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PostPosted: Sun Apr 25, 2021 1:05 pm 
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Location: Melbourne, Australia
Hi Bastiaan and All,

I am particularly interested in the subject line of this thread and how you are dealing with the following from your initial post:

"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?"

"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"

In Australia our building regulations require that we include these "weep holes" for the reason you described. As I am proposing a brick (concrete block) outer leaf and a timber stud wall inner leaf for my studio build in a new home, I am interested to know how you came to the conclusion that the weep holes are not necessary to prevent moisture buildup?

As was stated, leaving weep holes in the brickwork compromises the acoustic integrity of the two leaf structure, so is not an option, however once I have complied with building regulations, if I seal these holes I want to ensure I am not going to have wall cavity moisture issues in the future.


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PostPosted: Sun Apr 25, 2021 2:40 pm 
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Location: Australia
Quote:
Should I still consider the brick wall one of the leaves in a MAM even if it is not airtight?"


No - to achieve a soundproof room you must have two totally sealed rooms, an inner and an outer.

Remember, sound is air pressure.

cheers
john

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PostPosted: Mon Apr 26, 2021 10:39 am 
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Location: Melbourne, Australia
So in Melbourne's more temperate climate, you would advise NOT sealing an outer brick wall built with say Besser blocks to act as an outer leaf, but rather construct a standard brick veneer cavity wall with weep holes, then air gap, then another stud wall with 2 sheets of gyprock for the internal structure?

This would obviously reduce the internal studio dimensions somewhat, but would function as a two leaf system while preventing moisture retention?


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PostPosted: Mon Apr 26, 2021 11:34 pm 
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Location: Old Tappan, NJ USA
as John noted - the MAM works if there are two sealed rooms - in the case of the brick veneer - this is a facade with ventilation which has behind it has a sealed framed wall? so outer leaf is sealed. then you build an inner room which is also sealed. the outer brick veneer while technically a 3rd leaf is ventilated and likely more massive than either of the two inner layers of mass, so unlikely to be problematic.

so if you have:

brick (vented) -> small air gap -> plywood sheath w/ moisture barrier -> frame + insulation -> 1" air gap -> frame + insulation -> inner mass (plywood + 2x gwb)

my thought is you likely need to beef up that outer sheathing - install drywall or cement board between studs to increase the mass there.

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PostPosted: Mon Apr 26, 2021 11:52 pm 
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Location: Finland
gullfo wrote:
as John noted - the MAM works if there are two sealed rooms - in the case of the brick veneer - this is a facade with ventilation which has behind it has a sealed framed wall? so outer leaf is sealed. then you build an inner room which is also sealed. the outer brick veneer while technically a 3rd leaf is ventilated and likely more massive than either of the two inner layers of mass, so unlikely to be problematic.

so if you have:

brick (vented) -> small air gap -> plywood sheath w/ moisture barrier -> frame + insulation -> 1" air gap -> frame + insulation -> inner mass (plywood + 2x gwb)

my thought is you likely need to beef up that outer sheathing - install drywall or cement board between studs to increase the mass there.

Can you (generally) say that in 3-leaf design you should beef up inner/outer/midle leaf, or is there some generic guidelines for this?
ie. what has the greates effect or what is the best place to add mass (apart from tearing the wall and making a 2-leaf design :D )


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PostPosted: Wed Apr 28, 2021 2:41 am 
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if your outer brick facade needs to stay vented to comply with code, then you're either going to remove that or violate code and practical venting to reduce risk of moisture damage. and since it's vented, there is not really MAM on the inner layer although there will be some effect because of its mass. tradeoffs.

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PostPosted: Mon May 03, 2021 7:33 am 
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Joined: Sun Mar 01, 2020 1:04 am
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Location: The Netherlands
irecord wrote:

In Australia our building regulations require that we include these "weep holes" for the reason you described. As I am proposing a brick (concrete block) outer leaf and a timber stud wall inner leaf for my studio build in a new home, I am interested to know how you came to the conclusion that the weep holes are not necessary to prevent moisture buildup?


In my personal situation, we have some liberty in the Netherlands to build without a permit. The building still needs to meet the building code, but nobody will come and check it. I do the organization of the build and part of the actual building myself. Of course I follow 99% of the building code, because I don't want damage or unsafe situations. However, in this case, I make an exception for the weep holes, but only where the studio is located in my building.

There are two functions for the weep holes: the holes on the lower end of the wall are for water drainage in case water manages to get into the cavity between the leaves. It drips down and is guided with a foil to these holes. The holes further up on the wall are for ventilation, so damp can escape easily. The idea to use these holes originate from several decades ago. Back then, the general thought was that most of the moist related problems were due to moist coming from the outside, transfering to the inside of the building.

Since we started insulating buildings, the "moisture management" has gotten more attention. Due to the insulation the outer structure of the building gets colder and chances increase that damp condensates against the coldest surface in the cavity, turning it into water. If this water cannot escape, accumulation can cause damage. It turns out that water can escape from the cavity, also without the weep holes. The brick wall itself is porous and rather open for water damp. In the Netherlands it is fairly common nowadays to blow the cavity full with thermal insulation which effectively renders the weep holes useless. The dutch government investigated it, approved it, and even has subsidized it for some period.

Another modern insight is that, in most situations where moist is an issue, it orinates from the inside of the building as people release damp or their activities do. So in general, one should take care that it is very difficult for damp to enter the cavity from the inside, and that it is very easy for damp to escape from the cavity to the outside.

My plan of action is to use damp proof foil on the inside of the building, damp open (but water proof) foil between the brick wall and the wooden frame, and taking serious care of ventilation (with muffler boxes). Ventilation will prevent 99% of moisture issues anyway.

I am not saying my reasoning applies to your situation as well, but I think I am taking a fairly small risk.


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