Advice sought: should I build a new concrete floor?

Hi, This is my first post. I'm a newbie; I've read the rules and I'll try to follow them all but be gentle if I forgot something. I'll describe the project below, with the view of getting advice on the following two questions: - should I build a new concrete floor? - should I finalise the layout of the studio before putting the concrete in? The project: ---------- My wife and I have recently bought (and moved into) a house in Bristol (UK), which is a 1930s bungalow with a small annexe built in the 1980s. One of the rooms plus the annexe are to become the studio. Let's call the annexe the "live room" and the other room the "control room", which is the plan so far. The live room will be used mostly as a band rehearsal room but also as live room to record an acoustic drum kit with bass/guitar players playing through amps with gobos. The control room will be used mostly to compose, mix and monitor, and as my office (I'm a university lecturer teaching creating music technology.) The control room will also likely be used to record guitars and scratch DJing (so the layout will need to take into consideration a pair of turntables, a guitar or two and a small amp and pedalboard.) On the floor plan, you can see the annexe in the top right; to its right is the neighbours' wall (about 2metres away aprox, I'll have to measure). Below it on the plan is the room in the house that will be the other part of the studio. The outside walls are 280mm cavity walls, both in the house and the annexe. The live room has: - outside door at the top - double door on the left - ceiling height of 2m70 The control room has approximately the same ceiling height and a 1400mm window (in blue on the plan.) I am planning to build a small WC and a tiny utility room (just big enough for a washing machine) in the left-most portion of the room that will have the control room. You can see their approximate placement to the left of the proposed control room. The live room has a solid concrete floor. The control room had floorboards on joists; I have completely removed all of them all the way to the ground (approx 400mm below where the floor used to be.) Question: Should I build a new concrete floor in the control room and make it level with the existing floor in the live room? My plan so far is: - to build 2-leaf inner-room walls with two different thicknesses of plasterboard on each side with resilient channel on one side - have some form of HVAC with ducts suspended in the attic above the rooms - fit two sets of double doors between control room and live room - fit a second inner double door in the live room to allow access to the garden - fit a second single door to allow access at the far end of the live room - not to have a floating floor (from the great advice on this forum) I will do most of the work myself with the help of friends, but will employ professionals where needed. I have a builder booked to cast the concrete floor in a week. My budget is limited but I have some reclaimed materials) including many 2"x3". I have a small budget (£2000-£3000) but I can always borrow a little if I must. My priorities are: - sound isolation (from the neighbours) sufficient for rock band rehearsals - near-field monitoring - sufficient sound isolation between live room and the rest of the house so that my wife can go to sleep during band practice :) Question 2: is there anything I should plan or know (e.g. total layout) before the concrete floor gets poured? If anyone wants to see, I've also got a SketchUp plan, but I couldn't figure out how to link it on here. Any help and suggestion will be very much appreciated! - martin

HI, Concrete is the only way to go if you can aford it. You will have to get a contrator in to look at the options. Being a new slab you will be able to isolate it form the other studio room. Which is great. Not many of us have that. Before you pour you will need to run conduit for all your cables-mic,line,power,internet plus a few for future works. sit down and work out where and what you will need to run. Use electrical conduit with long wide bends. No water pipes.

Thanks for the very useful reply! I'm glad to know that concrete is a good choice. I hadn't given much thought about where to run the wires, so I'll have to think about that. Out of curiosity, would it not be easier and more servicable to run all the wiring above the "room within a room"? I will have some space above, since there is an attic above the LR and over half of the CR, which are unoccupied (that's where I'm planning to put the ducts for the ventilation.) Cheers, - martin

Hey Martin. Welcome! Luck you! You have bare earth to pour a new slab on! Envy! Envy! I wish I had that luxury... :( Anyway, Lil is absolutely right: Pour that new slab SEPARATE from your existing foundations. Leave a thin gap around the edge of it, to keep it decoupled from the existing structure. You can fill that gap later, with some kind of acoustic material that will seal the gap while retaining the decoupling. And of course, your inner-leaf walls must be built on the new slab, without touching the existing structure at all, anywhere. So the slab needs to be reinforced with metal, and also to have its own foundation / footing / whatever-you-call-it-where-you-live, since it will be supporting the entire weight of the new studio, including walls, ceiling, treatment, furniture, people, equipment, etc. Build it tough! But I did notice something in your post that caught my attention. The way I understand it, there are already some existing walls surrounding this space where you are going to pour the slab. Then you say that you plan to...:

build 2-leaf inner-room walls with two different thicknesses of plasterboard on each side with resilient channel on one side

If I understand you right, that would give you at least a three-leaf system. and perhaps even a four-leaf system (depending on how the existing walls are built). Not a good idea! Your low frequency isolation would be pretty lousy if you were to do that. Your kick drum would probably be heard all over the neighborhood, as would low bass notes. Can you find out how that existing wall is built? Is it something like bricks / rock / concrete block? Or is it built with a stud frame and gypsum board on both sides? The former means it is probably one leaf, the latter means it is two leaves. either way, whatever you have there is your outer leaf. But you need to know how it is built, in order to figure out how to proceed with your inner-leaf. Assuming that it is brick, then all you need for your new inner-leaf wall, is a stud frame with a couple of layers of gypsum board on ONE side of it, not on both sides. And you can skip the resilient channel, too: if you build a decoupled wall (like this would be) then the RC won't do anything extra for you. The purpose of RC is to decouple, but since your entire inner-leaf will already be decoupled, you don't need it. You also don't need different thicknesses of gypsum board (plaster board): the slight gain you get from the different resonant frequencies and different coincidence dips is not really worth the hassle, and is probably offset by the slight loss you get by not using the thickest possible gypsum board everywhere. Use the money you saved from NOT buying resilient channel to buy some Green Glue, and spread lots of that between the two layers of gypsum board. That wil be far more useful than either RC or different thicknesses of gypsum board.

