How To Install Vinyl Siding On Uneven Walls

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Whether installing vinyl siding around windows for the first time or repairing siding around the windows, this project can seem overwhelming. We have researched the best ways to install vinyl siding around the windows to simplify the steps for an elegant transition from straight siding to curves.

Get started by gathering safety gear, tools, and materials. Then follow these steps to create the transition from the wall siding to the window:

If removing to reuse, carefully remove existing siding two sections below the window. When installing new siding, stop the wall siding with two panels below the window to allow room to work.
Prepare the area around the window. Remove any caulking that could interrupt the installation of the new siding.
Inspect the flashing and building paper for any damage and tears that could allow water behind it.
Replace or install new flashing and building paper to maintain waterproofing.
If the window doesn't already have one, install a J-channel.
Cut the trim and side channels to fit around the windows.
Measure and cut the panel to fit below the window.
Snap the siding panels in place up to the window, nailing loosely. The piece directly under the window should fit up into the J-Channel.
Cut the siding to go along the sides of the window. As with the wall siding, leave 1/4 inch spaces at each end of the vinyl siding to allow for temperature changes.
Install the siding along the sides of the window and above the window. Finish the wall.
Install under sill trim if needed.

Now that the basics are covered, keep reading for more details on each step. We will also go over best practices to install vinyl siding, including steps to cut the J-channel.

Exterior of a modern two storey country home with light gray wooden sidings, dark green colored shingle roofing, and white painted shutters, How To Install Vinyl Siding Around Windows In 11 Easy Steps

Tools & Materials Needed

It's always best to have all of the tools needed for any project handy to avoid distractions once you get started. Basic tools for an entire vinyl siding project include:

Hammer
Level
Tape measure
Utility knife
Table or sawhorses

Some specialty tools are handy to have:

The Zip Tool

The zip tool unhooks the locking section of the vinyl siding panels from each other without damage.

Click here to see this zip tool on Amazon.

J Cutter

To simplify creating the notch or the J-channel tab without either tin snips or a utility knife, use the J cutter.

Click here to see this J cutter on Amazon.

Necessary building materials include:

Aluminum flashing
Building paper
J-channel
Siding
An under sill (if the windows protrude out more than 1/4 inch)

Best Practices For Siding Installation

If this is the first time you are working with vinyl siding, these tips will help the process flow. When replacing siding, mark each piece's position before removing it to help position the new siding.

Leave a quarter-inch gap at the ends so that the siding has room to expand and contract. The trim pieces will hide the edges, and the flashing and building wrap will keep the area waterproofed.

Lock each panel into the one beneath, then gently press against the building to smooth it out before nailing it into the building. Center each nail and drive them in, leaving a small bit of the shank exposed. If the nails are driven completely in, that will cause damage when the vinyl siding adjusts with the weather.

Prepare The Area Around The Window

Carefully remove any existing siding and trim. Trim usually breaks during removal so expect to purchase replacement trim. Intact siding can be reused.

Remove any caulking that will keep the siding from lying flat.
Clean up around the window.
Check the flashing and building wrap to ensure there aren't any spots that liquid can get into the wall.

Acquire New Siding Or Carefully Remove Siding to Reuse

Take a piece of existing siding and match it. Usually, a siding retailer or manufacturer can help you find the closest replacement siding. Vinyl does fade with time, so an exact match to the original may not be available. Alternatively, you can remove the siding with care to preserve it so that it can be used again.

Waterproofing – Inspect Flashing and Building Paper

Check the existing building paper and flashing to ensure there isn't any area where moisture can get through. If there is damage, replace it. Calculate where the water will flow and check that all the building paper and flashing will direct the moisture away from the wall and not behind the paper and flashing.

Windows and doors require flashing. Aluminum flashing works best with vinyl siding. Use a 10-inch-wide roll of aluminum, cut into 5-inch-wide strips, for the sides and the top of the window. The bottom flashing size will vary; it needs to direct the water flow to the top of the siding below. The aluminum flashing goes under the window nailing fin and over the vinyl siding's nailing hem.

The flashing should overlap the flashing under it by two inches on the vertical sections. The building wrap needs to be two inches over the flashing above the window. This prevents any moisture from seeping into the building materials. When installing new flashing and building wrap, the lower pieces should be overlapped by the higher ones to direct water flow out and away. Tape any tears with house wrap tape.

J-Channel Installation

The J-channel is the trim that fastens around windows and doors to help connect the siding's end pieces and create a finished look. For a new J-channel installation, cut the J-channel section two inches longer than the window's width and length. Mark out a notch one inch in from one end and either use a J cutter or score deeply with a utility knife and break out. Mark one inch from the other end and cut the sides to make a tab in the middle.

For the sides, cut with an additional two inches for each. At the bottom, cut one inch along the corner of the facing edge, bend the wide surface of this channel inward at this cut to make a drip edge tab, and slide the tab under the sill channel. At the top of the window, cut off all but the trim's face, flush with the existing top molding, and nail the trim in place.

