How to Install a Window

From helping with energy-efficiency to framing a room in your home, windows provide protection and added style. When it is time to replace old windows in your current space or install new windows in a new home, simple steps and a few precautions will help you get the job done.

Measure Opening and Determine Your Window Needs

  • Start by measuring inside the existing frame, including the height in the middle and left and right sides.
  • Next, measure the width at the top, middle and bottom.
  • Write down the measurements and use the smallest measurements for width and height to buy your new window. It is important that your new window be about 3/4-inches smaller than your window opening to keep you from reframing the opening.
  • Remove the Existing Window
  • Prep Area and Dry Fit New Window
  • Check the window jamb and the window stop for structural damage.
  • Replace any damaged areas.
  • Center the new window in the opening, supporting it with wood blocks and shims placed below the horizontal jambs. The shims are important so that the window will not sag over time.  If the window goes out of square, then the operators will not work making it difficult to open and close the window.
  • Make sure the window is plumb and level and adjust the shims if necessary.
  • Clamp or have a friend hold the moulding in place.
  • If you have vinyl or aluminum siding, you may need to install a J-channel to hold the trim.
  • Now, cut the siding along the outline with your circular saw adjusted so that the blade depth equals the thickness of the siding.
  • Start the cut with the toe of the saw plate on the siding, but with the blade and heel of the plate above the surface.
  • Slide the saw guard back, start the saw and ease the blade into the wood.
  • Complete the corner cuts with a sharp chisel.
  • Cut a length of drip edge to fit over the top of the window, then slide it between the siding and the building paper.
  • Next, caulk around the moulding. If it has brick mold, apply a continuous bead of caulk around the opening. If it has a nailing fin, apply the caulk to the back of the fin.

Set and Level the Window

  • Set the window into the opening and push the brick mold or nailing fin tight against the sheathing.
  • Check to see how much adjustment will be necessary to level and plumb the window unit.

Double Check Window and Pre-Drill Holes

  • Measure the diagonals of the window.
  • If they are equal, the window is square. If not, adjust the shims until the window is square. Always double check that the window is level and square after you adjust the shims.
  • If the window has a brick mold, pre-drill holes in it and drive 16d nails through it and into the framing.
  • If the window has a nailing fin, nail through it into the framing.
  • In either case, start at the corners and space the remaining nails as recommended by the manufacturer.
  • Drive all nail heads below the wood surface with a nail set.

Cut Siding and Apply Caulk

  • Use a circular saw adjusted so that the blade depth equals the thickness of the siding.
  • Start the cut with the toe of the saw plate on the siding, but with the blade and heel of the plate above the surface.
  • Slide the saw guard back, start the saw and ease the blade into the wood.
  • To avoid splintering, stop before the corner.
  • Complete the corner cuts with a sharp chisel.
  • Cut a length of drip edge to fit over the top of the window, then slide it between the siding and the building paper.
  • If it has brick mold, apply a continuous bead of caulk around the opening.
  • If it has a nailing fin, apply the caulk to the back of the fin.

Install Window

  • Place the window into the opening, pressing it tightly against the caulk.
  • Put shims where pre-drilled holes are to secure the window.
  • Drive screws into holes through to the shims.
  • Check that sashes are even, and the window is level.
  • Add shims where needed.

Trim Shims and Add Insulation

  • Trim the shims flush with the framing by scoring them with a utility knife and then snapping off the excess.
  • Fill the gaps between the window jambs and the framing members spray foam insulation.

Paint and Finish Window

  • When the caulk dries, paint to match the trim on the rest of your house.

Pointers

Windows will differ by material and design so it is important for you and the installer to know what type of window you currently have and what type of window you would like to install.

When centering the new window in the opening, make sure you or the installer support the window with wood blocks and shims placed below the horizontal jambs.  The shims are important so that the window will not sag over time.  If the window goes out of square, then the operators will not work making it difficult to open and close the window.

Needless to say, good, sharp tools should be used.

If you or the installer does not measure carefully, you may receive windows you have paid for that are either too big or too small for the opening.  If they are too big the installer may try to adjust the opening with possible negative affects on the structure of your house.  If the windows are too small, the installer may attempt to adjust the structure of the house resulting in unsightly space around the windows with greater potential for leaking.