basementbeamconcreteframing
I recently bought a house and it has an unfinished suspended garage (big concrete room with 12’ ceilings in the basement under the garage).
The walls, floor, and ceiling are all concrete and there are steel I beams in place for extra support.
I’d like to finish it and turn it into a theater room, but it isn’t framed. Given that the framing would not need to be load bearing, can I get away with something cheaper than 2×4’s? Or am I going to regret cutting this corner.
This will likely be a location specific issue, so it doesn't hurt to check your local codes.
All the fire rated work that I've done has been between units (both to other units and common areas) and any load bearing structures of a multi-unit dwelling. When we do that, fire blocking is installed in the ceiling space as well to prevent a fire from traveling through the ceiling to another unit. For everything else within a single unit, and in a single family home, we don't use any fire rated drywall.
Edit: A few reasons I'd disagree with Eric on this one. First, I'm presuming you already have a certificate of occupancy (or someone did) to move in with an unfinished utility room. That required an inspection that presumably allowed the space as is. Next, most codes for combustion devices (furnace, gas hot water) require that you have ventilation. Installing a vented door is perfectly acceptable and won't provide any fire stopping. And, finally, most HVAC's (if the furnace is forced air) will be connected to vents that run to every room in the house. From the little I saw, the furnaces and utility rooms in searches likely referred to multi-unit dwellings, and that does need to be fire stopped. You also have to use fire caulk around every hole. Our multi-unit buildings also have sprinklers throughout and spring loaded vents that snap closed in event of a fire.
That all being said, there's absolutely nothing bad about installing fire rated material around the furnace, other than the extra cost and that it's a bit more difficult to cut. If you want to do it, then by all means, do so.
Edit 2: One last note, realize that fire rated drywall increases the resistance from 30 minutes that you'd typically see with 1/2" drywall to 1 hour. Fire rated doesn't mean fire proof.
If the ceiling is not structural and is only there to hold up the drywall, you can get away with using 2x4s. 2x4s at 16" on center should easily span 11', while supporting only drywall.
Basically your going to support the ceiling rafters with the walls, so you end up with a structure like this crude MS Paint image.
The basic idea is to build a room inside your room.
If you are planning on using recessed lighting or HVAC ducting in the space, you may want to go with 2x6s for the joists (to allow enough room to install everything).
If the ceiling joists are going to be load bearing (especially if they are supporting the parking surface of your garage), you'll want to consult a structural engineer (and you'll likely end up using I-beams tied into the concrete walls as joists).
Best Answer
There aren't many options for framing cheaper than basic 2x4 lumber. You could go down to 2x3 which is sometimes cheaper but you'll find that interior doors and insulation are generally sized for 2x4 walls with 1/2" drywall.
You could also consider metal studs. These are available down to 1.5 inches in thickness (fine if all you want to do is hide the concrete.) The cost is often slightly higher than wood, but you won't get mold if the space is still a little damp. They are also usually available in longer lengths (owing to their primary use in commercial spaces) and they are always dimensionally straight. Installing metal studs goes really fast once you get a hang of it, but again doors can be difficult.