How to Install Vinyl Replacement Windows

By Kevin McDermott

Replacing those old wood-frame sash windows with nice, new, double-hung vinyl windows is a lot easier than you think. In fact, the most complicated part of the project is getting the old windows out. Windows used to be made up of separate parts that were individually built right into the wall, a complicated job that required professional installation. Today's vinyl replacement windows are pre-hung in self-contained units that pop right into the old opening all at once.

Things You'll Need

  • Tape measure
  • Hammer
  • Pry bar
  • Replacement window, sized to order
  • Fiberglass insulation
  • Level
  • Wood shims
  • Screw gun
  • Long installation screws (with replacement window)
  • Caulk

Step 1

Measure the opening for the new window while the old window is still in place. Measure the width of the opening from the widest part, just behind the piece of vertical stop-trim that's holding in the window sashes. Take the measurement from three different points along the width, then take the smallest of the three and subtract 1/4 inch from it. This is your width number for ordering. Do the same for the length, taking measurements from three spots, picking the smallest, and subtracting 1/4 inch from it. Order your window using your adjusted width and length numbers.

Step 2

When your new window arrives, measure it to make sure it's correct. Remove the old window by first carefully prying out the vertical stop-trim, using your hammer and pry bar. Don't break it, as you'll need to re-install it. Once the stop-trim is off, pull the top and bottom sashes straight out, removing the thin divider strip of wood between them. Leave the exterior stop-trim in place. Go around the edge of the opening with your hammer, and hammer in any nail heads or other obstructions.

Step 3

Put a strip of fiberglass insulation on the windowsill. Set the bottom of the window on the sill, on top of the insulation. Push the top of the window in, tucking more fiberglass insulation in around it as you do, until the window unit is set entirely in the opening. The stop-trim on the outside will prevent it from falling through. Use your level to check for level and plumb (straight up and down); adjust as necessary by tapping in wood shims with your hammer under the bottom or sides of the window unit.

Step 4

Once the window is level and plumb, secure it into the opening by sinking long mounting screws through the sides into the surrounding casing. Use as many mounting screws as came with the window (generally, two or three per side). Reinstall your interior stop-trim with your hammer, using the same nails and nail holes that were there before. Caulk all around the seam where the trim meets the new window unit, inside and out.

References & Resources