UK - Double garage build

[azurr]

Hi folks,

Offer made on house and accepted - touch wood everything will go through and the wife has donated me the double garage!

I haven't got exact measurements yet but i would estimate 6mx5m or approx 20ft x 16ft

First thoughts.

Leaf system - build stud wall on all inner sides of garage if possible with dry wall in between the brick and stud wall, leaving inner side of stud wall open. Then air gap, then stud wall with two layers of dry wall on inner wall of this stud. Is this the most efficient way of doing it?

Vocal booth - It would be nice to have it bit Im not sure if necessary?
Pros - looks 'pro' would be nice for 'getting lost in the performance'
cons - added cost, less space, more complicated build, may sound bad if too small. When we come to sell the house the new owner could use as cinema or something - vocal booth makes the space more defined as music studio only,

What do you guys think about this?

I want the space for mixing and composing music, I can't imagine recording live drums as music is mainly electronic with vocals and occasional guitar, there may be some brass instruments somewhere.

So one big space or smaller with vocal booth?

I will base the inner wall plan on those provided on website hexagonal type one. though I'm a bit worried about the lost space in the corners.

Thanks in advance.
Azurr (sam)

[Soundman2020]

Hi Sam, and Welcome!

Leaf system - build stud wall on all inner sides of garage if possible with dry wall in between the brick and stud wall, leaving inner side of stud wall open. Then air gap, then stud wall with two layers of dry wall on inner wall of this stud. Is this the most efficient way of doing it?

Nope. That would be a 3-leaf system, which would be a very inefficient way of doing it, and would not isolate well at all for low frequencies. Simple 2-leaf constructions is more efficient, costs less, and isolates better at low frequencies.

Vocal booth - It would be nice to have it bit Im not sure if necessary?

Do you need it? Do you do a lot of isolated vocal recording, acoustic instrument recording, or have a need to isolate bass or electric guitar cabs? If so, then build one. If not, then don't!

with vocals and occasional guitar,

There you have part of the answer to your own question! Would it possible / comfortable to record that in the control room itself, instead of in an iso booth? If so, then you don't need a booth. On the other hand, if you have equipment with fans, a noisy HVAC system, poor isolation, or can't stay quiet yourself, or need to monitor on the main speakers while tracking, then you do need an iso booth.

I will base the inner wall plan on those provided on website hexagonal type one.

Which website is that?

though I'm a bit worried about the lost space in the corners.

Any design that cuts of corners and removes them from the room is a bad design, based on myths and ignorance, not on solid acoustic principles. You are correct: it wastes a lot of space, and not just any space but precisely the space that is most desperately needed for bass trapping, and perhaps also for speaker soffits. Not sure which "website hexagonal " design you are looking at, but either is is badly designed, or you are not understanding what it shows.

- Stuart -

[azurr]

Thank you for your reply,

My reasoning was based on the diagram where in the 'excellent' 1 = brick wall and stud wall and 2 = inner studio wall

triple-leaf-diagram-600x297.gif

The hexagonal thing I was taking about was this pic, where the whole garage is one big control room. It may be squarish so I expect some battle with room modes that perhaps could be avoided somewhat by making room this shape??

Basic Plan 2.gif

So what would you advise in terms basic order of construction, just leave brick wall/garage door untreated? Im worried about transmission of sound at garage and of course door low frequency .

Regards,

I do enjoy using the colours
Sam

[Soundman2020]

OK, it looks like I missed the part where you said the garage wall was a brick wall! I was assuming it was a stud wall as well, with siding on the outside and drywall on the inside: But yes, if you have a single brick wall garage (not brick veneer: actual brick wall), and you built a framed wall with drywall on only one side, just inside that, then yes, you would have a two-leaf wall.

The hexagonal thing I was taking about was this pic, where the whole garage is one big control room.

