How do you frame around duct work?

Framing around duct work is a common challenge encountered when building or renovating a home. Proper planning and execution is crucial to ensure the ducts are accessible and the framing is structurally sound. This comprehensive guide will walk you through the key considerations and step-by-step process for framing around ductwork.

What are the main goals when framing around ducts?

When framing around ductwork, there are a few key goals to keep in mind:

• Maintain duct accessibility – The ducts need to remain accessible for future maintenance, repairs and cleaning. Any framing should allow access doors or panels.
• Prevent compression or damage – The framing should not place undue pressure or weight on the ducts themselves.
• Allow proper ventilation – There needs to be space around the ducts for efficient air flow.
• Maintain structural integrity – The framing needs to meet all structural requirements and building codes.

Proper planning is essential to meet these goals while also coordinating with other building systems.

What are the typical duct materials and sizes?

The most common ductwork materials are:

• Galvanized steel – This silver colored sheet metal is lightweight, inexpensive and easy to install. Round or rectangular shapes are typical.
• Aluminum – More durable but more expensive than galvanized steel. Used for flexible or insulated ducts.
• Fiberglass – Made from fiberglass reinforced plastic. Used for insulated flex ducts.

Standard duct sizes are:

• 6”, 7”, 8”, 10”, 12” – For branch runs
• 14”, 16”, 18”, 20”, 22”, 24” – For main ducts
• 26”, 28”, 30” – For large main ducts

Ductwork is fabricated in standard lengths of 2 to 5 feet.

Where will the ductwork be located?

Identifying ductwork location is crucial for planning framing. Ducts are typically located:

• Above ceilings (attic space)
• In interior wall cavities
• Below floors (crawl space or basement)
• Suspended from floors or ceilings
• Enclosed in soffits or dropped bulkheads

Access doors must be framed in for ducts in concealed spaces like attics or walls.

What code requirements apply?

All framing around ducts must follow applicable building codes. Key requirements include:

• Minimum clearance – Typically 1″ clearance from combustible materials required for metal ducts.
• Fire and smoke barriers – Where ducts penetrate firewalls or corridors, fire dampers and smoke barriers are required.
• Allowable spans – Framing sizes and spacing must conform to code allowable spans.
• Blocking – Supports must be placed every 4 to 6 feet to prevent sagging.
• Beam pockets – Required when ducts intersect with structural beams.

The local building department can provide code requirements for a specific project.

What tools are needed?

Framing around ductwork requires common carpentry tools:

• Circular or reciprocating saw – For cutting openings and access holes
• Drill/driver – For fastening framing members
• Pry bar – For positioning framing materials
• Hammer – For nailing framing connectors and blocks
• Tape measure – For measuring openings and layout
• Utility knife – For trimming out openings
• Carpenter’s square – For squaring and aligning framing
• Level – For verifying plumb and level framing

Safety gear like glasses, gloves and dust masks are also recommended.

What techniques are used for framing around ducts?

Here are some of the most common methods used:

Bulkheads or soffits

• Frame a boxed out enclosure suspended below the ceiling joists or rafters.
• Allows large ducts to run overhead while maintaining room height.
• Must be properly supported and braced.

Furring

• Install 1x or 2x furring strips perpendicular to the joists or studs.
• Creates a secondary framing surface offset from the primary framing to accommodate duct depth.
• Can be installed on walls, ceilings or floors.

Bulkheads

• Frame an enclosed box around the duct as it passes through the floor joists above.
• Allows ductwork to pass through intermediate floors while maintaining structural support.
• Must be properly braced and supported.

Chases

• Frame an enclosed shaft vertically between floors or horizontally between rooms.
• Often used when multiple ducts service a multistory building.
• Provides maintenance access via removable panels.

Beam pockets

• Cut or frame notches in structural beams to allow ducts to pass through.
• Requires temporary shoring and careful structural design.
• Steel or wood frame inserts may be required to support the beams.

How much spacing is needed around ducts?

Proper clearance is required around ducts for:

• Ventilation – 1″ clearance is a common minimum for proper airflow.
• Insulation – When wrapped with insulation, at least 3″ clearance may be needed.
• Access – 12″ to 16″ clearance required for replacing or servicing ductwork. More for elbows or dampers.

Insufficient clearance can lead to condensation or reductions in air flow and HVAC system performance.

What are the main steps for framing prep?

Key steps for preparing to frame around ductwork:

1. Review duct shop drawings – Identify all duct sizes and route paths.
2. Inspect the jobsite – Check for obstructions and interferences.
3. Coordinate with other trades – HVAC, electrical, plumbing routes may intersect.
4. Plan access points – Determine нуж doors and panels.
5. Layout framing – Mark studs, joists and openings to accommodate the ductwork.

