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Rules Permit Lower Load Factor for Attic

December 02, 1990|From Popular Mechanics

QUESTION: Three years ago, I acquired an English-style, 1 1/2-story all-brick, all-plaster house, 50 years old and in excellent condition. There is a full attic with a catwalk in the center.

I would like to finish the attic, but it only has 2-by-6-inch ceiling joists, 16 inches on center. I am told the joists have to be at least 2-by-8 inches, 16 inches on center, before rooms can be added.

First, why were houses like this built, and what's the remedy? Can I do most of the work myself?

ANSWER: In house design, the size of the floor joists depends on the distance between the joist supports (span), the on-center distance between the joists (usually 16 inches on center), the species of wood the joists are made of and the loading applied to the floor.

In residential structures, the floor loading is usually designed for a live load of 40 pounds per square foot, with attic floors designed for loading of 20 pounds per square foot. A live load is the load that is imposed solely by occupancy (persons, furnishings and appliances).

The attic's design load is less than the load for habitable rooms because the attic is normally not used for storing heavy appliances or furniture. Hence, ceiling joists are often smaller than the floor joists below.

In determining joist size for a given span, architects use tables that consider bending stress, deflection and stiffness (in order to minimize the springiness in the floor). Your floor joists are sufficient for a 40-pound-per-square-foot floor, providing their unsupported span does not exceed 9 feet, 6 inches (approximately).

To finish the attic properly, you would first need a building permit. Your local municipal building department will probably require you to have plans drawn by a registered architect or approved by a licensed professional engineer.

Difference Between De-Icing Materials

Q: With a large variety of walkway de-icers on the market, could you tell me the major differences between them, and which would be the safest for concrete?

A: According to the Portland Cement Assn., the safest de-icers for concrete are also the most common: sodium chloride (rock salt) and calcium chloride. Both of these de-icers rust metal, and sodium chloride damages vegetation while calcium chloride does not.

The association recommends against using on concrete those de-icers that contain ammonium nitrate or ammonium sulfates.

Paints Product Lasts Longer on Aluminum

Q: I have a home with finished aluminum soffits, fascias, gutters and window trim. I would like to paint these a different color. Is this possible? And, if so, will I be repainting every four years and lose out on the benefits of aluminum trim?

A: Not to worry. PPG Industries has a latex paint specifically formulated for repainting prefinished aluminum siding and trim. It's called Metal Siding Refinish, and comes in a variety of colors to match current popular siding colors. If the surface is prepared correctly and the paint properly applied, it will last for about 10 years.

Brown Spots on Deck Will Not Wash Away

Q: Dark brown spots are appearing in areas of my concrete deck. They don't wash away with soap and water. What causes these spots?

A: The type of discoloration you describe occurs when tricalcium alumino-ferride--the agent that gives portland cement its gray color--has not reacted thoroughly with the other chemicals in concrete. To remove the dark spots, try pouring on undiluted household vinegar. If that doesn't work, try a solution of one part muratic acid to 30 parts water.

Dirty Streaks Mar Siding of House

Q: We have been unable to find anything that will clean the accumulation of dirt and other particles on our aluminum siding. It seems the siding is clean from about 4 to 5 feet down from the eaves. Above that, the siding seems to have a rough or granular surface that will not wash off with a sponge and laundry detergent. What is the best way to handle this problem?

A: Stubborn soils start at the bottom and work up. This keeps hard-to-remove dirty streaks from running down the wall below the dirty under-eave area. After cleaning and washing, it's important that the siding be thoroughly flushed with water.

Special siding cleaners, available at your local hardware store can help. Mildew, which appears as black spots, usually shows up in areas isolated from rainfall. Try using a solution of one-quart Clorox, one-half cup of non-abrasive detergent and two-thirds cup of trisodium phosphate. Rinse the area with your garden hose after washing it.

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