That's actual a John Sayers designed room, which if I recall correctly is also in the SAE manual, which he wrote. It's not really a hexagonal room, and it does not cut off the front corners, although it looks like it. It uses John's design for speaker soffits, which has hangers under the speaker shelf. That's why the speaker soffits are labelled "bass trap" on there. The rear corners are also bass traps. So acoustically speaking, it is a rectangular room, even though visually it might look hexagonal or even octagonal.

It may be squarish so I expect some battle with room modes that perhaps could be avoided somewhat by making room this shape??

Changing the shape of a room by adding more walls to it, or by angling one or more of the walls, does not actually get rid of any modes: it just changes the form of the modes and moves them to different frequencies. It might switch an axial mode to tangential or even oblique, and it might shift it to a different frequency, but it will still be there. That might not be a bad thing, in some cases, but the mode doesn't actually "go away".

So what would you advise in terms basic order of construction, just leave brick wall/garage door untreated? Im worried about transmission of sound at garage and of course door

Most people in that situation block off the garage door, by building a wall just behind it. That completes the outer leaf. Yes, in theory the door itself could act like a third leaf, but in practice there's not much surface density on the average sheet metal garage door, and there are methods for compensating for the 3 leaf effect, if necessary.

With that wall in place, then you can just build the inner-leaf inside the now completed outer-leaf, as normal.

and of course ... low frequency .

Yep! But as long as you tune the MSM resonant frequency to be at least one octave below the lowest frequency you need to isolate, and as long as you have enough overall mass, with excellent seals all around, you can get decent isolation.

- Stuart -

[azurr]

Ahh ventilation. I'm hoping someone can steer me in the right direction.

My studio will be a detached garage with a pitched roof, and as i'll be aiming for a airtight space i'll need ventilation.

I want to keep it as simple as possible so aiming for a inline fine to push air in from the outside and have a passive vent letting air out.

Im really concerned about the noise from the fan (are they really silent) the noise from air flow and noise from outside to inside.

So far im thinking of this on the outside wall BUT bringing air in from the outside

exhust-system-600x330.jpg

Should I attach this to some acoustic ducting , which could lead to a baffle box placed inside the wall which then leads into the studio? Ideally should the opening to the inside of studio be wider?

For the passive outlet system would these 'acoustic air vents' work? I cant imagine they will be wide enough to span the oustide to inside given the room within a room approach. eg

vents.jpg

or maybe something like this?

vent1.jpg

Does the baffle box help reduce sound transmission from out to in and vice versa? or does it just reduce noise of air flow?

I dont want baffle boxes to be in the studio, I Have space on the rear of the garage to place things ie inline fans dead vents etc.

I would place the inlet and outlet on opposite sides of the same wall.

Apologies in advance for my lack of understanding !

[azurr]

That's why the speaker soffits are labelled "bass trap" on there. The rear corners are also bass traps. So acoustically speaking, it is a rectangular room, even though visually it might look hexagonal or even octagonal.

So for these corner bass traps, ive seen designs with insulation straddling corners and super chunks. Which is better? Im really unsure what to cover these with. Ive read on the forum you can cover with fibre board to make a low-mid bass trap, what about a think layer of drywall - would that reduce the efficacy? Ive seen some designs with wood membranes and wholes put in them..

Thanks in advance..

[Soundman2020]

and as i'll be aiming for a airtight space i'll need ventilation.

Yup! Very much so.

I want to keep it as simple as possible so aiming for a inline fine to push air in from the outside and have a passive vent letting air out.

Right, but I wouldn't use an inline fan for that. The way you show it, the fan is sealed inside your MSM cavity, where it won't be isolated from the inside OR from the outside, and would be inaccessible for maintenance, repairs, cleaning, replacement...

Im really concerned about the noise from the fan (are they really silent)

Nope, they are not silent, and yes you are right to be concerned about the noise.

the noise from air flow and noise from outside to inside.

That's why you need silencer boxes (also called "baffle boxes").

Should I attach this to some acoustic ducting , which could lead to a baffle box placed inside the wall which then leads into the studio?

