Hi there " nickhart", and Welcome!!
The space itself is a healthy 6.3x10m with a high pitched roof, starting at 3.5m high, pitching up to 4.9m.
Nice!
Bodes well for a great studio.
Drums playing measured directly next to kit - 113.6
Drums playing measured from live room - 67.2
So you are getting around 46 dB at present. You only measured with drums: do you also expect to have other loud instruments in there, such as bass guitar, electric guitar, or keyboards?
With these measurements in mind, if I can aim for a 10dB reduction between the two studios I think that would be an adequate isolation level for both.
In other words, you want to aim for about 56 dB isolation? Are you sure that will be enough? "Ambient noise = 55", and "drums = 67". Getting another 10 dB would mean that your drums will still be louder than ambient, and clearly audible. You need to be about 15 dB BELOW ambient to be inaudible. (Have you ever been in a cocktail party with dozens of people around you, talking, and high ambient sound, yet you can still pick out individual conversations of people quite a few feet away, even thou their voices are clearly LOWER than the ambient sound, since they are a part of creating it?).
A similar reduction would be required for the road noise to my unit,
What type of road noise? Any heavy vehicles, such as trucks, buses, farm equipment, even large motorbikes? Any vibration from that road, coming through the ground?
but I'm less concerned about the bleed into the upholstery unit.
What about bleed FROM them INTO your place? Do they use power tools? Staple guns? Nail guns? Power sheers? Do they have a compressor? What type of noise do they make?
I plan to add mass to the party wall between studios
That looks like a concrete block wall to me. It already has quite a bit of mass. How do you plan to add more? How much more?
The control room and live room will share a staggered stud wall,
Why staggered stud? Do you not need much isolation between the CR and LR? You do have the space to do it properly, so I'm not clear on why you would skimp here, to save an inch or two, and a few bits of lumbar.
which will eventually include a flat roof over the control room (I need to brush up on Rod's book again before finishing the proposed control room design).
It would definitely help to understand the complete concept if you include the CR in your model as well.
I've grouped items sensibly as to be able to hide parts in the Outliner to see inside and access detail etc.
It is MUCH better, and far more useful to assign those groups to layers, so you can manipulate them more easily. Also, make them into "components" not "groups".
In the current model, all exterior walls have additional plasterboard mass, but I question if this will be necessary.
The density of concrete is around 2400 kg/m3. The walls of a typical concrete block are around 40mm thick, and there's two walls on a block, so 80mm. The surface density is therefore around 190 kg/m2. That assumes they are hollow, not sand filled. If they are sand filled, the mass is much higher.
So your wall has a surface density of at least 190 kg/m2. The density of drywall (gypsum board, plaster board) is around 680 kg/m2. The surface density of a sheet of 12mm drywall is around 8 kg/m2. So if you add TWENTY-FOUR layers of drywall (in other words, 24 sheets thick), you would match the mass of the concrete blocks, which means you would have doubled the original mass, and therefore you would have gained around 5 dB isolation... Do the math, and see if this is cost effective.
If you just add one or two layers of drywall, you'd be increasing the mass by maybe 4% to 8%, and the effect on isolation would be negligible.
I would like to keep the budget for this build below the £6k mark,
19 layers of drywall, plus all that framing, would probably put you a bit over!
You have a total floor area of 63 m2. Your budget implies that you plan to spend around £95/m2 of floor area. That doesn't see very realistic to me. You could easily blow a third of your entire budget just on the HVAC system (yes you DO need one). I'd suggest that you draw up a simple bill of materials, go price them at your local hardware store, and multiply the price of each by the number you need, add up all the totals, and see how you are doing. I think you'll find that you are rather short on budget.
I plan to do all of the labour myself with the assistance of some very kind friends that have offered their time, so this budget is for materials only.
What about renting the tools and equipment you will need? You will be working up to 4.9 m above the floor, so you will have to rent scaffolding for that part, plus you'll need safety harnesses for that. Don't skimp on safety! It's not a lot of extra money (scaffold rental isn't too expensive, neither is safety gear), but it all adds up, and you are on VERY tight budget.
One thing that I've been made aware of that may make a small hole in this budget is moving the fuse boxes and electric meters, which I believe can only be carried out by the electricity distribution company, costing between £1-£1.5k. Is anyone able to shed any light on this?
