Build from scratch UK practice room / recording studio

Firstly hello all ! I am just venturing out in building a practice room / recording studio on the side of a house I have recently purchased and just moved in to. As a bit of background I am a UK based drummer / band member for a run of the mill covers band and handle all the PA and sound engineering myself. More recently I have become a recording / mixing enthusiast with a Pro Tools based system - I also have 2 teenage sons who are up and coming band members and I want to be able to support them by giving them somewhere to make a noise any time they fancy it ! Whilst I am no expert in sound isolation I have spent many hours researching this subject, my father is also a retired building regs officer and I am enlisting the help of a structural engineer / architect as this build forms the lower floor of a complete new 2 story extension to my house. Between us we should be able to construct a suitable / liveable building that complies with all UK building / planning regs and with a "reasonable" amount of sound isolation however I realise the devil is in the detail and I hope that the content and support of this forum will be the icing on the cake in achieving the best possible sound isolation whilst keeping the budget reasonable. The remit will be sound isolation first and internal sound control second - we would like our respective 4 piece rock bands to be able to practice at volume without disturbing our nearest neighbour (approx another 15 metres away to the left) as a priority. Recording will be a secondary function and I am happy to compromise sound / listening control to some extent as the layout of the build will be dictated by certain restrictions of the build fitting in with the existing house design. The house is an old 1890 Victorian Style building so the extension will need to complement that - including some sash style external windows. There currently is a single storey double garage which will be totally demolished to make way for the extension and we aim to keep the extension within the footprint of the original garage. We are only just starting on the actual design so I thought it best to initially give the general idea of what we would like to achieve and then hopefully with the aid of the architect and this forum we develop the design detail moving forward. Here is a very preliminary scale sketch of my initial thoughts where you will see the extension to the left and the main house to the right. The lone wall to the far left is the original garage wall so we are coming in a couple of metres to create more space around the property.

The key build aspect is that the complete 2 storey extension will need to be built to standard UK building design / regs, which being heavily orientated towards thermal insulation means a cavity wall type structure being the favourite for the main shell. So a 100mm thick external red brick and mortar skin then a 100mm (note changed from 50mm) air cavity and then with an internal Thermalite or concrete block / mortar skin with both skins tied together with wall ties. These would be on a common concrete foundation. The plan is then to have an additional concrete block "room within a room" (which is shown in the sketch with the slightly lower wall heights) built within the lower floor space and on its own concrete floor (strengthened at the edges but separate from the outer skin foundations) so that the 2 external skins and upper floor level are totally decoupled from the lower floor concrete room. In the event we ever sell the house then the inner room can be demolished if need be leaving a structure of conventional construction for normal living. The extension will be approx 5 metres x 4 metres. Not shown is the second floor where we intend to have a living room above the studio of the same dimensions. Internal room height is tall by UK modern standards at 2.64 metres so the hope is that this will help to accommodate a room within a room principle down below whilst still retaining an adequate height within the studio. One corner of the studio will have a control room which will effectively be outside of the inner concrete room perimeter. This will have its own studio facing window and also an external window of standard double glazed sash window type (the 2nd from left window shown) - which should also provide a means of fire escape to keep the regs guys happy (though this needs to be checked by the architect.) There is also a window (to the far left ) where the studio is exposed externally but the thought is to have a traditional double glazed sash window bridging the outer 2 skins (as per normal house construction) and then a studio style window set in to the inner concrete room to assist with sound isolation. I do realise that the wall layer count is 3 and the potential window pane count is 4 so as a first question, do these constitute the undesirable 3 or 4 leaf systems or does the manner of construction of near separate masses benefit the sound isolation properties overall? Then as the 2nd question I guess is from the above do we appear to be on the right initial track or does anyone see any immediate issues? I appreciate the further build detail needs to come but does this seem a reasonable initial remit to the architect? My gut feel is there will be enough mass in the walls to give us the reasonable sound isolation (and we will obviously use additional layers of plasterboard / Soundlam in the appropriate areas) but I am wondering if the windows will be too much of a weak link and not justify the inner concrete room? I have a meeting soon with the the architect to finalise the planning permission submission for approval but this relates to external appearances only - there will then be a period of about 6 weeks where we can start to work on the general / internal construction detail for building regs approval whilst we wait for the planning permission to come through. I therefore hope the the above level of detail is ok to get the ball rolling but will happily define more detail as and when possible if that assists with any further questions. Many thanks for taking the time to read this and I look forward to getting to know you folks better. All the best. Roger

Hi there, I'm no expert but I will look forward to seeing your build develop i'm sure one of the experts will get back to you especially if you add a few things to your profile :D

Thanks Rogue. Profile updated to add a bit of info - I'll hopefully add more to the site / thread shortly but it is chaos here as have just moved in to the house last week and am surrounded by tradesmen tearing the place apart to get new heating and water systems in along with trying to sort / decorate the existing structure as well - but trying to keep up the momentum in getting the new extension / studio designed and built amidst all the goings on here.... well we do need to keep priorities :wink:

Ok, so here is a bit more info about the concept we would like to consider due to being based on existing UK building techniques and then adding a straightforward inner, detached, room. But a key area of uncertainty is that as there are effectively 3 walls (at the left hand side) then does this constitue a 3 leaf system and therefore go against what we are trying to achieve which is as much sound isolation to the outside world as possible, especially to the left hand side of the house (as viewed in the picture below). I am hoping to get some sound measurements shortly but an initial prefferred target would be 70 - 75 dB reduction based on a loudish rock band practicing in the room not causing a nuisance to our only neighbour who has their garden boundary approx 5 metres from the side of the proposed studio and then their house which is a further 5 - 10 metres away.