Yes. Depending on how much isolation you want, you might need two silencer boxes: one where the duct comes through the outer leaf into the cavity, and the other where it goes through the inner-leaf, into the room.

Ideally should the opening to the inside of studio be wider?

The entire duct system has to be calculated correctly, so that all the ducts, silencers, fans, and registers are the correct size to provide the correct amount of air flow at the correct velocity. Don't guess! do the math...

For the passive outlet system would these 'acoustic air vents' work? I cant imagine they will be wide enough to span the oustide to inside given the room within a room approach.

You need a silencer box (or a pair of them) on the outlet too.

Does the baffle box help reduce sound transmission from out to in and vice versa? or does it just reduce noise of air flow?

Both! That's the entire purpose of having them. It allows air to flow through while preventing sound from getting through, and the dimensions are calculated correctly such that the air flow through the box is as silent as possible.

I dont want baffle boxes to be in the studio,

Then put them outside the studio! Or inside the wall cavities, provided that you make your walls thick enough for that. Or in the ceiling cavity. I often use the ceiling space between the inner leaf and outer leaf for HVAC.

So for these corner bass traps, ive seen designs with insulation straddling corners and super chunks. Which is better?

Superchunk, by far.

Im really unsure what to cover these with.

Fabric. You might also need plastic across the front (behind the fabric) to prevent the trap from sucking out to much of the mids and highs.

Ive read on the forum you can cover with fibre board to make a low-mid bass trap,

... in which case it would no longer be a bass trap! The point of a bass trap is to trap bass, not low mids. All of your modal issues will be under about 200 Hz, so deep bass trapping is what you need. Mids might need some treatment too, but it would be silly to waste perfect location for bass traps by putting mid-absorbers there instead...

what about a think layer of drywall - would that reduce the efficacy? Ive seen some designs with wood membranes and wholes put in them.

You seem to be confusing several very different types of acoustic treatment device, all at once! Bass traps are usually very thick porous absorption. It might be in the form of superchunks, or corner traps, or even hangers, but it is not tuned: it is pure broad-band low-frequency trapping.

If you put a membrane across the front, that makes it a tuned trap, so it is not longer a broad-band bass trap. It is now tuned to a very specif frequency. You might need that if you have a very problematic room mode that isn't fully damped by the broadband bass trap. If it has holes in it, the it is not a membrane trap! Membrane traps are sealed air-tight. Drilling a hole in it would kill the effect. Panels with holes in them are usually Helmholtz resonators of some type or other, and they are for mid range.

Those are three entirely different principles of acoustics that are involved there, and they are meant for very different purposes.

- Stuart -

[azurr]

Stuart, you are a legend. Thanks for your time.

Ok so I will have the keys in 2 weeks!!!
Excuse my lack of sketch up skills but heres the layout, it is completely seperate from the house and has its own pitched roof.

studio basic sketch pic.jpg

Questions/areas of advice needed

roof.jpg

1) Ceiling is 2.5m high to existing beams, Id like to leave them exposed and somehow decouple the inner wall to maximize height. any ideas?
Otherwise Ill attach the new inner walls to the existing ceiling using resilient channels (i know this is not ideal).
With ceiling clouds to go up I'm worried about the lack of height.

2) the inner door frame will be attached with plasterboard to the outer brick leaf door frame, is this a major problem?

3) With the inlet outlet fans going in the ceiling - how do i access them? I will need some access panels/hatches which will compromise the soundproofing. Any tips?
Is it ok to have both inlet and outlet in ceiling?

4) the door is in the very corner to the rear of the studio. So no symmetrical bass trapping in the corner. ive seen some solutions but they dont look pretty! I think i will have some perpendicular to door/either side of sofa.

Thanks in advance!!! both excited and stressed

[azurr]

Ok back to basics!!

Construction

Builder not too happy about building 2.5m walls and them not being attached to existing outer brick wall.
he's built cinemas and they were attached with acoustic/rubber wall ties?
I know stuart is NOT a fan of wall ties!!
Ive read posts from rob gervais about attaching inner walls to floor and ceiling only? and theres no real need to decouple the wall from the ceiling.
I take it there is some min width for stud wall to be able to stand stafely and be structural sound?

