Raised basement theatre room sub floor - AVS Forum
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post #1 of 13 Old 05-20-2010, 02:33 PM - Thread Starter
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Hi all,

I've been slowly building my theatre for a couple years now and I have finally had enough with the floor in my theatre room. It is in the basement of a 33 year old house and the concrete floor is quite unlevel, sloping towards the back left of the room.

I have been contemplating tearing up the flooring and using self-leveling cement to try to correct it, but lately I've been thinking of going a different route.

I was thinking of building a 2x6 wood subfloor over the entire floor of the room. I would have it carpeted with a rounded nosing where you enter the room so it would look nice. I have enough clearance in the room as it's got 9' ceilings. This way the floor would be leveled, it wouldn't be as cold, there wouldn't be as much reverberation from the concrete, and I could incorporate a sand filled "stage" inside the floor at the front as well as conduit and ducting within the flooring.

Would this be a "no-no" or would this actually be good? I had come across an article a while ago that stated:

An additional benefit of a raised wood subfloor is that it absorbs some low frequencies, which is good. Otherwise, these frequencies just reflect off of the original concrete floor. A wood floor also vibrates with low frequencies, to some extent, creating a more-tactile experience. A raised floor that has at least a 3- or 4-inch air space under it will vibrate even more. This technique is used in the screening rooms at Lucasfilm and Dolby Labs. Anthony's and Russ' clients like the added low-frequency feeling as the subwoofer's bass energy transfers through the floor.

Excerpt taken from:

w w w.hometheatermag.com/bootcamp/140/index1.html

Thoughts? Any help would be much appreciated!

Thanks!
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post #2 of 13 Old 05-20-2010, 02:58 PM
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Yes, I would very much recommend a raised subfloor. In fact, I'm going to be putting one in my basement rooms in a couple of weeks when the drywall is finished. I am putting Platon underlayment down on the concrete and then some 3/4" OSB T&G sheets on top of that.

If I were you, I'd just put the subfloor right up against the walls (with a 1/4" gap) and forget about the rounded nosing. Carpeting would also go wall to wall. Trim it with some baseboard molding and you're done.

Leveling the floor is recommended. I have a few spots that are low by 1/4" or slightly more, especially as the floor slopes down towards the sump pit. My plan is to just lay strips of the Platon underlayment on top of each other in the low spots to bring everything level. Or at least close to level. Doesn't have to be perfect, because the concrete screws (Tapcons) will pull everything down tight anyways. When the carpet goes on top, you won't notice the slight dips or sloping floor at all.

Anyways, bottom line is that subfloors are almost a necessity for basement rooms, at least around here. Another benefit is that if you get any moisture on the concrete (minor floods due to sump pump failure or water tank leakage), the subfloor will be lifted above it and stay dry until you can drain the moisture out.

I'll be installing my floor in a few weeks, so you can see the progress and method in my build thread (link in my signature). Others also have documented their subfloor installation, so you can look around some of the other build threads for help.

--Drew


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post #3 of 13 Old 05-20-2010, 05:18 PM
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I can't imagine using 2x6s for the subfloor unless your floor is about 5 inches out of level and you intend to cut the 2x6s down to level the floor.


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post #4 of 13 Old 05-20-2010, 05:59 PM - Thread Starter
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I was thinking a 2x6 subfloor because it would give me enough room to insulate it, run some conduit, HVAC vents, and I think it would add a nice dimension to the room with a step up when you enter it. The only drawback is the wife won't let me frame the room in completely and add a door to it, so I'm limited to what I can do and it has to look nice, almost as a raised living room would look.
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post #5 of 13 Old 05-20-2010, 06:04 PM
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I overlooked the OP's "2x6" idea. I agree that it would be a bit of a waste of ceiling height to raise the floor that much. My opinion stated above is to create a subfloor of approximately 1" overall height.

Then again, I do like the idea of a raised "living room style" floor with HVAC ducting and such underneath. That's fairly original and I'm not sure there are any other drawbacks (besides a loss of ceiling height and overall cost of doing insulation and ductwork).

