Should You Worry About Sloping Floors?

Written by Posted On Thursday, 08 February 2001 16:00

If you're buying an old house with sloped floors, here's what you're getting:

  1. Extra charm at no additional expense (the owner's perspective)

  2. A structurally-unsound home (the inexperienced home inspector's perspective)

  3. An ability to hose down your dining room floor (the practical homeowner's perspective)

In most cases, none of these choices is quite accurate. Sloped floors are common in older homes, and even in homes as new as 15 to 30 years.

Sloping floors are most often caused by normal and acceptable deflection (bend) in the wood joists which comprise the floor structure. In some cases, the slope is caused or aggravated by similar deflection in the girder (main bearing beam) that supports one end of the joist sets - but even this scenario there is usually not a problem that needs repair.

As an organic material, wood joists are prone to deflection under load. However, the amount of bend or deflection allowed by most building codes (typically joist length divided by 360) does not address the nature of lumber to "creep." Creep, in this sense, means to nominally bend over a prolonged period of time.

A new floor design that satisfies code requirements for bearing capacity and rigidity (resistance to bend), may still be appreciably sloped after many years of service. The likelihood a given floor has for bending is affected by many factors, but the most common primary cause is simply old age. Pronounced floor slopes can, however, be an indication of a structural problem that needs attention. If you are considering a purchase of any home with noticeably sloped floors, consider these four factors:

How old is the home?

Expect to find more slopes in an older home. Even a slope as great as an eight-inch per foot in an 80-year-old home may be no problem, while any readily discernible slope in a 5-year-old house would be reason for concern.

What is the direction and shape of the slope?

Floors that dip in the middle are usually caused by non-structurally significant joist deflection, but sloped or tilted floors that are straight (i.e., slope in one direction) may indicate a more serious foundation or bearing wall problem.

What are the joist sizes, spans, and spacing?

Assessing the design of a floor system usually requires a professional engineer, but as a gross general guide, joists that are 2" x 8" and are set 16 inches apart (standard), are suitable for spans of up to about 12 feet; joists that are 2" x 10" at the same spacing are suitable for spans of up to about 16 feet.

If you have sloped floors with 2" x 10" joists which run 18 feet between the end supports, you probably have or will have a problem.

The species and grading of the lumber also impacts in span ability; the Western Wood Products Association has an easy to use on-line span table at . (This is a "PDF" file which requires a free Adobe-brand reader to view.)

What wall crack patterns accompany the slopes?

Some wall cracks can indicate evidence of an on going problem. Look carefully at the interior door frames set in partition walls parallel to the joist runs. Look for diagonal crack patterns extending from the top corners of the doorway. Hairline cracks, or cracks that have been sealed indicate stability (assuming the house has not recently been painted), while larger newer cracks indicate a possible problem. If the house has a bathroom next to the sloped floor room(s), look at the wall tiles.

Ceramic tiles are non-resilient and will crack readily, so they are often good indicators of movement. For example, in a 100-year-old house we may not pay much attention to moderate floor slopes, but if the same house has a new bathroom with large cracks in the wall tiles, we know that the movement has recurred or worsened since the new bathroom installation -- this may be a problem.

Most importantly, if in doubt, consult an experienced home inspector and/or a registered engineer. While most sloped floors are simply "charming," such slopes can also indicate a serious problem.

For more articles by Andrew Kleeman, please press here .

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