garden room studio build help

(Originally posted to the 'Studio Design' section by mistake, sorry!) Hi all. I've been reading this forum (and books!) for well over a year now trying to learn what I can before I try and convert a small garden room into a home practice studio. It's a great resource and thanks for all the great advice I've read so far. I think I've got most things planned out now but had a couple of questions I was hoping for help with. Existing structure: 4.6m x 3.4m x 2m (height) free standing garden room. It appears to be well finished with existing power (with it's own consumer unit), insulated plasterboard walls, external wooden cladding, and double glazed pvc doors and window. It's currently got a laminate floor above chipboard and I assume floor joists. It was here when I bought the house (and I'm not a builder!) which is why I'm not certain of it's construction. Proposed: I'm planning on building a room within a room with the basic wall structure going: Existing wall New stud frame Genie clips + RC 2 layers 15mm acoustic plaster board sandwiched with green glue Auralex acoustic treatment and/or diy bass traps etc I planned to do similar with the ceiling and take up the laminate floor put down some form of DB Board or acoustic barrier mat, put the laminate floor back on and try and find a large rug for as much of the room as possible. For the window I was going to put in a new (additional) pre fabbed sliding window (thick acoustic glass) and build a heavy duty door. I'm going to try do most of the work myself to try and keep the costs down although assume I will need an electrician and plasterer at some point. I'm aware that perfect sound proofing isn't on the cards but hope that I'll be able to keep the noise down enough so that I can use it without having too many problems with the neighbours. It's a built up residential area with the closest other house about 8 meters away. Although I will have a recording setup in there it will mainly be used as a jam room so I'm not too worried about getting the perfect recording acoustics and more worried about keeping the noise down for the neighbours. I was planning on having an acoustic drum kit in there but if I can't get the sound levels down enough I could maybe get an electric kit. I'm mainly a guitarist so most of the time I'd probably be using it with 1 or 2 guitarists and/or a drummer but I could probably wrangle a bass player at times. I'd love any tips or advice on the above but my initial (and early build) issues are: 1) The use of neoprene or other rubber. I've seen that some people suggest backing the timber studs with neoprene to aid isolation of the new walls. I've also seen someone (probably on this forum!) say it's not necessary if I am using genie clips as they provide the isolation and adding 'extra' is unnecessary. That makes sense but I wanted to check as it seems fairly fundamental and it's obviously not something I'm going to be able to change later. If it is worth using rubber would I need to back all the studs where they contact the existing walls and ceiling and can you get away with using a cheaper material than neoprene? 2) My current thinking is to put floor boxes in 2 or 3 of the room corners to avoid making holes in the new wall structure. I'm not sure of the best routing for the cables to try and keep interference and hum down. I'm happy to get an electrician in to do the work but I wasn't sure how familiar with studio wiring a random electrician would be so I wanted to have as much as I could worked out in advance. It seems the simplest thing would be to run the electrical wiring under the floor (especially if I use floor boxes for power) but some of the advice suggests running the power cables around the top of the room and dropping them down the walls where they are needed. This would obviously keep the floor, where most of the audio leads would be, clear of power cables but it's such a small room anyway I'm not sure if it's needed. I think the existing spur is 40A, and is already split into 2 rings for the lighting and power sockets. I'm planning on using led lighting and was going to ask the electrician to remove (or just disconnect) the existing cabling and replace it with new shielded cable. I've tried to learn what I can but any advice would be great or is this all stuff any electrician will know? I hope I've provided useful info and would be very grateful of any advice. I'll happily answer any questions or add some pics if you think that would help. I've also got quite a lot of CAD work done but thought this was enough info for now! Thanks in advance, Ben

Hey Ben, smart move coming here before you pick up a hammer :D The one thing I can see your missing is budget. You'l need to have a realistic idea of cost to make this work how you want it to.

ben84 wrote:

Existing structure: 4.6m x 3.4m x 2m (height) free standing garden room. It appears to be well finished with existing power (with it's own consumer unit), insulated plasterboard walls, external wooden cladding, and double glazed pvc doors and window. It's currently got a laminate floor above chipboard and I assume floor joists. It was here when I bought the house (and I'm not a builder!) which is why I'm not certain of it's construction. Proposed: I'm planning on building a room within a room with the basic wall structure going: Existing wall New stud frame Genie clips + RC 2 layers 15mm acoustic plaster board sandwiched with green glue Auralex acoustic treatment and/or diy bass traps etc

