Improper Installation of windows could cause a water leak damaging the structure of your house or air leaking in around the window will raise energy cost to heat and cool your home. The tools required for installing windows are a level(at least a 4' level is recommended), hammer, and use 1-1/2" roofing nails to nail the window flanges about every 6"-8" around the perimeter of the window. It will also require two people to install a window, one person inside to plumb and square the window. And another person outside to nail the window into place
Before installing windows, double check the window opening in the wall should be 1/2"-1" bigger in width and in height than the window being installed. Windows require clearance around the window opening to allow for insulation around the window and this also helps to prevent the house from settling and asserting pressure onto the window making it hard to open and close. Double check the window opening checking that the sides and bottom are fairly level. Make sure that the window is all the way closed and locked, this helps keep the window straight and square while you are installing it.
Before you install the window apply a generous amount of caulk all the way around the window on the back side of the nailing flange. After the window is nailed into place, use water proof tape around the outside flange to seal out water and air. Then either stuff insulation into the gaps around the inside of the window or use a window and door grade spray foam to fill the gaps.
Use two pieces of 1/2" plywood placing one piece on each side, to hold the bottom of the window off the window sill, install the window into the window frame setting it on the pieces of plyood. Center the bottom of the window in the window frame so that you have the same clearance on the both sides of the window. Do not nail the window yet. Check the window to see if its level from the top to the bottom. If the window Is level go ahead and nail aroud the perimeter nailing 1 nail every 6" - 8".
If the window is not level with the bottom of the window centered in the hole, check to see which way the top of the window would have to move to make the window level. If the top of the window has to move to the right tack a nail at the bottom right corner, then move the top of the window over till the window is level and tack a nail in the remaining corners of the window.
Now open the window raising the bottom window all the way up, then close the window till the window is just cracked open about a 1/8". The reveal(or gap between the bottom of the window sash and the window sill) should be the same on both sides. If the reveal is uneven the middle of the window will need to be adjusted, move the middle of the window either left or right till the reveal at the bottom sash is equal on both sides. Check that the window opens and operates correctly and finish nailing around the perimeter of the window.
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