Definitely not the worst idea I've heard.

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post #6 of 13 Old 05-20-2010, 06:33 PM - Thread Starter
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Quote:
Originally Posted by Drew_V View Post

Yes, I would very much recommend a raised subfloor. In fact, I'm going to be putting one in my basement rooms in a couple of weeks when the drywall is finished. I am putting Platon underlayment down on the concrete and then some 3/4" OSB T&G sheets on top of that.

If I were you, I'd just put the subfloor right up against the walls (with a 1/4" gap) and forget about the rounded nosing. Carpeting would also go wall to wall. Trim it with some baseboard molding and you're done.

Leveling the floor is recommended. I have a few spots that are low by 1/4" or slightly more, especially as the floor slopes down towards the sump pit. My plan is to just lay strips of the Platon underlayment on top of each other in the low spots to bring everything level. Or at least close to level. Doesn't have to be perfect, because the concrete screws (Tapcons) will pull everything down tight anyways. When the carpet goes on top, you won't notice the slight dips or sloping floor at all.

Anyways, bottom line is that subfloors are almost a necessity for basement rooms, at least around here. Another benefit is that if you get any moisture on the concrete (minor floods due to sump pump failure or water tank leakage), the subfloor will be lifted above it and stay dry until you can drain the moisture out.

I'll be installing my floor in a few weeks, so you can see the progress and method in my build thread (link in my signature). Others also have documented their subfloor installation, so you can look around some of the other build threads for help.

Thanks Drew, I'll keep an eye on it. Lookds good so far, I wish I could start from a blank canvas like that. Maybe in the next house... :-)
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post #7 of 13 Old 05-20-2010, 06:40 PM - Thread Starter
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Quote:
Originally Posted by Drew_V View Post

I overlooked the OP's "2x6" idea. I agree that it would be a bit of a waste of ceiling height to raise the floor that much. My opinion stated above is to create a subfloor of approximately 1" overall height.

Then again, I do like the idea of a raised "living room style" floor with HVAC ducting and such underneath. That's fairly original and I'm not sure there are any other drawbacks (besides a loss of ceiling height and overall cost of doing insulation and ductwork).

Definitely not the worst idea I've heard.

The more I've looked, the more I'm thinking this IS a fairly original idea, as I pretty much can't find anything like I'm thinking of. Like I said earlier, most basements are 8 foot ceilings, some only 7 foot, and I've got 9 feet to work with so I am really confident I won't have a problem. Now, if I ever decided to build a bulkhead, that might change, but for now it's not on the list. If anything, the only thing I might do to the ceiling in the near future is a second layer of drywall on Hat Channel with clips to gain some more soundproofing between the theatre room and the bedrooms above.
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post #8 of 13 Old 05-20-2010, 06:48 PM
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I think you're right about the reasons why you don't see this type of floor too often. Besides the 7 and 8 foot ceilings, most people want to have as much headroom as possible in their HTs, so cutting 6 inches off of it for the floor isn't too desirable. Some folks even have 10 foot ceilings in their non-basement HTs. Most people would kill for 9 foot ceilings.

Anyways, it's your theater and you can do whatever you want with it. If the benefits outweigh the drawbacks, then go for it.

--Drew


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post #9 of 13 Old 05-22-2010, 12:08 PM
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TMC,

Long Post but...

This is what I did to my room. I was about 1/2 done with my first theater and we went out of town in the spring of 2008. The electricity went out during a heavy storm and when we came back to town on sunday I went down stairs. The sump pump had backed up and flooded the whole basement. Wicked throughout the carpet, up the drywall and it was trashed.

I had plans of a back up sump, drainage set up but did not get to it. I figured I had time.

I gutted the basement down to the foundation blocks and have been working on it ever since.

It was the only room in the house that the wife gave me so I started over.