We could possibly increase the airgap immediately next to the studio wall - or even double the thickness of the studio wall to 2 x high density concrete blocks. There will also be a window and a door which could possibly be the weak points but we can work on those next (We would be looking at a studio spec window to the front of the house and the door will be interconnecting with the main house in the opposite direction to the neighbours.) Therefore any thoughts / comments greatly appreciated. Many thanks.

Hi Roger, and welcome! :)

my father is also a retired building regs officer and I am enlisting the help of a structural engineer / architect as this build forms the lower floor of a complete new 2 story extension to my house.

It sounds like you are off to a good start, with a realistic plan and the right type of team. Putting the studio on the ground floor is a smart move: if you would have planned things the other way, with the studio upstairs, you would have multiplied your problems.

The remit will be sound isolation first and internal sound control second - we would like our respective 4 piece rock bands to be able to practice at volume without disturbing our nearest neighbour (approx another 15 metres away to the left) as a priority.

So then, the first order of business is to define the terms "without disturbing", in objective, measurable numbers. In other words, you need to determine how many decibels of isolation (transmission loss) you need. Do that with a sound level meter, to measure the level produced by the "respective 4 piece rock bands" in their wildest, loudest session, and also by measuring the quietest ambient level at your neighbor's place. The difference between those two is how much isolation you need. But there is another factor to throw in the mix: legal regulations. Also get a copy of your local noise regulations, and take a look at those. That's how much noise you can make legally, without having the cops or municipal inspectors come knocking on your door, delivering ultimatums and fines. So, whichever figure is LOWER for the "silent" level, is what you go with. So if you measure an ambient level of 50 dB at 4:00 AM, but the regs say that the limit is 35 dB, then 35 dB it is. So, with an objective, real-world, legally compliant number in hand for "How much isolation do you need", you can then take a look at the piles of documentation that is available on building techniques that actually provide that level of isolation. Look through several of those to find a method that meets your budget and skill level, and use that as the basis for your build. You cannot just guess at what might work: this is a process, and you need to start by defining the goal (how many decibels of isolation you need), then finding the structure that will attain the goal.

The house is an old 1890 Victorian Style building so the extension will need to complement that - including some sash style external windows.

That's fine. External styling is more cosmetic than acoustic. So if the style requires "sash windows", then you can indeed have what look like sash windows from the outside, but in fact are just thick acoustic windows masquerading as sash windows. Ordinary sash windows are out of the question for the level of isolation you need, but you can easily design windows that look just like them and still provide the isolation.

There currently is a single storey double garage which will be totally demolished to make way for the extension and we aim to keep the extension within the footprint of the original garage.

Great! So this is basically a "greenfield" build, starting form the ground up? Do you plan to re-use the original foundations and slab, or are you going to dig those out and re-pour them specifically for the studio? I would recommend "dig out and re-pour" if you can, since that provides the opportunity for maximizing isolation by pouring separate isolated foundations for the inner and outer leaves. For heavy drums at 3:00 AM, that's a big plus factor.

will need to be built to standard UK building design / regs, which being heavily orientated towards thermal insulation means a cavity wall type structure being the favourite for the main shell.

Excellent! Cavity wall is exactly what you need for high levels of acoustic isolation, so that's a good start. But it has to be done correctly, of course.

So a 100mm thick external red brick and mortar skin then a 100mm (note changed from 50mm) air cavity and then with an internal Thermalite or concrete block / mortar skin with both skins tied together with wall ties.

You were doing jsut fine until you got to "tied together with wall ties". That absolutely CANNOT happen with an acoustically isolated wall system. eav o the leaves must be built as a stand-alone, self-supporting structure, with ZERO mechanical connection between them- In other words: no wall ties. Or if regulations absolutely require wall ties, then you'll have to open your cheque book wider and use proper acoustic isolation ties. But even if you do that, then you need some very skilled bricklayers here: as they work, they CANNOT, absolutely and totally MUST not allow any mortar or other debris to fall into the cavity. If it does, then it will bridge the two leaves, thus negating the isolation. Keeping the two leaves totally isolated, decoupled and separate is paramount.

These would be on a common concrete foundation.

Once again, it would be MUCH better to pour a monolithic foundation-plus-slab for the inner-leaf, and a separate foundation around the outside of that for the outer leaf. The gap between the two is filled with suitable acoustically decoupling expansion compound, but the two foundations remain independent, separate, and isolated form each other.

The plan is then to have an additional concrete block "room within a room"

If you did that, you would be creating a three-leaf wall. Not a good idea if you want high levels of isolation for low frequencies.

One corner of the studio will have a control room which will effectively be outside of the inner concrete room perimeter.

... or rather, "... which will be built following the same principle of fully decoupled two-leaf MSM walls." In other words, the CR and LR should be built in the same way.

and also an external window of standard double glazed sash window type (the 2nd from left window shown) - which should also provide a means of fire escape

If you did that, then you would have no isolation for the control room, and your neighbors will, indeed, have the cops knocking at your door... Isolating the control room is every bit as important as isolating the live room. They have to be done in the same way. And since the live room cavity is, by definition, the same cavity as for the control room, you have no choice but to isolate both to the same level.

do these constitute the undesirable 3 or 4 leaf systems

Yup! :) Any time you have a hard massive surface followed by an air gap, then you have a leaf. The more leaves you have in the same space, the worse is the isolation.

or does the manner of construction of near separate masses benefit the sound isolation properties overall?

