*Treatment stage* Fen Cabin Studio - Build Diary. UK

[Gregwor]

So here's a very crude sketch just to clarify:

With your vapour barrier there, what will you do if it is screwing up your room acoustics? Every other studio has a bunch of insulation on the inside of their room (covering their vapour barrier). Maybe put your vapour barrier between your inner room insulation and it's sheathing?

Greg

[Paulus87]

So here's a very crude sketch just to clarify:

With your vapour barrier there, what will you do if it is screwing up your room acoustics? Every other studio has a bunch of insulation on the inside of their room (covering their vapour barrier). Maybe put your vapour barrier between your inner room insulation and it's sheathing?

Greg

The vapour barrier may or may not be desirable acoustically speaking, but if that is the case I am planning to cover the vapour barrier in Dacron. I may even find the vapour barrier is not necessary altogether as the problem with them is they only work well if the temperature is the same all year round. In the uk it is usually cold but recently we’ve had months of very hot summer, so who knows what the weather will be like in the future.

But yes, I will probably use a Dacron wadding over my insulation whether I use a vapour barrier or not as it is very cheap and will stop dust going out in to the room. It also had a nicer feel behind fabric than insulation.

[Waka]

So here's a very crude sketch just to clarify:

With your vapour barrier there, what will you do if it is screwing up your room acoustics? Every other studio has a bunch of insulation on the inside of their room (covering their vapour barrier). Maybe put your vapour barrier between your inner room insulation and it's sheathing?

Greg

The vapour barrier may or may not be desirable acoustically speaking, but if that is the case I am planning to cover the vapour barrier in Dacron. I may even find the vapour barrier is not necessary altogether as the problem with them is they only work well if the temperature is the same all year round. In the uk it is usually cold but recently we’ve had months of very hot summer, so who knows what the weather will be like in the future.

But yes, I will probably use a Dacron wadding over my insulation whether I use a vapour barrier or not as it is very cheap and will stop dust going out in to the room. It also had a nicer feel behind fabric than insulation.

Greg's probably right as you are doing inside out. The vapour barrier is used to prevent warm room air getting to the structure and condensing.

The sealed cavity wants this barrier. The insulation in your room is not going to get condensation behind it as there's insulation the other side of your inner leaf too.
I'm placing my vapour control layer on top of my inner leaf ceiling joists in my inside out ceiling design and this was checked off by building control. With 200mm of insulation below it. So place the VCL on the outside of your inner leaf when you build your outer leaf.

Dan

[Soundman2020]

I may even find the vapour barrier is not necessary altogether as the problem with them is they only work well if the temperature is the same all year round. ... it is very cheap and will stop dust going out in to the room. It also had a nicer feel behind fabric than insulation.

You seem to be misunderstanding the purpose of the vapor barrier. It is a very important part of a wall, in climates where it is needed, and wall construction methods that need it! It should also NOT be confused with an air barrier, or a water barrier! They are all different things, and each one goes in a specific location of the wall. A vapor barrier is more correctly called a vapor retarder, and it controls the diffusion of water vapor through the wall. It does not control air passage through the wall, nor does is function as a water barrier (or dust barrier!), and it has no acoustic purpose either, but still might be needed in an isolation wall. It has a very specific function, and should be placed at a very specific location inside the wall: up against the surface that is warmer in winter.

So it would definitely NOT go in the location you are showing on that diagram. If you do need one, it would go INSIDE the wall cavity, not outside it.

This might help you understand if you need one or not, and if so, where to put it:


https://buildingscience.com/documents/d ... r-barriers

A wall is a system, and both air and water vapor must be allowed to diffuse through it in the right direction, while liquid water must NOT get in.

A vapor barrier isn't something that you can just sort of throw in if you feel like it, or leave out if you want to save a few pennies: it is an integral part of the wall, and MUST be included if your wall construction and climate dictate that you need it, and can ONLY be left out in circumstances where it is not needed.

