A.Carl Hagstrom responds: I had a
foundation sub who always claimed that his work was within 1/4
inch. After talking to other builders in my area, I realized
that he meant his work was always within 1/4 inch of being
close enough. While I’m unaware of any universally
accepted standards for foundation and framing tolerances,
the Handbook of Construction Tolerances by
David Kent (McGraw-Hill) lists hundreds of suggested tolerances
for various phases of construction.
According to the Handbook , horizontal building layout
(including the foundation) involves both dimensional accuracy and squareness. For
measurements less than 10 feet, the tolerance is 1/8 inch;
between 10 and 100 feet, it’s 1/4 inch (see illustration,
below). For squareness, the tolerance for the dimension of the
5-leg in a 3-4-5 triangle measured with a steel tape is 3/4
inch in 100 feet. Use the same ratio for diagonals of less than
100 feet. For example, when measuring a 50-foot diagonal, the
acceptable tolerance would be 3/8 inch (one-half the tolerance
for the 100-foot diagonal).
Foundations walls should be level within 1/4 inch in 10
feet, while the entire foundation should be level within 1/2
The Handbook states that there is no single
accepted tolerance for rough framing, although a tolerance of
1/4 inch in 10 feet is frequently used and is acceptable. The
second edition of Standards for the Professional Remodeler
(NAHB Remodelors Council, available from the NAHB Bookstore at 800/223-2665)
requires that walls and floors be plumb and level within 1/4 inch in 32 inches.
This seems overly generous when you consider that it would
allow an 8-foot wall to be up to 3/4 inch out of
In residential construction, acceptable tolerances are often
talked about but seldom specified. Document the accuracy you
expect and give a copy to your subs before they bid the job.
That way, everyone will understand what’s "close