Blog Post One

This educational is to assist plan reviewer’s other subcontractor in understanding NFPA guidelines and our recommendations for freeze protection, specifically multifamily. It is our mission to design and install reliable fire sprinkler systems. Here are some of the installation methods that we hope to explain.

Dry Barrel sprinklers:

Most freeze breaks occur on balconies facing north, where wet pipes are installed in exterior walls or to close. The chart in NFPA is a bit confusing. Chart 8.4.9.1(a) far left side details “discharge end” of the dry sprinkler, in which the coldest temperature of the building location is used. San Antonio, we use 20 degrees, Austin 10 degrees, and Dallas 0 degrees. The three other measurements reference “exposed barrel length” to the coldest ambient temperature. If the temperature can not be assumed, NFPA requires a heat calculation, and if exposed to wind assuming 30 MPH. This measurement can NOT be taken inside a 4” or 6” wall, here is why”.

Exterior wall interior dimensions.

2x4 walls have 3 ½”

2x6 walls have 5 ½”

Dimensions to install a “0” inch dry barrel sprinkler:

· R11 & R13 Insulation is 3.5”

· Sprinkler head tee is 1.72” (not including the threads)

· Minimum .75” inside wall to backside of sprinkler fitting

To install a zero-inch dry barrel sprinkler requires 6”, which means in 2x4 walls you have negative 2 ½” and 6” walls you have negative ½”. San Antonio and Houston would require a 10” wall assuming 40 degrees could be maintained inside the exterior wall, and an 8” wall assuming 50 degrees could be maintained inside the exterior wall.

This is why there are freeze breaks that occur every year, the systems are improperly installed.

Flexible dry sprinkler:

Flexible dry sprinklers are the obvious solution, if installed correctly. In DFW area, the flexible dry sprinkler requires 12” from the exterior wall assuming 40 degrees will be maintained. In DFW

areas, we have a conservative approach and utilize 50” dry flex. Fully blown insulation settles year 3 and 4 and creates a cold area that wind can reach and freeze pipes 14” inside the truss. We will not install wet pipe within 20” of an exterior wall. Diagram 8.4.9.1(a) states “where more than 30 MPH wind is expected, longer barrel lengths will help avoid freezing” However, it’s not the dry sprinkler that freezes, it is the wet pipe. We have seen wet pipe break not associated with the dry flex, we use a longer length to keep the pipe further in the truss. In southern regions like Houston and San Antonio, we have not seen this problem and 4” barrel is sufficed.

Attic installations:

Installing dry systems in combustible attics is a challenge and subjective. Most of the work is in design, however the main recommendation is to have a quality control team checking the installation, limiting the drum drips when possible and making sure they are labeled in the riser location so that the owners can service the system. When possible, locate the drain valves in conditioned space so if a maintenance coordinator cannot make it out on icy roads he has more time.

CPVC dry systems:

We stopped designing CPVC dry systems for several reasons. First, we find that vertical pipe requires 45-degree fittings, if 90-degree fittings are used the pipe will sag, hold water and freeze. Second, we find a separate dry valve is required for many reasons, but mainly water reaching the sprinkler. NFPA assumes systems less than 500 gallons will activate timely. This is inaccurate. Water delivery relies on pressure, resistance, and distance. CPVC dry systems have small pipes, so the volume is low, but long distances. In our internal testing, a 400-gallon CPVC dry system, when a remote sprinkler on the top floor was flowed, it did not activate the alarm for 3 minutes, and water delivery took almost 7 minutes. However, the first-floor inspectors test operated correctly giving misleading approval. Lastly, the listing of CPVC requires less than 15 psi, and there are no dry valves that can operate that low except the Victaulic dry valve, which requires 18 psi so the compressor to activate before the low air alarm is engaged as the Victaulic dry valve activates at 7 psi.

CPVC dry systems would be for very small scenario’s,45-degree fittings for anything vertical, maintain less than 15 psi, with the high-pressure switch set at 15 psi, and test water delivery to the remote sprinkler on the top floor.

NFPA recommends that wet systems should be installed where possible. The simplest, most reliable easy to maintain scenario.

Antifreeze systems:

There are new antifreeze solutions available. However, they must be installed in areas that do not exceed 150 degrees, they require a “listed” expansion tank, and not over 40 gallons. They should be installed where the wet system cannot be utilized. The cost to maintain these systems is expensive and should require approval from the owner so he knows the responsibility. Developers usually sell properties before the maintenance cost occurs, so potential buyers should do due diligence, so they know the potential cost of ownership.

Antifreeze is NOT an option for us.

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