How to Build an Extension on a House


Building an extension on a house not only will add to your living space but also will add value to your home. You can use the extension for any extra room in the house. Tackling this project yourself will give you a sense of accomplishment and save you a lot of money.

Things You'll Need

  • Hammer
  • Nails
  • Screws
  • Drill gun
  • 2-by-4s
  • 2-by-8s
  • Plywood
  • Level
  • 4-by-4s
  • Tar paper
  • Shingles
  • Tape measure
  • Post hole digger
  • Concrete
  • Joist hangers
  • Lag bolts
  • Rolled R12 insulation
  • Drywall
  • Drywall compound
  • Drywall screws
  • Drywall tape
  • Primer
  • Paint
  • Paint brushes
  • Paint rollers
  • Staple gun
  • Sand paper
  • Measure the width, length and height of the room you want to add. Then figure out how many 4-by-4 posts you are going to need for the platform. For example, every 3 feet you should need a 4-by-4. If the platform is 6 feet long, you will need two 4-by-4 posts. Using the post-hole digger, dig out the holes for the 4-by-4 and make sure they are at least 24 inches deep.

  • Measure the 4-by-4s from the bottom of the hole to the platform of the new addition. Set the 4-by-4s in the ground and make sure they are square by using the level. Put in the concrete and let it set overnight. Attach one 2-by-8 board horizontally to the existing house with lag bolts and make sure it is level. Attach this with the nails. Measure the length and width of the 2-by-8s for the outside framing of the platform. Attach this with nails too.

  • Measure 16 inches on center of the width on the platform, which is the floor. You should measure 16 inches on the center depending on the size of the room you are adding to your house. Put the joist hangers on the 2-by-8s that you have already hung. Set the rest of the 2-by-8s to complete the framing of the platform. Cover the platform with plywood.

  • Take the 2-by-4s and measure and cut them. Take the 2-by-4s and measure the height you want the room to be. Cut the 2-by-4s. Before you start framing the walls, measure 16 inches on the center for the top and bottom plate which will be the 2-by-4s. Using the measurements of the top and bottom plate, start attaching the 2-by-4s and cut them as needed where you are putting the windows and doors.

  • After making the walls, stand them up and attach them to the platform with the nails and screws. After attaching all three of the walls to the platform, check to make sure they are level and square.

  • Take the 2-by-8s that you will be using for the rafters and measure 16 inches on the center and attach to the top of the walls. Box everything in with the plywood to the edge of the frame. Put the tar paper and shingles on the roof. After the roof is done, put the windows and doors in. Now you are ready for the electrician to do the electrical work.

  • After the electrical work is done, measure and cut the insulation. Put the insulation in between the studs. Staple the edges of the insulation to the studs with the staple gun. Do that for the whole room.

  • Hang the drywall on the ceiling using the drywall screws. Now hang the drywall on the walls starting from the ceiling down. With the drywall tape, tape all of the seams. Using the drywall compound, go over all of the seams where the drywall tape is at. Also, cover all of the screw holes with the drywall compound. Wait at least 24 hours for it to dry. Using the sand paper, sand everywhere you put the drywall compound. Repeat two more times. After you are satisfied that the walls are smooth, you are ready to primer and paint.

  • Take a damp cloth and wipe all of the walls and ceiling down to make sure there is no dust on them. With the paint brush and the primer, cut around the corners, doors, and the windows. Roll the walls and ceiling out with the primer. Let it dry and repeat with the paint. Choose either carpet or tile for the floor and lay it down.

Tips & Warnings

  • Remember the old adage: Measure twice and cut once.
  • Always have other people there to help you with this project.
  • Always wear a mask and goggles while sanding the drywall compound.

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  • Photo Credit Jupiterimages/Pixland/Getty Images
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