Hi,
Since my HT room is already paint and carpeted, I would like to build a soffit without using drywall. It is also because I have no skills with drywall, but even if I did, would want to risk the mess. I thought I came across some people making it out of MDF. If this can be done, what it the best way to finish/texture it or is this necessary? I have a very dark purple ceiling so would just painting the MDF in this do the job?

Any help/advise/comments are greatly appreciated.

What is the soffit for? Aesthetics? Or a function e.g. HVAC, lighting, etc.

If just aesthetics, consider using fabric and turning it into a bass trap like this diagram Sandman made me:
http://i167.photobucket.com/albums/u129/dc_pilgrim/soffit.jpg
Or a variation I looked at for my rear soffit (my side soffits are plastered as they contain HVAC):
http://i167.photobucket.com/albums/u129/dc_pilgrim/soff_new-1.jpg
I don't have a decent pic of my rear soffit, but it is essentially wood for the side, and MDF for the slats. The MDF will be covered by fabric, and we are planning to add joint compound to the wood so that the painted part will blend with the other soffits that are plastered.

Good luck.

If you are doing fabric put it on before the crown molding that way you can staple it to the wall hiding the staples, then pull it over the lip and staple the fabric on the over hang before putting on the crown modeling.

I built my soffits out of MDF, the side is covered with 5/8 drywall. This was easy since my ceiling is a float ceiling. I had to use caulk between the drywall and ceiling. The MDF option is a good one you don't have to have drywall.

Thank you Dave and Don.

First, to answer Dave's question, it is plainly for astechtics. However, I do have a register close to the wall on the ceiling and I have a small trap door on the ceiling in one of the corners. To not move the return register I was hoping not to completely create a box soffit, but where the crown/rope light will be, to make it a half, i.e. so that side does not go back up to the ceiling. Will that work?

OK, so if I understand correctly, I can use the MDF and fabric (what type of fabric) to cover the MDF, no paint or dry wall needed?

Fabric - I think that there is less pressure for treatment fabric to be AT (accoustically transparent) - so you could probably use almost anything. People here commonly use GOM or Dazian (Expo or Celtic or Janus), as they are AT (important for screenwalls w/speakers behind) and fire treated. GOM has tremendous variety, but isn't cheap. Dazian is cheaper with less selection.

For the register - you probably could extend it, or carve it out like you suggested. If you put fabric over it, it would become a dust filter. For your trap door, you can make a removable fabric panel, then put any treatments in a bag on a hook or something (or omit).

If the fabric covers both the bottom and side of the soffit, then no paint or drywall is needed. I might paint it the same color as the fabric anyways so you don't get any bleedthrough the fabric if its not thick enough.

Don is right - if fabric, plan your staple strategy.

I built a pretty soundproof design, and therefore didn't want any penetrations in the box of drywall I built. Problem was, when I finished the room with drywall, I could immmediately tell the issues with the acoustics, and planned on adding controls. Wound up building frames (cut down 2/4s) and added 4" of rigid fiberglass as a soffit running 3/4 of the way round the room. Covered in GOM material to allow sound in to be trapped and absorbed by the fiberglass. worked like a champ. The soffits also hold recessed lighting which provides a cheap solution to lighting but with the design, avoids having the holes penetraing the solid walls of the room.

Good luck.

Jeff,
So you built the soffit out of 4" fiberglass? How was that done? Please post pics if you have. I am looking more towards Sandman's and Dave's designs because I want to drop my fiber-optic starlight panels on the lip or the crown.

Trade -

Looks like Jeff built a wood frame around his insulation, then covered in fabric.

If you go crown instead of light tray, I recomend putting a 1x1 on the side of the soffit and attach the crown to that (not in my diagram). It protrudes the crown into the room a bit, making a nice healthy channel to rest the rope in. Can work w/o it, but I think its better. You can see the wood in this pic (mine is raised, as I will be adding more trim after the fabric is stapled):

http://i167.photobucket.com/albums/u129/dc_pilgrim/thinker.jpg
Here is the rope in action:
http://i167.photobucket.com/albums/u129/dc_pilgrim/bluefront.jpg
Oh, and paint the crown before you hang it (oops).

Thanks Dave, I have opted (the boss made the decision) to go with star fiber optic ceiling so I will be going that route instead of the rope. I am looking to make the star 12 x 8 with about 4 fibers per sq/ft. The cost is not bad at all, actually would cost less than the crown, I would have used for the rope channel. Therefore, I may choose to go with Sandman's variation you posted and rest the 8' ply across two channels. It may (will) have a belly so I need to figure a way to prevent that.

Good decision. I love the star ceilings. More of a down the road item on my list. Good luck. Lots of good stuff in Ruben and Swithey's thread on the star ceilings.

yep, didn't think it was affordable and I WOULD NOT (sorry :-) do halogen, so now that LEDs systems are affordable, it is an easier decision.

BTW, I noticed in Sandman's "T" joined area and your "L" joined area, you both didn't use any extra 2" x 4' support. Were screws already holding these in place firmly? i.e. are screws (and wood glue) adequate for MDF at these locations?

What ever you choose to do, I highly recommend caulking seams, green glue if you can and glue. Seal everything build it like a submarine...

Hi Don. I have seen this advise before but I am not sure what seams we are talking about.