Planning ahead for all aspects of the duct layout streamlines the framing process.

How are ceiling joists cut and framed?

When passing perpendicular through ceiling joists:

1. Mark plumb lines for the duct on the top and bottom of joists.
2. Cut openings in each joist at least 2″ larger than the duct diameter.
3. Frame headers between the joists above and below the openings.
4. Secure headers to joists with joist hangers or blocking.

For large ducts running parallel between joists:

1. Cut 1-1/2″ x 1-1/2″ notches every 2 ft. to pass hangers.
2. Install full depth blocking between joists below notches for support.
3. Lag bolt duct hangers through notches into blocking.

Size headers based on required joist spans and duct weight.

How are wall studs framed?

When passing perpendicular through studs:

1. Mark openings centered on studs at least 2″ larger than the duct.
2. Cut horizontal top and bottom plates to fit duct.
3. Install jack and cripple studs to frame the opening.
4. Attach studs with screw nails to the top and bottom plates.

For ducts running within the wall:

1. Install cripple studs spaced about 2 inches from the planned duct route.
2. Secure duct with metal strapping attached to the studs.
3. Allow space for insulation between duct and drywall.

Blocking may be нужеd for additional duct support.

How are floor joists framed?

When passing perpendicular through floor joists:

1. Mark openings centered on the joists at least 2″ larger than the duct.
2. Install headers between joists above and below the duct opening.
3. Secure headers with joist hangers or blocking.
4. Add framing below for ceiling finishes.

For ducts running parallel between floors:

1. Install 2x ledgers horizontally under the joist bays.
2. Bolt the ducts to the ledgers using duct hangers.
3. Place full depth blocking between joists above ledgers.

Size headers based on required joist spans.

How are access doors and panels integrated?

To provide access:

• Size panels at least 18″ x 24″ for shoulder access.
• Locate along straight runs every 10 ft and near all elbows, tees and dampers.
• Frame opening with double studs and sill framing similar to a window rough opening.
• Secure access door with hinges or removable fasteners.

Clearly label and make access points known to the owner/occupant.

What firestopping is required?

Fire and smoke barriers must be installed where ducts penetrate:

• Fire walls – Seal openings with approved firestop materials.
• Occupancy separations – Use fire dampers in ducts at wall penetrations.
• Corridor walls – Use smoke dampers activated by smoke detectors.

Firestopping reduces the spread of fire and smoke between building areas.

What are best practices for support and bracing?

Properly supporting ducts prevents damage and maintains air flow. Best practices include:

• Install #12 gauge hangers every 6 ft. max for main ducts, 8 ft. max for branches.
• Use angle iron braces at elbows, branch connections and changes of direction.
• Place transverse struts every 4 ft. below rectangular ducts over 12 inches wide.
• Set ducts on 2×6 sleepers over rigid insulation on ceiling drywall for solid support.
• Anchor vertical ducts top and bottom and support intermediately as needed.

Follow manufacturer specifications for proper duct support.

What are common mistakes to avoid?

Some common duct framing errors to avoid:

• Inadequate access doors – Too few or too small will make duct maintenance difficult.
• Insufficient clearance – Blocking airflow or compression can reduce HVAC performance.
• Disregarding ductwork layout – Improvising versus following the design can cause conflicts.
• Lack of blocking – Can result in sagging, misaligned or damaged ductwork.
• Improper penetration firestopping – Can allow fire and smoke to spread.
• Not accommodating duct insulation – Undersized framing won’t allow insulation to fit.

Careful planning and duct coordination avoids these issues.

Key Takeaways

The main takeaways for properly framing around ductwork include:

• Coordinate closely with HVAC design and installation schedule.
• Plan duct layouts and access doors early before framing begins.
• Allow proper code clearance for safety, ventilation and insulation.
• Cut openings in framing members at least 2 inches oversized.
• Use headers, joist hangers and blocking to support framed openings.
• Install durable duct hanging and support methods per specifications.
• Incorporate needed firestopping at firewall and corridor penetrations.
• Avoid common errors like compression, lack of bracing and access.

With careful planning and attention to detail, ducts can be effectively integrated into the surrounding framing. Following the recommendations outlined here will result in a ductwork installation that is accessible, structurally sound and helps achieve optimal HVAC system performance in the building.

Conclusion

Framing around HVAC ductwork requires careful coordination with other trades and attention to structural, ventilation and firestopping requirements. By planning duct layouts ahead of time, providing adequate access and clearances, and using appropriate framing techniques, contractors can successfully integrate ductwork with the surrounding framing. This allows ducts to be properly supported while maintaining utility and maximizing energy efficiency. Keeping these best practices in mind when framing around ductwork will result in an installation that meets code requirements, avoids common errors and enhances the building’s function.