Each pair of leaves is a tuned system, a resonant system, that will resonate at a specific fundamental frequency, called "f0". The frequency is set by two things: the amount of mass on each leaf, and the distance between them. If you decrease the mass, or decrease distance, then the frequency INCREASES, and overall isolation DECREASES. If you add another leaf close by, then that also increases the resonant frequency and decreases overall isolation. In fact, with a two leaf system you no longer have a single fundamental frequency, but now you rather have two fundamentals, called "f-" and "f+", and BOTH of them will be higher than f0 would have been for a wall built with the same total mass and thickness. So, all other factors being equal, turning 2-leaf into 3-leaf means reducing isolation, and turning 3-leaf into 4-leafs makes it worse still. You can compensate for 3-leaf and 4-leaf systems if you have no choice, by increasing the total mass and increasing the individual cavity depths. You also need to have twice as much mass on the middle leaf in a 3-leaf system (in other words, the middle leaf must have the same mass as the masses of the other two leaves combined). So if you do choose to go with this 3-leaf design, then you should set aside a lot of extra space for the walls, since you will need to make them much, much thicker. You should also set aside a lot more money, since you will need to to buy all that extra mass! :)

Then as the 2nd question I guess is from the above do we appear to be on the right initial track or does anyone see any immediate issues?

There are several issues there, mostly related to the isolation: The image form the SKP file is not very detailed, but it seems to show multiple flanking paths all over the place. Also, the shape and size of the control room are not realistic.

My gut feel is there will be enough ...

Unfortunately, sound waves aren't much into "gut feelings"! :) They tend to only obey the actual laws of physics, and react to the actual mass and cavities they run into. So the only way to be certain that you have "enough" is to do the calculations.

I am wondering if the windows will be too much of a weak link

Windows are always a weak link, in any studio. There are several reasons for that, but none of them are being addressed in your design, yet. You need to take into account several things with your window design. The most important points are firstly that the air gap between panes of glass in a 2-leaf wall must be much bigger than the air gap between the leaves themselves, since there is no way you can have insulation between the panes, and insinuation is key to providing the necessary damping in the cavity. The theoretical difference is a factor of 1.4. So if there is a 20 cm gap between the two leaves of the wall, then you need at least a 28 cm gap between the panes of glass in those two leaves to compensate for the lack of damping. Secondly, you need to have the same surface density in the glass as you have in the rest of the leaf. And thirdly, the window MUST be sealed totally air-tight. In other words, the window must be non-operable. Meaning that it is fixed in place, and cannot be opened. So even if it looks like a sash window, in reality it cannot be one. It can only be a fixed plane of glass, heavily locked and sealed into position. One more thing: you didn't mention anything about your HVAC and electrical systems yet, and those are critical to good isolation, so you should probably look into those major aspects next.

I am hoping to get some sound measurements shortly but an initial prefferred target would be 70 - 75 dB reduction

That's a pretty steep goal. Do-able, for sure, and especially so considering that you plan to use mainly concrete and brick, but not easy to achieve in practice, especially if the builders have no experience in building studios. There are many things they will have to differently, and if they don't understand the reasons for them, or just plain work carelessly, then that is a major potential source of disappointment...

here is a bit more info about the concept we would like to consider

The basic idea is OK, but I fail to see the need for the triple-leaf. Why not just do a plain brick or concrete wall for the outer leaf, and another for the inner leaf? You have your "cavity wall" like that anyway, if that is what you are worried about. You are wasting a lot of materials, time and money with that triple-leaf concept, not to mention the potential acoustic issues.

There will also be a window and a door which could possibly be the weak points

Windows and doors are ALWAYS the weak points, and therefore have to be designed with extra care. Doors are even worse than windows, since windows are permanently sealed and inoperable, but doors kind of have to open and close! So that implies massively heavy doors, with multiple seals. Your doors are going to have to weigh hundreds of pounds, and each pair will need six seals, at least (three on each door), to get to the level of isolation that you are talking about.

We would be looking at a studio spec window

It will be much better (and cheaper) to design and build the window yourself. The basic concept is the same as for the walls: Two-leaf, fully-decoupled, MSM. In other words, one pane of glass in the inner leaf, and one in the outer leaf, each with suitable mass, and separated by a suitable distance. The masses and distances depend on the wall design, of course.

and the door will be interconnecting with the main house

for this level of isolation, a single door is out of the question. You will need a pair of doors, back to back. One door in the inner-leaf, the other in the outer leaf. Just like for windows, the mass on each door and the distance between them is determined by the same rules. But unlike windows, here you have the problem of how to make them operable: the hinges must be very heavy duty, there must be enough of them to easily handle to weight, the door closers must be dimensioned correctly and adjusted correctly, and above all the perimeter seals must be perfect: As mentioned above, you will need three full seals per door, running around the complete perimeter of each door (top, sides and bottom). The bottom seal must be a threshold-type seal that gets out of the way when the door is opened, and drops into place when it is closed. And at least one of the seals must be magnetic, to keep the door closed, since you cannot use through-latches to do that. The final point in your "construction.JPG" mage is the floor above the studio: it looks like that is just a simple wood joist plus plywood deck, but that is no use at all for your purpose. That floor will have to be built to the same surface density as the rest of the outer leaf, in order to correctly complete the isolation system, so you'll probably need to replace that with a concrete slab floor. There's no easy way to get the mass that you'll need with just a wooden deck. - Stuart -