Cut the top channel two inches longer than the window's width and use the excess to create drip edges. Cut off the back of the channel flush and let the facing edge run long. Set the channel in place, secure it, and trim the excess from the facing edge.

Lastly, install the top channel carefully over the side pieces to direct any water away. Cut off all but the trim flush's face with the top molding and nail it in place.

Click here to see this J-channel on Amazon.

Install Siding (New or Reused) Around the Window

When installing new siding, stop installing the house siding approximately two siding pieces below the window to allow room to maneuver new siding around the window for cutting and measuring purposes. When replacing siding, use a zip tool to disconnect the existing siding and a flat bar to remove the nails. Do not slide the flat bar behind the siding, as the flat bar can create damage.

Cutting Vinyl Siding

Vinyl siding needs to hang loosely to allow for expansion and contraction during temperature changes. For more information about how temperature affects vinyl, look at our article regarding "How Much Does Vinyl Siding Expand And Contract?" for more details. Here are a few special considerations when cutting and nailing vinyl siding:

Leave a quarter-inch gap at all ends so that the slat can slide behind the vinyl trip pieces, which will hide the gap and cut ends.
Lock the panel into the one below it and snug it in before nailing.
When removing existing panels, mark each piece's position before your remove it will help you position the piece without stretching it.
Center the nails in the nailing slots. Leave a 1/16 inch section of the nail's shank exposed so that the vinyl can expand and contract.

A basic utility knife or tin snips can be used to cut straight lines on vinyl siding.

Click here to see this utility knife on Amazon.

Click here to view our article about "What Is The Best Tool To Cut Vinyl Siding?"

Fitting Around Standard Windows

To fit the siding piece up under the window, position the siding below the window, mark the siding on each side of the window allowing a 1/4 inch gap on each side, then measure from the locking side of the siding piece below to the under sill trim or J-channel to determine the depth of the notch. Make the cuts.

Install each panel along the window's sides, making sure to tuck the ends into the J-channel. At the top, slide the piece into the J-channel.

Fitting Around Decorative Windows

Differently shaped windows can seem daunting to add vinyl siding around. However, with a few extra measurements and cuts, they can also be accentuated by siding.

Half Round and Quarter Round

The key to installing a J-channel around a round window is a flexible J-channel. Starting at the bottom of the window, measure an inch extra on each side of the J-channel, then notch out that inch and install under the window. Measure the circumference of the arch adding two inches to the measurement. Install a flexible J-channel starting from the top, leave one inch below the end of the window on each side and install around the window.

Align the flexible J-channel along one side of the arch, leaving a one-inch extension. Starting at the top of the window and in the middle of the J-channel, drive nails in to attach the J-channel to the building, wrapping around the circumference of the arc of the window. Make sure to leave the ends of the channel loose until the ends have been trimmed.

With a utility knife, cut the back of the channel inwards, where the channel extends beyond the arch's end. At the front of the channel, cut up one inch or the length of the extension. Repeat at the opposite end of the arc. Bend the back of the channel into a 90-degree bend. The back and the inside will bend. The outside should not.

Slide the bent channel into the insert hole of the bottom channel. Finish nailing the end of the J-channel. Do the same on the other side. Use a pop rivet to secure the corners on the outside of the J-channel. Use a washer on the inside to keep the rivets from pulling out.

Under sill Trim

Due to the beveled nature of the siding, the window may stick out from the wall. If the window sits out more than 1/4 inch from the wall, add under sill trim to lock it in place. If the window sits out less than 1/4 inches, skip the trim and rely on the J-channel. If trim is needed, cut the trim channel to match the length of the sill and nail securely into place.

Should I caulk around windows with vinyl siding?

Correctly installed vinyl siding will not need caulk around the windows. There will be a separate vinyl piece at the side of the window that the ends of the siding tuck into. Any other obstructions that protrude around the siding may need caulking.

Do you need a J channel around windows?

The J-channel is a trim molding that fastens around windows and doors to help connect the siding's end pieces siding to create a finished look. Modern vinyl windows already have the J-channel included in the window design, and there is no reason to install another J-channel. If replacing or putting in a new window that does not have the J-channel included, you will need one to help divert water and cover the siding ends.

Do you need flashing for vinyl siding?

Yes, flashing is a form of waterproofing used to prevent water from saturating the structure. It should be fitted around windows and doors. As we've mentioned, aluminum flashing works well with vinyl siding –typically cut into 5-inch strips with varying widths for bottom side flashing. Please refer back to our "Waterproofing" section for detailed instructions on flashing installation.

In Closing

Installing siding around windows can seem overwhelming. Measuring, cutting, and carefully putting the pieces together will give you the satisfaction of a job well done. Remember to allow the 1/4 inch room at each end of the siding and use the J-channel to neatly trim the window.

Here is another vinyl siding article to read: Can You Power Wash Vinyl Siding?