- Stuart -

[Waka]

To be honest Paul I struggled with this problem with my wall design. Because vapour in the UK is almost always controlled by ventilating the external skin and blocking internal moisture reaching the cavity. That's why I'm doing 3 leaf (external cladding). You may need to get building regs to help. Stuart might know this: would cement render on cement board that is painted be vapour permeable and allow the condensation to dry outwards over time like brick does?
Also that link you sent Stuart seems to advise not applying a vapour control layer in the UK at all or only a "smart vapour control layer" on the inside, which isn't what everywhere in the UK says. The UK isn't considered a cold climate but the standard method in the UK is described as only for cold or very cold climates in that article.

[Paulus87]

So I have actually been doing a lot of research on ventilation, vapour control and vapour retarders recently and there really is no clear straight forward answer - at least for use of vapour retarders in the uk. Just like trying to research “soundproofing” online, it is a mess of contradictory information making it hard to know what to do. A lot of the info is years old, some of it is marketing, some of it is new.

Btw, though it is easy to confuse vapour barriers with air barriers or moisture barriers or whatever other barrier you might find, I am aware of the purpose of the type of vapour retarders we are discussing here.

The truth is, a lot of houses in the uk will not even have a vapour barrier installed or the houses will use polystyrene insulation which does not require a vapour barrier.

There may be a vapour barrier in the bathroom but it’s certainly unusual to find them in other living areas.

They seem to be constantly debated, some say they are vital some say they only work in a stable climate - even in the USA it is a hot topic.

What I have found out though is that in passive houses they are usually not installed. Passive houses are extremely similarly designed to recording studios as they have a double wall assembly (albeit non decoupled) they’re extremely air tight buildings, they have a lot of insulation and perfect ventilation.
They will use a weather barrier on the outside but on the inside they do not install a separate vapour barrier.

Here’s another interesting tid bit - OSB itself IS a vapour barrier. Osb is not very air tight but is pretty water resistant and yet it is also vapour permeable. So in other words it’s very good at keeping water out but also has a good slow release rate of letting vapour out from the other side. This is what a lot of passive houses use as their vapour barrier. Apparently they also use osb as a vapour barrier in Canada too. I even read that those cement boards I’ve been asking you about can act as a vapour barrier too.

So, as my inner leaf consists of a layer of osb on the warm side of the cavity insulation I may find I do not need to use a separate vapour barrier. If I find out through building regs that I do need a separate one then I will just install it over the osb before putting up my outer leaf.

The only thing I don’t want to do is install it and finding out it actually makes things worse by causing the opposite of what they’re designed to do

[Soundman2020]

So, as my inner leaf consists of a layer of osb on the warm side of the cavity insulation I may find I do not need to use a separate vapour barrier. If I find out through building regs that I do need a separate one then I will just install it over the osb before putting up my outer leaf.

That would, indeed, be the correct way to proceed, but it would not go over the OSB; It would go over the drywall. If you do use it, then it goes in the wall CAVITY. Not between layers of the leaf. If you put it over the OSB then it would be between the OSB and the drywall, so it would not be protecting the drywall the way it is supposed to. It would have to go on the cavity-facing face of the drywall.

But that's not what you are showing on your diagram on the previous page of the thread! You are showing an inside-out wall design, with something labeled "vapor barrier" inside the room, (NOT inside the wall), as the final layer, on top of your acoustic treatment. That would not be a vapor barrier, and would in fact be an acoustic device: as Greg mentioned, it would have an effect on the frequency response of whatever treatment is behind it, and it would also change the sound of the room. But it isn't a vapor barrier, and would not work as a vapor barrier. That's the point I was trying to get across, but I guess I didn't explain it very well...

If you were to install the type of plastic that is typically used for vapor barrier, all around the room, over your treatment (or just over the insulation in the stud bays), that would at as an acoustic foil, reflecting back some frequencies while allowing others through, and following the equation for such foils. There is a reflection curve for foils (plastic is a foil too, acoustically) that defines the point where foil of any given surface density will be 20% reflective (80% transparent) to sound (allowing 80% of that frequency through to the other side, reflecting back 20%, or coefficient of reflection = 0.2). The curve rises to about 99% reflective above that (1% transparent), at about 6 dB/octave, and falls off to practically 0% reflective (99% transparent) below that, at the same rate:

F = 90 / m

F = The frequency at which the foil transmits 80% of the sound
m = The surface Mass of the foil in kg/m2

So that would be the effect of putting plastic around your room, over the insulation in the stud bays: acoustic foil. It might also trap moisture in the air between the foil and the leaf itself, and depending on whether or not the rest of the wall was constructed with vapor retardation in mind, that trapped moisture might have no means of escape, possibly leading to the growth of fungus or mold.

