Installation layer (45-70 mm), moisture trap or not?

[Prosit]

I discussed a bit with an architect the other day, he argued that one should not have any installation layer like studs 45-70 mm on the inside of the plastic in the outer walls, but that you should attach boards (like plywood and gypsum) directly on the furring strips that are inside the plastic.

I am tempted to place e.g. 70mm studs and insulate with mineral wool so that sockets and pipes for electricity and other things wouldn't have to puncture the plastic. The architect says that the VP pipes can go between the furring strips and perhaps the sockets can also be fit without puncturing the plastic.

Here we are talking about a wall that is blown with loose-fill insulation.

In principle, he is right that the plastic should be as close to the warm side as possible, but many modern houses have an insulated installation layer of 45-70mm, right? Paroc has such a variant in their suggested constructions: http://www.paroc.se/channels/se/building+insulation/solutions/external+walls/nr303.asp

 

[FredrikR]

This is what Fiskarhedenvillan's walls look like:
http://www.fiskarhedenvillan.se/bygg_med_oss/Var-vagg/

 

[Prosit]

28 mm there, that's roughly what the sparse panel usually is inside the plastic if you're blowing insulation or?

 

[Matti_75]

You should not listen to what your architect says. An installation space of 45mm is perfect as you don't need to make any holes in the plastic, thus achieving a more airtight building. I have just built 32 apartments with such a construction.

 

[cheetah1]

Your architect needs to read up. At least 2/3 of the insulation should be on the outside of the plastic, then it works great.

 

[Prosit]

Anyone have any reading tips regarding this? I'm personally interested in knowing how it all works - intuitively it feels like the plastic closest to the warm side is best...

 

[Prosit]

Hmm, now the question is: Is 45 mm or 70 mm the most suitable thickness for the installation layer? Should one have the same in walls and ceiling for any reason (it feels easiest to have a little more in the ceiling if you’re going to have spotlights...the ceiling also has more insulation in total)?

Planning to have about 300 mm of insulation in the walls, 400-500 mm in the ceiling (not sure about the thickness there yet).

 

[FredrikR]

Isn't 28mm (sparse panel) enough on the walls?
And don't you have sparse in the ceiling?

For spotlights, you'll probably need to put pots that build a +150mm or similar in height?

 

[Prosit]

Isn't 28mm (sparse paneling) enough on the walls?
And don't you have sparse in the ceiling?

For spotlights, you probably need to install pots that build a +150mm or something similar in height?

Wouldn't it be difficult to fit electrical boxes in just 28 mm? (Although they do stick out through raw wood/plywood + drywall, so some of the box's depth disappears there...)

The idea was also for the electrical conduits to go in the installation layer; wouldn't it be problematic with vertical conduits if you have horizontal sparse paneling? Or should you run them between plastic and sparse paneling at the risk of scratching the plastic?

 

[Mats]

28+13 assuming regular gypsum is a bit thin for standard boxes if you want them.
Therefore, it becomes easier with 45.

 

[FredrikR]

Double layers?
OSB or chipboard, so you can hang things on the walls without needing plugs?

 

[Prosit]

Double layers?
OSB or chipboard, so you can hang things on the walls without needing plugs?

Either plywood (or OSB) + drywall, or maybe more likely tongue and groove + drywall. This is to make it easier to screw things up, yes.

Tongue and groove adds a bit more thickness than plywood/OSB, not sure if 17 mm tongue and groove is the most sensible choice, maybe 21 mm.

 

[Ola78]

Raw paneling works well, excellent

 

[imported_jo]

I would recommend 45 mm installation space and OSB+13 gypsum. Not tongue-and-groove boards! I tried it on a construction site but it wasn't great, the quality of the tongue-and-groove boards must be DEAD STRAIGHT (and how often does that happen?), otherwise, there will be quite a few drywall screws that go through the outer layer of the gypsum board (as the board rests on 2 heights and you screw in between, for example) which results in it not being securely attached. OSB is faster and completely flat.

 

[Prosit]

I would recommend 45 mm installation space and OSB+13 gypsum. Not tongue and groove boards! I tried that on a construction with the quality of the tongue and groove boards needing to be DEAD STRAIGHT (and how often does that happen?), otherwise you end up with quite a few gypsum screws that go through the outer layer of the gypsum board (since the board rests on 2 heights and you screw in between, for instance) which results in it not being attached as it should. OSB goes faster and is completely flat.

Hmmm, how is it that some prefab house manufacturers use tongue and groove boards + gypsum, do they have such good quality materials that it works? I thought they tried to keep costs down...

One reason I would want tongue and groove boards is to have as little as possible of glue and other things that could be emitted into the dwelling inside the plastic sheeting.

Without having calculated it much myself and just going by what I've heard, tongue and groove boards could also be cheaper if you do the work yourself and don't count labor cost that is...