I will do most of the work myself with the help of friends, but will employ professionals where needed. I have a builder booked to cast the concrete floor in a week.

Can you delay that? I would really, really suggest that you not do ANYTHING until you have a complete plan in place. It would be very sad to pour that slab now, then watch it crak later, as you find out that it isn't thick enough to support the weight you need to put on it. Or to realize that you could have run conduit through it. Or that it is coupled to the existing structure because the builder didn't know how to do it right. Or because.... There are many things that could potentially change the way that slab is poured. You are a luck, luck guy, since you have the opportunity to do what many of us only dream about: build the entire studio on a decoupled slab! It would be very sad to see an opportunity like that wasted!

My budget is limited but I have some reclaimed materials) including many 2"x3"

I don't want to seem like a wet blanket, but 2x3s probably wont be any use for you: Perhaps for some bracing, or framing acoustic treatment, or something like that, but not for the structure itself. 2x6 is what Rod recommends in most places, and 2x4 as an absolute minimum. The things you are going to build have to be very massive, meaning heavy. Meaning that you need a sturdy structure to stop them falling down... So the 2x3s might be useful in some places, but not for building walls, and certainly not for the ceiling.

Question 2: is there anything I should plan or know (e.g. total layout) before the concrete floor gets poured?

This may seem a little sarcastic, but it's not meant to be: What you "should plan and know" before the pour is to plan the entire studio, down to the last nail and screw, and to know everything you possible can know about acoustics and studio construction, BEFORE the floor gets poured. Really, this is the single smartest thing you can do in your build: not pour, not nail, not even buy a single stud, until you have the entire design finished, and yo understand exactly why each part is the way it is, and how it all works acoustically. I came here to this forum about seven months ago, raring to go just like you are, and I'm no very thankful that I didn't, and still have not, started building. The design I had in mind back then was lousy. It would not have worked very well as a studio. When I started asking questions here and getting answers, I realized how much I didn't know, so I put the build on hold until I could learn. I'm still learning, but I think I've gotten far enough to start now, many months later. My design is practically ready, but still not 100%. I'm ready to start now, but I wasn't ready then, even though I thought I was. I realize now how little I knew back then, and I see with horror all of the mistakes I would have made. I'm so glad I took the advice that Im offering you: stop the pour, and don't do anything until you have a solid plan in place, with a complete design. For example, even something as basic as your room ratio: I didn't see you mention it anywhere, and it can be very important. What is it? Did you figure it out yet? You can't pour a slab and build walls on it, if you don't know if you have a good room ratio... And there are about a thousand other things like that, that you need to consider. - Stuart -

Thanks Stuart for the very informative reply. That will give me lots to think about. I think I will take your advice and put the concrete pouring on hold and try to design the studio as completely as I can. I should probably mention that there is a time factor in all this; some of the building work must be completed before December. Ideally the work should start pretty soon because I need to do the bulk of the work over the summer. I didn't figure out the room ratio yet because I wanted to ask about my options for layout in that room. I was going to pretty much try to fit the "components.skp" CR in my CR space, but I realised that the double-door that will lead to the LR would be in an awkward place. I also need to fit a small WC and a tiny utility room at the west end of the CR. That room (which will have the CR, WC and tiny utility) is not a complete rectangle either because the lower left corner (on the plan) is actually the main house corridor. The room itself is 4m35 wide, 2m70 high, and 5.98 at its longest. On the plan, I have drawn (in red) a possible layout that would accomodate the WC and utility. It would make the length of the CR 5.067m. Cheers, - martin

some of the building work must be completed before December.

That sounds doable, and realistic, if you are a fast learner. A few months to learn and design, then a couple more to get the slab laid out and poured, the framing done, and some drywall up. How far do you need to be by December?

the lower left corner (on the plan) is actually the main house corridor.

Will there be a door into the CR there?

On the plan, I have drawn (in red) a possible layout that would accomodate the WC and utility. It would make the length of the CR 5.067m.

With that layout, I guess the front of the room would be the straight wall on the right, and the rear would be the angled walls on the left? That's actually not a bad room ratio. It works out to 1 : 1.61 : 1.87, which is pretty close to Louden's best ratio of 1 : 1.4 : 1.9. You can probably nudge the dimensions a bit to get closer to Louden, but as it is, it is reasonable. You'll have a rather long RT60 at the low end of the scale, around 63 Hz, but you'll need plenty of bass trapping anyway, so that will probably help to control that. However, the dimensions that you need for your room ratio are measured from the final finished surface of the walls of the room (ie, the faces of the inner leaf, surrounding the empty room, without any treatment yet), not from the outer leaf, as you are showing now. So as you go moving your walls around in the design stage, to fit things in, or get better sight lines, or whatever, your ratio will be changing all the time.... this is part of what makes the design stage so much "fun"! You nudge a wall a couple of inches to get a better sight line, angle the ceiling a little less to deal with a problematic joist, and then discover that your ratio just went south, and now you need to nudge another wall to fix it, but that clashes with the place where you wanted to put the door, and you can't move the door because the bass traps are in the way, and... well, you get the picture... I hope you like jigsaw puzzles! :) One other question: Where is the door into the WC? - Stuart -