There's also the issue that if you stretched the plastic tight across the studs, it would no longer act as just a foil, but also as a resonant membrane, tuned to a certain frequency, or set of frequencies: that's probably not a good thing! So if you do go down this path, then don't stretch it tight!

But all of this begs the question: Why do you want it in that location anyway?


- Stuart -

[Paulus87]

So, as my inner leaf consists of a layer of osb on the warm side of the cavity insulation I may find I do not need to use a separate vapour barrier. If I find out through building regs that I do need a separate one then I will just install it over the osb before putting up my outer leaf.

That would, indeed, be the correct way to proceed, but it would not go over the OSB; It would go over the drywall. If you do use it, then it goes in the wall CAVITY. Not between layers of the leaf. If you put it over the OSB then it would be between the OSB and the drywall, so it would not be protecting the drywall the way it is supposed to. It would have to go on the cavity-facing face of the drywall.

But that's not what you are showing on your diagram on the previous page of the thread! You are showing an inside-out wall design, with something labeled "vapor barrier" inside the room, (NOT inside the wall), as the final layer, on top of your acoustic treatment. That would not be a vapor barrier, and would in fact be an acoustic device: as Greg mentioned, it would have an effect on the frequency response of whatever treatment is behind it, and it would also change the sound of the room. But it isn't a vapor barrier, and would not work as a vapor barrier. That's the point I was trying to get across, but I guess I didn't explain it very well...

If you were to install the type of plastic that is typically used for vapor barrier, all around the room, over your treatment (or just over the insulation in the stud bays), that would at as an acoustic foil, reflecting back some frequencies while allowing others through, and following the equation for such foils. There is a reflection curve for foils (plastic is a foil too, acoustically) that defines the point where foil of any given surface density will be 20% reflective (80% transparent) to sound (allowing 80% of that frequency through to the other side, reflecting back 20%, or coefficient of reflection = 0.2). The curve rises to about 99% reflective above that (1% transparent), at about 6 dB/octave, and falls off to practically 0% reflective (99% transparent) below that, at the same rate:

F = 90 / m

F = The frequency at which the foil transmits 80% of the sound
m = The surface Mass of the foil in kg/m2

So that would be the effect of putting plastic around your room, over the insulation in the stud bays: acoustic foil. It might also trap moisture in the air between the foil and the leaf itself, and depending on whether or not the rest of the wall was constructed with vapor retardation in mind, that trapped moisture might have no means of escape, possibly leading to the growth of fungus or mold.

There's also the issue that if you stretched the plastic tight across the studs, it would no longer act as just a foil, but also as a resonant membrane, tuned to a certain frequency, or set of frequencies: that's probably not a good thing! So if you do go down this path, then don't stretch it tight!

But all of this begs the question: Why do you want it in that location anyway?


- Stuart -

Hey Stuart, I think our lines have got crossed somewhere along the way! Sorry about that. Also sorry to Dan for hijacking this thread, it should be about your build not mine... but maybe this will be useful to someone.

So my diagram was based on me misunderstanding the post by Dan that I was responding to. I knew where the vapour barrier should go in a non-inside-out room, but I was trying to work out where the vapour barrier would go in an inside-out room and so I drew up a diagram to demonstrate what I thought was the correct place for it based on the advice given. So it's not a case of me wanting to install it over my insulation, it's just that's where I wrongfully thought it had to go and was asking for confirmation.

In my last post I didn't mean that the vapour barrier should be sandwich between my leaf layers, I meant that it be on the outside of my inner leaf, inside the cavity. This is presuming that I simply beefed up my inner inside out wall (so the drywall would be on the inside face of the wall, between the studs) and left the outer most layer as OSB. So the vapour barrier would be on the outside of the OSB. Confusing?