Hi Stuart, Thank you so much for your helpful and comprehensive reply - truly appreciated. It looks like you have answered the main area of doubt / misconception I had which was that my initial plan does turn out to be a 3 leaf system. I did start to get my head around the aspects and downsides of 3 leaf systems etc. from reading up on articles that looked to cover timber and board construction but I was not sure if the same applied to heavy block walls. My thinking (rightly or wrongly) was that the 2 outer leaves were what a typical UK house construction would be (including wall ties and all sat on common foundations etc) so my approach was to build that in accordance with normal UK house techniques and THEN address the decoupling / extra mass etc. by then putting an inner separate room within a room which made up the 3rd layer. Overall I guess you could say my train of thought was to make a self contained and isolated concrete bunker, with its own studio type windows as the innermost layer - and then drop a traditionally built house (with its own 2 brick layers and outer windows AND including the top floor) over the top of it (and not touching it) to make it look pretty :D But it sounds like this is not the most effective route and I would be better off doing away with the inner (concrete bunker) 3rd layer and then redesigning and working with just the outer and inner leaf of the traditional 2 wall design normally used to build houses over here but modifying them to achieve what we need to. So yes, I can have a chat with the architects to see if the building regs will allow staying with just 2 walls and putting the outer and inner walls on separate foundations and also not tying them together - and I note your comments about keeping the walls totally separate including "dropped muck" down the cavity! And if we do away with the 3rd layer then this does give me more real estate to widen the air gap between the outer 2 walls which I understand will help. Maybe best that I first run that past the chaps here to see if they have any immediate issues and if it looks like they can accommodate that then I can run through and address your further areas of advice in detail - which all make good sense to me and are very helpful. And yep - regarding the doors and windows I have a skilled joiner as a good friend (also happens to be the Dad of one of the bend members in my sons band so an active interest there!) and he will help out creating those multi layered / sealed heavy doors. I've have been reading Rod Gervais's book which has given a good insight in to that. We will accommodate fresh air and air con requirements - though have you experienced the climate over here ? :mrgreen: it would be nice to actually need aircon for the usual reasons - but I do understand there are climate / moisture control issues with the airtight rooms etc. Thanks again Stuart and I'll pop back later once we have got our head around if sticking to the 2 leaf design will sit with the build regs here. I am sure they will but there will no doubt be some areas to address. Cheers Roger

My thinking (rightly or wrongly) was that the 2 outer leaves were what a typical UK house construction would be (including wall ties and all sat on common foundations etc) so my approach was to build that in accordance with normal UK house techniques and THEN address the decoupling / extra mass etc. by then putting an inner separate room within a room which made up the 3rd layer.

I hope I didn't give you the wrong impression: You CAN build it that way, and with the amount of mass you have in those walls it probably will give you good isolation, but the issue (to my mind) is the amount of space and money it takes with that plan: You'd be putting in way more mass than is necessary for a two-leaf design, and mass costs money. It also takes up space. Those are the points I was trying to make: There's an example here on the forum of a studio that was built using an unbelievable SEVEN leaves in some places, and it turned out to have good isolation. But the amount of mass, money and wasted space that went into it is astonishing. It could have been built for far less, and would have turned out bigger and just as well isolated. So that's the issue here: If your UK regs force you to build a coupled two-leaf outer wall, then you can still go with your plan (although it would need some modifications), and it can be made to work, but at the expense of wasted space and extra cost. Hopefully, your team can come up with a good two-leaf method that meets your local regs. But if not, then your plan will work. Brick and concrete are very massive and do a great job of isolating air-borne sound, but they also do a great job of transmitting structure-borne (impact) sound. Tap on a concrete wall and you can hear the sound many meters away, in other rooms, so decoupling is important. You might want to consider a drum riser and bass cab decoupling pad for the live room, if you can't decouple the two foundations. That keeps the impact and low frequency vibrations out of the slab, which helps considerably. I'm looking forward to seeing the updated design, and to seeing the project move ahead! - Stuart -

If we can avoid the extra cost, area and weight of the 3rd layer by going to a decoupled 2 leaf / layer construction then that would be a huge win, I had just assumed (my bad) that we would have to go down the standard uk cavity wall design (coupled type) and then add a further 3rd layer but it is now well worth me asking the architects if we can decouple the 2 walls / foundations and still keep within regs. I'll let you know! Cheers

Ok, so we are continuing to look at the ability to accommodate the 2 leaf system. Firstly just to answer a couple of your earlier questions just to assist with this initial discussion point -

Soundman2020 wrote:

Great! So this is basically a "greenfield" build, starting form the ground up? Do you plan to re-use the original foundations and slab, or are you going to dig those out and re-pour them specifically for the studio? I would recommend "dig out and re-pour" if you can, since that provides the opportunity for maximizing isolation by pouring separate isolated foundations for the inner and outer leaves. For heavy drums at 3:00 AM, that's a big plus factor......... Once again, it would be MUCH better to pour a monolithic foundation-plus-slab for the inner-leaf, and a separate foundation around the outside of that for the outer leaf. The gap between the two is filled with suitable acoustically decoupling expansion compound, but the two foundations remain independent, separate, and isolated form each other.

Yes - we would be looking to demolish the old foundations and start from scratch again to enable us to have separate foundations - 1 for the outer leaf and then one for the inner leaf + main slab.

Soundman2020 wrote:

You were doing jsut fine until you got to "tied together with wall ties". That absolutely CANNOT happen with an acoustically isolated wall system. So the leaves must be built as a stand-alone, self-supporting structure, with ZERO mechanical connection between them- In other words: no wall ties. Or if regulations absolutely require wall ties, then you'll have to open your cheque book wider and use proper acoustic isolation ties. But even if you do that, then you need some very skilled bricklayers here: as they work, they CANNOT, absolutely and totally MUST not allow any mortar or other debris to fall into the cavity. If it does, then it will bridge the two leaves, thus negating the isolation. Keeping the two leaves totally isolated, decoupled and separate is paramount.

