Backflow Preventer Enclosure Installation Guide

This guide is written for civil and plumbing engineers, water authority specifiers, facility managers and installing contractors. It covers which location is best, how to select and size a backflow preventer enclosure, and the step-by-step process for a compliant, lasting installation grounded in ASSE 1060 requirements and field-tested best practices.

Outside and above-ground within an ASSE 1060-certified enclosure. This is the safest, most code-compliant and most cost-effective method. Two common alternatives — underground vaults and indoor mechanical rooms — create the very problems backflow prevention is designed to prevent.

It's not advised to install backflow prevention assemblies in underground vaults or inside buildings. Here are the reasons why you should choose an above-ground enclosure instead.

An RPZ discharge event inside a mechanical room resulted in over $1 million in structural damage at a hospital, with water volume sufficient to push a wall into an adjacent telephone and low-voltage wiring room. The property insurer sought recovery damages from the engineer, architect, contractor and most recent tester.

Above-ground installation in an ASSE 1060-certified enclosure eliminates the risks of vaults and indoor locations. Maintenance personnel can access critical equipment without special safety protocols, and the relief valve can discharge safely outside. When the outdoor enclosure is properly designed, the assembly is protected from freeze damage, vandalism and environmental damage for decades.

Here's the case for above-ground enclosures, by the numbers:

• Above-ground enclosure installations get approved approximately twice as fast as underground vaults on average.
• Las Vegas Valley Water District saved $60,000 per installation by eliminating vault rehabs.
• Enclosure lengths and cost can be reduced when using N-pattern assemblies. For example, a six-inch N-pattern assembly has a lay length 25 percent shorter than a traditional straight-line model.

Specifying the wrong enclosure is as consequential as choosing the wrong installation location. Material, ASSE 1060 class, size and clearance all determine whether the enclosure protects equipment and how it performs over its service life.

ASSE 1060 requires that all test cocks and shutoff valves be within 24 inches of the access opening and that equipment inside the enclosure remains accessible for maintenance and testing without removing the entire structure. Adequate clearance is a certification requirement. Field experience and our free Standard Details Guide define the following working clearances:

• Assembly-to-wall clearance: 6-12 inches on all sides to allow test equipment connection to test cocks
• Below the RPZ relief valve: 12 inches minimum from relief valve to concrete pad to prevent submersion and allow drainage
• Multiple assemblies: 12 to 24 inches between centerlines of piping runs when more than one assembly shares an enclosure
• Gate valve to enclosure roof: Six inches minimum clearance to allow wrench operation of the valve handwheel, for both OS&Y and NRS gate valve types

Specifying an N-pattern assembly allows for a correspondingly smaller enclosure, reducing cost and site footprint length by 25 percent. Placing multiple assemblies and water meters in a single enclosure can further reduce the total footprint. Use the Safe-T-Cover sizing guide to confirm dimensions before specifying.

The following sequence applies to above-ground installation on a reinforced concrete pad. Safe-T-Cover enclosures ship flat with all assembly hardware and instructions included.

Site Selection and Preparation

• Choose a location that avoids flood-prone low areas and high-traffic zones.
• Place the assembly near the property line where possible to simplify tester access and eliminate the need to enter the building.
• Avoid positioning the enclosure at the front entrance; a setback location that moves it out of primary public view reduces aesthetic concerns without compromising access.
• Confirm local plumbing codes for setback requirements and minimum service clearance.
• Verify with the water jurisdiction that the above-ground enclosure design is acceptable and request written approval before finalizing the specification.

Concrete Pad and Anchoring

• Mark anchoring points and the concrete pad position based on the enclosure footprint and assembly dimensions.
• Confirm all utility locations and underground conflicts before beginning any excavation.
• Pour a reinforced concrete slab per local structural requirements; use 3/4-inch crushed stone as a sub-base for drainage.
• Allow concrete to cure fully before setting the enclosure.
• Anchor the enclosure to the substrate using the specified hardware; proper anchoring deters removal and ensures structural stability.

Freeze Protection, Heaters and Insulation

• For Class I applications, install a heater rated for the local climate. Safe-T-Cover’s patented slab-mounted heater maintains a steady internal temperature and is bolted directly to the concrete. The heat can penetrates down the vertical riser pipes by about 16 inches. A thermostat controls heater activation.

Initial Certification and Functional Testing

• Schedule a certified backflow tester for initial certification before the enclosure is closed out.
• Perform a full leak test and functional test of the assembly.
• Document test results and attach records inside the enclosure or to the project file.
• Hand over operation and maintenance instructions to the property owner or facility manager.

• Undersized enclosure: An enclosure that blocks access to test ports will fail inspection. Size to ASSE 1060 clearance minimums, not to the bare physical footprint of the assembly.

• No drain for RPZ assemblies: Omitting drainage is a code violation and a flood risk. Every RPZ installation requires a compliant drain sized to handle full discharge flow.
• Improper anchoring: An unanchored enclosure can shift, be moved or be removed entirely. Anchor to concrete with the specified hardware.
• Vault specification for RPZ assemblies: RPZ assemblies cannot be installed below grade. If a vault is specified for an RPZ, the design is non-compliant by definition.
• Indoor RPZ installation without drainage planning: Floor drains in mechanical rooms are rarely sized to handle RPZ relief valve discharge for assemblies 2 1/2 inches and larger. Design the drainage system for worst-case discharge, or move the assembly outside.
• Skipping water jurisdiction approval: Before finalizing an above-ground enclosure specification for a new project, send the design to the water jurisdiction and request written confirmation that it will be approved.

Now that you know how to install your enclosure, it's time to choose the right one! Use our free sizing guide to select the perfect aluminum cover for your next backflow project.