Raising basement ceiling strengthen joists ??

[Bob Crooks]

I have a house built in 1940 that has a 6'3 basement ceiling that I want to raise .It has 2x10 yellow pine ?? joists on a 16 in center with a 14'0 span .I want to leave the floor joists in place and cut them down to say a 2x4 or 5 and sister them with some material to strengthen them..Question is what should I use ?Microlam ??Plywood ?? Steel plate ??.I want to of course keep the structural integrity but I need the additional height .This seems like an easier route to go than lowering the floor .The only thing above is the living room with only minimal furniture and no other load bearing walls .Any help is appreciated !!!

[Richard A Hetzel]

Not possible. Joist strength is principally a function of the joist depth, so reducing the depth is going to reduce the strength, and will probably mean more defelection and less stiffness. At best, you would probably need steel channels in both sides of the joists, carefully bolted through them in a particular pattern. Plywood is worthless, microlam doesn't come in small depths, and steel plates strong enough to do the job would possibly be heavier than the channels.

This is a job for a structural engineer, or a competent architect. By the way, whatever is above them, such as furniture, is not how structures are designed. Building codes require designing for a certain live load, probably 40 pounds per square foot in your case, and at least the dead load of your resulting structure, which could be well in excess if 10 pounds per square foot. A party with lots of people could easily produce loads close to the code-required loads.