RTU penetration head spacing

[ShawnO1]

A little background...
Unobstructed noncombustible bar joist retail construction.
EH density with standard coverage heads - 100 square feet max spacing.
Green represents ductwork dropping down from RTUs.

I am told to apply the 3X rule to the vertical ductwork and therefore maintain 24" clearance from my head to the ductwork. However, I have heads beneath the ductwork. I don't believe this is correct after reviewing NFPA 13 but want other opinions since I have been in this long enough to know I can be wrong.

The plan reviewer is stuck on coverage of the roof.

If he is correct then since I am applying the 3X rule do I need heads on the North and South sides of the ductwork?
or would you guys consider the 3x rule to take care of this?
Does the drawing below appear to be correct?

TIA

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[ShawnO1]

Anyone want to take a stab at this?

 

[skdesigner]

ShawnO1,

I've always taken the conservative approach and done exactly what the plan reviewer is requesting in your case. As this is a non-continuous obstruction (i.e the sprinkler can be expected to get water to both sides of the obstruction), installation in this area would be governed by NFPA 13-13 8.6.5.2.1.3, the "three times rule" you've stated. Note that the three times rule only applies if 8.6.5.2.1.4 through 8.6.5.2.1.9 cannot be satisfied. From your information, I suspect they can't. The sprinkler on the middle line would need to be located at least 24" from the vertical ducts.


R M Arsenault Engineering Inc.

http://www.rmae.ca

 

[ShawnO1]

Thanks for your reply skdesigner.

I really don't mind meeting the plan reviewer's request. My issue is I like to understand his argument and remove this problem from future submittals on similar future projects. If I don't understand his argument it's going to be difficult for me to prevent comments in the future.

I made a pledge to myself several years ago to not get upset with rejection comments but try and understand the comments (instead of just making a change to appease the reviewer). I've built job specific templates and checklists to prevent future comments instead of getting mad about them. It's worked and my drawings are better than they were 5 years ago by leaps and bounds.

Here is where my head hurts trying to meet the request. If I move the middle line to 2'-0 off of the vertical duct that would make the sprinklers (left to right) approx. 11' apart. Would you then consider the heads over spaced (10x11=110) even though I have a head under the HVAC? Or must I shrink spacing along the branchline to correct this?

Thanks for your time...

 

[skdesigner]

Yes, I would consider them over-spaced. I'd then do exactly as you've said and tighten up spacing along the line by adding an additional sprinkler.

R M Arsenault Engineering Inc.

http://www.rmae.ca

 

[ShawnO1]

Sadly that's what I thought. Nothing like retail work - moves so quick there's never time to wait on approvals. Thanks for your opinion and have Merry Christmas!

 

[skdesigner]

That's what keeps it interesting. Drawings done and stamped just in time to put them in the As Built package

Merry Christmas to you as well Sir.

R M Arsenault Engineering Inc.

http://www.rmae.ca

 

[TravisMack]

I agree with SK on this one. I would apply the 3x rule which would likely mean an extra sprinkler on that branch line. I would also have the sprinkler under the duct as you show.

It may be overkill, but I know that I have met all I can in the standard by doing it this way.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

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