Whether it calcs or not it would be wise to strongly recommend that a
structural engineer review the impact of the change of roof material. If
the building authority still insists that is unnecessary then you may have
an ethical obligation to register your serious concerns. Then if something
happens you can say, "I told you so".
Thor Tandy P.Eng MCSCE
From: Tom.Hunt(--nospam--at)fluordaniel.com <Tom.Hunt(--nospam--at)fluordaniel.com>
To: SEAINT(--nospam--at)seaint.org <SEAINT(--nospam--at)seaint.org>
Date: Wednesday, April 14, 1999 11:44 AM
> 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
> 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