House Wrighting Without Headaches

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Like the tripled 2 X 10s, a 6 X 8 center beam needs support every 6½' or 7'; if you have to set additional columns to upgrade your structure, follow the footing and spacing rules of thumb or refer to your local building code for specifics.

Another fix for sagging floors is something that's common in older houses and is even used today where joist spans are long or surfaces are expected to support greater loads. It's nothing more than a heavy beam set perpendicularly beneath the floor joists at mid-span. This girder can extend a short distance or the full width of the house, and it's supported from below on posts or concrete piers.

Normally, you'd place the girder where joist sag is the greatest—right at the center of the span. Occasionally, other factors like poorly planned additions or weakening of the wood can cause joists to deform at other points along their reach. Determine the cause of deflection so you can set the support at the right place; a joist may trick you by sagging at its center even though the load is bearing on a point closer to either end.

Assuming you've located the best bracing spot, figure out how long you need to make the girder by evaluating the notes you took earlier. Since it's easier to construct a beam than it is to hand-dig a half dozen or more footing holes, plan on sandwiching three 2 X 10s together with clamps, construction adhesive and 16-penny nails if the girder is longer than 7'. If it isn't, a five-block wall (80" long) and wooden shimming of whatever height necessary will probably be all you'll need for support.

Mark the positions for the pier footings by hanging a weighted string from the floor joists at the appropriate spacing. Footings should be 6" to 8" wider than the block or post they're supporting and needn't be more than 12" thick. It's standard practice to place footing bottoms 12" below the frost line, but check with a contractor or your building inspector for local rules concerning interior footings.

A 16 "-wide trench should have two parallel lengths of ½" reinforcing bar set horizontally near its base. Two more pieces driven vertically into the ground and leveled to the height of the completed footing at each end will allow you to trowel the poured concrete to the correct plane. A standard packaged premix will suit the job nicely.

To make a pier, just mortar a block to the surface of the footing and lay more on top as needed, checking with the level to make sure each course is true. If you're building a small wall, stagger the joints and check for bowing as well. You can fill the block cores with rebar and concrete for additional strength.

Once you've come within girder distance of the joists, you'll have to jack the floor to slide the beam in place. Follow the procedure given earlier, except in this case you'll need to use a flat 2 X 6 as a temporary beam to hold the floor up on 4 X 4 props placed at least every 4'. Jack from one end to the other, and set the posts on pads as you go. Shim between the joists and the permanent girder if you need to fill space, then remove the temporary beam and props. If you're supporting the girder with wooden posts, make sure they rest on concrete above the earth; some codes require that you use metal feet, as well, to secure the posts.

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