings 
	     and it seems this will only make it worse.  Any other comments
on 
	     reroofing concerns/problems??  
	     
	     I should also note that we are located on a slight hill and
each unit 
	     is half slab on grade and half elevated.  The elevated half is
about 6 
	     feet above grade.
	     
	     Thomas Hunt