Hello! A new challenge: studio in a CLT building

[simmessa]

Hello everybody!

My name is Simone Messaggi, I'm from Italy and I've recently joined this forum to learn more about studio construction.

I've recently completed construction of a new home and designed a nice room (sized by Sepmeyer C ratio) to dedicate to my Music / Studio.

I realize now putting this room on the elevated floor has several disadvantages, but unfortunately that's exactly what I did, wish I had knew that before :/ now it's too late!

The whole thing is complicated by the fact all the building is made of CLT (Cross Laminated Timber), a technnique which is rather new and not so many acoustical studies have been done so far.

I have accurate drawings of the room, photos of the CLT walls and floor slab and other kind of info I have gathered but I need your help to find a solution for the floor insulation, a timber building is a complex thing and I'd like to hear your experience to make the right choices.

Let me know if any of you want to know more and I'd be happy to post the details!

Thank you for the wonderful knowledge you host on this forum.

See you soon!

S.

[simmessa]

Hello gents,

As per my first post I’m new to the forum and after lurking a bit here I’m posting some more details about my studio project.

I’ve tried searching to no results and I believe nobody has discussed this on the forum before, but let’s get straight to the issue:

I live in Europe (Italy, to be precise) and I’m building a new house for my family, this is our dream house and it’s been designed to be a very power efficient house (almost passive in nature, that is, a house that needs almost no energy to heat up in winter or air condition in summer) where nearly all of the house is made of timber.

The wood we’re using is no ordinary wood, but a product called Xlam, which falls in the category of CLTs (Cross Laminated Timber).

Almost every wall in our new house is therefore made with 3 (7cm) or 4 ply (9cm) CLT, and we have two floors, (ground and 1st floor) so the upper floor is also made of CLT, a 5 ply structure (16cm).

When planning this house I had to make some architectural compromises and ended up having my Music / Studio room on the first floor, a huge mistake as I now realize after checking out the forum and some literature including the excellent Rod Gervais book.

But way before discovering all this I spoke with an Auralex rep. and following his suggestion I thought I could decouple the wooden floor via U-boats (aargh, I know). To be honest with you right now I’m kinda pissed at them and myself for not better checking out their claims

What I need is being able to perform music at SPL averaging 100 dB without causing acoustical discomfort to the rest of the family (which is bound to grow quickly as soon as we move to our new home!) and vice versa. That applies in a similar form also to the neighbours, which are about 15 meters far from my future music room.
I’d be happy to reach an acoustic isolation of about 60 dB

The room has been designed with acoustics in mind and I chose the Sepmeyer C ratio (1:1.6:2.33) to minimize 1st order modes, the size of this room (in metric dimensions) are:

Height (m): 2.5 (but this is only virtual, see below)
Width (m): 4.055
Depth (m): 5.805
Area (square m): 23.54
Volume (cubic m): 58.85

Real ratio: 1:1.62:2.32 which is quite close to Sepmeyer C, at least I hope so
Please keep in mind these are the measures of bare CLT walls/floor BEFORE any technical treatment for sound isolation.

I attached to this post some drawings to better illustrate the room:

• - PDF drawing (plan) showing the size of the room
  - PDF drawing (section) showing the varying height of the room
  - A picture, showing some sections of CLT you can see the composition of floor slab (5ply - 16cm), internal walls (3ply - 7cm) and external structural walls (4ply - 9cm)
  - A study of the acoustical insulation performance of CLT which has been completed this year by the National Research Council for Construction (Canada) (dropbox link: https://www.dropbox.com/s/vj6e3638s9tfg ... 7.pdf?dl=0)

Some more notes:

The pavement of the rest of the 1st floor is made with a concrete slab (concrete + sand mix) for about 10 cm laid over 3cm of medium density rockwool, but in my future studio I decided to keep the floor bare, so it’s just 7ply CLT and now I have to understand how to proceed further with insonorization, a similar amount of concrete should be ok in the studio room as it’s been accounted for in the structural engineering of the home.

CLT itself is pretty new in the construction of residential buildings, therefore not much research has been done in terms of acoustical properties, the file I attached is a free study I’ve been able to track down online.

As you can observe in the dwg file, the walls giving to the house exterior have some more thermo-acoustic isolation, made of toasted cork, the product is called Corkpan and here’s a tech specs sheet (http://www.tecnosugheri.it/wp/wp-conten ... an_R02.pdf).

I’m eager to measure soundproofing of this wall toward the house exterior but unfortunately I’ve just received a non working SPL meter so I must wait a little longer, my bet is that maybe the current insulation might be a good base and that I won’t need major insulation on the walls that face the exterior

The ceiling has slopes for the roof so I’m aware that if I really want to stick to Sepmeyer C ratio I need to build a counter-ceiling. In the attached PDF you can see the section as it is right now, and if not absolutely necessary for sound isolation I’d like to enjoy the bigger volume, knowing that the Sepmeyer C ratio doesn’t work anymore, and it’s kinda stupid, I know :/

But the really important part at this point is laying out the foundations for future soundproofing, starting with the floor, can I achieve a floating floor with a safe resonation frequency (10 / 20 Hz) ? Can I avoid the propagation of low frequencies to the floor below, CLT behaves like wood and if you produce mechanical vibrations the structure will bring them everywhere!

