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How to Build A Soffit Around Ductwork

Building a Soffit to Hide HVAC And Other Ceiling Obstructions:

Learning how to build a soffit around duct work is not a difficult process and there are many ways to do it. Some ways are better than others and some methods are more preferable depending your specific situation.


A soffit is basically a box framed with wood and covered with wall board that surrounds existing duct work, piping, or beams.

As a remodeler I often need to build soffits in basements or kitchens to hide items that are not easily moved and are lower than the finished ceiling.  Sofits in kitchens are often used to lower cabinets from a tall ceiling.

Soffits Conceal ducts

 Using a soffit to conceal duct work is a great way to hide duct work and create a flat or better looking basement ceiling and is also useful as termination points for acoustical ceilings in basements.

 Constructing a soffit is easier than you may think. Many folks like to use 2×4 framing lumber to construct a series of U-shaped or L-shaped braces. I do not.  In most cases, I prefer using 5/8″ or ¾” plywood to cover the duct or obstruction. The reason for this is it’s faster, more efficient, provides a straighter, more rigid and stronger structure.

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Steps on How to Build a Soffit around Ductwork:

First decide on whether the item you’re considering

boxing in can be moved higher or relocated. Often times this involves the input from a plumber, HVAC or electrician and many times it’s more cost effective and aesthetically pleasing to move a few water pipes than build a soffit.  Below are some tips and steps that will help you make your decision and explain how to build a soffit.

Determine Finished Ceiling Height:

The next step is to determine the lowest obstruction in the room and compare that to your desired finished ceiling height. Sometimes I find myself “splitting the difference” on ceiling obstructions. What I mean is there is often a steam pipe / duct or item that is too low and a decision is made to install soffits and a finished ceiling to conceal everything but that item. Sometimes, as often the case of pitched steam radiator pipes, we leave a low pipe exposed below the finished ceiling and paint it.

Identify what needs to have a soffit. If there are going to be different ceiling heights you will need termination points for them. This means soffits or skirt walls.  [see photos]

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Building a Soffit:

I build most of my soffits with 2x material and plywood. It’s faster, stronger and more reliable.  It’s also less prone to error.

When creating a soffit I try to keep it simple. I use a combination of parallel tape measuring points, string lines and use the 3-4-5 triangle method to mark the location of my soffit.  The goal is to create an equal ceiling space and this is critical if you’re using an acoustical ceiling grid.

Tip:  DO NOT trust that a duct or pipe is lined up parallel or perpendicular to a wall. The last thing you want is a crooked soffit and a series of differently cut acoustical ceiling tiles running along it.  It’s amateurish and I’ll make you sit in the truck for the rest of the day if you get caught doing it!

Once I have located my soffit I determine how I am going to build it.

Build A Simple and Straightforward Soffit:

I use a caulk string line to mark a continuous line along my tape measure measurements.

Then I install the longest, straightest 2×4 I have along the length of the line and fasten it into each floor joist.  I keep this 2×4 or “smaller” 2x  nailer on the inside [not finished side] of the soffit.

Then I determine the depth of coverage that I need in order to cover the obstruction and then cut a length of 5/8 or ¾ inch plywood to that depth.  To create a straight, rigid soffit, try to maximize plywood along it’s length and minimize joists.

Tip: Use a table saw to keep your cuts perfectly straight.

Straight, Level and Square:

You should be concerned about leveling the soffit and this is the time to think about it. Check your nailing along the floor joists with a level.  You can install your plywood to lower [out of level] section of the joist nailer.

When securing the plywood, push it almost tight to the joist and install only one nail. [Too tight may create squeaks]  On the other end of this plywood you can then use a level to move the plywood up and down [pivot on nail] to achieve a level edge.

Tip: Make sure to use a string ling to check the soffit for straightness.

Once level, secure the plywood to the horizontal nailer with a nailer every 12 to 16 inches with 8 penny nails.

At the bottom of the plywood edge I screw on another straight 2×4 or larger to the inside edge. This is also another opportunity for you to adjust for level.  Move the bottom edge 2×4 up or down a bit as needed. The 2x material at this edge becomes a nailer for a bottom panel or in the case of a skirt wall – for wall board corner bead.

Depending on the soffit I may need to do this same procedure on the other side of a duct and then add a bottom piece of plywood, or I may need to return the bottom of the soffit to an adjacent wall.

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Soffit Skirt Wall: different Ceiling Heights

In some situations [photos above] you may be separating two different ceiling heights. In these situations the vertical plywood panel may be all that you need.  If this is the situation make sure that the lower ceiling terminates into the 2x material and for a better look and less error make sure the 2x material is ½ to 1 inch lower than the lowest ceiling.

When framing a skirt-wall soffit make sire to include bracing to keep the plywood from bowing or twisting.

By leaving the 2x lower I can have my plasterer install blue board and plaster on the exposed plywood and then install two lengths of corner bead on the lower 2x and plaster up the side of the 2x. This way the lowest ceiling terminates into a plastered surface.  It’s results in a sharp, clean look.

Note on the photos in this article:

There are way too many soffit situations to detail in this article so I will show photos from a most recent project. The photos show a room that is being finished into an exercise room and how to build a soffit around duct work.

The floor joists are over 9 feet off the floor and floor height was truly amazing. Originally we were going to install an acoustical ceiling at 7’4” to completely cover the duct-work and create a flat ceiling.

The homeowner then changed her mind and decided to purchase some exercise equipment that necessitated an 8 foot ceiling. We decided to build a skirt-wall soffit around the HVAC duct work and have a taller ceiling in half of the room and a 7’4″ ceiling at and around the HVAC duct-work.

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