If you're building a room witihn a room structure then you only want two leaves. At the moment you're existing structure has two leaves. Adding your internal walls and framing to this would be adding a third leaf which is what you don't want, especially for bottem end isolation. The external wooden cladding would be fine as a weatherprroof outer leaf, but id guess that it won't be sealed airtight. In order to make this a two leaf construction, you'd have to remove all the plasterboard from your existing walls, build your new walls and ceiling which are not mechanically connected to the existing walls in any way (no nails, bolts, screws glue etc etc) and then plaster the new wall framing. Two leaves. Problem is, that your external leaf of timber cladding isn't giving you much mass. Mass (and an airtight seal) is what will give you isolation. So when you take the plaster off your existing walls, you'll need to beef up that external leaf in some way. Thick ply, cement sheet or something along those lines. This in turn leads you to how much isolation you need, which appears to be the main issue. You need a real world figure in dB of how much isolation you require. Figure out how loud you are going to be when you're jamming. If you've got a drums, bass and elec guitars, this figure is going to be over 100dB and then figure out how quiet you'll need it to be outside so the neighbours aren't pissed off. Subtract the small number from the large number and you get the figure for transmission loss that you need to build for. That's where you can start to figure out how many layers, and what material you need to make this construction work.

ben84 wrote:

1) The use of neoprene or other rubber. I've seen that some people suggest backing the timber studs with neoprene to aid isolation of the new walls. I've also seen someone (probably on this forum!) say it's not necessary if I am using genie clips as they provide the isolation and adding 'extra' is unnecessary. That makes sense but I wanted to check as it seems fairly fundamental and it's obviously not something I'm going to be able to change later. If it is worth using rubber would I need to back all the studs where they contact the existing walls and ceiling and can you get away with using a cheaper material than neoprene?

Your new stud frame will not be touching your existing frame in any way, therefore, no neoprene!! I don't believe you'll require isolation clips as you are decoupling the new frame from the existing frame. My understanding of isolation clips is they aid in isolating the plaster from the stud wall when you have a single frame assembly. Your existing structure is a single frame, so if you were going to take the plaster off and re-hang it then you'd use isolation clips in that scenario.

ben84 wrote:

2) My current thinking is to put floor boxes in 2 or 3 of the room corners to avoid making holes in the new wall structure. I'm not sure of the best routing for the cables to try and keep interference and hum down. I'm happy to get an electrician in to do the work but I wasn't sure how familiar with studio wiring a random electrician would be so I wanted to have as much as I could worked out in advance. It seems the simplest thing would be to run the electrical wiring under the floor (especially if I use floor boxes for power) but some of the advice suggests running the power cables around the top of the room and dropping them down the walls where they are needed. This would obviously keep the floor, where most of the audio leads would be, clear of power cables but it's such a small room anyway I'm not sure if it's needed. I think the existing spur is 40A, and is already split into 2 rings for the lighting and power sockets. I'm planning on using led lighting and was going to ask the electrician to remove (or just disconnect) the existing cabling and replace it with new shielded cable. I've tried to learn what I can but any advice would be great or is this all stuff any electrician will know?

yep, keeping your audio and power away from each other is the way to go. never run them close and paralell to each other and if they have to cross, cross them at 90 degree angles. If you run your power from the top of the walls and your audio at the bottem, that should eliminate any interference. It's pretty reasonable to assume that an electrician will not understand the need to isolate your audio from your power, and in general, any contractors you hire won't understand the level of detail or some of the concepts required for building a studio. Post up some pics and drawings of your plans if you can. It's always helpful and it's easier to sopt any possible issues that you may not have noticed yourself :D cheers, steve

Hi Steve, Thank you so much for your reply, sorry It's taken me so long to get back to you. I knew the budget would be important but I guess I was a little self concious about it since it's pretty low! I'm hoping to spend less than £4000 on materials and do as much of the work myself as possible. I've done a fair amount of planning / budgeting (which I've now attached) and my current material plan works out at just under 4k but some of the prices are almost a year old now so there are bound to be adjustments needed.

If you're building a room witihn a room structure then you only want two leaves. At the moment you're existing structure has two leaves. Adding your internal walls and framing to this would be adding a third leaf which is what you don't want, especially for bottem end isolation.

