The dry pipe protects the overhang of a walkway, no attic. the original
install is about 20 years old. About 6 years ago, 2 more low hazard
buildings were built and the dry pipe system was extended. The 2 new
buildings are each protected by a separate wet system. All the fire water
comes from the original street connection. The extension increased the
protected area about 35-40 %. I assume hydraulic Calcs were done by a
licensed person. I tried to type that with a straight face. No increase in
pipe sizes were done. I do not know what edition of 13 was used for any of
the sprinkler work. I doubt that any water supply information is on file
anyplace. So if Calcs are needed, I will have to have a qualified person do
that for me. My local AHJ allows do whatever I want. So the decision will
be up to the client and his engineer.
I will print this out, we have a meeting at 9:00 AM. After the meeting I
am sure I will have more questions.
-----Original Message-----
From: Todd Williams
Sent: Wednesday, January 12, 2011 4:06 AM
To: [email protected]
Subject: Re: Hydraulic Calcs
Are you replacing only the 3" pipe or branch
lines and heads as well? Was the existing system
hydraulically calculated or pipe schedule? How old is the system?
Depending on the age of the existing system, new
hydraulics could open cans of worms. If it is
pipe schedule, the system has probably never been
calculated so there is no indication of how the
hydraulics looked in the first place. If it has
been calculated, was the 30% increase for dry
systems, 30% increase for roof slope and the
new(er) minimum end head pressures included? If
not, you may not have an adequate system, based
on current Code. But it may have been fine when
it was installed. Is there a compelling reason to
bring this attic up to current Code?
This probably needs to be hashed out between you,
the Owner, Engineer and AHJ. I hope your quote
included a provision so you get extra $$ if the
pipe sizes increase due to the hydraulics.
At 02:10 AM 1/12/2011, you wrote:
I am bidding on removal and replacement of an existing dry pipe system.
This is about 1,000 feet of 3 inch. Part of the specification is
“Contractor shall submit working plans that have been approved by
authorities having jurisdiction, including hydraulic calculations, prior to
starting work.†Is it normal to have new calculations done when just
replacing rusting pipes? If so, where do you draw the line at needing new
calculations? There has been new construction, since the building was
built. Three new low hazard buildings have been built, with a new low
hazard rehabilitation facility going in a block down the street.
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Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, CT
860.535.2080
www.fpdc.com
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