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Re: Single Family Residence Plans & Construction

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Hello Kirk,

I used to have my office in Huntington Beach so I am familiar with the
area.  In the 2 years I was there, I designed over 150 buildings in
Huntington Beach alone.

1.  I agree with you assumption that the plywood is a diaphragm whether
you state it as such or not.  Unless there is some other bracing system,
it would seem far fetched to assume the plywood is not a diaphragm.
Stick to your guns and make him do it right.

2.    Your plans should indicate the 2' requirement for horizontal
diaphragms, I believe it is 18" for walls.   I have typical details
showing plywood layout for both horizontal and vertical diaphragms.
Each of these details describes the minimum size requirements, blocking
requirements and defines the nailing.  I don't think it is reasonable
for you to assume the contractor will read the code, especially when he
has a set of engineered plans to go by.  If you did not call for
blocking or the minimum 2' requirement on your plans, the contractor has
an arguable point for an extra.

3.    Plywood on the roof can be something other than a diaphragm.  My
own house and office have no plywood roof diaphragm.  Both have wood
bracing as the horizontal load resisting element.  A house I recently
designed and is under construction has a layer of plywood but is not a
structural lateral load resisting diaphragm.  Lateral loads are taken by
the diagonal wood sheathing between trusses.  There is stripping on top
of that creating an area for insulation and plywood on top of that to
provide a surface for attaching the roofing.

Kirk Pysher wrote:

> I have provided a set of plans for a waterfront home in Huntington
> Beach.  The
> framer called in for a roofing inspection and the inspector denied the
> request
> because the framer had used plywood panels less than 24" wide w/o
> blocking
> (rightly so) along both sides of the ridge.  The Inspector told the
> framer
> that if he could get written approval from the engineer he would buy
> it off.
> Well I did not give him the approval beacuse it is explicitly stated
> in the
> code that the plywood panels shall be 24" wide minimum w/o blocking in
> seismic
> zones 3 & 4.  I told him that he would have to block the minimum width
> panels.
>  At his point he became irate and wanted to know how he should have
> known that
> this was a diaphragm roof.  And hence the question.  I did not
> explicitly
> state on the plans that this was a diaphragm roof.  The basic reason
> was that
> why could it be anything other than.  The nailing was explicitly
> stated etc..
> The shear walls were also stated via shear wall table.  I was
> wondering if
> anyone out there a) explicity states that this is a roof diaphragm on
> the
> drawing and b)  If any one is designing single family resisdences in
> So. Ca
> w/o roof diaphragms.