Ultimate Guide to DIY House-building -- Footers

A footer, as the name implies, is that lowest part of a house upon which the rest of the dwelling is placed. And like anyone's foot, if it's not firmly planted on the ground, proper posture or position of the rest of the body (or in this case, the house) becomes difficult if not impossible to maintain. A house footer serves to firmly situate the building onto and into the ground. And because it plays such a basic and critical role, it's important to make sure that the footer is done correctly.

Footers are largely inaccessible once covered and landscaped over, and if ineptly constructed, major problems will result in huge expenses and inconveniences to homeowners.

Few people realize exactly what a house sits on, and how the house is joined to the earth. There are right and wrong ways to construct a footer; the main idea is to evenly spread or distribute the weight of the house over a large enough area of soil so that settling or moving will never occur. The chief enemies are gravity and time. Downward pres sure that's not evenly supported from below will ultimately result in cracked floors, foundations, and telltale symptoms such as doors that will not close, cracks in plaster, and worst of all, an obvious tilting of the house.

Construction Guidelines

Consider the following when planning your footer:

1. It must be built on virgin soil if conventional building practices are to be followed. Sure, some houses are constructed on swamp land-but they require extra engineering, expense, and effort. The standard-type house should rest upon solid ground. This means shy away from a building lot that has been filled in and graded to bring its surface up to a respectable level.

Consider arranging for a soil test hole to be dug where the basement will be. It will identify soil types and may detect the presence of water or boulders below grade. Digging the test hole will also help get more accurate prices on excavation, foundation, and drainage work, plus it will prevent major surprises and possible delays.

2. If you realize the land consists of recently filled loose soil, and you still desire to build on it, several options exist. You can have the soil compacted through mechanical means. Contractors can use a heavy-duty tamper that hammers the soil down, plus huge rollers that pass back and forth over the surface, compacting as it moves.

Together these machines press the soil until the proper "load level" or ability to support weight is reached that's similar to that of virgin earth (undisturbed ground).

If the depth of uncompacted soil is too great to be efficiently compacted, and a deep cellar might lend itself to the house's structure, you could excavate and remove the disturbed ground until you hit virgin soil, then build from there.

A last and most radical alternative could apply if virgin ground is entirely too far below grade to fix by either compacting or excavating. Here the solution is to architecturally design a one-of-a kind footer of the floating nature to adequately support the house you plan. In most cases, though, the expense is too great to bother with. It is better to find a more suitable site.

Either of the first two options will also cost more than an ideal lot, but they're necessary if you are to prevent the house from shifting and being subject to the difficult-to-correct ailments described earlier. Unless concrete is poured onto undisturbed or properly compacted soil, its weight, when coupled with that of the foundation and the rest of the house, will slowly press down the loose soil below. This will result in cracks, heaving, and tilting which naturally will disturb the framework of the rest of the house. Suddenly the windows won't go up as easily, the doors will no longer fit their frames, plaster walls will crack-all indicating that stressful pressures are at work that will probably brand the house as shoddily constructed.

3. The frost line must be taken into account. The earth is an insulator, and in northern sections some of the top ground freezes and offers protection to the unfrozen soil below. The frost line is an imaginary undulating plane located at some depth below the surface, or the average depth of ground that can be expected to freeze during winter, year after year. In the northern parts of the United States for instance, it ranges from about 2 to 5’ below typical ground level. If a footer is not placed below that frost line, the alternate expansion and contraction of the earth above the frost line might cause the footer to move-to heave upward or list downward, causing cracks to occur in rigid concrete footers and foundations, with their accompanying ill effects. In general, national building codes recommend that footers should be located at least 12” below the frost line (Ill. 1).

Ill. 1 A footer and foundation below the frost line.

4. The type and condition of the soil must also be taken into consideration.

For example, it's an unwise practice to build on organic type soils such as peat: they haven't the proper load-bearing strength to support the weight of a house. Groundwater content likewise influences the ability of the soil to support weight and greatly affects the installation of proper drainage to prevent water from seeping into lower levels. Be careful not to build over a spot where a large tree root system still exists: the roots will slowly disintegrate, leaving voids that will undermine the footer and lower-level floor. Major tree roots should be removed and the holes left by them filled in and compacted.

Ill. 2 A step footer.

Ill. 3 A straight footer, wall, post, pilaster, and chimney footers.

5. Naturally, the contour of the building site and the distribution of the house's weight can have a major effect on the footer's construction demands. A two-story dwelling with one floor directly above another, even if it weighs the same as a multilevel that's spaced out over more area of ground, will distribute its weight in a different manner-thus the need for a different footer than that of the multilevel. In many cases, footers must be custom designed for lots having substantial slopes. "Steps" are commonly included to compensate for grade differences (Ill. 2). When preparing for a block foundation, as a general rule, the depth of each step should be in a multiple of 8”, which happens to be the height of the standard concrete building block. That helps build uniformity into the foundation so you won't end up having to add a half-course of block somewhere along the top of the foundation, with the accompanying waste and bother.

