What Is Vertical Utility Concealment? (Chases)
A vertical utility chase is a framed, accessible enclosure that carries pipes, ducts, cables, or other services between floors. It has no universal code-defined size or airflow rate. Its layout must fit the services, preserve access, protect rated assemblies, and follow local building, fire, plumbing, mechanical, and electrical codes, along with each product’s installation instructions.
A bright blue pipe on a plan is easy to spot; the challenge is making room for it without hiding a safety problem behind finished walls. A well-planned chase gives services a clear route and keeps inspection and repair possible. I treat it as a coordinated building assembly, not simply an empty gap between studs.
What a vertical utility chase is
A utility chase is a framed enclosure or designated building space used to route services vertically, often between floors. It can contain plumbing, wiring, ducts, or several coordinated systems. The chase is not automatically a rated shaft, duct, plenum, or fire barrier; those functions require code-compliant design.
Unlike a closet or storage cavity, a chase is planned around the services it contains. Its size depends on pipe and duct dimensions, insulation, fittings, supports, required clearances, and access points. There is no standard chase width or depth that suits every project.
It may run beside a stair, within a partition, or through a purpose-built enclosure. Wherever it passes through floors or rated walls, the surrounding assemblies and penetrations need specific attention. A chase enclosure alone does not protect a floor opening from fire or smoke.
Planning the chase: services, structure, and rated assemblies
Planning means mapping every service and the building elements it crosses before framing starts. I first identify the route, floor and ceiling construction, structural members, rated boundaries, and service points. Then I compare that information with local code requirements and the manufacturers’ instructions for the systems going into the chase.
Start with a measured drawing or marked-up plan. Include the outside dimensions of pipes and ducts, insulation thickness, fitting locations, supports, and the space needed to install and maintain them. Note where valves, junction boxes, dampers, cleanouts, or equipment will need access.
Before cutting or drilling, identify the joists, beams, studs, and other structural members. Do not notch, bore, or remove framing based on a convenient route alone. Structural limits depend on the member, its location, and the applicable code or design; ask a qualified professional when the proposed route conflicts with the structure.
Next, mark each floor, wall, and ceiling assembly that the chase crosses. Some assemblies may have a required fire-resistance rating. Confirm whether the design needs a rated shaft or another approved method of protecting the opening. The right detail depends on the construction and locally adopted code, not just the chase’s appearance.
For wood-frame construction, IRC R302.11 addresses fireblocking in concealed spaces, including locations such as floor and ceiling levels and intersections between concealed spaces. Where the provision applies, some concealed openings must be fireblocked at intervals no greater than 10 feet. Confirm the adopted code edition and the specific condition before building.
| Planning item | What to record | Why it matters |
|---|---|---|
| Services | Type, outside dimensions, insulation, and fittings | Establishes the space needed for routing and supports |
| Structure | Joists, beams, studs, and proposed openings | Helps prevent unsafe cuts or drilling |
| Assemblies | Floor, ceiling, wall, and any rated boundary | Determines fireblocking and penetration protection |
| Access points | Cleanouts, valves, boxes, and equipment | Keeps inspection and service possible |
| Product details | Clearances and installation requirements | Avoids conflicts with listed equipment instructions |
A useful first pass is a full-height section drawing, not just a plan view. It can reveal conflicts that a floor plan misses, such as a pipe fitting landing exactly at a beam or a cleanout facing a wall.
Access and clearances: cleanouts, equipment, and working space
A chase must leave enough room to reach components that need inspection, operation, or repair. Clearance is the usable space around a particular item, not spare room that can be filled later. Check each component’s code rule and installation instructions, then show the access location on the plan before closing the wall.
Do not bury cleanouts, valves, junction boxes, dampers, or serviceable equipment behind fixed finishes. Use an access panel or another approved arrangement where needed, sized and placed so the component can actually be used. A small opening that exposes a valve but does not allow a tool to turn it is not useful access.
The IPC, where adopted, addresses cleanout access in §708.1.1. As a general reference, cleanouts for piping 3 inches and larger typically require 18 inches of clearance, while smaller cleanouts typically require 12 inches. Verify the adopted text and the exact cleanout arrangement; do not treat these figures as a universal panel size.
Electrical working space is another common source of confusion. NEC 110.26(A) applies to covered electrical equipment that requires working space. In applicable conditions, the minimum is generally 30 inches wide or the equipment width, whichever is greater, 36 inches deep, and 6 feet 6 inches high. This is an equipment working-space rule, not a standard dimension for every chase.
| Situation | Planning check | Important distinction |
|---|---|---|
| Plumbing cleanout | Confirm clearance and a usable access opening | The required reach depends on pipe size and arrangement |
| Electrical equipment | Check working-space rules under NEC 110.26(A) | These dimensions do not define the chase itself |
| Duct or damper | Check service access and installation instructions | A duct path may need access to serviceable components |
| Shutoff valve | Keep the handle visible or reachable through a panel | A concealed valve can delay shutoff during a leak |
If services from different trades share a chase, coordinate the layout before installation. Their routes, supports, heat, moisture, and access needs can conflict. Follow the applicable trade codes and product instructions, and involve the relevant licensed trades when the work or local rules require it.
