It all starts with a good foundation Tradition, building codes require concrete footing for most construction.


April 06, 1997|By Karol V. Menzie and Randy Johnson.

In construction, "a firm foundation" is no cliche. It's a matter of tradition, good technique and honoring the building codes. How well the structure will stand--and stand up to time and weather--depends on how good the foundation is.

It's true whether you're building a skyscraper, a house or a gazebo. You may be dreaming of barbecues and planter boxes, but even a backyard deck starts with a good foundation.

Think of it as going deep (well, baseball is back). The first step toward a good foundation is a concrete footing. The concrete has to cure to achieve its full strength, and the foundation has to be attached to the footing. If the foundation is made of cinder blocks, they need to be set in a bed of mortar on the concrete. If you're using posts (as for a deck), they need to be bolted to the footing.

Randy recalls that part of the foundation of a pre-Civil War house in the Shenandoah Valley where he spent childhood summers was made of loose rocks. He and his cousins were forbidden to play with the rocks, and every now and then a grown-up would restack the stones, maybe inserting a little mortar. Meanwhile, that part of the building shifted, rising and falling with the seasons, and the floors creaked constantly.

These days, building codes demand you do more than dig a little hole, put a big rock in it and start stacking rocks on top. (There is one occasional exception: When a structure is not going to be used for human habitation or needs to be portable -- such as a shed -- it can be built without concrete footings and with a foundation that may be no more than 6-inch by 6-inch beams laid in a shallow trench. Check local building codes for rules in your jurisdiction.)

Conventional building requires a concrete footing poured on undisturbed earth. If you're using cinder block for the foundation, the footing needs to be twice as wide as the block.

The footing should be at least a foot deep, with the bottom resting below the frost line (30 inches in Maryland; it gets deeper as you go north and more shallow as you go south). The footing needs to cure for about a week before any weight is put on top of it.

Foundation walls can also be made of poured concrete, or, you can save some time and energy by pouring the footings to a level above grade, and building the structure directly on top of the footing. Some jurisdictions allow below-grade foundations of pressure-treated wood, but we're not comfortable with that because the wood's probably not guaranteed for as long as your mortgage.

Decks are built on concrete footings placed exactly where they are needed, usually at the corners. The footings should be reinforced with steel bars, especially if they extend more than a few inches above grade. (The top should always be a little above grade.) The footings support pressure-treated posts that in turn support the deck. Unless the deck is small and/or close to the ground, the posts should be 6-by-6s; 4-by-4s are too likely to twist.

The posts are attached with metal post anchors that are bolted to the concrete footing and then nailed into the post. when the footings are poured, a 12-inch by half inch J bolt should be inserted in the wet concrete, with about half an inch sticking out. That's the bolt that will be used to attach the post anchor. The anchors create an air space so the posts are not in contact with the footing.

There's a hook in the end of the J bolt that helps anchor it in the concrete, and the top is threaded. When you pour the concrete, be sure the threads are clean so nothing interferes with installing the nut. After pouring the footings, trowel the top so it is smooth and level. That will make installing the posts easier. Randy uses a square form at most home improvement centers that makes the process easier.

The pressure-treated wood used in building decks needs attention at each step. If you cut it, you may expose inner portions of the wood that have never seen chemicals -- especially in larger pieces such as 6-by-6s. Randy likes to soak (or paint, if it will show) the ends of the posts in a wood preservative before the posts are set in the anchors, for an extra measure of protection. He keeps a can of wood preservative on hand while he's building a deck so he can treat the cut ends of any board that may be damaged by weather.

Next: Laying out and assembling the structure.

Randy Johnson is a Baltimore home-improvement contractor. Karol Menzie is a feature writer for The Sun.

If you have questions, tips or experiences to share about working on houses, e-mail us at, or write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.

Pub Date: 4/09/97

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