From your response it sounds like I need to rethink my wall design. I have read about keeping it down to 2 leaves and been though all the diagrams showing location of additional plasterboard on internal walls and their respective performance. These often seemed geared towards 'internal' walls and I was assuming the fact that my room was outside would make a difference. Also since this is my first build I thought it would be much easier and cheaper (and less destructive) to just build off the existing walls. Obviously if this is going to completely ruin the performance of the studio I'll have to think again which is why I always intended to run things by this forum! The last thing I want to do is spend a lot of money and end up with an unusable room. Obviously the budget is important but also since it's already a small room I was trying to keep the wall thickness down as well. One of the first things I settled on was the use of genie clips since they seem to have a good reputation for keeping the isolation and TL high while reducing the need for a large air gap. I think in my mind I had black boxed the existing wall and was treating it as a single leave. Then the new frame + double layer of plasterboard would be applied (with genie clips to provide isolation) as the 2nd leave. It sounds like my initial assumptions were wrong (no surprise there!) so I guess I need to weight up the potential benefits of doing it another way against the additional cost/risk/effort of pulling down the existing plasterboard. I know this is probably pretty hard but is there any way you can quantify the performance difference between the 2 wall designs or do you really just need to pick one which fits in with budget and other constraints and hope it works satisfactorily?

This in turn leads you to how much isolation you need, which appears to be the main issue. You need a real world figure in dB of how much isolation you require. Figure out how loud you are going to be when you're jamming. If you've got a drums, bass and elec guitars, this figure is going to be over 100dB and then figure out how quiet you'll need it to be outside so the neighbours aren't pissed off. Subtract the small number from the large number and you get the figure for transmission loss that you need to build for. That's where you can start to figure out how many layers, and what material you need to make this construction work.

Since your response I moved an amp and kit into the room to do a little testing. With a phone SPL meter (supposedly calibrated but probably not super accurate) I recorded around 100dB inside the room while playing. Directly outside the room registered around 70dB. I don't really have any experience working with real numbers for sound levels but it seems to me to the current walls are offering around 30dB sound reduction. I think I'd like to get the outside level down to around 40dB (so increase the wall performance by 30dB to 60dB) but I don't really know if this is achievable (or under or over speced) either by building onto the existing walls or with first pulling down the existing plasterboard. Thanks for the tips on neoprene and the electrical work. Really they both are affected by the wall design so I need to get that finalised first. I've attached loads of planning work to this post. I have 8 pages of CAD work, a materials schedule, excel budget, a possible floor plan and some pics of the existing structure. Some of the CAD work gets pretty serious (I have an architect friend who did it) but he isn't familiar with acoustical design so really he worked from my wall designs. At one point I wanted to do sketchup designs too since they would be much easier to grasp the design at a glance but I haven't had the time so hopefully the CAD work will be useful. I had to reduce the pics to post them here and convert the excel stuff to a pdf to upload. I also had to split the pdf to get the filesize down to < 500k. Even so I couldn't reduce page 2 down enough. The full pdf is available at http://www31.zippyshare.com/v/73976056/file.html If more pics or info would help just let me know! Thanks again for all the advice so far. This has been something I've wanted to do ever since I moved here and I'm finally beginning to feel like I'm getting somewhere close to actually starting the build! Ben

ben84 wrote:

The last thing I want to do is spend a lot of money and end up with an unusable room.

and believe me, no one else on the forum wants that for you either :D That's why you'll end up getting a lot of advice that might sound like people are trying to get you to do things the hard way, but at the end of the day everyone wants you to get the most out of the space and limitaions you have.

ben84 wrote:

Obviously the budget is important but also since it's already a small room I was trying to keep the wall thickness down as well.

Yep, in a room that size you want as much usable space as you can. It might be possible to get the kind of isolation you need by retaining the single wall frame you have, removing the existing plaster, beefing up the external leaf and hanging several layers of 16mm plaster on genie clips with green glue as the internal leaf. I use the word possible, because all of that takes some fairly serious calculations regarding material weight and the ability of your existing structure to cope with that weight. Removing the existing plaster, beefing up the external leaf and then building a completely seperate frame for your internal leaf might give you the same isolation with less layers of internal plaster, but at a cost of room space :roll:

ben84 wrote:

I know this is probably pretty hard but is there any way you can quantify the performance difference between the 2 wall designs or do you really just need to pick one which fits in with budget and other constraints and hope it works satisfactorily?

