Q.: The city is giving us trouble about an 8-inch-thick, cast-in-place reinforced concrete wall we want to build. They say we have to show them a fire rating for such a wall from an established agency, though they say they are ready to accept an 8-inch concrete block wall.

A.: Page E-80-1 from the so-called "Green Book" published by the American Insurance Association gives estimated ratings for reinforced concrete. For the least fire-resistant cast-in-place concrete (that is, concrete made with siliceous or what they call Group II aggregates) the rating is 4 hours for a cast-in-place wall 7 1/2 inches thick. A 5 1/2-inch wall gets a rating of 2 hours. The "Green Book" may be obtained from the Publications Department, American Insurance Association, 85 John Street, New York, New York 10038. The price is $4 per copy, but residents of California, Illinois, New Jersey, New York, Pennsylvania and West Virginia are required to include the amount of their state sales tax.