Here is what I did:

1. My room was 19' x 21' open floor plan with Heating, Sump Pump, and water softner againt one wall.

2. I built a wall with a door to separate all of this from the final room leaving an 19' x 16' space to work with. The HVAC room is 5' x 19' for my HT.

3. From Floor to Ceiling I had 8' 4" so I could sacrifice a few inches.

4. The stairs comes down and the HVAC room is to the right and the Theater Room is to the left.

5. I made a small hallway as you come down the stairs that was 4 wide between the HVAC room and the HT.

6. Then I basically built a framed a regular 2"x 4" 16" On Center studded wall and laid it on the floor with treated lumber and pink gasket for the entire 19 x 14 space leaving 1" away from the foundation blocks.

7. I still strapped down the wall to the concrete with Tapcons so it would not move.

8. I completely sealed around the perimeter on both sides of the platform and drilled some 2" holes every 24" in the studs in the middle of the internal studs for airflow (Explained later)

9. put down 2 layers of foam gasket (pink)(helped with squeaks) on each stud and screwed down 3/4" plywood and caulked all the seams with 50 year caulk.

10. Then another layer of 3/4 Plywood with 3 tubes of Green Glue per 4 x 8 sheet.

11. Then built walls on top of that staying 1" away from foundation and rubber under the bottom plate and these for the top plate and the joists.



12. resilience and clips for ceiling

13. Backer boxes on all lights, switches, outlets.

13. 2 layers of 5/8" double drywall with green glue walls and ceiling.

14. Insulation in walls and ceiling.

15. layer of Mass Load Vinyl on floor under Carpet.

16. Ran HVAC from other room through some soffits I built inside the Double Drywalled room.

17. In the HVAC room I have a high out put dehumidier that circulates air around the outside of the room and is split and piped in and out of the subfloor to circulate dehumidfied air.

18. The hallway is Tiled like a bathroom with a 3 inch tile trim that runs the whole length of the subfloor.

I was not looking for 100% soundproof room and so far nothing vibrates upstairs which is good.

The door is my next project to keep the sound in the room.

There is a small stage that is filled with sand on top of this and the sub is isolated with a 4 inch Auralex SubDude-Like board on the stage.

I have a riser as well for a couch and 2 recliners for front.

I believe final demensions for ceiling height is:

Riser area 7'
Main Floor 7' 8" (Still Taller then my parents unfinished basement)
Soffit 7'

I know I lost some ceiling Height but in a test, I took a hose and ran water to test and it worked great.

We'll see when I get the door in an run some sound tests to see if the floor causes some booming but without the door so far so good.
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post #10 of 13 Old 05-22-2010, 03:39 PM - Thread Starter
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Wow, thanks for the info. Do you find the 2x4 gave you enough height or does it feel funny stepping onto it? Why did you run ventilation through it? Do you have a lot of humidity where you live?
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post #11 of 13 Old 05-22-2010, 05:24 PM
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Yes there is some good humidity in the spring/summer. The Dehumidifier keeps the basement between 25-35% in the summer. Was in the high 60% in the past

I have a large-whole house one



The ceiling height- I am use to it now but it is really only about 4 inches shorter than 8 feet. I think the soffit makes the illusion that it is higher in the middle, but any black ceiling can make it look small (even a normal ceiling)
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post #12 of 13 Old 05-23-2010, 04:22 PM - Thread Starter
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Thanks for your insight, I appreciate it. One concern I think I forgot to include in my original post was regarding having the sub on the concrete floor. I have heard from some people that having a sub on concrete creates a much different experience than you'd get from a sub placed on an insulated wood floor. Is building this subfloor going to get me any difference in the way my sub sounds and feels vs leaving it on the concrete floor (my whole floor is covered in laminate with an 8x12 area rug - very bad for acoustics, I know)?
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post #13 of 13 Old 05-23-2010, 04:38 PM
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As far as I can tell from reading through the various build threads, nobody has their subs on the bare concrete. It's either on carpet or over a subfloor.

I'd be surprised to hear if anyone says they've got their subs on the bare concrete.

--Drew


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