When replacing a mudsill or sections of a foundation whose joists run perpendicular to that foundation wall (see p. 210), place a 4×8 or 4×10 carrying beam on edge under the house, within 2 ft. of the foundation. A jack every 6 ft. under the beam should suffice.

When joists run parallel to the foundation wall being replaced, you’ll need to run needle beams through exterior walls, and support each beam with one post underneath the house and a second post outside, roughly 2 ft. beyond the foundation wall. For this, you’ll need to remove sections of siding so you can insert a beam every 6 ft. to 8 ft. If the siding is stucco, you’ll need to punch large holes through it. To keep the rim (outer) joist from deflecting under the load, nail a second rim joist to it, doubling it before jacking. Also, add solid blocking from those doubled rim joists to the first adjacent joist. Use metal connectors to affix the blocking and 10d nails to face-nail the rim joists.

Supporting the structure: When joists run perpendicular to the foundation wall you’re working on, support their load with a beam parallel to the wall. Allowing yourself room to work, put this beam as close to the wall as possible – in most cases, 2 ft. is optimal.

2. Level and set the footing blocks or crib­bing on compacted soil. Each jack base should be about 2 ft. by 2 ft. Or, if you’re using a single tim­ber block, use a 4×12 at least 3 ft. long or, if the soil is crumbly, at least 4 ft. long. If you spend a little extra time leveling the footings, the posts will be more likely to stay plumb. To support a single-story house, set posts every 5 ft. or so beneath an adequately sized beam—typically, a 4×8 or 4×10 set on edge.

3. Positioning a jacking beam requires prep work. Ideally, the crew should raise the beam into place and then immediately plumb and set the jacks. But they may need to catch their breath or gather equipment before setting the jacking posts. In that event, cut two 2x4s approximately h in. longer than the distance from the underside of the beam to the top of the cribbing plates and use a sledgehammer to wedge a 2×4 under each end of the beam. Caution: This setup is inherently unstable, so workers should monitor both 2x4s continually to make sure they don’t kick out.

4. As soon as the beam is in place, cut posts 10 in. shorter than the distance from the under­side of the beam to the top of the footing blocks. This 10 in. is roughly the (closed) height of a hydraulic jack plus a little room to move. With a helper, place jacks and posts under both ends of
the beam, plumb the posts, and start jacking. Center each jack on its footing blocks so there’s plenty of room for the shoring post(s) that will follow shortly. (If you use hydraulic jacks, you can position the shoring posts 3 in. to 4 in. from the jacking posts.) As you jack, try to raise both ends of the beam evenly, using a 4-ft. or 6-ft. spirit level to check for level.

The amount you raise the beam beyond that depends on whether you’re leveling floors, taking weight off joist ends before replacing a founda­tion, or just supporting the structure where it is. When the beam is at the desired height, measure down to the tops of footing blocks to determine the height(s) of the shoring posts. (If you jack up an additional ‘/ in., you’ll find it easier to slide shoring posts in.)

5. After you’re done jacking, install the shoring posts, which are more stable than jacks on posts. To keep the shoring posts in place, nail steel caps to their tops before installing them. Once you’ve placed the posts under the footing beams, attach the post caps to the beams, and add cross bracing or plywood gus­sets to keep the beam from rotating. Once you’ve plumbed the shoring posts and braced the beams, lower the jacks slowly till they no longer bear weight, and then remove them.

With shoring supporting all necessary bearing members, you’re ready to begin repairs.

Note: Some foundation contractors install two shoring posts—one on either side of the jacking post—for greater stability. Once the jack is removed, nail two 3-ft. long 2×4 diagonal braces between the two shoring posts; for this, use a pneumatic nailer. Hammer blows could dislodge the posts.

6. When your repairs are finished, begin to remove the shoring by reinserting the jacking apparatuses and then simultaneously raising all the jacks slowly and evenly to take weight off the shoring. Leave the cross bracing in place till those loads are removed. Then, keeping the jack­ing posts plumb, carefully remove the post-and – beam bracing and carefully lower and remove those elements. Gradually lower the building onto its new pads, posts, and foundation, and then remove the jacks.

Minor Repairs and Upgrades

The category minor repairs includes anything short of replacing a failed foundation, which is covered in the next section. Repairing surface cracks is explained on p. 205.

REPLACING POSTS AND PADS

If floors slope down to a single point, there’s a good chance that a post or pad has failed. If a floor slopes down to an imaginary line running down the middle of the house, there’s probably a girder sagging because of multiple post or pad failures. Fortunately, the cures for both condi­tions are relatively straightforward.

Post repairs. The most common cause of wooden post failure is moisture wicking up through a concrete pad, rotting the bottom of the post. To replace a damaged post, use the tech­niques just described in "Jacking and Shoring.” Place footing blocks as close as possible to the existing pad, and jack just enough to take the load off the post—plus ‘/ in. Remove the rotted post, measure from the underside of the girder to the pad (remembering to subtract the ‘/ in.!), and cut a new post—preferably from pressure-treated lumber.

To keep this new post from rotting, cut a sheet-metal plate to put under the bottom of the post; use aviation snips to cut the 22-gauge sheet aluminum. The metal will prevent moisture from seeping up through the concrete. Place the plate

For safe jacking, you need to proceed slowly and observe the following precautions.

