DIY Vinyl Window Sills & Trim

Replace any rotted window areas before adding new vinyl. Remove old window shutters outside and any decayed framework that will support new casement or actual window weight. Cut old wood with a reciprocating saw or gently chisel sections with a hammer and chisel to take out a rotted section of framework in the opening. Work with a razor knife to cut through joints with caulking.

Measure any vinyl material you will use to replace or wrap existing wooden sills. Cut vinyl sections in small increments, so you will not cut off too much and leave unsightly gaps. Fit vinyl covering into place and caulk neatly before proceeding to any further steps. Add any sloping pieces you will need to slope the sill to prevent water drainage under the sill covering versus on top of it.

Select quality windows with appropriate instructions. Read the installation papers, if possible, so you can agree with suggested instructions. Don't buy vinyl windows that instruct you to place nails in all four corners, for example; windows need expansion room in the corners to avoid cracking over time. Stay away from buying windows with hastily written instructions.

Choose vinyl windows that have jambs at least 31/4 inches thick. Check to ensure the internal cavities of the windows have five to seven chambers to hold encapsulated layers of air for sound insulation. Stay away from vinyl windows that have only two or three chambers, because they will drive up your energy bills.

Get framing in place so the window will have 1/4 inch of space on each side when dry fitted in the opening. Leave this same 1/4-inch gap at the top and bottom as well when moving the window into position.

Staple a strip of 3/16-inch lathing, using an electric stapler, on the bottom of the window frame to rest the window on. Use lathing this size to fill the gap instead of lathing 1/4-inch thick, so the window is not overly tight.

Add flexible flashing around the perimeter of the window opening. Staple roofing felt around the opening, and also staple this material to any builder's felt or house wrap on the wall areas beside the window. Cover the felt with a peel-and-stick rubberized membrane, approximately 9 inches wide, that extends 12 inches beyond the edges of the window. Peel the backing and press the membrane over the sill with no gaps or seams. Cut additional membrane strips to cover wood inside the rough opening at the top and over the jack studs.

Fold out nailing fins of a window unit and place the window sill into the bottom of the opening. Tip the frame into the opening, situating the window until all fins are snug. Ask someone to stand inside the house to help you guide the window placement, ensuring space between each jack stud and sides of the window are the same on both sides. Drive a 1 1/2-inch nail into an upper corner to hold the unit, but avoid driving the nail all of the way into the house sheathing.

Install the window by driving nails into the four corners, but check to ensure the window is plumb and level before driving all four nails all the way into the house sheathing. Drive 1 1/2-inch nails, or whatever your product guidelines state, into all pre-drilled holes. Follow the manufacturer's guidelines, so your warranty will be valid.