Help with raise floor

[newood2]

Our church is building a sound booth in the back of the hall and we want to raise the booth floor 18" from the main floor. The size of the floor will be 8' X 8'. How do I go about building the floor joist? Should I use 2 X 4's or 2 X 6's, and how do I frame it out. Does anyone know how, or know where I can find a plan or layout diagram? I have no idea how to frame out a raise floor, I only know that plywood goes on top.

Howie

[Crash2510]

it depends is it going to be connected to the walls? Also what kind of floor will be supporting it? Concrete, wood?
We could help you a little more with some more info

[drumpriest]

Assuming that you are talking of wood construction, you would build a torsion frame for under the plywood. We typically use 2x8 or 2x10 as floor joists, even then there is some deflection over a long span. 16" centers with blocking in between to ensure reasonably good alignment. You can build it like a deck depending upon the floor. If the sub-floor is concrete, you can attach posts to it (pressure treated if in contact with potentially moist concrete), then build a platform floor such that the top will be 18" up.

[LarryG]

For an 8' x 8' room, you can use 2x8 joists. If you support them at mid-span, you could use 2x6s but that'll be more labor and the material costs will probably be a wash.

We specify that pressure-treated material be used for ALL wood in contact with ALL concrete, no matter how dry it is.

We typically call for two layers of 5/8" plywood for the floor decking, with the joints in each layer offset from each other.

Fill the joists spaces with batt insulation, for sound deadening. An elevated floor structure in close proximity to another floor below it is typically pretty boomy.

[crokett]

Howie,

Frame in an 8'x8' square with 2x8s. This square is your rim joists. Rip an 8' 2x4 in half and attach to the bottom of the inside face of opposite sides of the rim joists to create a ledge. Notch the corners of the rest of your 2x8 joists to fit around this ledge. Drop these in at 16" centers so the notched corners are sitting on the ledges. Cover the framing with your decking. Ply decking is better than OSB sheathing but is more expensive.

[newood2]

Thanks guys, I got some ideas from your responses on how to do this. The main floor is wood and the raise floor will be wood. The booth will be in the back corner of the church where the side and back walls meet.

I'll go with the 2 X 8's with 16" on center between joists.
But do I need two layers of 5/8" ply on top, I was thinking of using layer of 3/4".

Howie

[crokett]

Howie,

The 3/4 should be enough. That 1 outside corner is going to need a post for support. What you want to do is attach one of your rim joists to the wall and level it. Then attach the other to the wall and level off the 1st one. Then build the other half of your square and level it. Pin a 2x4 at that outside corner to hold it temporarily at the correct height. Then you can cut a 4x4 that the outside corner can sit on top of.

[LarryG]

If you use a single layer of 3/4" ply, you'd need to decrease the joist spacing to 12" OC. (I should clarify that I'm talking from the standpoint of a design professional who always likes to see good, sound, normal construction practices. A single layer of 3/4" over 16" OC joists will work, but for something that's going to be there for a long time ... IMO it's a corner not worth cutting.)

[crokett]

Larry, we may have to agree to disagree. Not sure what code is in your area but my dad's addition passed inspection with 3/4" ply subfloor over joists 16" OC. It would have passed with OSB but my dad wanted the ply since he was putting down hardwood floors.

My house is pushing 40yrs and is built the same way. The floors are still in great shape - only prep I had to do for the glue down wood floor in my daughter's room was fix a few squeaks where nails had backed out.

Plus, this is a structure that is going to get used but a few times a week for a few hrs at atime.

Howie, whichever option you choose use construction adhesive to glue down your decking then back that up with deck screws.

[os1kne]

I'm no engineer, but I suggest that you over-engineer the support of the stage area if there is any chance that it will be called upon to support a great deal of weight. I've seen some choirs where 40 people (most with considerable mass) were crammed shoulder-to-shoulder into an area about the same size as your stage.

The stage may not support much weight most days, and will likely only need to support weight for a short period of time on the days that it is used - but you'd hate for it to collapse when it is used.

Good luck!

[atgcpaul]

16" on center would do it, but if you take it to 12" on center, you're talking
about only 2 more floor joists and a only a little more hardware and work.
Since it's just a sound booth where there will be stationary equipment and
probably only enough space for a few people, 16" OC should do it with 3/4" ply.

[newood2]

Thanks a million guys. Think I'm ready to do the project.

Howie