I'm still awaiting word from the folks if we can do without the wall ties - if not then I see there are numerous acoustic wall ties available and if it comes to that I will look in to making sure we go for the right ones. But yes - reverting to a 2 leaf structure and therefore being able to accommodate as larger air gap as possible does look attractive. And yes we have some options on being able to ensure a totally clear cavity is left by the builders - not only from their working practices but also ensuring some access to the the cavities to clear them out if need be - though this would be then properly sealed up again in order not to compromise the wall integrity. There is a key discussion point we are having if we do away with the 3 leaf system that gave us the lower floor inner room within a room concept and we went for the 2 leaf method (the reasons you give for this making perfect sense). Where we have 2 floors with the studio on the ground floor and the upper floor being a living room - with the original 3 leaf system the studio was in a self contained "concrete bubble" which was decoupled to everything above it but if we go for the 2 leaf system then because the whole 2 floor structure will need 2 leafs (standard UK construction) then the upper floor now shares the same side walls and floor / ceiling threshold as the studio so the key question is where do we look to put in the decoupling of the structure with relation to the outer leaf? i.e. do we now treat the lower and upper floor as one homogenous mass and look to decouple everything from the outer leaf - OR do we building in decoupling between the lower and upper floor so that and coupling going on between the upper floor and the outer leaf does not matter as much?. I hope this makes sense but the issue here is there will be roof lights / ceiling windows in the upper floor and also an internal door from the upper floor room to the main house structure. Hopefully the below diagram will show where I am coming from... excuse the simplicity but I trust it shows the concept. Above you will see the original 3 leaf design and below the 2 leaf. You will see the 2 roof lights and the door on the upper floor which couple the inner structure to the outer leaf. I do understand totally where you are coming from with the benefits of the 2 leaf over the 3 leaf but in my mind the 3 leaf did have the benefit of separating the lower floor from the upper floor (well in my mind anyway but I may have been missing other important points :D ) and this was why I went for that approach to begin with. But if we are going to go with the 2 leaf design (which I am keen to do if this is the best option) then in order to get my folks continuing to work in the correct direction as they formulate further design detail the question is which areas would we build in the decoupling regarding the 2nd floor? An easy first move is to not have the roof rest on the inner leaf (which it is currently shown doing on the lower sketch so I cannot see that being too much of an issue. But then would we work on decoupling the upper floor's walls from it's own floor (in which case would this lessen the issue of the first floor's roof lights and doorway being coupled) - or do we not worry too much on the floor to wall coupling but instead concentrate on decoupling the roof lights and having a double door set up in the upper floor. Or is it a mixture of both ? I can start to do the sums on which would be more cost effective but thought it would be best to ask this upfront in case there are any glaring issues I am missing or very pertinent advice that you may have. Many thanks.

Yes - we would be looking to demolish the old foundations and start from scratch again to enable us to have separate foundations - 1 for the outer leaf and then one for the inner leaf + main slab.

Great! That should give you an excellent start on good isolation.

with the original 3 leaf system the studio was in a self contained "concrete bubble" which was decoupled to everything above it but if we go for the 2 leaf system then because the whole 2 floor structure will need 2 leafs (standard UK construction) then the upper floor now shares the same side walls and floor / ceiling threshold as the studio so the key question is where do we look to put in the decoupling of the structure with relation to the outer leaf?

I'm not sure I understand what you are saying there. The upstairs living room will have nothing at all in common with the inner-leaf of the studio: it will simply be part of the outer-leaf, which is fine. In other words, the building shell (which is a single leaf) is the outer leaf for the studio, and the ONLY leaf for the rest of the building. The studio itself is built as a separate, stand-alone single-leaf structure, within the ground floor area of the outer leaf.

An easy first move is to not have the roof rest on the inner leaf

The roof cannot possibly be part of the inner-leaf: the inner leaf is just a simple self.supporting structure inside the ground floor shell of the building. The roof is part of the outer-leaf. The upper floor is outer-leaf only: there is no inner-leaf at all up there (unless you decide to build a second studio up there, for example, in which case that one would have it's own inner leaf, that would be entirely unrelated to the studio downstairs. It seems to me that the problem is your insistence on using a cavity wall for the building structure, when there is no reason to do so. If you would just build the shell of the building as a single-leaf (no cavities) then you should be able to see how the whole things works. That's the concept you should be looking for. The exterior wall is not a cavity wall, but you do still have a cavity in the wall, which is all that your code requires, probably. The cavity is between the outer leaf and inner leaf, not within the outer leaf. - Stuart -

I am not an expert on here or with building code for the UK, only for ground works but I think you will struggle to get the go ahead as the drawing above, mainly as the flooring joists for the upstairs room go into the outside skin, if this an outside wall that would not be acceptable. The only thing I can suggest is to speak to your drawings man and see if he thinks it is possible to revise your drawings for the work with the outside skin downstairs being built solid with the brick facing and a block, ideally a concrete block for more mass :) wide enough so that when you get to the height of the joists a separate skin can pick up the joists, this would probably mean something in the region of 250mm-300mm wide depending the size of cavity required. Downstairs you could then build the stud work on an isolated slab which would be separate from your foundation for the outside skin running your ceiling joists in between the flooring joists for upstairs so as to gain as much height as possible. :D i'm sure there are some better ideas than that but like I said I'm not an expert. Carl

