Expert: Dan Griffin - 2/23/2009

Question
I am trying to suspend something form the joist in my roof, I have access to the attack and the joists are 2x4's. My question is if i place a square tube ontop of the joist's and tap into the tube to hang my item, how many joists should i place the tube along? would 3 or 4 be okay? also the item I am hanging is about 150lbs, but it's going to have a max weight of about 700-800 lbs.

thanks


Answer
Raman,

I'm sure you meant that the eeiling joists in the attic are 2x4.  The really big deal here is how long are the 2x4's and what are they sitting on?  Are you talking about hanging something out in the middle of the 2x4's?  The next big deal is how heavy a tube are you talking about?  What on earth are you hanging that will weigh 700 pounds?  2x4 are not strong enough to carry a ceiling by itself over 8 feet on 16" centers.  An additional point load at mid span will probably bring it down.  I would not increase the load on that ceiling system unless the load was close to one of the bearing ends or the room was notably smaller than 8 feet across.

It would be best to use a heavy enough steel beam or doubled up lumber header that will span from wall to wall above the joists. Use solid blocking to raise the beam high enough.  Doubled 2x8 would have good control of that type of point load even at mid span at around 12-14 feet.