Preparatory steps

► Survey the building, noting structural failings and their probable causes as well as which walls are load bearing. Also determine whether joists or beams are deflecting because of heavy furniture, such as a piano; which pipes, ducts, or wires might complicate your repairs; where the gas pipe shutoff is; and so on.

► Have a plan that anticipates everything.

If excavation is necessary, who’s going to do it? And where will you put the displaced dirt? (Disturbed dirt has roughly twice the volume of compacted soil.) Will you need to rent equipment, such as jacks, compressor, and jackhammer? Where will you store materials? How will rain affect the materials and the work itself? Can a concrete-mixer truck reach your forms or will you need a separate concrete pumper, an auxiliary pump on wheels that pumps (pushes) the concrete from the mixer truck to the pour?

► Assemble safety equipment. This is mostly hard-hat work. You’ll also need safety glasses that don’t fog up, sturdy knee pads, and heavy gloves. For some power equipment, you’ll need hearing protectors. Update your tetanus shot. Set up adequate lighting that keeps cords out of your way—and, on a post near a suitable light, mount a first-aid kit.

Even though a cell phone is handy if trouble strikes, never work alone. Workers should stay within shouting distance.

► Have all necessary shoring materials on hand before you start jacking. Remember, jacks are for lifting, not supporting. Within reason, level the ground where you’ll place footing blocks or shoring plates. As soon as a section of the house is raised to the proper level, be sure to set, plumb, and brace the shoring. Hydraulic jacks left to support the structure too long may slowly "leak" and settle or—worse—kick out if bumped or jostled.

Certain conditions make raising houses diffi­cult. When foundation contractors see the fol­lowing conditions, they get a second or third opinion from engineers and house movers before bidding on a job:

► Sloping sites, unstable soil, site erosion, or excessive ground water.

► A masonry building.

► Multiple-story house or single-story dwelling with heavy materials, such as stucco exterior walls; plaster interior walls; and tile, slate, or three-layer roofs.

► Quirky framing visible in the basement, such as undersize or cut-in girders, joists running in several different directions, and multiple additions to the original structure.

► Floors that pitch in different directions or are badly out of level.

► Catastrophic foundation failures, such as foundation rotation and sinking corners.

Jacking basics

► Support jacks adequately. The footing blocks or cribbing beneath the jacks must be thick enough to support concentrated weights without deflection and wide enough to distribute those loads. It’s difficult to generalize how big such a support must be; a 4×12 footing block

3 ft. long or two layers of 4×4 cribbing should adequately support a jack beneath the girder of a single-story house. In this case, the soil must also be stable, dry, and level. If the soil isn’t level, dig a level pit for the cribbing, as shown on p. 208. (Avoid precast concrete piers as jacking blocks because their footprints are too small and the concrete could shatter when loaded.)

► Don’t place jacking or shoring platforms too close to the edge of an excavation. Otherwise, the soil could cave in when the timber is loaded. The rule of thumb is to move back 1 ft. for each 1 ft. you dig down. Also, don’t put jacks or shoring where they could be undermined later. For example, if you need a needle beam to support joists parallel to the foundation, excavate on either side of what will be your new foundation, and place jacking platforms in those holes. In that manner, you can remove foundation sections without undercutting the jacking platforms.

I Jacking Components

Beam

DON’T DO THIS!

When the jack is loaded, bearing blocks placed unsafely close to the edge of an excavation can cause it to collapse.

► Level support beams, and plumb all posts. The logic of this should be evident:

When loads are transmitted straight down, there is less danger that jacks or posts will kick out, injuring someone and leaving shoring unsupported. Accordingly, cut the ends of the posts perfectly square, plumb the posts when you set them, and check them for plumb periodically as the job progresses.

Where the ground slopes, dig a level footing pit into the soil, as shown in the bottom drawings at left, so footings or cribbing can’t migrate under pressure. (Typically, the foun­dation contractor digs the pits and prepares the site before the house mover arrives to install the cribbing.) Surrounded by the walls of the pit, the bearing blocks have no place to go.

► Keep checking for level and plumb as you jack. If supports sink into the soil, posts tilt, or the jack starts "walking” under pressure, lower the jack, reset those elements and begin anew. First thing each day, check jack supports and shoring for plumb and level.

Diagonal bracing, plywood gussets, and metal connectors will each help posts stay plumb. When cross bracing temporary posts and beams, use screw guns or pneumatic nailers to attach braces. Hand nailing braces could knock posts out of plumb or cause beams to rotate or jack heads to migrate.

► Raise jacks in small increments—say,

% in. per day—to minimize damage to finish surfaces inside the house. When you’re jacking a structure to be repaired, as when replacing a mudsill, jack just enough to lift the weight off the sill to be removed. If many jacks are involved, raise them simultaneously if possible, so excessive stress (and damage) doesn’t accrue above any one jack.

Steps in jacking and installing shoring.

Setting jacking equipment varies according to the type of jack; the structural elements to be raised; and site conditions, such as ceiling height, access, and soil stability. That noted, the follow­ing observations hold true in most cases.

1. Position the jacks and jacking beams as close as possible to the joists, girders, or stud walls you’re jacking. If you’re adding posts under a sagging girder, support may be directly under the girder; but more often, it will need to be off­set slightly—say, within 1 ft. to 2 ft. of joist ends—to give you working room. In other words, close enough to joist ends so they won’t deflect, yet far back enough to let you work. Again, don’t put jacks or shoring where they could be under­mined by unstable soil later.