Hi guys, Thanks again for your help Stuart - and also Carl for your input. I think I am understanding where all sides are now thinking (but it is never easy in print!) but yes, the crunch here is that before we even get to thinking about studios, normally building practices here will require a cavity wall (i.e. a 2 leaf wall construction) for all standard home style rooms, well those that are external walls (internal walls can be simple single leaf stud partition). This cavity requirement is partly because of thermal requirements due to the crap UK weather :D and it has therefore been adopted by the UK contraction industry here. And as Carl points out, the norm is for floor joists etc. to be supported by the internal wall (leaf) of the 2 walls and not the external wall. So the upstairs room "should" require those 2 leaves as well even though it has nothing to do with the studio and hopefully you can therefore see where my initial train of thought stemmed from in that I had to start with 2 leaves being the basis for a normal house build - and then bring in the extra layer to add a decoupled barrier between the studio and the rest of the structure. Hope that makes sense. Where I say "should" I can now have a proper meeting with the architects tomorrow as I have now just received their layout drawings of the existing and proposed external plans in order to start the planning permission process (purely for external / cosmetic reasons and therefore does not involve internal structure / detail at this stage) but it does mean we have the whole place fully dimensioned and drawn so we can now have some proper discussions with them tomorrow and can constructively table the cavity wall requirement with them to see what the options are - and I'll report back shortly. Cheers

Well, if code absolutely requires cavity walls where you live, then cavity walls it will have to be! No choices there... :( But in that case, I'd do my damnedest to make sure that they two parts of that wall act as one leaf, not two, by using as many ties as allowed by code, and making them as big and hard and rigid as code allows. I would also try to make what is effectively the "middle" leaf (the inner one of the outer pair, if that makes sense) as heavy and massive as possible, since a 3-leaf wall is most effective when there is twice as much mass on the middle leaf as on the other two. In other words, the mass of the middle leaf is supposed to be the same as the mass of the outer leaf plus the mass of the inner leaf. It may not be possible to do that fully (code, budget, space, etc.), but getting close would help. That kinda takes us back to your original plan. It will be interesting to see what the architects say. - Stuart -

Fear not, I shall do all within my power to have a 2 leaf system!..... ...... or maybe I put the funding for all that mass I need towards moving to a warmer climate 8) I'll let ya know what comes of the meeting later today.

Any news mate?

"normally building practices here will require a cavity wall (i.e. a 2 leaf wall construction) for all standard home style rooms, well those that are external walls" Are we discussing brick/rock and or block as the external boundary? The assumption that you will construct a two leaf assembly may have some merit...but guess what? A two leaf assembly is what you are going for. My thinking is that you are developing a coupled double sided assembly, and that is different. And that is a common exterior/interior wall assembly, exterior facade, interior sheathing. In respect to a thermal break, indeed a double wall assembly is going to get you that, I do not know if it has been adopted as quickly as you are saying it has...maybe it is simply a matter of where you are doing this construction at in respect to where you live within the country.

Hi all, Had the initial discussion which was mainly down to being that the existing house has now been fully modelled in to their design system and they had laid out the existing house and also a preliminary model of the 2 storey extension based on my initial rough mandate - so most of the time was spent tweaking / detailing a lot of other areas to get the general proportions and other detail right (we are also doing work elsewhere in the existing building.) But when we got to the studio area - yes they took on board what you guys were saying and whilst they were already understanding a lot of sound isolation principles (they currently work to existing UK building regs which do dictate certain aspects of sound isolation for certain building circumstances here) they did speak much of the same language (which was good to hear) but they also recognised that what we are trying to achieve is a whole big step further so they were going to look in to this further and float a few concepts around with these walls. It does sound like there is some flexibility in wall construction to a certain extent so the whole cavity wall thing is more along the lines of preferred building technique for most dwellings with the interests of thermal and dampness in mind - but that is not to say that different techniques can be used to try and embrace as much of the advice here. I'm catching up with them later today and will see what pans out - although their immediate priority is to get the external views sent off to the authorities for the planning permission process (aesthetic approval) which then means a 6 - 8 week wait for approval there, but during that time we can then focus on the internal detail prior to submitting that for the Building regs / code approval side of things. Thanks all.

Sounds hopeful! Fingers crossed... - Stuart -

Well we are now officially in the Planning Permission period with all the external details submitted to the authorities and brought to the attention of the neighbourhood for their comment over the next 6 weeks - let's hope there are not too many objections !! :D Just before we get fully in to the detail of the way forward for the actual structural / sound isolation design I thought it would be nice to have a short period of rest and celebration and am therefore implementing a little thing called Xmas ! :yahoo: So before I get too distracted in that have a Great Christmas all and a Happy New Year and I look forward to catching up on things very shortly.

Merry Christmas to you too, ( a little late....) and Happy New Year. Hopefully, it will also be a "Happy New Studio" year! :) - Stuart -