For the ceiling itself I was thinking - from top to bottom

------- attic air space
-------fluffy insulation
------- flooring boards (for storage)
------- original Joists
-------resilient channel
-------plywood (so i can hang stuff)
-------green glue (subject to budget)
-------plasterboard

Ventilation

Stuart you mentioned you wouldnt use an inline fan for ventilation? what would you use.
Original idea was positive pressure ie intake fan but passive outlet directly to outside (through both inner and outer walls)
from your posts youre not a fan due to airflow? (no pun intended)

Many thanks

[Soundman2020]

Builder not too happy about building 2.5m walls and them not being attached to existing outer brick wall.

This is an issue that pops up every now and then, from people who might be really good at building stuff but don't have a clue about how the structure actually works, or what keeps it in place!

I would ask your builder about this structure:

timber-shed-SML-ENH.jpg

Does he think that the owners should build a brick wall around that, and put ties across the gap, to hold it up?

More to the point: WHAT does he think is holding it up at all? ? ? Why does it not fall over?

Ditto for this one:

shed-ENH-SML.jpg

How come it is standing up just fine, yet there are no brick walls around it to hold it up? Ask your builder to explain what keeps that in place...

flat garage medium-ENH-SML.jpg

Even more interesting, is this one:

carport-ENH-SML.jpg

How come it does not fall over? Magical incantations? Invisible skyhooks? Photoshop?

All of those represent exactly what you will be creating: A timber framed structure that is self-supporting. There will be four walls and a ceiling, and they will be tied together in such manner that the structural loads are correctly handled and transferred to the right places so that it does not fall down, sag, tilt, warp, twist, or otherwise deform.

20 years ago I built a shed similar to the ones above in my back yard. Since then, that shed has survived two earthquakes of greater than magnitude 8 (one was 8.3, the other was 8.8 ), plus probably several dozen other quakes over magnitude 6, and it did not fall down. It didn't even budge or wobble. I also did not build any brick walls around my shed to hold it up: it is just four timer-framed walls, with plywood sheathing that caries the sheer loads, and a timber-framed roof resting on top, correctly attached to the walls. It satys put, because it is self-supporting, just as your studio will be.

That's what you will be building. The ONLY difference is that you will be building it inside an existing structure, but that does NOT create any need to attach the two structure to each other! If a timber-framed shed can stand up all by itself out in the open, why would it be any different if you build it inside a bigger structure? In what way would that change the structural integrity?

he's built cinemas and they were attached with acoustic/rubber wall ties?

Good for him! Just ask him one question about that: Did he design that cinema? Did he do the structural calculations? Did he do the acoustical calculations? Did he do the seismic calculations? Who determined that the cinema needed resilient ties? Was it him? Or did he just follow a set of plans that were prepared for him by an architect, who had already consulted with an acoustic engineer and a structural engineer?

A cinema is not a recording studio. Not the same structurally, or acoustically. Not even close. There might well be very valid reasons why a cinema wall would need extra bracing.

This like someone who once worked on a truck, looking at your car and saying that four wheels is no good: you need at least 16, because that's what trucks have...

I know stuart is NOT a fan of wall ties!!

Not true: I use them when I need them, which is usually when there is no other realistic alternative.

I live in the most heavily earthquake-prone country on the planet: the largest quake in recorded history hit here half a century ago. We learned from that, and now have the toughest building code in the world: two really huge quakes that would flatten pretty much any other city on Earth have rolled through here in the last few years, plus dozens and dozens of smaller ones, all of which were at least as big as the one that wiped out Haiti a few years ago, yet the city (and country) is mostly still in tact, with just a few sub-standard buildings damaged. I am very, very well aware of how structures move under extreme seismic forces, and what keeps them together, since I go through it in person several times per year, on average. I'm not a structural engineer, but I've studied the principles enough, and lived through them enough, to have a reasonably decent grasp of what keeps buildings standing up, and what causes them to fall down. And I use sway braces, resilient mounts, and seismic snubbers when they are indicated. Plus, I always get a REAL structural engineer involved to check my designs and make sure they are safe. I might think I know a a bit about structures, but he's the guy who is qualified to say if it is good nor not. That's just the smart thing to do!

