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The following are case studies of select large/complex commercial retrofits of radon mitigation systems:

   McChord Air Force Base Mission Support Center
McChord AFB MSC

The McChord Air Force Mission Support Center building has 100,000 sqft of basement and crawlspace and is over 900 feet long. Portions of the basement slab were removed and re-poured with seismic upgrades, while other portions remained intact. Asbestos was found in the crawlspace so special measures were required.


The original specifications for this building called for a minimum of 50 and as many as 100, residential type systems to be installed (like the one seen here, installed by a previous contractor) around the exterior of the building.

The drop ceiling throughout the entire building is being utilized as the cold air return. With the porous soil and high air volume, this would make a large number of residential type systems necessary around the exterior of the building. Our system is incorporated into the remodeling work and will be almost completely hidden when the project is completed.

The pictures that follow show the unique aspects of installing a commercial radon system in this type of structure.

Exterior view of radon system

Building footing before concrete was poured

1¼" steel rebar and 5/8" steel rebar were added to the footings for seismic upgrade before the concrete was poured. The 1¼" rebar was tied to the existing foundation. With the large amount of rebar in the footings, it is not feasible to go through the footings with the radon pipe.

This footing is 10' across and 6' deep. The soil underneath the footings is highly compacted. The footings in this building divide the foundation into sections. Each section must be depressurized separately.

Rebar

Building footing after concrete was poured

A 12" thick sheer wall will sit on top of the footing and extend through all four floors of the building to the bottom of the roof. This wall ties all the horizontal and vertical foundation components together.

As can be seen in this shot from the east side of the riser, the tee ties these three runs of 6" ADS double wall, non-perforated pipe to the 12" riser (the pipe was lightly perforated to facilitate condensate drainage).

Rebar

Building footing after concrete was poured

This view is from the west side of a 12" riser. The tee was manufactured with a 12" x 12" x 12" tee, two 10" x 6" wyes, and two 8" x 6" wyes. The wyes were used to minimize pressure drop.

Because the building is four-stories, the 12" radon riser was enclosed in a 2 hour fire wall chase from the basement floor to the 4th floor ceiling. The framing for the chase can be seen around the pipe in the pictures below left and the finished chase below right. Four chases like these and the fans on the roof (as seen below center) is all that is seen of the four radon systems after installation.

Fire chase during contruction
Finished chase
2 1/2 WC; 1800 CFM; 5 HP fan

Floor supports were needed for the 12" risers. Running through 4 floors, the riser weighed several hundred pounds.

Floor support close-up

Portions of the existing slab were to remain intact. In these areas, the floor was saw cut and trenched for the radon pipe (see picture, lower-left). Here, our patented tester was placed on a 4" line after the cement was repoured (see picture, lower-right). We did this to test for air flow and negative pressure across the entire slab.

Trench

Trench after re-pour

Pipe run

This 6" run is routed down a long storage area.

This 6" run goes below-grade and through a 10" thick wall.

Pipe run below-grade

Core Drill

We had to core drill a 5" hole through a 10" thick wall. The ladder seen in the picture is 7 feet.

This is a 6" 3034 PVC riser in the crawlspace with Geotech cloth to minimize asbestos transfer.

Pipe run below-grade

Core Drill

Two 4" double wall runs join to the 6" double wall main line. Both are non perforated pipe that we drilled holes in to evenly distribute the negative pressure extension.

Here the 10 mil. plastic is seen over the 6" x 6" x 6" 3034 tee and 6" riser.

Crawlspace detail

Crawlspace

Here is a portion of the 10,000 sqft of 10 mil plastic that was laid during Phase 1 of the project. In all, 50,000 sqft of 10 mil plastic will be laid the crawlspace.

2" of CDF concrete was sprayed over the Visqueen in the crawlspace to completely encapsulate the asbestos.

Crawlspace detail


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   Academy Retirement Community
Academy Retirement Community Academy Retirement Community

The Academy Retirement Community consists of two large buildings. Originally built in 1890, the Academy was known as Holy Names Academy, a boarding school for young women. The last class graduated in 1975. In 1987 the building was renovated into a retirement community.



Wall detail

The larger of the two buildings (above left) has two separate crawlspaces totaling 10,000 sqft separated by a 5,000 sqft basement. The crawlspaces and basement are all tied into one large system. The piping starts as 4" ADS pipe and exits the building using 10' PVC .

To control the negative pressure extension in the crawlspace, we utilized solid ADS pipe (4" and 6") and drilled 1/4" holes to maximize the negative pressure extension and condensate drainage.