Well it has been a while since the last post but we have been pretty busy in the meantime with the key thing being that we have just been granted Planning Permission to proceed with the build ! So we have been looking at the construction method and for a number of reasons it looks as though we will need to stick with having the conventional UK style Cavity wall construction being 2 outer walls - and then have an additional inner decoupled inner shell. One benefit of this is that I can leave the builder to construct the main shell of the extension in a reasonably straightforward way and he can finish the 2 storey extension and be on his way, leaving me with the basic lower floor room to then, in my own time, build the inner shell as meticulously as I want to. Therefore from a walls point of view we are looking at: Outer layer = 100mm thick Red "Engineering style" brick and mortar wall. Then 100 gap - filled with Rockwool Batts. Then inner wall - but instead of the usual lightweight thermalite block we will use high density concrete blocks (again 100mm thick.) It has then been recommended to render the inside face of this wall. Building regs dictate the above walls will need to be tied together. They will also be on a common concrete foundation. THEN on a separate inner concrete floor slab which is decoupled from the above wall and outer foundation assembly we are looking at constructing an inner shell (wall and ceiling) from timber joists (infilled with Rockwool) supporting the shell made from multiple layers of plasterboard (using RC2 channel and green glue where relevant.) We can refine the exact construction / layers on that later. The upper level room floor above this will be constructed from concrete and we are looking at various methods at the moment based on practicality and density etc. I will shortly sketch out all of the above to show it a bit more clearly - but whilst this is probably not the best or optimum approach from the sound isolation point of view it does provide a practical way forward for me and should still give a reasonable level of sound proofing (provided doors / windows and other detail are also up to scratch ). But a key question at this stage though is regarding the floor (of the ground level room which will be the practice room. There currently is an existing concrete slab of 100 to 125mm thick which is then on at least 250mm hardcore which is then on the earth. We were originally intending to rip this all up and start again however the slab is in better condition than we expected and also appears to be incredibly hard ! Lump hammers and cold chisels just bounce off it and even a decent masonry drill struggles to get through it. Maybe they used a particularly high grade of concrete? but to the extent that the architect has said why not use the existing slab and just cut away the edges to allow the new outer wall foundations to still be poured around the outside in a manner that they will still be decoupled. Then as the floor height of this slab is still 100mm below the existing floor height of the rest of the house and therefore needs to be raised it has been suggested to use Regupol 6010 BA (for its sound isolation properties) and then on top of that another concrete layer to effectively give a floating slab whist bringing it up to the required level. So your thoughts on that would be appreciated - I have read the other various threads that lean towards not necessarily needing to float such a floor in these circumstances, however it would be nice not to have to break up this existing slab and it does need raising by approx 100mm. Regulpol 6010 Ba is quite expensive though but would this be better than using traditional "celotex" insulation form a sound point of view? I recognise that if I am intending on a 4 to 5 layer plasterboard shell that the top surface will need to support the weight so the architects are just running some calcs on that front. Many thanks.

Welcome back! :) I was wondering what had happened to your build...

THEN on a separate inner concrete floor slab which is decoupled from the above wall and outer foundation assembly we are looking at constructing an inner shell (wall and ceiling) from timber joists (infilled with Rockwool) supporting the shell made from multiple layers of plasterboard (using RC2 channel and green glue where relevant.) We can refine the exact construction / layers on that later.

Since you are building an entirely decoupled inner-leaf wall, on its own separate foundations, you don't need the RC as well. The purpose of RC is to decouple the inner-leaf surface from the outer-leaf surface, bur since you are already accomplishing that with the decoupled foundations and walls, you don't need to do it again: it won0t gain you anything more.

the architect has said why not use the existing slab and just cut away the edges to allow the new outer wall foundations to still be poured around the outside in a manner that they will still be decoupled.

Yes, but since you will be putting walls and a ceiling on top of the inner-slab, you will also need to undercut the edges and pour some type of footing under there, then leave a small gap (to be filled filled later with something that seals and decouples), then the new foundation for the outer walls. That footing is needed, since the old slab will be supporting heavy structures.

Then as the floor height of this slab is still 100mm below the existing floor height of the rest of the house and therefore needs to be raised

Why does it need to be raised? :) Why not just leave it a little lower, and make the most of the extra room height?

it has been suggested to use Regupol 6010 BA (for its sound isolation properties) and then on top of that another concrete layer to effectively give a floating slab whist bringing it up to the required level.

I don't see that as being necessary: the slab will already be totally isolated from the rest of the structure: I see no need to float a floor on top of an already decoupled slab. The only reason might be if the old slab and new foundations are both tied to the same bedrock, but you said it rests on earth, so that seems unnecessary. It's the same as with the RC: If the leaf is decoupled, then it does not need to be decoupled again.

I have read the other various threads that lean towards not necessarily needing to float such a floor in these circumstances,

I agree with those threads! It isn't necessary.

however it would be nice not to have to break up this existing slab and it does need raising by approx 100mm.

I don't think you need to do either! Leave it there, trim the edges as suggested by the architect, pour new footings under the trimmed edges, and you are done! Why waste that extra 100m of free room height? Just put a step down into the studio, and be done with it. More height is practically always good in a studio, so don't throw it away unnecessarily! There are even people on this forum who have gone the OPPOSITE way: dug out their basement slabs, dug down so more, and poured a new slab several cm lower down, just to GAIN room height. Height is a precious thing, in acoustics: don't wast it.

I recognise that if I am intending on a 4 to 5 layer plasterboard shell

Do you really need to go to such extremes? I'm betting that you'd be fine with two layers of 16mm drywall, and seldom is it necessary to go to more than three layers, even in complicated cases. John once mentioned that he does many of his rooms with just ONE layer. So unless your isolation needs are very, very extreme, I can't see you needing five layers of drywall. And finding drywall screws 10cm long for the last layers might be a bit of a challenge too... :) :!: I know you are aiming for 70 to 75 dB of isolation, and that is a tall order, but the rest of the structure seems to be well on the way to getting you there, and I would be concentrating my design efforts on the rather complex issues of doors, windows, HVAC and electrical: Getting those to 75 dB is going to be the biggest challenge you face. - Stuart -

