The first step to building a soffit is to measure out the size of your intended soffit and mark it on the wall and ceiling with a pencil. Determining the size depends on your needs. If you’re merely trying to conceal pipes, ducting or wires on the ceiling, you may want to tailor the soffit size so that it is simply able to adequately cover whatever needs hidden. Soffits can also be used as a decorative architectural detail, such as building a soffit down to meet upper kitchen cabinets. If this is the case in your design, be sure to factor in the size of your cabinets when measuring and marking the wall and ceiling for your soffit.
After the desired dimensions have been determined and the marks made, you will need to cut wall and ceiling plates. These plates are the anchor positions that the rest of the soffit frame will attach to, so they need to be strong and sturdy. Use 2x4 lumber, cut to your measurements with a miter or table saw (Image 1), and attach it to the wall and ceiling studs with a framing nail gun (Images 2 and 3). It’s important that you hit the studs and/or ceiling joists with each nail, as these nails will be supporting a significant amount of weight.
Using your measurements as a guide, create a simple box-frame out of 2x4 lumber. For the greatest precision, make your cuts using a miter saw and use the framing nailer or a screw gun and drywall screws to assemble the unit. Cross sections should be installed every 16 inches so the drywall can be securely attached (in Step 6).
This step is not difficult, but it can be cumbersome, so ask a friend for help. If a friend is not availble, use some simple slide clamps to hold the frame in place (Image 1) while you attach it to the ceiling and wall plates with 2-1/2” or longer drywall screws (Image 2).
Before you cut and hang the drywall, here’s a great little tip to save you some aggrevation: Use a pencil to mark out the location of the studs on your soffit box-frame. Mark these studs on the ceiling or the wall next to each stud, so that when the drywall is placed over top of the frame, you’ll be able to quickly and easily identify where each stud is located. This way, you’ll be sure to hit a stud with every screw.
Use a tape measure and a pencil to transfer the dimensions of your box frame onto the sheets of drywall. Then, cut the drywall with a utility knife (Image 1). The strength of the drywall is in the paper, so if you simply cut deep enough to get past the paper on both sides of the sheet, the sheet should separate easily by bending.
With the drywall cut, install it to the framework using drywall screws (Image 2). The marks you made on the wall and ceiling in Step 5 will help you find the studs when screwing the drywall to the frame.
With the drywall in place, the work is nearly done. It’s time to install the corner bead for nice, smooth corners (Image 1), and then finish off with the regular drywall work of taping, spackling and sanding (Image 2). When the spackle is dry and smooth, complete the process by painting the soffit (Image 3).