Is a non airtight wall part of an MAM

[Bastiaan]

Hi all,

This is my first post on this forum, but I have been reading quite a lot on studio design, like Rod's book, Everest's book, and many many threads on this forum, gearslutz and studiotips.

I'm designing a building in my garden that will contain my small home studio. The total building will be 6.5m wide and 11.5m deep, and 3m high with a flat roof. My home studio will be 1/4th of this building. I intend to pursue a high level of LF isolation as I am not too far from an airport, and therefore I think I should pursue to build a 2-leaf wall. I am currently trying to make a decision on the building style. The exterior wall will be made out of bricks.

Humidity is an attention point in the dutch climate, and therefore a brick wall will have several openings in it for ventilation, and possible water drainage. The purpose of those openings are to prevent that moisture enters the inner building. Should I still consider the brick wall one of the leaves in a MAM even if it is not airtight?

One of the common building styles in the Netherlands is brick - 4 cm air cavity - thermal insulation - inner leaf of 10 cm calcium silicate blocks or concrete. Both leaves are interconnected with steel anchors. The roof construction is carried by the inner leaf to prevent a cold bridge. This provides an isolation of 45 - 50 dB, and I would like to aim for more.

If a non airtight brick wall is the first leaf, and the second leaf carries the roof, I cannot build a proper room in a room with this building system unless I build a triple leaf system. That would be a pity, because it does provide quite some mass.

The second option I'm exploring is to carry the roof on a wooden frame that is hollow and then build a room in a room with wood and gypsum board.
The construction would then be brick - 4 cm air cavity - wooden frame - air cavity - 2x 16 mm gypsum board - studwall (an inside out wall). This construction will have far less mass, but it will be a 2 leaf system and a room in a room.

What would be your suggestions?

[Gregwor]

Humidity is an attention point in the dutch climate, and therefore a brick wall will have several openings in it for ventilation, and possible water drainage. The purpose of those openings are to prevent that moisture enters the inner building. Should I still consider the brick wall one of the leaves in a MAM even if it is not airtight?

Do the openings entirely penetrate the brick?

Greg

[Bastiaan]

Hi Greg,

Thanks for your reply.

Yes indeed the openings penetrate the brick entirely, see below for an example.

Open_stootvoeg.jpg

[bert Stoltenborg]

These penetrations will not improve the isolation, of course.
If the contractor insists on venting the airgap you can eventually think of a system you can close 'm when you're working.
For maximum isolation you should consider to place the outer and inner leaf of the wall on seperate foundations.
And don't use ties, you should build without them (ankerloos).

A 120mm limestone - 50mm gap - 120 mm kalkzandsteen wall that is coupled by the foundation will have a sound reduction of (Jellema, Bouwkunde):
125 Hz - 52 dB
250 - 55
500 - 65
1000 - 89
2000 - 100

A 120mm limestone - 50mm gap - 120 mm kalkzandsteen wall that is decoupled will have a sound reduction of:
125 Hz - 45 dB
250 - 47
500 - 54
1000 - 63
2000 - 71

A 100mm limestone - 50mm gap filled with mineral wool - 100 mm kalkzandsteen wall that is decoupled on the foundation will have a sound reduction of:
125 Hz - 56 dB
250 - 54
500 - 62
1000 - 87
2000 - 99

A 100mm limestone - 50mm gap filled with mineral wool - 100 mm kalkzandsteen wall that is coupled by 20 ties per square meter will have a sound reduction of:
125 Hz - 50 dB
250 - 52
500 - 60
1000 - 79
2000 - 93

At lower frequencies these trends will continue to resonance.

The next challenge is to design a roof, doors, windows and a ventilation system that performs ass well as the walls.

[Bastiaan]

Thanks Bert for your reply. I make up from your reaction that I cannot remove the exterior brick wall from the equation just because there are a few holes in it. I must admit it was wishful thinking from my side I think I can come away with omitting the openings, as the current insight is that it is not necessary. So that will define my first leaf.

There are two more complicating factors for the system with calcium silicate blocks:
-I'd like to be compliant to the thermal insulation rules for this building (rc 4.5 m2K/W for walls). I will not meet that with 5 cm of rockwool, it should be something like 22 cm. This will take up a significant amount of space.
-The inner building will be subdivided further. The beam supporting the roof will be a flanking path from the studio to the workshop.

