"Dave" wrote in message
om...
(Or How to correctly shim floor joists)

The existing 2x8 floor joists on my 50+ year old home are 7 1/2
inches. The 2x8's I plan to sister next to the old ones are only 7
1/4 inch.

Can someone tell me the approved method for shimming the difference
between the joists.

Why are you "sistering?"

If it is because the old wood has been damaged and you need "good" wood to
hold up the floor they you align the TOP of the new wood with the top of the
old wood.

If your floor sags too much under load or you would to jack it up and then
attach the "sisters" you should align the BOTTOM of the new wood with the
bottom of the old wood.

If you have BOTH problems, you should consider getting the next size up
(10") and ripping it to match the existing wood. Alternatively, you can
rip out some 1/2" (or whatever wood and glue it to the TOP of the new wood.

Wood tends to be more "spingy" is tension than compression so you add sound
stuff to the tension side of the beams (bottom, in your case) to stiff the
floor.