I’ve been thinking about this for weeks and I don’t really know how to start dealing with the soundproofing, so I’m kinda desperate and I need all the help you can give me.

Thank you all for your time and interest, I know this is not going to be easy but thanks for trying!

Simmessa.

p.s.: This is my first time posting here so please feel free to tell me if I make formal mistakes or if you'd rather see me post anything differently, I'd appreciate that!

[Soundman2020]

Hi Simone, and Welcome!

I'm not familiar with CLD, so I'd only be guessing what it's properties might be.

But way before discovering all this I spoke with an Auralex rep. and following his suggestion I thought I could decouple the wooden floor via U-boats (aargh, I know). To be honest with you right now I’m kinda pissed at them and myself for not better checking out their claims

Well, you aren't the first person to be in that situation, and I'm sure you won't be the last either, so don't feel too bad!

What I need is being able to perform music at SPL averaging 100 dB without causing acoustical discomfort to the rest of the family

Wow! That's a tall order, for a studio on an upper floor. That would imply isolation in excess of 60 dB, which is hard to do anyway, even more so on a timer-framed upper floor. This is not going to be easy, and will require a large budget...

I’d be happy to reach an acoustic isolation of about 60 dB

I wrote the above before I saw your comment on the desired isolation.... Yup, that is about what you'd need, and it is hard to do.

The room has been designed with acoustics in mind and I chose the Sepmeyer C ratio (1:1.6:2.33) to minimize 1st order modes

That's actually a myth. Choosing a good ratio does not "minimize" modes: it just ensure that they are spread evenly across the spectrum, without any modes being too close to each other in frequency, nor too far away. A good ratio won't makes modes go away, or reduce their effect: it just means that they are arranged well, in terms of frequency.

Please keep in mind these are the measures of bare CLT walls/floor BEFORE any technical treatment for sound isolation.

That's great, but it isn't what matters. The real modal response of the room will be defined by the inner-leaf which will probably end up with a different ratio. Since you need a very large amount of isolation, you will be losing lots of space due to the deep air gaps that you'll need. You might also need to "beef up" the structure of the floor, in order to support the large amount of mass that you'll need.

- A picture, showing some sections of CLT you can see the composition of floor slab (5ply - 16cm),

At a very rough estimate, a solid wood floor 16cm thick will give you around 40 dB of isolation, from empirical mass law. That's for airborne sound. Impact sound would be rather different. I noticed that you mentioned an NRC paper on CLT, so I'll download that and take a look at it later.

Do you know what the load-bearing capacity of that floor is? How much dead-load and live-load?

The pavement of the rest of the 1st floor is made with a concrete slab (concrete + sand mix) for about 10 cm laid over 3cm of medium density rockwool, but in my future studio I decided to keep the floor bare, so it’s just 7ply CLT

You are saying that hte rest of the house is done like that? All the rooms have the same 16cm 5-ply CLT, then a layer of Rockwool, then a 10cm thick concrete slab on top? If so, that's good news.

a similar amount of concrete should be ok in the studio room as it’s been accounted for in the structural engineering of the home.

If that's true, then you can probably float your floor properly, using proper isolation mounts, but you'd need to check with a structural engineer: Even though your sub-floor can apparently handle the load of the slab, if you did it like the other rooms then that would be spread evenly, but if you do it with isolation mounts, there would be very high point loads right where each mount is. So you'd need the engineer to look at that, and tell you if it is safe.

my bet is that maybe the current insulation might be a good base and that I won’t need major insulation on the walls that face the exterior

If you want 60 dB of isolation, then you WILL need some major isolation. 60 dB is a lot of isolation. Not easy to get.

The ceiling has slopes for the roof so I’m aware that if I really want to stick to Sepmeyer C ratio I need to build a counter-ceiling.

Are you building a control room? Or a rehearsal room? It's not very clear from your post what the purpose of this room is.

But the really important part at this point is laying out the foundations for future soundproofing, starting with the floor, can I achieve a floating floor with a safe resonation frequency (10 / 20 Hz) ?

Possibly, yes... but not easily. With a 15 cm air gap on suitable isolation mounts (Mason Industries), it should be possible to get 50-something dB of isolation from that floor, assuming a 10cm concrete slab on isolation mounts over a 15cm air gap, with some insulation in the cavity. The resonant frequency could be just under 20 Hz.

CLT behaves like wood and if you produce mechanical vibrations the structure will bring them everywhere!

That's why you need proper isolation mounts! I would suggest that you talk to the folks at Mason Engineering, and ask for their suggestion.

But your isolation is not just your floor: You need to isolate the entire room to the same level, including the floor, walls, ceiling, windows, doors, HVAC system and electrical system. Getting a floor isolated to 60 dB is one thing, but getting a door to isolate to the same level is another thing entirely! And getting 60 dB of isolation from your HVAC system is not easy to do either.

There's a lot of challenges involved in doing what you want to do. I would suggest talking to Mason first, to see what they say about your floor. If they have a solution that will get you to 60 dB, and it is approved by your structural engineer, then it is worthwhile looking at the rest of the isolation plan too. But first you need to know how far you can go with that floor. There's no point in designing walls and windows for 60 dB if your floor can only get you 50, for example.


- Stuart -