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How To Replace An Aluminum Window When You Have Wood Siding

In this article and in the video above, I’m going to share how to Replace an aluminum window with a nailing fin when you have wood siding.

I’ve personally replaced about 15 windows using this method and have had no issues with water infiltration – which is the main concern any time you are installing a new window.

Materials Needed:

Tools Required:

  • Circular Saw
  • Razor Knife
  • Level
  • Measuring Tape
  • Hammer
  • Pry Bar
  • Screw Gun
  • Caulking Gun
  • Multi-tool (optional but recommended)
  • Reciprocating Saw (optional but recommended)
  • Staple Gun (optional)

Step 1: Remove the Exterior Trim & Caulking

To remove the trim on the outside of the home, first use a razor knife to cut the caulking so the trim is easier to remove. Then, simply use a pry bar and a hammer to remove the trim. If you plan on using the trim again, take care while removing it so it doesn’t become damaged.

Once you’ve removed all trim, scrape off any caulking left over on the siding. You can do this with a putty knife as I’ve shown in the video above.

Step 2: Cut the Siding With A Circular Saw To Reveal The Nailing Fin

The trick here is to cut the siding without cutting the house-wrap moisture barrier directly behind the siding. First, carefully measure the thickness of the the wood siding. You’ll want an accurate measurement, as this is important for the setting the depth of your cut. Once you have an accurate measurement, set the depth of your circular saw to about 1/32″ less than the thickness of the siding.

Then, using the window as your guide, cut the siding with your circular saw all the way around the window to reveal the nailing fin on the old aluminum window. Watch the video if you are confused on what I mean by this.

Since you didn’t cut all the way through the wood siding, it’s now time to remove the siding you just cut. Since it’s just holding on by a small amount, it should be able to peel right off. If not, then you might consider cutting just a fraction deeper with the circular saw. Remove that siding and you’ll be able to peel back the house wrap to expose the nailing fin.

Step 3: Remove the Window

You’ll now have access to the nailing fin. Simply remove the nails around the window using a pry bar and a hammer. This is an easy step, but if you have a large window, you’ll need at least two people.

Step 4: Cutting the Drywall and Sill

In most cases, your new window will be deeper than your old aluminum window. That means you’ll need to cut some of the drywall and the sill back a bit so the new window will fit in properly.

To do this, measure the distance between the new window’s nailing fin and the interior surface of the window. Take that measurement and trace a cut line around the window frame, where you will be cutting the drywall and sill.

Once you’ve made a line all the way around the window, use a circular saw to cut the sill plate and use whatever you deem appropriate to cut the drywall (I recommend a multi-tool with a wood bit since it creates minimal dust). You can use a razor knife, multi-tool, a circular saw, or an angle grinder.

Step 4: Level the Sill

Take a level and make sure the bottom of the window frame rough opening is level. If it’s not, add some shims so that when you set the new window in place, it will automatically sit level while resting on the window frame. To keep the shims in place, tack them down with a staple gun or just tape them.

Step 5: Apply Flashing Tape To The Bottom of the Window Frame

Before you put the window in, get some flashing tape and put it on the bottom of the window frame, all the way across the window. You’ll want this to fold over the edge of the window opening and overlap the house wrap below the window opening. Also, you want the flashing tape to go up the sides of the window opening about 2″. The purpose of this is to keep moisture from absorbing into the wood below the window in the event that water does penetrate that far.

Step 6: Dry Fit The Window

Now it’s time to place the new window in the frame to test for proper fit. Once you’ve put the window in, make sure it is sitting level. Then, put in at least one screw on the top to keep it in place. This will allow you to go inside the home to see how the window is fitting on the inside. Make adjustments until the window is level, square, and is sitting centered in the opening.

Step 7: Secure the Window

If everything looks good on the interior and exterior, go ahead and secure the window using either wood screws or nails. Typically, you’ll want to add a fastener on every other hole in the nailing fin. Putting a screw in every whole is only necessary if you live in a hurricane area.

Note: Make sure the house wrap is on the outside of the nailing in and not pinched between the nailing fin and the house.

Step 8: Apply Flashing Tape To The Bottom And Sides

Install a second layer of flashing tape on the bottom of the window, this time covering the nailing fin and going onto the wood siding. Then, apply flashing tape to the sides of the window, covering the nailing fin and overlapping onto the house-wrap to create a water tight barrier.

Step 9: Install Z-bar Flashing On Top of The Window

Once you’ve flashed the bottom and sides of the window, you can add a strip of z-bar flashing to the top of the window. You’ll want to work the top of the flashing so that it sits behind the house wrap and the siding. That way if moisture gets behind the siding anywhere above the window, the flashing will direct it to the outside of the home and not behind the new window. There’s no need to nail this down, the siding and trim will keep it in place.

Step 10: Install Exterior Trim

Simply nail or screw the new trim around the new window. You can use the old trim you removed if it’s still in good shape and doesn’t have any moisture damage. You can either use screws or nails to install the trim, just make sure they are long enough to penetrate the siding and hit the wood studs behind the siding.

Step 10: Caulk The Window

Get a high quality indoor/outdoor window sealant to caulk all of the edges around the exterior trim – both where the trim meets the siding and where the trim meets the window. Here’s the caulking I recommend. Make sure to get the same color sealant as your window.

You’ll also want to caulk the interior of the window, where the drywall meets the window so there are no gaps and you end up with a professional finish that is ready to paint.

And Thats it! All you have to do is paint the window and you have a nice, new, hopefully energy efficient window.

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