Installing new construction windows in an existing home may sound like an intimidating task. But if you follow these step-by-step instructions, you'll be a window installation wiz in no time.

This tutorial is for installing windows with integral nailing flanges with sheetrock return interiors. Wood windows with brickmould or flanged windows with wood interior casing have a slightly different process. The basics are the same however. So let's get started.

Let's assume the new window has been measured for and purchased.

• Using the cat's claw, remove the existing nails from the current trim boards framing the window.
• Cut any existing caulk beads around the trim boards.
• Pry the trim boards slowly from the exterior and remove.

You should now be able to see the existing siding and complete frame of the old window

• With the circular saw, set the blade depth just deep enough to cut the thickness of the siding. Setting the blade too deep will make cutting more difficult; too shallow and it won't clear.
• Make your cuts as straight as possible and about 1" beyond the edge of the existing window's nailing flange.
• Remove all nails between your cut and the edge of the siding.
• Remove the old siding keeping as much intact as possible. You may wish to re-use it later.

You should now be able to see the entire window and flange with securing nails exposed.

• Begin removing all nails from the existing window's nailing flange. I usually pull the bottom and sides first and finish with the top. You should probably have someone assist you once the final nail is pulled to keep the window from falling on you.
• Remove the old window from the rough opening. A gentle nudging might be needed, but the unit should come out easily.

• Measure the distance from the backside of the new window's nailing flange to the edge of the new window's frame. Our window has a measurement of 1 7/8".
• Measure the distance from the outside of the rough opening's framing stud to the edge of the interior sheetrock return. The difference between these two measurements determines how much sheetrock needs to be removed. Our installation needed 1 1/8" removed from the interior sheetrock.
• Using your tape measure, mark this distance on the sheetrock at various points and mark a line with a straight edge.
• With your straight edge as a guide, score the line a few times with your utility knife.
• Remove the excess sheetrock from all sides and clean up the edges.
• With the window wrap tape, cover the entire length of the bottom sill plate and about 3-4" up each side. This will provide a waterproof dam on the sill in case of any water infiltration.

You're now ready to install the new window.

• With assistance, (and the window locked) center the new window in the rough opening and check for square. This is done by placing your tape measure on the top left outside corner of the window frame and measuring the distance to the bottom right corner. Record this measurement.
• Next, take a similar measurement from the top right outside corner to the bottom left corner.
• These two measurements should be within 1/8" of each other. If not, you'll have to adjust accordingly by shifting the window right or left in the opening. I tend to shift in increments of 1/8" with good success.
• Once the unit is square, soft nail the top left corner to secure.

NOTE: DO NOT HARD SET ANY NAILS UNTIL THE WINDOW IS PLUMB, LEVEL, AND SQUARE!

• With the 2 foot level, check the sill plate for level and shim if necessary.
• Check for plumb on the side you soft nailed and adjust accordingly.
• Check for plumb on the right side and adjust accordingly.
• Recheck for square.
• Once both sides are plumb and the sill level, you can soft nail the sill. I usually put nails in each corner and the center.

NOTE: Chances are pretty good if you properly squared the window, the sides and sill will be plumb and level.

• Recheck both sides for plumb, the sill for level, and the unit for square. (Sounds like I'm beating a dead horse, but this is the key to proper operation of the window).
• Once all the measurements are correct, you can hard set each nail and add additional nails. Nail every 8" on each side, every 6" on the sill, and allow the top to float.
• With window tape, cover the new flange and extend to the edge of old siding.
• Nail into place, either new siding (ripped to size with your table saw), or the existing siding if not overly damaged, and install over the new window's flange to the edge of the existing siding.
• Caulk any major voids.
• With window tape, cover up all seams; to the edge of the window to about 1" past the outside seam.
• Back caulk the tape to the edge of the window on all four sides. This is done as prevention against any water that may infiltrate the primary trim boards and caulking.

WE'RE GETTING CLOSE.

• Flash the entire top of the new window with standard window flashing. Make sure you extend the flashing the width of each side trim board. (If your new window rests directly under a wide soffit, you can usually skip this step).
• Cut your trim boards to size and notch as needed; as if in under a soffit.
• Nail the trim boards in the following order: 1) Top 2) Sides 3) Bottom.
• Nail each trim board into place.
• Caulk the top and sides of each trim board but not the bottom edges. This is done to ensure proper drainage.

YOU'RE DONE!

Give yourself and your help a nice high five and move on to the next window.