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For an addition that looks like a part of the original house plan, begin with a foundation that is structurally sound. This allows you both to match the floor level in the house and to make a seamless extension of a house wall if your plans call for it. -- Important Details: Equalize floor levels by building the foundation of the addition to the same height as the top of the house foundation. If necessary, you can compensate for slight errors in building the foundation by shimming or notching floor-framing members to bring the addition subflooring flush with that of the house. It’s usually a simple matter to expose the top of the foundation of a frame house covered with shingles or siding by removing a portion of the outer layers. Establishing the foundation height for a house of solid masonry or veneered in brick is less direct; take careful measurements of flooring thickness and floor-framing height inside the house and transfer them to the exterior. Addition framing is connected directly to the house by means of a board called a ledger—unless your house has truss joists or I-beam joists. If that is the case, follow the procedures shown for this kind of construction. Future access to a crawlspace is best assured with a removable panel built into the addition floor, say inside a closet. -- Dealing with a Concrete Slab: If your house is built on a slab rising no more than 12 inches aboveground—and if the frostline is less than 2 feet below grade—pour a turned- down slab, one that descends to the frostline around the perimeter. In colder climates—or if the slab rises more than 12 inches above the ground—build a combination slab-on-block foundation. -- Inspection and Termite Treatment: After excavating a foundation that conforms to lo cal code, have the trenches checked by the building inspector. If your soil is wet or poorly compacted, the inspector may demand either more digging to reach firm soil or a professionally designed foundation that is stronger than the one shown. Finally, if you live in an area where termites pose a threat, your lender may require that you hire a professional to treat the ground with a powerful insecticide before you pour the footing. CAUTION---Before excavating, establish the locations of underground obstacles such as electric, water, and sewer lines, and dry wells, septic tanks, and cesspools. CAUTION---Before cutting into the house wall, have siding tested for asbestos or lead-based paint. TOOLS:
MATERIALS:
SAFETY TIPS: Goggles protect against small, flying pieces when hammering at eye level or operating power machinery. Guard yourself with a dust mask when cut ting pressure-treated lumber. A THREE-SIDED FOUNDATION 39--- • To the foundation attach two 8-foot 1 -by-4s as marker boards with 2.5-inch masonry nails, shimming the boards to make up for missing siding. Position each board to extend 3.5 feet inside the cuts in the siding; adjust the boards so that they are flush with the house foundation. (Let the nailheads protrude to simplify marker board removal later.) • At the addition side-wall locations, drive a nail partway into the top of each of the marker boards to serve as corner nails. If the addition will extend an interior house wall, position the nail 4 inches—8 inches for an addition to be veneered in brick—beyond the outside edge of the end stud of the wall. When extending an exterior wall, align a corner nail with the house foundation. 2. Making the addition square. Lay out building lines using the 3-4-5 triangle method: • Drive a nail partway into the top edge of one of the marker boards, 3 feet from the corner nail. • Have two helpers cross measuring tapes hooked to the two nails so that the 4-foot mark on the corner nail tape meets the 5-foot mark on the other tape. • Drive a 3-foot-long, 2-by-2 stake at this point, then hammer a nail partway into the top of the stake. • Repeat the procedure at the other marker board. • With mason’s cord, extend the line between the corner nails in the marker boards and the nails in the stakes. • Drive stakes to mark the ends of the addition side walls. • Measure the diagonals of the resulting rectangle; if they are not equal, move the end stakes to make them so. 1. Attaching marker boards. • Remove a strip of siding and sheathing between the projected corners of the addition exposing the sole plate and a couple of inches of the studs. (Don’t cut into a masonry facade.) 3. Marking batter boards. 40-- • Drive 2-by-4 stakes to form right angles at the end stakes, 5 feet outside the building lines. With a water level, mark the height of the house foundation on the 2-by-4s. • Nail 1 -by-6 batter boards between the 2-by-4s, aligning the top edges with the marks . • Extend mason’s cord from the corner nails, past the nails in the corner stakes, to the top edges of the batter boards. Mark these points with nails. • Using the inset’s dimensions—representing distances from the building line—hammer nails into batter boards and marker boards for the main trench, the footing trench, and the inside of the foundation wall. (For brick veneer drive the inner foundation wall nail 11 5/8 inches from the building-line nail.) • Stretch mason’s cord between the two side batter boards so it touches the nails in both end stakes. Drive a marker nail where the cord meets each batter board. • Remove the cord and end stakes. • Excavate a main trench. Make the depth a multiple of 8 inches below the top of the house foundation. Dig a footing trench 8 inches deep. BUILDING LINE; FOUNDATION WALL 4. Leveling the trench. • Drive 1 -by-2 stakes at the corners of the footing trench—and in a zigzag pattern every 3 feet along it, 3 inches from the sides. • Mark the top of the footing trench on one stake and transfer the mark to the other stakes with a water level . • Deepen the footing trench where marks are less than 8 inches from the bottom. • Drive a 16-inch length of reinforcing bar next to each stake to serve as a grade peg. Hammer peg tops even with the marks on the stakes. • Remove the stakes and tamp the dirt around each grade peg. • If a termite treatment is required, have it applied now and wait several days before proceeding. 