So I don't use wall ties when they are not needed, and when they are needed I first look for other ways of accomplishing the job. But if there aren't any viable alternatives, then I'll use them, especially if the structural engineer tells me to.

Ive read posts from rob gervais about attaching inner walls to floor and ceiling only

I agree with Rod. And I'd do that too... assuming that you don't need high levels of isolation, and don't mind some sound flanking through the structure, causing the entire building to vibrate slightly! If that's the case with your studio, and you don't mind some leakage, then that is one way of doing things.

It all depends on what your numbers are: How much isolation do you need, and at what frequency do you need it? If you only need, say, 40 dB and mostly in the mids and highs, then by all means connect your walls to the ceiling! But if you need more like 60 dB across the full audio spectrum, right down to low bass frequencies, then don't.

I use whatever method fits the specific project, just like Rod does. I'm betting that the posts you saw by Rod were for projects that did not need high isolation. Rod would not tell someone to tie their inner-leaf walls to their outer-leaf ceiling if the project required high isolation.

I take it there is some min width for stud wall to be able to stand stafely and be structural sound?

Yep! That would be 2x3 lumber... provided that it's a rather small structure, without any great loading on it, such as maybe a garden shed, or small carport. If not, 2x4 lumber is the norm.... as long as you don't need to have your roof higher than about 12 feet or so, in which case you'd probably need to switch to 2x6. In all cases, assuming suitable bracing and sheer handling. For your ceiling joists, you need to do a bit more math, taking into account the span, live load, dead load, deflection, joist spacing, and type of wood. Then you can determine what dimensions of lumber you need. Or you can use span tables.

Of course, in all those cases, you'll still need to get your design checked by a structural engineer.

For the ceiling itself I was thinking - from top to bottom
------- attic air space
-------fluffy insulation
------- flooring boards (for storage)
------- original Joists
-------resilient channel
-------plywood (so i can hang stuff)
-------green glue (subject to budget)
-------plasterboard

Which would limit your maximum isolation to around 40-something dB, since your inner-leaf ceiling would be only partly decoupled from your outer-leaf walls. And in this case, you probably would need isolated sway braces on your inner-leaf wall tops, since they would not have the benefit if the ceiling structure to tie them together, thus creating the self-supporting structure of the inner-leaf room...

You'd also need to get a structural engineer to tell you if your existing joists can handle all that extra load. The original design was for a certain dead load and a certain live load. You cannot go beyond those limits, or it will collapse. The only person qualified to tell you how much extra load you can hang on those joists, is a structural engineer.

Ditto if you attach your inner-leaf walls to those joists: that puts additional lateral loads and stresses on the joists that may or may not have been considered in the original design.

Stuart you mentioned you wouldnt use an inline fan for ventilation? what would you use.

I would either use an extractor fan at the far end of the exhaust duct, probably on the outside surface of the outer wall, or I'd use a supply fan on the intake end of the supply duct, probably on the outside surface of the outer wall. Or if the studio is a bit larger, with two or more rooms, I prefer to use a single AHU to both condition and drive the air flow around all of the rooms, plus a smaller intake and exhaust system. If you design carefully, you can get by with just the AHU fan and use variable dampers to control the flow in the various ducts. Worst case, you add am extra fan to drive the fresh air into the mixer plenum, then the over-pressure automatically pushes the stale air out the exhaust duct. It all depends on the studio, the requirements, and the budget.

Original idea was positive pressure ie intake fan but passive outlet directly to outside (through both inner and outer walls)

That's fine. That will work.

from your posts youre not a fan due to airflow?