Hi Stuart, It's great to hear from you again and to be back here getting things progressing again. Many thanks for the helpful and constructive feedback - which I shall go through and add in to our considerations. As for the raising of the floor, sorry but I did not explain that Building regs will require a certain amount of thermal insulation to be in the floor which is a key issue over here these days. The normal method would be to have an approx 70 mm thick Celotex layer within the floor construction and as we are hoping to avoid the huge task of removing what looks to be an already decent slab (which does not currently have a viable insulation value) then the insulation layer will need to go on top of the existing slab. Being Victorian era the house already has extra high ceilings (nearly a foot higher than standard these days) so this is handy in allowing us a bit of extra room to accommodate the various materials that will be going in - but I hear what you say about the benefits of higher rooms. As to the number of layers of plasterboard then if I do not need to go to the extremes of that number then all the better. The good thing I guess is that more layers can be added if need be. The weight of the inner shell is indeed something I have got the architect working on to ensure that our inner slab is strong enough to support it. I'll come back with some clearer detail shortly along with some sketches / diagrams of the design we are looking to be working towards just to ensure we are on the right track. Then yes, we have the doors, windows and HVAC to cover - which we have always kept in mind and have some proposed ways forward on but will report back here for comment / critique etc. Cheers

Outer layer = 100mm thick Red "Engineering style" brick and mortar wall. Then 100 gap - filled with Rockwool Batts. Then inner wall - but instead of the usual lightweight thermalite block we will use high density concrete blocks (again 100mm thick.) It has then been recommended to render the inside face of this wall. Building regs dictate the above walls will need to be tied together. They will also be on a common concrete foundation.

Doesn't help to give up all that air space/real estate if you have to couple all this wall assembly together. Fact it is looking like moving towards more of a TL issue than a higher TL assembly

THEN on a separate inner concrete floor slab which is decoupled from the above wall and outer foundation assembly we are looking at constructing an inner shell (wall and ceiling) from timber joists (infilled with Rockwool) supporting the shell made from multiple layers of plasterboard (using RC2 channel and green glue where relevant.) We can refine the exact construction / layers on that later.

Classic multiple leaf wall assembly if I am reading this correctly. You should post a drawing, really, it is critical to get a handle on this now rather than later.

Hi Brien, Thanks for your input. Yes, we are having to approach this in a more unorthodox way to just building a studio - Just to step back a bit to recap / explain, what we are building first and foremost is an extension to a house - then inside part of it we aim to have an informal practice space with some degree of sound reduction built in but the whole build must really (for numerous reasons) be initially built like a standard UK house and then we do what we can to have an inner cell built to improve the sound isolation. The thought process is that we have the extension built as a standard UK house construction build which is heavily biased towards cavity walls and thermal ratings. And to address your first point - yes the two main walls (with the rockwall filled cavity) will need to be tied in together to conform to regs. Maybe there are some resilient wall ties available but also thinking along Stuart's comment that we look to couple those walls together by using an excess amount of wall ties to get them as close to one big dense single wall (leaf) as possible. There is a lot of mass and density there already so although it will not be optimally working for us it should give towards the end goal to a certain extent. If we start to veer away from that too much it gets over-complicated and costly from the onset so I would prefer to have a UK builder construct me the main extension (including a couple of tweaks - decoupled slab and concrete upper floor) which gives me the low cost and straightforward build for my main extension and then the builder can walk away and then in my own time (and using my own free labour) I then build the inner shell from wooden joist / plasterboard etc. which will be decoupled from the main shell of the building. I understand this is not the perfect way forward but having looked at it from many angles, and bearing in mind this is a home first and a performance room 2nd, that I may be putting some extra cost and materials in to that inner shell which I may have been able to avoid had I approached the main build differently - but after balancing it all up this is the most practical approach for us though maybe not the totally cost effective or best sound isolation method. The priority then is to get the outer shell design firmed up first so that the builder can do his bit, and then I have more time later on to detail the inner shell. Things like HVAC and decoupling various things are being borne in mind up front though - for instance the builder will be including some brick columns at the rear of the property to allow the HVAC inlet and outlets to be hooked up to at a later date etc. Here are some sketches which I hope help - excuse the basic format of some of them but I trust they give you the general concept. Below is the final intended design showing the main house to the right and the extension to the left. The lower floor (with the 2 windows) will be the practice room and the upper floor is the living room (the room is inside the pitch of the roof with velux windows in the rear roof pitch). Each floor will have its own doorway in to the main building. Below is the plan view where the practice room is labelled "Spare Room" - **note that this does not show the inner shell, only the outer cavity wall construction** and also that this drawing needs updating i.e. the door from the main building will be in a separate lobby inside the main building to allow a 2 door system between the house and Practice room. also the room labelled "Office" will be outside of the main inner shell threshold. Although it will effectively be a control room there will only be low level monitoring going on. It will also be my office for my usual job so I would like it outside of the sound proofed envelope (again double doors and studio style windows will be used to separate it. The wall marked "new stud wall" will now be a solid concrete block wall. Below is an overview of the basic shell construction which is primarily in accordance with Standard UK regulations but then we are tweaking it by: 1) Decoupling the floor slab from the main wall foundations 2) Building the inner wall from High Density Concrete Blocks (instead of the usual light density thermalites) 3) constructing the upper floor form concrete - a few methods are being considered but we are aiming to end up with approx 200mm thick of concrete and screed.

Finally, once the builder has finished I am looking to build the internal shell as per the below diagram from joists and plasterboard layers - this whole shell will be self supporting and decoupled wherever possible from the main outer shell. Exactly how may layers of plasterboard and whether we use RC2 channel and or Green Glue etc. can be defined at a later date once we have progressed the main outer shell and the builder hands over to me. I acknowledge that windows, doors, electrical hook up and HVAC will also need specific attention so we do need to bear in mind certain provisions during the first stage of the build so that when I come to construct the inner shell it will be as straightforward as possible.

Just to note that my initially indicated goal of approx 70db was aiming high but due to the conditions here with only one neighbour and the infrequent use of the room then there is room to compromise, but I would still like to keep on that path where possible