Adding a new room to your home isn't a simple procedure, but the process is fairly straightforward. Before you begin, check with your local building inspector to learn about the necessary permits and requirements for adding a new room. Materials:
2" x 4" lumber
Transit level
Steel rebar
Backhoe, with large and small shovels
Cement truck
Concrete
Wheelbarrow
Shovel
Concrete float
Concrete blocks
Anchor bolts
Measuring tape
Speed square
Framing square
Pencil
Chalk line
Level
Hammer
Sixteen-penny and eight-penny nails
Drill, with drill bits and spade bits
Ratchet and sockets
Nuts and washers to fit anchor bolts
2" x 8" pressure-treated lumber
2" x 12" engineered joists cut to the length of your room
2" x 12" lumber (for rim joist)
3/4" tongue-and-groove plywood
- First you'll need to build a foundation for the room. Start by constructing batter boards (figure A) to establish a rough perimeter.
- Use a transit level to establish reference points to guide the excavation (figure B).
- Excavate the site to the proper depth (figure C), dig trenches for footings, and reinforce the trenches with steel bars (figure D).
- Pour concrete into the trenches to create the footings (figure E). You may have to transport the concrete with a wheelbarrow if it's not possible to get a cement truck into the area.
- Complete the foundation by installing concrete blocks (figure F) and anchor bolts, which will support the sill plate.
- After the foundation is in place, you're ready to start framing the room. The first thing you'll work on is the floor.
- Measure the locations of all anchor bolts, and transfer the measurements to the sill plate, made from 2" by 8" pressure-treated lumber. Use a speed square to draw a line across each mark (figure G). Measure and mark the center of each line, and drill out each center with a 3/4" spade bit (figure H). Countersink the holes with a drill bit the same diameter as the washers you plan to use.
- Set the boards in place over the anchor bolts, and tighten washers and nuts over the anchor bolts (figure I).
- Toenail the boards together where they meet at corners (figure J).
- Now you're ready to install the floor joists. You could use standard 2" by 12" lumber for the joists, but for a large room you'll find it easier to use engineered joists (figure K), which can be made longer than standard ones. In many cases engineered joists can be made to span the entire subfloor for a large room. Install the joists perpendicular to the rest of the house: that will make installing the ductwork for the heating and cooling system easier. When measuring for the joists, subtract the thickness of the rim joist, which will cover the exposed ends of the joists.
- Attach joists to the sill plates that are perpendicular to the house. The remaining joists will also face this direction. Secure the joists to the sill plate and the rim joist of your house with eight-penny nails (figure L).
- After you attach the joists on the sides of the room, you can begin attaching the intermediate joists, using joist hangers (figure M).
- Set the joists 16" on center and nail them into place. Rest one end in the joist hanger, and rest the other on top of the sill plate (figure N). Attach the rim joist after all the other joists are in place (figure O).
- Begin attaching 3/4" tongue-and-groove plywood subfloor. Stagger the seams to prevent weak spots in the floor. The subfloor should be lined up flush with the edges of the joists.
- After the subfloor is in place, snap a chalk line to show where the inside edge of the outer walls should line up.
- Now you're ready to start building the walls. First, mark the placement of the wall openings, partitions and studs. Lay the sole plate and top plate (the top and bottom boards of each wall) beside each other, and temporarily secure them to the floor. That permits you to use a speed square to mark both plates at the same time.
- Measure and mark the center of each wall opening. Then measure and mark the outer edges for the openings. For example, if you have a 48" window, measure out 24" from the center line, and mark the boards, then measure another 1 1/2" (the thickness of a 2" by 4") from that mark to allow for the framing studs. Mark the inner line to indicate that it will be used as a reference for placing the supporting studs; mark the outer line to indicate that it will be a full-length stud.
- Mark the positions of the partitions, where the interior wall will join the outer wall. These areas will use three studs: two will be perpendicular to the room, and the third will face into the room, sandwiched between the two outer studs (figure P).
- Mark the locations for the corner posts, which consist of three studs side by side (figure Q). Measure from the outside corner, and mark the sole and top plates every 16" on center for the studs.
- Dry-fit the wall together on its side, and nail the studs in place from underneath the sole plate and above the top plate, using 16-penny nails (figure R).
- Next you'll need to cut headers, which support the weight of the roof over the windows and doors in the outside wall. Check with your local building inspector to determine the proper thickness for the headers. In most cases headers created from two pieces of 2" by 12" lumber with a piece of 1/2" plywood sandwiched between them (figure S) will meet or exceed local codes. The plywood gives the thickness needed for the header to be flush with the studs on both sides of the wall.
- The header is supported by a partial-length stud known as a lap stud or a jack stud (figure T). Set the lap studs in position next to full-length studs, and nail them in place.
- Install sills for the windows, using the same basic principles you used to install the lap studs and header. You'll need short support pieces known as cripple studs (figure U) beneath the sills.
- After the wall is assembled, begin attaching exterior sheathing (figure V), which is made of low-grade plywood. Don't attach sheathing to the ends of the final wall you're raising: the sheathing will extend past the corner so that it covers the sheathing from the adjacent walls.
- When the sheathing is in place, get some helpers and lift the wall (figure W). Start with the walls at each end, and raise the one that goes between them. As you set each wall in position, make sure it's plumb and brace it with temporary supports.
- Attach a second top plate, sometimes called a connecting plate, to tie the corners of the walls together.
- Adjust the bottoms of the walls so they line up with the chalk lines you established earlier. Nail the sole plates in place.
- Attach 2" by 4" blocks to the outside top corners of each wall, and stretch a piece of string between them. Adjust the tops of the walls so the string is 1 1/2" away from the wall down its entire length (figure X). Secure the wall with 2" by 4" braces, set at an angle and nailed in place (figure Y).
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