Not sure about the UK; but where I live you can so the internal work (on your side of the meter) with a qualified electrician, or maybe even do some of it yourself under the supervision of a qualified electrician, but you WILL need to pay the power company to move the meter. And they WILL rob you blind. Been there, done that, several times. And they WILL take longer than anticipated, and they WON'T work to your schedule: they'll pitch up when they feel like it, not when you need them there.... Just a word to the wise...
Be prepared... Your estimate for the cost of moving the meter seems about right. That's what I would expect to pay, where I live.
Question: Do you NEED to move the meter box? Is there an alternative layout that would allow you to keep it where it is?
1) The concrete slab is currently very uneven and the surface is heavily pitted, is my best bet levelling off the current floor and laying laminate flooring?
Yes, you will likely need to level that, but since you are on a VERY tight budget, you probably won't be able to afford laminate. Just stay with plain concrete. Use self-leveling compound. You will probably need to rent a pressure washer to clean the existing slab properly, before you can level it.
2) Will my current plan supply the required level of isolation? Do I have too much/too little mass?
You'll have to do the math on that, because it's hard to figure out what the air gap will be, what the masses will be, and you didn't mention insulation. Also, without having the CR in there, it's impossible to say what the total isolation will be, since that's going to affect it. You didn't mention your plans for doors, windows, the HVAC system (yes you WILL need one), or the electrical system isolation, and all those play a part in total isolation. Sealing, too: sealing is critical. If you don't seal your rooms properly, you can easily lose a dozen dB of isolation... which could take you right back to where you started!
It is certainly possible to get 56 dB of isolation, and you could get even more with careful planning and some extra effort.
3) The corner framing topic in the reference area helped me work out how to build my wall corners (although I haven't aligned the boards in the model correctly yet), but how do I acheive this in the 90 degree angles where the wall meets the ceiling?
It depends on how you plan to build your walls, and your ceiling. There are different techniques. For example, if you build your walls conventionally, but your ceiling inside out, that's one technique, but if you do them both inside-out, that's a another technique, and doing them both conventionally is yet another technique. From the SKP file it seems you are planning to do it all conventionally?
However, there are several issues with your framing plan, among them:
1) You are showing only single top plates, but pretty much everywhere I've seen requires double top plates.
2) You are spanning the long way in many places, which implies using much larger lumber than spanning the short way.
3) You are using ordinary 2x4 lumber everywhere, but many of your ceiling spans are far too long for that, with a load of three layers of drywall
4) As above: You are using ordinary 2x4 lumber for your studs, but most places only allow that up to 10 feet or so (3m, roughly). You are going up to 4.8m in places, so you will likely need 2x6 lumber for that.
5) You are using an RSJ across the middle of the LR ceiling: have you accounted for that in your budget? Including the rental of the crane to get it raised? Did you check with your local building code to see if you are allowed to support an RSJ on timber studs? Did your structural engineer approve that? I'd be surprised if it is legal, especially when it is only supported on a single top plate over three 2x4 studs. That doesn't look right to me
6) You show drywall attached to the flanges of the RSJ: how do you plan to achieve that? You can't just nail it on! Nor can you glue it on, or screw it on.
7) The joints between all of your drywall layers line up exactly: you should stagger them by at least one stud / joist, to ensure good seals.
8 ) There are no headers above your doors, and no jack studs either. Those are load-bearing walls, and will need substantial structural support. I doubt that would ass inspection, and even if it did, I would still not do it that way. Over time, those doorways will sag, trash your isolation, and end up binding on your doors. Your door closers won't be able to handle that, so they wont seal properly, further trashing your isolation.
9) You don't have cripple studs at the ends of your window sills, and the framing dimensions seem deficient, considering the heavy glass load they will be carrying.
10) There are no trimmer studs in the window framing, yet those are load-bearing walls.
11) There's only one king and one jack stud on each side of your door frames: that won't be enough to support the very heavy doors that you will need. The framing will bend and twist as the doors are opened and closed
12) There are no noggins anywhere.
Those are the main issues. There's a few other minor things too, but those are the ones that are dangerous, illegal, or will bring you major grief down the road, if you do it like that.
So, there's great possibilities for that space, for sure, but your plan needs some correcting.
- Stuart -
Well that saves the unnecessary effort, existing walls will stay as they are, which means leaving the electric meters where they currently are is now a much more feasible option 