Don't hope :wink: if there's one thing that'll bite you in the arse with completing this construction, it's hope!! You need solid numbers and facts, combine that with the right construction and you'll get the isolation you need. A + B will equal C, as long as you do A and B correctly. quantifying wall performance isn't hard, although I don't posses the maths to be able to tell you. Have a hunt around the forum for some numbers on wall constructions, especially posts from Stuart (soundman2020). He knows the math and the freq response and has commented on it many times.

ben84 wrote:

With a phone SPL meter

sorry, not good enough for real measurements. ( i've been cracked over the knuckles for this one too :oops: ) get yourself a dedicated SPL meter. There's a few links around the forum. Mine's a galaxy cm140 (or something) and it measured up to 20 dB different from my phone. that's a lot of dB!!

ben84 wrote:

(so increase the wall performance by 30dB to 60dB) but I don't really know if this is achievable (or under or over speced) either by building onto the existing walls or with first pulling down the existing plasterboard.

Getting to 60 dB transmission loss is doable, but you're really, really going to have your work cut out for you. And given that you're on a stump and bearer floor, you need to think of your floor as 'another wall' along with the ceiling. I'd have to say that Green Glue is going to come into this build somewhere as it's effectivly isolation-in-a-can (if used correctly) but it does come at a price....which is...price :roll: Have a search around the forum and you'll find some figures on isolation vs layers of drywall for sure. It's something along the lines of: 1 layer of 16mm gives you 32 db TL, 2 layers gives you 37 db TL, 3 layers 40 db and so on. Apply GG and this figure changes dramatically, as does budget.

ben84 wrote:

Thanks again for all the advice so far. This has been something I've wanted to do ever since I moved here and I'm finally beginning to feel like I'm getting somewhere close to actually starting the build!

no probs, glad to be able to help :D It's been said elsewhere, and I can't remember by who (or whom) that building a studio is 90% planning and 10% construction. Having been through my own build I can say that's 100% accurate. steve

stevev wrote:

It's been said elsewhere, and I can't remember by who (or whom) that building a studio is 90% planning and 10% construction. steve

It is in the sig of Avare: memberlist.php?mode=viewprofile&u=746

Hi Steve and all, After the advice given previously I've been rethinking the wall design and here is what I've come up with... It doesn't really need a model but the above is the existing wall structure. External cladding, almost certainly some form of MDF or chipboard layer, stud frame, insulation and an internal plasterboard layer. I'm afraid I'm still getting the hang of Sketchup so please excuse my slightly hacked modelling! 1) My initial wall design: As was pointed out by Steve (and I should have know better anyway) this ends up in a 3 leaf system so would not be ideal. The advantages though (at least in my mind) were a 'less destructive' build and avoiding removing any wall mass which would probably need to be replaced in some way. 2) Double leaf design: The above is the same design except with the existing inner plasterboard leaf removed to move it back to a double leaf construction. In this version I've left in the RC channel and clips although (as previously mentioned) since the new frame is entirely isolated from the old frame (with an air gap) they may not be necessary. I'm somewhat reluctant to ditch the RC design since I've been thinking it may provide some level of 'tolerance' and if there was some part of the construction I don't do perfectly then between the two systems (double frame + RC clips) I'd still maintain a good level of isolation. (This is potentially more relevant since I'm going to be DIYing most of the build and this is my first studio build.) 3) Single frame with RC: It seems to me the above is the way an RC system 'should' be implemented. This is removing the existing plasterboard, not adding a new independent frame, and adding the clips, channel + plasterboard layers onto the existing frame. The advantages to this are obviously reduced wood costs and labour and in theory should provide the same isolation at reduced wall thickness. Downsides are since the overall wall thickness is quite alot less I assume the overall TL performance would be quite a bit less. Since I'm trying to get as high a performance design as I can, and I'd already accepted losing the room space from the larger thickness wall, I think this is probably a less appropriate design in my situation. 4) Double leaf no RC: As attached to a sound clip design as I have become it seems I should also consider the above. With a properly isolated new stud wall it seems I could build a proper double leaf wall of the same performance (or potentially even higher since I could just increase the air gap between the new and existing frame) and save the money on channel and clips. (Or use the money for an extra plasterboard layer or for building up the external leaf...) The external leaf: As Steve also pointed out if I do remove the existing inner PB leaf I would almost certainly want to beef up the existing external leaf. Suggestions were thick ply, cement sheet or similar. Would it be a good idea to use another layer of plasterboard backed with green glue on the inner leaf? Or would the effect of green glue be reduced as there would already be a layer of green glue on the inner leaf? (diminishing returns / stacking effect, a bit like not needing the genie clips on an already isolated wall...) Alternatively I could use a layer of mass loaded vinyl (or tecsound or some other acoustic mat). I think the main goal of beefing up the external leaf is to add mass so should I be looking at purely the density vs cost of a particular material? Since whatever I end up using will need to go between the existing studs rather than as a continuous sheet are any of the mentioned methods more or less effective between the studs? So I suppose I'm leaning towards design 4) with some form of beefing up of the existing external leaf. (Although I still might feel 'safer' doing 2). I've tried to summarise all of my current wall design thinking in this post with the hope that any glaring mistakes I've made would easily show up. I'd really love any more advice on which design to pick, any corrections or suggestions to my thinking and any more suggestions on beefing up the existing external leaf. I tried to upload the sketchup skps as well but they are too big. If anyone would like them (or any other info) just left me know and I'll get them uploaded somewhere. Thanks again to all! Ben