Here's a new diagram to demonstrate. If I end up using cement board, then the vapour barrier would go over the cement board on the cavity side, as that would be the outermost layer of my inner leaf wall. My whole wall assembly would look something like this:

[Paulus87]

Is that the correct place Stuart? Or do you mean behind the "outer insulation" over the outer leaf drywall?

OR do you mean behind the “inner insulation” in front of the beef up dry wall ?

[Soundman2020]

Is that the correct place Stuart? Or do you mean behind the "outer insulation" over the outer leaf drywall?

Assuming you need it where you live (check your local building code...), and that your climate is cold and damp in winter, then yes, that's where it would go.

Mystery resolved!


- Stuart -

[Paulus87]

Is that the correct place Stuart? Or do you mean behind the "outer insulation" over the outer leaf drywall?

Assuming you need it where you live (check your local building code...), and that your climate is cold and damp in winter, then yes, that's where it would go.

Mystery resolved!


- Stuart -

Sorry Stuart, are you confirming that my diagram is correct or that my later preposition of placing it behind the outer insulation is correct? Which one?

[Waka]

I changed my mind on resilient clips to attach the silencer boxes to the joists as they are annoyingly hard to get hold of singularly. And I'm not paying £50 for 8 clips.

So I went with anti-vibration rubber cylinder mounts. They will probably isolate similarly to the resilient clips (they should be better due to resilient clips being such thin rubber anyway) and I'm not expecting much energy below 100Hz anyway through the ventilation.

Here's how I attached the mounts:

insert.jpg

cylinder mount.jpg

Wood 1.jpg

wood 2.jpg

screwed to mount.jpg

ready to mount.jpg

compressed before screwed to box.jpg

one mount attached.jpg

Insulation is complete:

ceiling and wall inner leaf insulated.jpg

[Waka]

Hi guys,

In the new year I should be getting the electrician in. I'll be doing all the "monkey work" and he'll be connecting everything up and signing off on it. So before I put up my polythene vapour control layer and inner leaf OSB I thought I'd get the electrical entry point ready. I'd love your opinion on my current plan.

Current plan for electrics:

A single hole for entry, drilled through external leaf just above the sole plate, wires tacked to the inside of the outer leaf studs, run up within the wall and a hole drilled through the inner leaf just below the header plates.

Through this hole I'll put the electrical supply wire, a wire to lead to the outdoor condenser and ventilation fan and any wires for external security lighting. They shouldn't be pulled tight through the inner leaf in order for them to remain resilient and not provide a flanking path.

The holes will be caulked until I can't caulk anymore

Electricity will be run off of the existing supply from the house. Internally in the studio I will place a garage consumer unit.
20A Radial circuit for sockets all surface mounted.
Separate radial for both internal lighting and external security lights.

That's the plan for electrics.

With my mini-split I'm going to try and get the installer to run the pipe similarly to the electrics. That is: run some pipe inside the cavity and drill the inner leaf hole away from the out leaf holes. I'm not sure whether there's a way to make this resilient though.

Is there anything you'd change about my plan here Stuart (You're an electrician by trade originally if I remember right?) or Greg?

Dan

[Soundman2020]

Use conduit: don't leave the wiring loose in the cavity. Two pieces of conduit, one for each side, but with a gap in between: line them up to aim at each other, then wrap them with something flexible, such as neoprene rubber:

Conduit-isolation-0-SML-ENH.png

Conduit-isolation-1b-SML-ENH.png

Conduit-isolation-2-SML-ENH.png

Conduit-isolation-3-SML-ENH.png

Bend it in gentle, wide-radius curves, not sharp! And use conduit that is much larger diameter than you need. At least 20mm, but 25 or 32 would be better.


- Stuart -

[Waka]

Thanks for the quick reply Stuart,

Something like this:
25mm Conduit

It's listed as "flexible conduit", is that the right stuff?

The neoprene stuff to connect the two, for you got a link to something like that?

Thanks,

Dan