Execution: framing, fireblocking, and penetration sealing
Execution is the stage where the plan becomes a safe, serviceable enclosure. Frame the chase to suit the approved route without weakening structural members. Before covering it, install required fireblocking and protect rated penetrations with an appropriate tested system. Ordinary foam or caulk is not automatically an approved firestop.
Frame for the actual outside dimensions of the services, including insulation, fittings, and supports. Leave room to install them without forcing bends or removing required clearances. Do not assume an open stud cavity can serve as a duct, plenum, fire barrier, or sound or thermal separation.
At floor and ceiling lines, provide fireblocking where required by the adopted code. Fireblocking limits concealed draft openings; it is not the same as firestopping a penetration through a rated assembly. These terms address different details, so one should not be substituted for the other.
Where a pipe, cable, or duct penetrates a rated wall or floor, use a tested and listed firestop system suitable for that assembly, the penetrating item, and the annular space around it. IBC §714 and applicable IRC provisions address fire-resistant protection of penetrations. The correct system depends on the specific materials and configuration.
A continuous chase can create a vertical path for smoke and fire if floor openings and boundaries are left unprotected. Do not assume that enclosing the chase solves this problem. The floor assembly, chase boundaries, and each penetration need the protection required for that particular design and code condition.
If the chase carries supply, return, or exhaust air, treat it as an air-distribution system. Size and construct it under the adopted mechanical code and relevant duct, fire, and smoke rules. There is no default airflow rate for a utility chase. An incidental framing cavity is not automatically a compliant duct or plenum.
Verification: inspection, testing, and serviceability
Verification means checking the hidden work while it is still visible and confirming that the finished chase remains accessible. I use a pre-close inspection to compare the installation with the plan, code requirements, and product instructions. Photographing routes and access points can also help future repairs, but it does not replace required inspections.
A practical sequence is:
- Confirm the permits, adopted code editions, and any required inspections.
- Check service routes, structural openings, supports, and manufacturer clearances.
- Verify fireblocking and listed firestop details at the locations that require them.
- Test the installed systems using the procedures required for that trade.
- Confirm that access panels open fully and that valves, cleanouts, and equipment can be reached.
- Photograph the open chase and keep the images with the project records before finishing.
Illustrative case: stacked plumbing. A homeowner plans a chase beside a bathroom wall to carry a drain and supply lines between floors. The early drawing shows the pipe route, cleanout location, floor assembly, and nearby framing. During review, the cleanout access is moved to a reachable panel, and the floor penetration detail is checked before the wall is closed. The exact design still depends on local code and the products used.
Illustrative case: a vertical duct route. A remodel requires an air duct to pass between floors. The installer checks duct dimensions and support needs, then confirms whether the route crosses a rated assembly and whether dampers or other serviceable parts need access. The duct is sized under the applicable mechanical rules; the chase itself is not assigned a generic CFM value.
These examples describe planning checks, not completed projects or guaranteed solutions. For either case, the next step is to have the proposed details reviewed by the relevant building official or qualified trade professional before concealment.
Conclusion and frequently asked questions
A sound vertical chase is sized around its services, coordinated with the structure, and detailed for access and fire protection. There is no single code size, airflow rate, or one-size-fits-all enclosure detail. Check the locally adopted codes, listed systems, and inspection requirements before closing the work.
Does a vertical utility chase have a standard size?
No. Its dimensions depend on the services, insulation, fittings, supports, access needs, structure, and applicable code. Draw the actual components and clearances rather than relying on a generic chase size.
Is a utility chase the same as a plumbing or electrical shaft?
Not necessarily. “Chase” commonly describes a route or enclosure for services. A shaft may have specific construction and fire-resistance requirements. Confirm the terms and requirements used by your local code and project design.
Does every chase need fireblocking?
Not every configuration has the same requirement, but concealed spaces may need fireblocking at locations set by the adopted code. In wood-frame construction, IRC R302.11 includes requirements for concealed draft openings, including some intervals up to 10 feet. Verify the applicable condition and edition.
Can I use expanding foam around a floor penetration?
Do not assume ordinary foam is a compliant firestop. A rated assembly may require a tested, listed firestop system matched to the assembly, penetrating item, and opening. Check the listing and local requirements.
How much space does a chase need around a cleanout?
As a general IPC reference where adopted, cleanouts for pipes 3 inches and larger typically require 18 inches of clearance, and smaller cleanouts typically require 12 inches. Verify the adopted text and the specific cleanout arrangement.
Does a chase have a required airflow rate?
No. A utility chase has no default CFM requirement. If it carries supply, return, or exhaust air, size and build that air path under the adopted mechanical code and applicable duct and fire rules.
Can an open stud cavity be used as a return-air path?
Do not assume it can. A framing cavity is not automatically an approved duct or plenum. Check the adopted mechanical and fire requirements before using any cavity to convey air.
Can I close a cleanout or valve behind a wall?
Not if it needs inspection, operation, or service access. Provide a suitable access arrangement and confirm that a person can reach and use the component after finishes are installed.
What should I check before closing the chase?
Confirm the route, structural work, supports, access, fireblocking, and required firestop systems. Complete required tests and inspections, then document the concealed work. Keep access panels usable after finishing.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