You are on the right track with #4, for sure! It's the least expensive and should give you the most isolation. Least expensive, as RSIC clips and hat channel are not cheap, and most isolation because it has the largest air gap between the leaves, and therefore the lowest resonant frequency. So, all other factors being equal, it should give you the best deal. For the "beefing up" of the outer leaf, the easiest (and least expensive) way to do that is to cut strips of 5/8 drywall to fit snugly between the joists, caulk all along the edges very carefully, then hold them in place with small cleats nailed sideways into the studs. Green Glue is probably not worth it here: but do use it on the inner-leaf, between your two layers of drywall there. That's what I'd do, if that were my place. - Stuart -

Hi all. I hope everyone had a great Christmas and New Year. My studio build has made a little progress but after plenty of distractions I'm hoping to start making some serious progress! I have taken the first step though and pulled up the laminate flooring and taken down the existing inner leaf of plasterboard on all the walls and the ceiling. I have two current issues / questions... 1) What plasterboard to use to beefing up existing outer leaf? As previously discussed I was planning on removing the existing insulation, getting 19mm plasterboard in 600mm planks, cutting it to fit snuggly between the joists, caulking the edges (with acoustic sealant) and using cleats screwed sideways into the joists to secure them and replacing the insulation. I assume that still sounds like good plan but I've noticed the existing joists are at nowhere near 600 centers (most are around 350mm). I was planning on getting the 600mm planks as they are thicker and to save wastage but now it seems I could just get full size boards. So should I just go for 12.5mm (or thick as possible) standard plasterboard, 19mm planks, or, since it's going on the outside of the insulation, should I opt for a vapour blocking plasterboard. (The current insulation looks dry and in perfect condition and I assume there must be a DPM behind the chipboard layer in the wall. It looks to me like I shouldn't need to worry about it, and would obviously rather avoid the cost, but it was mentioned by one of my friends so thought I should check it out...) 2) Wall structure / strength concerns. I don't need to have this completely tied down immediately but since It's pretty fundamental to the build I thought I'd try and get some advice early... In my initial plans for the wall I was planning on fixing the new (supposedly isolated) frame for the walls into both the floor and the ceiling with a strip of neoprene (or other rubber) in between. I realise this would provide some physical connection but was hoping the neoprene below the base plate (iso-sil or similar) and the fact that the new walls (and new ceiling) would be hanging on resilient clips would alleviate that problem. Since the new design doesn't use resilient clips in the walls I'm back to being worried about the isolation. It seems the neoprene on the floor would do a good job of isolating the new wall but if I did the same at the top since the weight of the wall would not be spreading the load across the neoprene I'm worried it would seriously reduce the isolation. It seems the 'correct' way to solve this would be not to extend the new walls all the way to the ceiling but then I'd be worried about hanging the new, very heavy, internal door off the new wall. In the current plans I have much larger studs (100x100 I think) used in the door frame but they are still connected to the existing ceiling. Since the ceiling in the room is already very low I wasn't planning on adding new ceiling joists but was planning (and still plan) on using resilient clips to hang the new ceiling off the existing ceiling joists (see pics, the forum rotated the ceiling pic for some reason...). If I was planning on floating new ceiling joists on top of the new walls then I guess that would strengthen the new frame without causing isolation issues but I don't think I have the space to do that. So I guess I'm asking if I should be screwing the new walls into the ceiling, leaving the walls short of the ceiling and assuming they won't collapse inwards when the door is opened (or learning more so I'm sure they wont), supporting the door in some other way or doing something else completely. I really hope that all made sense and I'm not making an obvious mistake. Any suggestions gratefully received and thanks for all the help! Ben

hey Ben, happy new year mate :D

ben84 wrote:

1) What plasterboard to use to beefing up existing outer leaf? As previously discussed I was planning on removing the existing insulation, getting 19mm plasterboard in 600mm planks, cutting it to fit snuggly between the joists, caulking the edges (with acoustic sealant) and using cleats screwed sideways into the joists to secure them and replacing the insulation. I assume that still sounds like good plan but I've noticed the existing joists are at nowhere near 600 centers (most are around 350mm). I was planning on getting the 600mm planks as they are thicker and to save wastage but now it seems I could just get full size boards. So should I just go for 12.5mm (or thick as possible) standard plasterboard, 19mm planks, or, since it's going on the outside of the insulation, should I opt for a vapour blocking plasterboard. (The current insulation looks dry and in perfect condition and I assume there must be a DPM behind the chipboard layer in the wall. It looks to me like I shouldn't need to worry about it, and would obviously rather avoid the cost, but it was mentioned by one of my friends so thought I should check it out...)

here its a case of as thick/dense/heavy as possible. You might be a ble to re-use the stuff you've taken off the inside if it's still reasonably intact. If your original insulation looks dry and theres no water marks on any of the other internal timber then it would be reasonably safe to say there isn't any issue with water entering the outer shell. Keep in mind that you'll be beefing up the ceiling the same way that you beef up the walls, so you may need to get some professional advice on whether your existing roof structure can take the additional weight.

ben84 wrote:

2) Wall structure / strength concerns. I don't need to have this completely tied down immediately but since It's pretty fundamental to the build I thought I'd try and get some advice early... In my initial plans for the wall I was planning on fixing the new (supposedly isolated) frame for the walls into both the floor and the ceiling with a strip of neoprene (or other rubber) in between. I realise this would provide some physical connection but was hoping the neoprene below the base plate (iso-sil or similar) and the fact that the new walls (and new ceiling) would be hanging on resilient clips would alleviate that problem. Since the new design doesn't use resilient clips in the walls I'm back to being worried about the isolation. It seems the neoprene on the floor would do a good job of isolating the new wall but if I did the same at the top since the weight of the wall would not be spreading the load across the neoprene I'm worried it would seriously reduce the isolation. It seems the 'correct' way to solve this would be not to extend the new walls all the way to the ceiling but then I'd be worried about hanging the new, very heavy, internal door off the new wall. In the current plans I have much larger studs (100x100 I think) used in the door frame but they are still connected to the existing ceiling. Since the ceiling in the room is already very low I wasn't planning on adding new ceiling joists but was planning (and still plan) on using resilient clips to hang the new ceiling off the existing ceiling joists (see pics, the forum rotated the ceiling pic for some reason...). If I was planning on floating new ceiling joists on top of the new walls then I guess that would strengthen the new frame without causing isolation issues but I don't think I have the space to do that. So I guess I'm asking if I should be screwing the new walls into the ceiling, leaving the walls short of the ceiling and assuming they won't collapse inwards when the door is opened (or learning more so I'm sure they wont), supporting the door in some other way or doing something else completely.

Regarding the neoprene under the new internal walls. For the neoprene to be effective it has to be loaded properly, which means a whole heap of maths regarding the thickness of the neoprene and the weight that is being loaded on it. Not enough weight and it won't compress enough, to much and it over compresses. So i'd say not to use it and make sure you do your sealing of the new internal wall very thoroughly using acoustic caulk. Regarding fixing your new internal walls to your existing ceiling. don't do this :!: You need to build a room within a room. this means the new walls, with another ceiling built on the new walls, does not touch your outer leaf/walls in any way. no nails, no screws, no glue, no timber....nothing. If you aren't going to build a new ceiling as well as your new walls then i'd say it's not worth doing the walls. The whole construction is only as strong (isolation wise) as it's weakest link. If you build walls that isolate to 60db and only get 30db with your ceiling then you've only got 30db of isolation. Your doors only need to be as heavy/dense as the wall they are going into. Again, you don't need a custom made door that isolates to 80db if you're putting it in a wall that gives you 60db. Steve

A couple of things to consider. MDF is not interested in being on the exterior of an environment, in any manner. So you should use whatever is the local sheathing applied to an exterior, be it chipboard or OSB or plywood. Not MDF. Second, if you choose to use RC, if this winds up being your choice you are not held hostage by the existing airspace. You can install rips from a 2X4 nailed directly to the existing framing which will increase the air cavity. Granted if you use RC on the wall framing you should use it on the ceiling framing as well.