Basement joists support drywall ceiling??
#1
03-18-01, 03:49 PM
I am in the process of finishing my basement. We are framing the walls with 2x4's, and planned to use drywall on both the walls and ceilings. The joists on the floor above are 2x8's, 16" on center, and the subfloor above is doubled up 3/4 plywood. There is some uneveness with the joists (only 1/4" to 1/2", here and there), so I had planned to install strips perpendicular to the joist to attach the drywall ceiling to so that it will be more even. A large portion of the basement space is righ below our kitchen/dining area (where we have installed ceramic tile about a year ago).
The problem I have is that a family member who helping us out with the project says that because of the added weight of the ceramic tile and backerboard on the floor above, adding a drywall ceiling to the basement area will put too much weight on the joists and cause them to sag. He wants to "sister" new 2x8 joists against the existing ones, and replace all of the blocks between the joists. I'm not convinced that this is necessary. The house is only 11 years old, and we have no problems at all so far. Any suggestions?
The problem I have is that a family member who helping us out with the project says that because of the added weight of the ceramic tile and backerboard on the floor above, adding a drywall ceiling to the basement area will put too much weight on the joists and cause them to sag. He wants to "sister" new 2x8 joists against the existing ones, and replace all of the blocks between the joists. I'm not convinced that this is necessary. The house is only 11 years old, and we have no problems at all so far. Any suggestions?
#2
03-19-01, 10:23 AM
The weight of the drywall shouldn't make much differance. But consider the following:
A 4x8 sheet is 32 square feet and weighs 64 pounds (just to keep the math simple). That comes out to 2 pounds per square foot.
It is my understanding that a 2x8 can span no more than 12 feet. If the distance from the foundation to the I-beam is less than that you are in better shape. If you have the blue prints for the house, they should say the psf rating for the floor.
I would agree that you will have some sag- you normally do. The issue I have with the 2x8s is that the floor has too much bounce, which usually causes the ductwork to "oil can". For that reason, I added 3 wood I beams (homemade) beside the ductwork (parallel). That made it very easy to frame around the ductwork. I also screwed 2x3s to the underside of the joists (perpendicular) which helped the bounce, the unevenness, and corrected the spacing (some of the joists were not centered correctly. The 2x3s also give me the ability to run wires thru the ceiling if I ever need to. Any bounce in a tile floor will cause it to crack.
Another advantage of the 2x3s is the recessed lighting I picked. Most cans are 7.5 inches deep, the same as a 2x8. The cans need to be at least 1/2 inch from any combustable surface (non-IC).
My finishing of the basement ceiling with drywall and the solutions above actually firmed up the floor above.
Hope this helps.
A 4x8 sheet is 32 square feet and weighs 64 pounds (just to keep the math simple). That comes out to 2 pounds per square foot.
It is my understanding that a 2x8 can span no more than 12 feet. If the distance from the foundation to the I-beam is less than that you are in better shape. If you have the blue prints for the house, they should say the psf rating for the floor.
I would agree that you will have some sag- you normally do. The issue I have with the 2x8s is that the floor has too much bounce, which usually causes the ductwork to "oil can". For that reason, I added 3 wood I beams (homemade) beside the ductwork (parallel). That made it very easy to frame around the ductwork. I also screwed 2x3s to the underside of the joists (perpendicular) which helped the bounce, the unevenness, and corrected the spacing (some of the joists were not centered correctly. The 2x3s also give me the ability to run wires thru the ceiling if I ever need to. Any bounce in a tile floor will cause it to crack.
Another advantage of the 2x3s is the recessed lighting I picked. Most cans are 7.5 inches deep, the same as a 2x8. The cans need to be at least 1/2 inch from any combustable surface (non-IC).
My finishing of the basement ceiling with drywall and the solutions above actually firmed up the floor above.
Hope this helps.
