How to Install Soffit

What Is Soffit?

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Soffit can be compared to vertical siding and its installation entails more than the actual panel itself. Soffit is used to protect the underside of eaves and porch ceilings and also provides a hidden vent system. Aluminum and vinyl are the predominant materials used for this installation that can also determine the positioning of the inside and outside corner posts. The availability of the material varies from solid, fully perforated or lanced, or combination soffits. 

Choose the Installation Method

The soffit installation method will depend on the construction of the eaves. Remodeling projects will normally have enclosed eaves while new construction has open eaves (exposed rafters). Now let's see how this can be done fast and easy. Soffit panels are available in 12-ft. lengths, 12- or 16-in. widths and vented or unvented. 

How Much Soffit Do I Need?

Now its time to determine how much soffit we will need.The amount of soffit needed is easy to calculate and using some simple calculations we will get the amount needed. Multiply width by length of each soffit surface and add them up to get the total square footage needed and divide by 16 or 12. 12 and 16 are the corresponding square footage of a 12 or 16 inch width soffit panel.Add 5 percent extra for waste and overlaps.

Soffit Installation: Prep the Area

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Prior to start check the surfaces as they should be uniform and straight. Be sure to reattach any loose board or shingle that might affect your installation procedure. Remove any existing trim. Consider possible obstructions such as utility lines. Panels may be cut to fit around them or contact your utility company for removal or replacement.

Soffit Installation: Open Eave F-Channel


If you need to go with the open eave installation method, start by installing the receiving channels. F-Channels or J-Channels can be used as receiving channels so be sure to use the same method used to create the eave. Channels should be attached by nails every 12 inches, or locating the nail in the center of the slot. If the span is greater than 16 inches, you will need to install nailing strips and install the channels on the nailing strips. When the soffit will turn a corner, the channel will then need to be installed with a 1/4 inch gap that can allow for expansion at the walls. Do not overdrive fasteners.

Soffit Installation: Open Eave J-Channel

You can substitute the F-channel for a J-Channel by simply cutting slots in the nail flange where it would be attached to the wall. Bend the flange back and nail it to the wall.

Install the Soffit


Start by measuring from the wall to the fascia and subtract 1/2 inch to allow for movement. Cut the panel with a circular saw. You can cut two panels at one to expedite the process. Insert the soffit panel into the channel attached to the wall and then into the second channel. Make sure the panel forms a 90 degree angle with the wall and nail. If you are nailing to the fascia board, it is recommended to use small-headed nails (face nailing is allowed). The soffit panel will expand so be sure to leave space in the receiving channel. If you’re using a nailing strip, do not nail tightly. Repeat the procedure as needed. Make sure that panels are locked along their entire length.

Finish the Installation


The installation won't be completed until you have apply utility trim and all fascia cap has been fastened using trim nails. You can also drill holes for the trim nails to reduce denting of the aluminum (where required).

Enclosed Eave Soffit Installation

For details on how to install the soffit over enclosed eaves, click here.