Skip to main content

What Are Cast-in-place Tub Boxes?

tub box

Contractors have several options available to them when they need to firestop pipe and conduit — cast-in-place sleevessealantsputty pads and more. Tub boxes may not be as well known, but they’re designed to meet firestopping needs when laying out bathtubs with the accompanying drain and overflow assemblies. In fact, HoldRite updated its HydroFlame Pro Series tub boxes recently to give contractors more flexibility during installation. Discover how tub boxes work, why you need them and how the enhanced HydroFlame Pro Series models help you work even faster.

What is a Tub Box?

These are pre-engineered firestop devices for bathtub drain and overflow assemblies. Just like other firestopping technologies like sealants and sleeves, they serve as a fire barrier to guard against the spread of fire, smoke and gases.

When Do I Need to Use a Tub Box?

While tub boxes aren’t specifically mentioned in building codes, firestopping floor penetrations is a building code requirement. This is especially true for buildings that house occupants, such as hotels, multifamily buildings and high-rise apartment buildings. These structures are more likely to have floor penetrations where bathtubs would be installed. Tub boxes are a quick way to comply with building code firestopping needs.

Since HoldRite HydroFlame tub boxes are pre-engineered with firestop already built into the device, you don’t have to fuss with makeshift methods or traditional installations involving mineral wool, sealants or messy firestop mortars.

tub box on site


How Does a Tub Box Work?

In the case of HoldRite HydroFlame, the UL Listed tub box works like our line of HydroFlame Pro cast-in-place firestop sleeves. It comes with two components that work together in one unit: a firestop sleeve and a tub box shell that holds the space for the drain and overflow assembly.

Before pouring concrete, simply fasten the tub box to the form deck using nails or screws and adjust the height of the tub box legs if needed. Once concrete has cured, contractors can simply remove the Styrofoam that sits on top of the tub box plastic shell.

With HydroFlame Pro, contractors have their choice of picking either a 2- or 3-in. diameter sleeve that can attach to the bottom of the tub box shell within one of two unique knockout locations. The 3-in. sleeve allows maximum flexibility for contractors looking for additional wiggle room during drain and overflow installation. It can also help with drain layout locations that may not be exactly in the spot they should be in.

Watch HydroFlame Pro Series Tub Box - Product Highlight | HoldRite on YouTube.

What Kind of Tub Box Options Are Available?

You’re probably only going to find tub boxes for use with flat deck concrete floors because concrete decks over corrugated metal don’t provide a thick enough slab under the tub box shell. Without enough concrete underneath it, the shell will completely melt away during a fire test. HoldRite HydroFlame Pro Series tub boxes require a minimum slab thickness of 4-½ in.

Tub boxes also come in different sizes. HoldRite options are designed to meet different concrete thickness at pre-set heights right out of the box, making the job easier for the contractor. Standard models allow contractors to choose tub boxes in heights of 8, 9 or 10 in. to accommodate most slab thicknesses. Tub boxes can also be cut in the field to meet thinner floor thicknesses as low as 4-½ inches.

Benefits of HydroFlame Pro Series Tub Box

HydroFlame Pro Series tub boxes are now longer than before, which will help reduce the need to chip out concrete during bathtub installation. This extra-long and deep space within the slab will give contractors maximum room to install the bathtub and fasten the drain and overflow assemblies properly.

In addition, HydroFlame Pro Series tub boxes support contractors with the following features:

  • Two separate knock-out locations for standard and exotic tub drain and overflow locations — no need for extensions, couplers or field modification positions.
  • Built-in fire, smoke and gas protection.
  • Provides a UL listed W rating for watertight slab protection for all drain pipe types.
  • Code-approved.