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posted: 12/8/2012 8:00 AM

Home fix: Add joists, beam to correct sagging floors

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By Dwight Barnett

Q. I have an older home with a crawlspace foundation. My problem is the floors sag in the living room to the point where it's hard to keep a lamp steady on the end tables.

My other problem is there is no room in the crawl to work; the house is about 6 inches off the dirt floor. One contractor wants to jack the whole house up and put in a new foundation but that's more than I can afford and more than the home is worth. Is there a way I can fix the floors myself without digging out under the home?

A. I have inspected homes like the one you are describing and, yes, there is a solution, but the repairs will take time, effort and cash. The best way to approach the problem is to remove all the flooring and floor coverings in the room to be repaired. This will give you direct access to the floor joists.

Older homes were often constructed with the materials at hand and little consideration was given to the proper size, spacing and length of the floor joists. As an example, 2-by-6-inch No. 2 grade wood floor joists set 16 inches apart can span up to 10 feet 4 inches, whereas a 2-by-8-inch floor joist can span 14 feet and a 2-by-10-inch floor joist can span 18 feet. Span indicates how far it is between supporting columns, walls, beams, etc., and depends on the type and size of lumber used. I would suspect you have a 2-by-8-inch floor joist that is over 14 feet from the exterior foundation wall to the center beam. The weight of the floor decking and furniture will cause the joists to sag.

Another cause of sagging floors is decay, termite or wood-boring insect damage. Being so close to the ground, the lumber may be so damp that the wood has lost most of its strength. The waterlogged wood fibers will stretch under the weight of the floor above. Once the flooring is removed, have a pest control company inspect for insect damage and treat the foundation if needed.

Once you have determined the cause of the damage, you can begin to replace each joist as needed. It is extremely difficult to change the size of the joists without compromising the strength of the wood. You can, however, add a beam halfway between supports to reduce the overall span of the joist. This will give you a structurally sound floor system. Do not attempt to raise the old joist or to take the sag out of a support beam. Add new joists and new beams wherever possible and most importantly place a 6-mil thick plastic vapor barrier over the soil to prevent future condensation problems.

• Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at C. Dwight Barnett at d.Barnett@insightbb.com.

Scripps Howard News Service

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