×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

8'-0" max spacing perpendicular to deck slope

8'-0" max spacing perpendicular to deck slope

8'-0" max spacing perpendicular to deck slope

(OP)
I have an attic space that is currently protected by BB attic sprinklers and AP sprinklers, it was an unoccupied attic area. Roof pitch is around 12/12.. They are going to occupy this space with offices and install a wood plank ceiling directly onto the roof structure so no roof joist will be exposed. It will not really be a "concealed space" at this point. There will be exposed wood truss's beams going across the space spaced 8'-0" on center +-.. They are proposing to remove the ATTIC sprinklers since it will be an occupied space, and want to install standard uprights for the new occupancy.

Per 2010 Nfpa 13, 8.6.2.2.1 (A) it says: For combustible concealed space under a pitched roof having combustible wood joist or combustible truss construction with members less than 3'-0" on center with slopes greater than 4 in 12 pitch. To the right under the Max Spacing column it says: 15'-0" parallel to the slope 10'-0" perpendicular to the slope, with an asterisk * that refers to 8.6.2.2.1.1 which says when 8 foot max spacing perpendicular to the roof slope is exceeded the minimum pressure shall be 20 psi...


Since this space will no longer be considered a concealed space, does the 8'-0" max spacing perpendicular to the roof slope rule still apply because of the roof pitch?

Does that rule apply to an occupied space in addition to combustible concealed spaces ?

I know I need to increase the remote area for the roof pitch, but 8'-0" max spacing will really kill the job as I will end up calculating the entire space, and it will not work most likely.

Thanks in advance.

RE: 8'-0" max spacing perpendicular to deck slope

A couple thoughts:

1 - If the space is occupied, it should be conditioned. At that point, you can use 4.2k sprinklers and a wet system. That will drastically cut down on the over-discharge.
2 - I would say that you no longer have a concealed space and the concealed spaces requirements are not applicable.

Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...

RE: 8'-0" max spacing perpendicular to deck slope

Following off Travis, it would appear to be 8.6.2.2.1 (a) "Combustible Unobstructed with exposed members greater than 3' O.C." and also with a sloped ceiling so don't forget your 30% design are increase.

RE: 8'-0" max spacing perpendicular to deck slope

If the peak is less than 20' and the system is wet with QR sprinklers you could reduce the remote area as well.

RE: 8'-0" max spacing perpendicular to deck slope

Yeah, I assume you will still be limited to 130 sq ft per sprinkler. A 12:12 slope would lead me to believe that the 20' height will be surpassed pretty quickly. But, you will have the 30% increase for sure.

Since you "space on the slope and calc on the flat," you may even want to look at 2.8k sprinklers as that area per sprinkler on the flat projection is going to be pretty small. That is provided you have a wet pipe system.

Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...

RE: 8'-0" max spacing perpendicular to deck slope

(OP)
Travis,
Are you sure about the 130 sq. ft spacing? If it falls under Combustible unobstructed with exposed members more than 3'-0" O.C (The exposed beams/ trusses) 8.6.2.2.1 says I can go to 225 sq.ft spacing with a calculated system.

It's 18'-4" to the peak.. Would I still be allowed a slight reduction in my remote area for qr sprinklers if I have to initially increase it by 30% for the steep pitch deck?

Thanks guys!

RE: 8'-0" max spacing perpendicular to deck slope

I was assuming your trusses would be the standard 24" on center. In that case, you would be limited to the 130 sq ft for combustible members less than 36" on center. I missed your 8' on center in the original post. Is your construction considered obstructed? That would put you at 168 sq ft max.

Yes, you can apply multiple reductions. At 18.333', you would be 1438 sq ft design area.

Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...

RE: 8'-0" max spacing perpendicular to deck slope

(OP)
It's very old construction. The roof joist are 2'-0" o.c, but they will all be covered up by the new wood plank ceiling, so I am thinking the roof joist are no longer a factor in considering the spacing of the sprinklers, am I correct in that thinking? It's really just a steep pitch ceiling at this point,with exposed cedar columns and beams. No, it's not obstructed construction.

RE: 8'-0" max spacing perpendicular to deck slope

(OP)
I just got onsite for the first time today and the horizontal "beams" that I said were 8'-0" on center are actually wood collar ties spaced anywhere from 24" to 34" on center. Most are around the 24" mark, tied into the roof joist. (The cad files and pdf plans leave a lot to be desired on this job.)
The collar ties do not make this space "obstructed construction" but would these collar ties put the sprinkler spacing under the category of Combustible unobstructed with exposed members less than 3'-0" on center? for a max spacing of 130 sq.ft per sprinkler? This seems like it would, but I am just trying to be sure before I move ahead with my layout.

Sorry for any confusion.

Thanks for your help


RE: 8'-0" max spacing perpendicular to deck slope

(OP)
I spaced @ 130, and I am close to getting it to work with 2.8 k sprinklers.. I have lousy pressure and it's 55'0" in elevation to boot!

Thanks for all your help.

RE: 8'-0" max spacing perpendicular to deck slope

(OP)
Is the minimum psi for a 2.8k head 7psi?

RE: 8'-0" max spacing perpendicular to deck slope

(OP)
What is the formula for determining the min psi if it is over 74 sq.ft spacing?

Thanks

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources