Raising concrete floor... best acoustic solution?

[atomicus]

I am planning to convert my garage in to a small home cinema. It's not the biggest of spaces, and will only be about 2.4m x 4.5m when completed. The floor is solid concrete which needs to first be leveled. I assume it is fine to do this with leveling compound?

Once this is complete, I need to raise the floor approximately 180mm so it's level with the hallway. What is the best method for doing this and what would be the best combination of materials to use? There seems to be a bewildering array of products on the market, and I see recommendation and condemnation of them all in equal measure it seems lol!

I have seen some very expensive and complicated solutions for floors, but I am somewhat limited by budget... flexible, but I don't have thousands to spend on it alone, as much as some people may say I should.

I will be going with a room within a room setup, so my stud walls will be built off the floor, with new ceiling joists off these, entirely decoupled from the existing brickwork.

Any advice would be much appreciated.

[Soundman2020]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

will only be about 2.4m x 4.5m when completed

Height? Sound is 3D, not 2D, so height is important too. In fact, height is VERY important.

I assume it is fine to do this with leveling compound?

Right.

I need to raise the floor approximately 180mm so it's level with the hallway.

That implies LOSING 18cm of ceiling height. That's a lot. Unless your ceiling is very high already, then it would not be good to lose height. It would be better to just have one step down into the home theater.

What is the best method for doing this and what would be the best combination of materials to use?

If you really are intent on doing that, then the best materiel is simply concrete. Nothing better.

There seems to be a bewildering array of products on the market, and I see recommendation and condemnation of them all in equal measure it seems lol!

First, you MUST avoid having any type of air cavity down there. If you are thinking of any type of floor that has air in it (such as a raised wooden floor with insulation inside), then that would be a bad idea. That's a resonant cavity, and it WILL resonate at whatever frequencies it is tuned too...

I am somewhat limited by budget... flexible, but I don't have thousands to spend on it alone, as much as some people may say I should.

Then you have basically three options:
1) Don't do anything! just level it, and have a step down. That's the best, easiest, and cheapest.
2) Fill it with concrete 18cm thick.
3) Fill it with loose, dry sand, then put a wooden deck on top.

I will be going with a room within a room setup, so my stud walls will be built off the floor, with new ceiling joists off these, entirely decoupled from the existing brickwork.

Excellent! And that rules out option 3: you can't have your inner-leaf walls resting on a sand-filled deck. That leaves you with options 1 and 2.

- Stuart -

[atomicus]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

will only be about 2.4m x 4.5m when completed

Height? Sound is 3D, not 2D, so height is important too. In fact, height is VERY important.

I assume it is fine to do this with leveling compound?

Right.

I need to raise the floor approximately 180mm so it's level with the hallway.

That implies LOSING 18cm of ceiling height. That's a lot. Unless your ceiling is very high already, then it would not be good to lose height. It would be better to just have one step down into the home theater.

What is the best method for doing this and what would be the best combination of materials to use?

If you really are intent on doing that, then the best materiel is simply concrete. Nothing better.

There seems to be a bewildering array of products on the market, and I see recommendation and condemnation of them all in equal measure it seems lol!

First, you MUST avoid having any type of air cavity down there. If you are thinking of any type of floor that has air in it (such as a raised wooden floor with insulation inside), then that would be a bad idea. That's a resonant cavity, and it WILL resonate at whatever frequencies it is tuned too...

I am somewhat limited by budget... flexible, but I don't have thousands to spend on it alone, as much as some people may say I should.

Then you have basically three options:
1) Don't do anything! just level it, and have a step down. That's the best, easiest, and cheapest.
2) Fill it with concrete 18cm thick.
3) Fill it with loose, dry sand, then put a wooden deck on top.

I will be going with a room within a room setup, so my stud walls will be built off the floor, with new ceiling joists off these, entirely decoupled from the existing brickwork.

Excellent! And that rules out option 3: you can't have your inner-leaf walls resting on a sand-filled deck. That leaves you with options 1 and 2.

- Stuart -

Hi. Thanks for that, very helpful! Sorry, the height floor to ceiling is just shy of 2.7m. That is from the concrete to the underside of the floor above (which is also concrete), old plasterboard ceiling and joists have been removed. My plan was to construct a new joist ceiling off the new stud walls.

Leveling is going to be a pain as it is to be honest, it's a 50mm drop so that's A LOT of leveling compound. If I just got it all re-concreted and leveled that's fine with me. What about insulation though? The concrete is freezing, so just using that as my base floor, even with an intended carpet on top surely won't be optimal?

The other consideration though is surely weight? If I had new concrete poured to level and raise the floor that much, that is obviously a HUGE amount of weight to be adding in there. A question for a structural engineer no doubt, but is doing this overkill in the first place?

FYI, as I am in the UK, I believe I do need insulation to adhere to building regs, so just pouring a load of concrete isn't an option. Exactly what form that insulation must take however I don't know... no doubt there are options there.

[atomicus]

Any further advice on this?

I do NEED insulation due to building regs, so I can't just put down 18cm of concrete without insulation. I believe this could be satisfied by underfloor heating, but that does require insulation board, which is typically stuck to the concrete.

I had considered insulation (Celotex type) under a screed layer but have been told this would create a drum effect... which I obviously don't want.

I believe you can get certain proprietary screeds that have insulating materials in them, negating the need for separate insulation... but the problem here would be the amount required. The 18cm is just at the top end... the 50mm fall means that will be 230mm at the far end, and laying that much screed will literally take months and months to dry. I've spoken to a few screed laying companies in my area and have been told they would NEVER typically put that much screed down.

So I'm a bit unsure what to do. I could look at the floating floor idea again, perhaps a sand filled deck of some sort? Rod indicates in his book these are effective, but he doesn't go in to any detail about them, he only mentions it in passing.

[Soundman2020]

I had considered insulation (Celotex type) under a screed layer but have been told this would create a drum effect...

I don't see why. There are several different grade of Celotex for different purposes. Call the manufacturer, explain what you want to do, and get their recommendation on which grade is best for you. It basically acts as an acoustic damper in that situation (as well as a thermal insulator), so there's no reason it would create a drum effect.

So I'm a bit unsure what to do. I could look at the floating floor idea again,

If you absolutely have to raise your floor, and are given no choice, then yes, a floated floor makes sense. It won't be cheap, but it can be done.

- Stuart -