6. When a full basement is specified for a house, there should be an excavation of proper width, length, and depth to accommodate the foundation walls, piers and support columns, pilasters, entry ways, fireplaces, chimney stack, basement floors, garages, patios and porches, and an adequate drainage systems (Ill. 3).

7. Pour separate footers wherever steel-support columns will be located (concrete columns that support the house's main steel beam or beams). This helps relieve downward pressure and will help prevent the basement floor from cracking. A footer for a pier, post, or column should be square and should have a pin or fasteners to securely anchor the post bottom. Check local building codes.

Ill. 4 A footer with gravel and rebar.

Ill. 5 Footer design.

8. A bed of gravel must be laid under and around the planned footer and foundation wall, no matter which type of footer is used ( Ill. 4).

9. Footers for single-story and one and one-half-story houses should be at least 8” thick and 16” wide; for a two-story dwelling, 12” thick and 24” wide. Larger footers are needed for homes constructed on unstable earth or on filled land. In general, a rule of thumb is that footers be at least as deep as the foundation wall is thick, and twice as wide (Ill. 5). With concrete slab construction, contractors often simply increase the thickness of the slab under the load-bearing walls instead of pouring separate footers. The width of footer and foundation walls should be increased when brick or stone veneer is used on the exterior of the house. A single-story-home footer may go from 8 by 16 to 12 by 24” with foundation walls 12” thick.

The contractor's engineer and local building code should determine the proper footer size and foundation wall thicknesses. In all cases the footer must meet the local building code minimum specifications. When the footer excavation takes place, make sure it's not dug too deep. You don't want the excavators to backfill fresh soil before the footer and basement floor are poured. It's critical to pour both onto virgin soil.

Ill. 6 Footer reinforcement-rebar on chairs.

10. As mentioned before, if the earth on a potential building site is unstable, you would do best to avoid such a lot in favor of another with virgin soil. If you decide to build on a filled lot anyway, have a structural engineer design the footer. He or she may have to go extra lengths to compensate for soil weaknesses.

11. The concrete used in footers should have a strength of at least 4,000 or more pounds per square inch. The footer strength must also meet local building code requirements.

12. Reinforce a footer for extra strength. This applies to all footers, including those for fireplaces and support columns or piers. In normal situations, embed at least three steel reinforcement rebars lengthwise throughout the footer (Ill. 6). Typically, steel rebar should be at least 5/8” thick and elevated from the ground during and after the concrete pouring through the use of "foundation chairs" concreted right in, about every 6’. Thicker steel rebar may be required depending on the application, and on local building codes. The bars are usually situated so they will be covered by a minimum of 3” of concrete at all points. Overlaps should occur wherever the bars meet, and those overlaps should be wired together. The use of 20’ or longer rebar rods will minimize the number of overlaps necessary. The overlaps should occur in straight runs, never at corners, and parallel runs of rebar should have staggered overlaps so two or three overlaps will not occur at the same point in a run. The rods should be bent and continued in single pieces around corners. The local building code may specify rod and overlap dimensions. Vertical support rods for the foundation walls should also be placed in the footer before the footer is poured, so those rods are securely anchored.

13. If you're going to have solid poured concrete foundation walls, consider placing a 2” keyway in the footer. Once the footer is poured and setting up, a 2” keyway can be formed into its top to allow the solid poured concrete wall to have a solid water resistant connection with the footer.

14. Allow concrete used for footers two days to set to gain most of its strength before anything is done on top of it. Make sure footers are level, with no visible cracks.

15. Depending on the type of foundation your house requires, there are a number of items that might have to be prepared for while the footer is being installed. These include drains and sewers, plus water, gas, electric, and phone lines. If the necessary holes or trenches are dug for these items while the backhoe/shovel is pre sent for excavating the footer and basement, they can be completed at less cost. The backhoe/shovel won't have to come back a second time, nor will the contractor need costly labor to dig them by hand.

16. Special attention to the sewer or septic lines prior to pouring the footer will prevent basic sewage problems. If your house will be connected to a street sewer, this connection should be made at the excavation/footer/foundation stages of construction. The sewer usually runs under a wall footer and basement floor to the main stack location. If a septic system will be used, the same sanitary sewer pipe installation must be made from the septic tank location to the stack. In any case, you don't want to end up with your house sewer discharge line below the line it needs to be hooked up to.

17. Last, make sure the contractor grades and stones the driveway while the footer is going in-before the construction of the foundation and rest of the house begins. An early graded and stoned drive where the finished driveway will go is convenient for receiving material deliveries and for simply getting onto and off the site in bad weather. It will also encourage the heavy cement trucks needed for the footer, foundation, and basement floor to pack down the gravel and earth driveway long before the finished driveway will be poured or asphalted. All of the heavy equipment and delivery traffic will result in a stronger driveway base.