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The easiest way to provide access to an addition above a garage is to cut an entrance through the second story of the main house. Another option is to build an exterior stairway. Or you may prefer to add a stairway inside the garage, as described here. A stairway opening in a floor built with I-beam joists is similar to one in a floor made of lumber joists —both use the framing techniques. A stairway perpendicular to joists must be sup ported by a load-bearing wall, since as many as six floor joists may be cut; build parallel to the floor joists to simplify the work. - Safely Requirements: Before be ginning, check local building codes for dimensions such as step heights and depths, stairway width, and headroom at the downstairs end of the stairwell opening. Stairways in a garage require fire-safety features not needed else where. The walls must be sheathed with fire-resistant wallboard. And if the door at the bottom opens into the garage, rather than out to the yard, the stairway must have a fire resistant metal or wooden door. - Establishing Stair Dimensions: Begin by measuring the stair’s total rise—the distance from the garage floor to the surface of the upstairs finish floor. Divide the rise in inches by 7, a typical step height in inches, and round off the result to get the number of risers. Round fractions down for a steeper stair, up for a shallower one. Divide the total rise by the number of risers to get riser height, or unit rise. To determine the unit run—the tread depth less the overhang—subtract unit rise from 17.5, then round to the nearest inch for convenience in measuring. For example, if the unit rise is 1/8 inches, the unit run comes to 9.5 inches. Unit run and unit rise are used to mark and cut the 2-by-12 boards, called carriages, that support treads and risers. But you’ll also need the stair’s length along the floor, or total run, in order to frame a stairwell opening. To calculate total run, multiply the unit run by the number of risers. The length of the opening usually equals the total run, but you can shorten the opening modestly to gain floor space upstairs, as long as headroom stays within code. TOOLS:
MATERIALS:
SAFETY TIPS --- Hammering can produce flying woodchips and nails, as well as loud noises. Protect your eyes with goggles and ears with earplugs. Add a dust mask when operating a power saw. 94a--- 1. Strengthening a joist. • Install a doubled I-beam joist at a distance from the wall equal to the width you have chosen for the stairway. Assemble this I-beam using the technique shown, and attach the ends to the header joists as shown. • Mark the doubled I-beam and the band joist for the upstairs end of the opening. • Measure and mark the total run on the I-beam and the band joist, then transfer the marks to the garage floor with a plumb bob. BAND JOIST 94 2. Framing the stairwell opening. • Install headers, each made of two boards, between the doubled I-beam and the band joist at the marks you have made for each end of the stairwell opening. • Double the band joist between the headers, and fasten the headers to the band joist with framing connectors. • Cut I-beam tail joists to reach from the headers to the outside edges of wall top plates. Attach the tail joists to the headers with I-beam joist hangers and to the wall top plates and header joists as shown. 3. Marking the carriage. 95b--- • Measure between stairwell marks on the doubled joist and garage floor to find the approximate length of a carriage. Cut a 2-by-12 about 2 feet longer than this distance. • Set a framing square near one end of the 2-by-12 with the unit-rise and unit-run figures— in this example, 8 and 9 inches—at the edge of the board. Square gauges attached to the square simplify alignment. • Outline the corner of the square on the board, then extend the unit-run line across the board. • To the right of this line, at a distance equal to the thickness of a tread, mark a parallel line for cutting the bottom of the carriage. • Move the square to the right, aligning the unit run and unit-rise figures with the edge of the board as before, but also placing the unit-run figure at the end of the first unit-rise line. Outline the square. 95 4. Completing the carriages. 96a--- • Moving along the board, mark runs and rises until you have marked one more riser than the number calculated for the stairway. • Extend the top unit-rise line across the board, and cut along this line to fit the carriage to the header in the stairwell opening. • Trim the board along the carriage bottom line marked in Step 3, then finish the carriage by cutting out the triangles between the unit-rise and unit-run lines. • Use the carriage you have cut as a template for cutting two additional carriages. 5. Installing the carriages. • Set the carriages against the header and tack them in place. • Shim under the carriages as needed to make the unit-run cuts level, then secure the carriages to the header with multipurpose framing connectors. Use one connector on each of the outside carriages, two on the middle carriage. If a connector extends below the header, bend the connector and nail it to the bottom of the header. When the bent portion overlaps a joist hanger, bore nail holes in the joist hanger through framing-connector nail holes. • Nail the outer carriage to the doubled joist of the stairwell opening. Also nail the carriage along the wall to the wall studs. 6. Installing spacers. • Cut four 2-by-4 spacers to fit between the carriages. • About a third of the way up the stair, nail two of the spacers end-to-end between carriages, positioned as shown at left so that they won’t interfere with attaching treads and risers in Step 7. • Install the second pair of spacers two-thirds of the way up the stair. 96 7. Adding trends and risers. 97a--- • Cut risers from 1 -by-8s or 1 -by-10s to the correct height and width, and secure them to the riser cuts with 2-inch finishing nails. • Add at least 1 inch to the unit-run measurement to allow for the nosing of the tread to overhang the riser, then cut treads to the depth and width you have chosen. Apply construction adhesive to the carriages, and fasten the treads with 2-inch finishing nails or 2-inch trim screws. • Working under the carriages, nail through the risers into the rear edges of the treads. 8. Putting in a sole plate. 97b--- • Cut a 2-by-2 to fit against the sole plate of the garage wall and overlap the outer carriage. • Nail one end of the 2-by-2 to the carriage; toenail the other end to the garage-wall sole plate. 9. Framing the stairwell wall. 98a--- • Beginning at the top of the stairs, cut 2-by-4s to match the slope of the outer carriage and to fit, at 16-inch intervals, between the lower edge of the carriage and the bottom of the doubled i-beam in the stairwell opening. • Nail the 2-by-4s to the carriage, then toenail the upper ends to the I-beam. • Complete the wall framing with studs that are toenailed to the 2-by-2 sole plate. • Along the bottom of the carriage between studs, nail 2-by-2s to serve as nailing surfaces for wallboard. 10. Framing upstairs walls. 98b--- • Lay a subfloor over the I-beam joists, and frame the walls of the second story. • Frame two more stud walls, one at the stairwell opening above the bottom of the stairs and one on the side of the opening long enough to accommodate a landing at the top of the stairs. • There frame a third wall with a rough opening for the upstairs door. • Frame an exit door in the garage wall at the bottom of the stairs. • Attach a handrail 30 inches above the level of the steps, screwing the rail brackets to garage-wall studs with 1.5-inch wood screws. Have the stair and landing walls down stairs, undersides of the carriages, and garage ceiling sheathed with fire-resistant wallboard. Use standard wallboard on up stairs walls around the stairwell. |
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Friday, April 4, 2014 22:12 PST