Design Area - Attic Space

[Fe02C]

You will have to excuse my question if it seems simple, I am still new to fire sprinkler design.

We are sprinklering a combustible attic space in an Ordinary 1 building. The building footprint is 1690 ft2.

The sprinkler system is a preaction system, and the roof slope is larger than 1/6, so the design area is required to be 2850 ft2.

Since the attic space (after taking account of the roof slope) is less than the design area, should a portion of the floor space below the ceiling be included to meet the 2850 ft2?

The code says that you only have to go the extent of one floor if it is less than the required design area, but does this apply to attic spaces?

Thanks

 

[MedullaOblongata]

If you are using .15 gpm/sq.ft.. you just need to calculate 2535 sq.ft. Hydraulic calculations must be performed for the floor space area and size the pipes in attic based on your floor space area calculation.( But confirm the hydraulic most demanding area i.e sprinklers in attic space or sprinklers in the ceiling)
Any way your calculation will either be just for attic space or the floor space.

 

[Fe02C]

Thank you for the quick response! 2535 sp. ft... right. I don't know where I got the other number from.

That is what I figured it is supposed to be for the area. I just couldn't find anything that explicitly said so. To take it further... is there a requirement for the ceiling construction (eg fire rating) between the space and attic?

 

[TravisMack]

The attic and ceiling sprinklers are calculated independently. If your building is only 1690 sq ft, then that is all you can calc.

You will calc every head in the attic. If you are unsure of what the most demanding area is, then you would separately calculate every head at the ceiling? If I understand correctly, you would calc the combustible attic space at light hazard densities and then you would calc the ceiling sprinklers at your OH1 density.

Are you really putting a preaction system in the attic? You are going to need detection in the attic to release the preaction valve. Seems odd, but I have seen stranger things in this industry, for sure!

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[cdafd]

PRE ACTION in the attic???????

Or do you mean dry pipe???

If pre action what type of detection are you going to use in the attic to trip it???

 

[Fe02C]

We are putting a pre action system throughout the whole building with heat detection.

 

[pipesnpumps]

You do realize the attic will need to be heated right? That is assuming the design winter conditions for your area is below freezing.



Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[cdafd]

Ok pipe

Why do you need to heat the attic ???

 

[cdafd]

Feo2c

Why not keep it simple and do a dry pipe

Instead of adding a full blown fire alarm

And making sure you have a heat detector in every area/room that sprinkler protection is in????

Almost every system I have seen has missed detection in some area,

Let alone sticking heats in the attic

What state is this in??? Roughly how many sq ft building???

 

[pipesnpumps]

Cdafd I thought that preaction required heated space, no? Because the pipe can fill and sit there awhile and maybe get slushy before a head pops? Even if nfpa 13 allows it smoke detectors are only listed down to 32. Not sure about heat detectors.

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[TravisMack]

Preaction does not require a heated space. It is often used in freezer applications for rack storage and things such as that. I could see your concern in a single interlock, but not in a double interlock.

But, if the single interlock system trips and there is no fire, then I have to assume it would be drained rather quickly. If there is a fire, there should not be a significant delay between valve trip and water flow due to head fusing.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com