I have tried to sketch the situation in the picture below

plattegrond kalkzandsteen forum.jpg

An option that may be better is the following: Instead of the calcium silicate blocks I use wood. I use a wooden frame with no plating to support the exterior roof, and then build a true box in a box. This solution has less mass, but (as far as I can see) further only advantages. More space inside, a double leaf solution. I cannot fully judge if the LF isolation of this system will be better. Please let me know what you think.

plattegrond houtskelet forum.jpg

In intend to use a floor like this one. There will be at least 4 cm of reinforced concrete on top as a pressure layer, and on top of that 6 cm of screed to add some mass, and to be able to install underfloor heating:

Broodjesvloer.png

I am going to explore your very interesting advice to use separate foundations. Despite the fact that I have given this design many many hours of consideration already, this option had not ocurred to me. I had been thinking about using separate floors between the studio and the rest of the building on the same foundation which can be done with almost no cost adder.

For the sake of completeness, I have sketched the details of the heigth of the building. In the garage I need to raise the floor a bit above the foundation to ensure the floor is on the same level as the driveway, but in the studio I want to maintain maximum inner height.

hoogte detail.jpg

[bert Stoltenborg]

You can encapsulate the steel beam by glueing Agglomer on it and then put someting like MDF of OSB around the beam; the agglomer decouples the board.

The wood version will perform about 8-10 dB worse as the stone version.
The wood will isolate about 50 dB of sound with a music spectrum, the stone 58 to 60.

Floating the floor means you have to calculate how to do it right.

[Bastiaan]

I suppose that the stone building isolates the LF better because it has more mass?
So is it safe to assume that the version below would isolate equally well as the stone version?

plattegrond houtskelet en kalkzandsteen forum.jpg

[Gregwor]

I suppose that the stone building isolates the LF better because it has more mass?

More mass = more isolation.

So is it safe to assume that the version below would isolate equally well as the stone version?

Don't ever assume. Punch some density/surface density numbers into the transmission loss calculator and it will give you theoretical isolation figures

Greg

[bert Stoltenborg]

I suppose that the stone building isolates the LF better because it has more mass?
So is it safe to assume that the version below would isolate equally well as the stone version?

plattegrond houtskelet en kalkzandsteen forum.jpg

That seems a good design to me, if the doors, roof and ventilation are balanced.

[Bastiaan]

Greg, Bert, thanks a lot for your responses! I checked the transmission loss calculator. The stone version is indeed a better option, the isolation value is higher, and the resonance frequency is lower. However, the isolation values are extremely high. How does this translate to reality?

Wood version

TL calc wood.jpg

Stone version

TL calc stone.jpg

I am going to use the calculator as well for the ceiling and the floor, great tool!

[Gregwor]

How does this translate to reality?

Without floating your entire room (6 figure cost), I believe the flanking limit of the slab would put you slightly above 60dB of isolation and that's it. Having said that, you could split your inner and outer leaf slabs to get some degree of improvement.

I am going to use the calculator as well for the ceiling and the floor, great tool!

I'm glad you're finding it useful! I'm always open to ways to improve it. Just PM me if you have any ideas or materials you'd like me to add to it. I also have to get my HVAC static pressure calculator fixed up here eventually.

Greg

[bert Stoltenborg]

You have a 100 mm brick wall, a 160 mm woolfilled gap and a 100 mm kalkzandsteen wall?
And that would deliver about 80 dB sound reduction @ 60 Hz?
Corrected that is 107 dB, if that were real Eric Desart wouldn't have had to go through the problems with putting bunkers on springs when designing Galaxy Studio's.

[bert Stoltenborg]

How is that second wall constructed?\
OSB-gap-brick with what dimensions?

[Bastiaan]

I was also pleasantly surprised to see Galaxy numbers

From my perspective as an amateur, the MSM TL calculator is a great tool because it offers the opportunity to evaluate design choices and get a prediction of results over the audible frequency spectrum. I've searched the internet for hours to find useful and detailed information on soundproofing. Most sources I found only provide STC ratings, or empirical data where the experiments do not match your situation and then it is still difficult to predict the performance of your design.

I realize that the calculator does not take flanking and leakage, etc. into account which will limit the performance in reality for sure.

I would be quite happy with the 58-60 dB of isolation across the music spectrum you indicated if I take proper care of decoupling, and make sure the floor, ceiling and HVAC system are properly designed.

This weekend I will look into those further.

[Bastiaan]

How is that second wall constructed?\
OSB-gap-brick with what dimensions?

Its two times 18mm OSB on a 2x4 wood stud frame, with the gap between the frame and the brick being 16 cm filled with insulation