5. Adding concrete. • Support reinforcing bar on bricks in the footing trench, and wire the bars to the grade pegs . • Where two pieces of bar meet, overlap them 16 inches and join them with tie-wire. • Mix and pour concrete to the tops of the grade pegs. • Allow the concrete to cure under sheets of 6-mil polyethylene for 24 hours. • Run mason’s cords between the building-line nails on the batter boards and marker boards. • Transfer the lines to the footing with a plumb bob and chalk line. • Remove the mason’s cords, batter boards, and marker boards. FOOTING TRENCH LINE; MAIN TRENCH LINE 6. Beginning the wall. 41--- • Lay leads, stepped sets of blocks, three courses high at the corners and ends of the foundation . • Fit a single-course dry run of blocks between the leads, trimming a block if necessary. Set the blocks aside. • Lay each course with a mason’s cord as a guide, placing wire-mesh reinforcement in the mortar bed for the fourth course, every third course thereafter, and the top course. • On opposite sides of the addition, substitute a ventilator for a block in the middle of each wall. Pack mortar around the ventilator edges, sloping the mortar at the bottom for drainage. In the next course, lay two solid blocks over each vent. For brick veneer, build the wall with blocks 12 inches wide to a point just below ground level, then switch to 8-inch blocks laid flush with the inside of the wall. 7. Setting anchor bolts. • Mark anchor-bolt positions on the foundation 1 foot from each corner and doorway and every 4 feet between them. • For each bolt, cut a length of 2-by-6 to serve as a jig, and drill a 0.5-inch hole along the centerline. Place a 4- by 8-inch anchor bolt through each jig and fit it with a washer and nut. • Fill the cores of the top course with mortar, installing the anchor bolts as you go: Set the jig 0.5 inch back from the edge of the foundation wall—or match the setback of the house sill plate if extending an exterior wall. Tap the anchor bolt into the mortar as far as it will go . • After 24 hours, remove the jigs from the bolts. 8. Installing the sill plate. • From a pressure-treated 2-by-6, cut a sill plate 0.5 inch shorter than a foundation side wall (measured from the house sill plate). • Set the plate on the wall and mark it on both sides of each anchor bolt with a combination square . • On the centerline of the board, drill 5/8-inch holes centered between the marks, and set the sill plate aside. • Center a strip of sill sealer on the bolts, and press it against the foundation. • Bolt on the sill plate, shim it level, and check for squareness. • Bolt the two remaining sill plates in the same way and toenail the ends of all the plates together. TYING THE NEW FLOOR TO THE OLD 1. Framing the perimeter. 42--- • From lumber the same size as the house joists, cut a ledger to fit atop the side-wall sill plates, flush with their outer edges. • Fasten the ledger to the exposed house with 0.5- by 4-inch lag screws and washers . Don’t attach a ledger to a masonry facade; toenail it to the sill plates at each end. • Cut two band joists 3 inches shorter than the side-wall sill plates. Toe nail them to the ledger board, flush with the sill plates’ outer edges. • Nail a header joist to the ends of the band joists and toenail all three to the sill plates. 2. Completing the rough flooring. • Install joists every 16 inches with joist hangers (above). • One-half inch inside each band joist, install another joist . Nail bridging midspan between joists for flooring reinforcement. Stagger the boards for ease of nailing. • A the foundation exterior with a 0.5-inch layer of mortar up to grade level—or higher, to match your house. • Trowel asphalt waterproofing onto the mortar below grade. • Fill the trenches. For drainage, slope the earth outside the foundation at least inch per foot to a distance of 6 feet from the wall. • Cover the earth inside the foundation with polyethylene sheeting weighted down with rocks as a vapor barrier. • Place insulation batts between joists, stapling the edges of the vapor barrier to the tops of the joists. Leave an area open for future access to the crawlspace. • Install subflooring as shown. A slab foundation. 43--- PRECISION FITTING FOR A CONCRETE SLAB Most slabs such as this one rest on a block wall and footings identical to those built for a crawlspace foundation (Steps 1-6), except that air vents are omitted and the final course of the wall is laid with L-shaped header blocks to form a shelf. The area between the foundation walls is filled with compacted gravel to the level of the shelf. The gravel is covered with polyethylene, and plastic- foam insulation lines the perimeter of the slab. Welded wire mesh reinforces the concrete, which is separated from the house by expansion-joint material. In warm climates, omit the block foundation. Instead, dig trenches and build forms to shape a concrete slab with turned-down edges that serve as footing and foundation. To the mesh used to strengthen the slab at left are added vertical reinforcing bars for the edges. = = TRICKS OF THE TRADE: Cutting Multiples: To cut several joists at once, mark two joist boards with the desired length. Place other joist boards side by side between the marked ones, supporting all of them on two 2-by-4s positioned under the portion that will be come the joists. Use another, straight 2-by-4 to help align the ends of the joist boards farthest from the marks. Snap a chalk line in between. Cut along the line with a circular saw. |
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Tuesday, April 1, 2014 0:58 PST