As with most aspects of studio design, there are pros and cons for each approach. From some points of view, it is better to have a slight over-pressure inside the studio (EG, it helps keep dust out) but from another point of view it is better to have a fan on the outlet "sucking" air through the room, as you can gain a couple of extra dB of isolation like that, since the airflow is towards the fan, not away from it, and fans do make a bit of noise, plus create turbulence....

It's like the old argument about using different materials or different thickness of material to make your wall leaf, as there is a slight advantage to doing that for acoustical isolation... but on the other hand, if you make all the layers the same thickness of the highest density material, you get more mass, which also improves isolation...

Six of one, half a dozen of the other... pros and cons... It all depends on the specific project, and the specific situation. Sometimes, it might be undesirable to have a fan at the point where the intake is, or where the exhaust is, or there might be insufficient space for a full AHU, or the budget might be limited, or there might be a need for extremely quiet HVAC, or there might... When I'm designing a studio, there's hundreds of factors to take into account in making decisions on which method to choose when there are several alternatives, each with advantages and disadvantages.

Designing a studio is a lot more complex than people think at first glance! It's a balancing act... sometimes I feel like one of those Chinese acrobats, balancing a dozen spinning plates on top of long poles held in their hands, feet, teeth, balanced on their nose, head, shoulders, elbows... and trying to keep them all spinning without falling!

One final question for your structurally confused builder: Ask him what is holding up the house at present! How come it does not need additional walls around it, to keep the existing walls in place? And more walls around those walls to keep them in place... and yet another set of walls around those, to keep all the others in place... and even more...

He needs to study self-supporting structures, load-paths, sheer, geometry, structural capabilities of building materials, ....


- Stuart -

[tomugli]

Hi, my in laws live just down the road from you in Cotterstock, lovely part of the country!

For the ceiling itself I was thinking - from top to bottom

------- attic air space
-------fluffy insulation
------- flooring boards (for storage)
------- original Joists
-------resilient channel
-------plywood (so i can hang stuff)
-------green glue (subject to budget)
-------plasterboard

Can I confirm whether you intend to make your floor boards an air tight leaf, your roof space will most likely be vented, and this would constitute a cool roof system, so this space would need to be vented anyway, the two leaves below being sealed and decoupled from one another. There is a bit in Rod's book I think on this type of roof and this which will constitute a triple leaf system (please correct me if I'm wrong Stuart), but can still be designed effectively for isolation.

At a glance your ceiling joists look like 3x2s, structural engineer will almost certainly not allow you to add all this weight to this roof structure alone. You can often pay for a walk round from an engineer if you just want preliminary advice.

All cavity walls need wall ties when building in brick/block. This is most likely what your builder is used to. He's reverting to basic building regs but as Stuart says, Not really relevant in this scenario (engineer will be able to confirm.) I don't think Oundle is prone to earthquakes!

Cheers,

Tom

Ps, who's your builder?

[azurr]

Ps, who's your builder?

Hi Tom,

nice to hear from you! The builder is my brother in law, so whilst I appreciate stuarts advice I didnt quite put it in quite those terms

I've been speaking to the council and reluctantly going submit full plans, so they can check and approve.
The floor board mentioned in my post are just for storage in the loft of the detached garage, there wont be many just to put a few boxes etc.
As building regs at the council are likely to complicate everything Im trying to simplify the design including the roof.

would you have any alternative suggestions?

hope you can pop round when done as your not too far from me, I go to leicester monthly for meetings.

regards

[BarneyJ]

Wow! The last picture is really cool!

[Soundman2020]

Wow! The last picture is really cool!

Wow! The last spammer is really banned!

(And so QUICKLY too! In less than half an hour!)


- Stuart -

[azurr]

Hopefully only 3 weeks away from the build.

Quick questions,

Before the inner leaf is built, could someone recommend an easy way to seal the internal side of the existing brick wall. Don't fancy rendering, perhaps some masonry paint?

thanks