Piping detail

Crawlspace detail

All of the air volume from the north crawlspace (5000 sqft) had to be piped across the basement of the structure through the foundation wall.

The basement in the main building consisted of 5 floor penetrations and extremely high air volumes. The highest air volume sump exceeded 200 cfm at 3/4" wc. (Photo at right).

Piping detail

Piping detail

The six-inch pipe (at left) carries the air from the north crawlspace. The 4" pipe was used to handle the high air volume from the 4" floor penetration. They were piped together to provide condensate drainage.

The fire sprinkler line (at right and seen below) could not be moved. The pipe slopes both directions from the sprinkler line.

Piping detail
Piping detail

Piping detail

Piping detail

This custom fitting consists of a 10" x 10" tee, two 10" x 8" reducers, two 8" x 6" tees, an 8" x 6" wye, two 8" x 6" reducers, and one 6" x 4" tee with 6" x 4" reducer.



Piping detail

The foundation of the facility is made up of two feet thick rock and mortar material. We used a 40 lbs jackhammer to notch the bottom of the crawlspace vent to allow the 10" duct to exit the facility below grade. We installed a 45-degree elbow as we came through the foundation to allow the duct to extend to 24 inches below grade.

Piping detail

Piping detail

The duct installed in the trench (lower left) runs to a small maintenance shed 75 feet away (lower right). Small holes were drilled in the pipe to drain condensate.

Piping detail

Piping detail

The shed footing extended greater then 24" below grade. We cut a hole in the footing and extended the pipe into the shed.

Piping detail

Piping detail

A 1½" thick PVC Flange was added to the end of the Schedule 40 12" PVC to mount the 3 hp fan. Both glue and screws were used.

Cook fan for main building

  • 3" wc
  • 1500 cfm
  • 3 hp
Fan detail

Building detail

The Assisted Living Building is 5,000 sqft and has a 4" sunken floor for the boiler. This was the only location to install the sub slab depressurization system.

Cook fan for Assisted Living Building

  • 3" wc
  • 650 cfm
  • 2 hp
Fan detail

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   U.S. Courthouse and U.S. Post Office
U.S. Courthouse, Spokane, WA

The U.S. Courthouse was our most interesting radon mitigation project. This structure is nine stories in height. The sub basement is beneath the below grade parking garage, leaving the sub basement slab over 20' below grade. With the parking garage directly over the sub basement and the exhaust requirements of a parking facility, this situation created substantial negative pressure in the structure. The pressure differential between the sub basement and the sub slab environment were over 1/3" w.c. The normal stack effect of a nine story structure would be approximately .050" w.c. The amount of negative pressure in this particular structure is almost never encountered under normal conditions. Several methods for radon reduction were utilized to reduce the radon constrictions in the sub basement.

  1. Active soil depressurization
  2. Repair of several HVAC Systems
  3. Sub basement pressurization
Step 1:

The sub slab depressurization system has eighteen floor penetrations and long duct runs. The numerous existing systems (HVAC, Steam, Plumbing, Electrical etc.) made routing of the radon system complex. We decided to run the radon mitigation system through the steam tunnel into the U.S. Post Office instead of up through the nine stories of the courthouse.


Piping detail

Piping detail

Piping detail

Piping detail

Step 2:

The complete HVAC control system was upgraded at the same time as the installation of the mitigation system. This repaired several defects in the HVAC system that affected the radon levels in the sub basement. For example, the parking garage exhaust fan (44,000 cfm) was running continuously with no make up air. Even small bathroom exhaust fans running continuously will elevate radon levels. One can imagine what a large parking garage fan can do.


Piping detail

Piping detail

Step 3:

Sub basement pressurization was used to reduce the radon levels even further. The chiller room has two cabinet exhaust fans (4500 cfm and 6500 cfm) to remove heat. We rebuilt one of the fans and turned it around to pressurize the chiller room instead of depressurize it. The amount of air remained constant, but at a positive pressure not a negative one.


U.S. Post Office

The U.S. Post Office had a radon mitigation system that was designed by our parent company, Thomas J. Gerard & Associates, Inc., and installed by the HVAC contractor during a complete remodel several years earlier.

U.S. Post Office, Spokane, WA

Fan Detail

Knowing the capabilities of the U.S. Post Office system we tied the two radon systems together and changed the fan from a 2 horsepower belt driven roof top blower to a 5 horsepower belt driven inline blower. The combined systems have 48 floor penetrations and approximately one city block of slab area. This is one of the largest radon mitigation systems in the U.S.


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