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How to Mount Porthole Windows in a Wall

Updated February 21, 2017

Porthole windows are round and come in many sizes. A porthole window offers a new look and a unique view of the world. Installing a round window requires a bit of preparation. The exterior siding, whether it is vinyl, wood or masonry, must be removed prior to the project. The inside of the wall must be disassembled and inspected for wires, pipes or other obstructions that will prevent you from doing the job. Once the inside and outside of the wall is prepared your window is ready to be installed.

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  1. Place the porthole window, face down, onto the dust sheet. Use your tape measure to measure the diameter of the widest point of the inner rim of the nailing lip around the edge of the frame of your window. Tie one end of the string around the pencil. Place the pull blade on your tape measure in the centre of the pencil and stretch the tape along the string. Tie a knot in the string around a roofing nail at a distance equal to ½ of the diameter of the window frame.

  2. Drive the roofing nail tied to the string into the plywood sheeting on the outside of your house where you want the centre of the window to be mounted. Leave the nail head protruding slightly from the plywood for easy removal later. Pull the pencil until the string is taut. Press the tip of the pencil against the plywood sheeting and draw a circle on the wall, while keeping the string tight between the pencil and the nail.

  3. Use the ¾ inch bit on your drill to make a hole just inside of the highest point of the circular outline. Drill another hole touching the inside of the pencilled mark every 90 degrees around the circle in a north, south, east, west compass pattern.

  4. Go inside of the house and locate your four holes. Find the highest hole in the north position. Place a 14 ½ inch board between the studs just above the top hole. Use your hammer to drive two nails through the stud and into the end of the board on both sides. Nail a board between the two studs to the left of your west hole, to the right of your east hole, and just below the hole to the south.

  5. Go outside, slide the blade of your reciprocating saw through one of the drill holes and cut around the circle. Remove and discard the plywood and studs that you cut out with your saw. Attach 15-pound roofing paper around the hole with your staple gun. Cut the paper as needed with your razor knife. Nail a series of 14 ½-inch boards between the studs on the inside of your wall around the cutout to brace the wall.

  6. Slide the porthole window into the hole from the outside. Have an assistant hold the window on the inside while you drive a roofing nail through every other nail slot in the frame of the window to secure it to the house. Caulk around the seam between the outside wall and the outer lip of the window frame to complete the installation. Wait 24 hours for the caulk to cure completely before covering the window frame with siding.

  7. Warning

    Work gloves, safety glasses and hearing protection are required at all times when using power tools. Always maintain three points of contact between your body and the ladder when climbing or working at heights. Check for pipes and wires inside of the wall before drilling of cutting into the surface. Always read and follow the manufacturer's instructions before operating a power tool.

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Things You'll Need

  • Hammer
  • Framing nails, 16d
  • String
  • Pencil
  • Tape measure
  • Dust sheet
  • Porthole window
  • Drill with 3/4 inch bit
  • Reciprocating saw with bimetal blade
  • Roofing paper, 15-pound
  • Staple gun with ¼ inch staples
  • Razor knife
  • Galvanised roofing nails, 1 1/2-inch
  • Boards, 2 inches by 4 inches by 14 ½ inches
  • Caulk gun with 30-year silicone caulk
  • Ladder
  • Work gloves
  • Safety glasses
  • Hearing protection

About the Author

After learning electronics in the U.S. Navy in the 1980s, Danny Donahue spent a lifetime in the construction industry. He has worked with some of the finest construction talent in the Southeastern United States. Donahue has been a freelance writer since 2008, focusing his efforts on his beloved construction projects.

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