Stud frame, additional insulation, wind barrier?

[krumbukt]

Not entirely quick and easy to find values for vapor permeability (delta, m2/s) and vapor resistance (Z, [s/m]) for different building materials, even harder to find comparable values. But, after some googling and browsing the Moisture Handbook, I come up with figures that I consider adequate for this comparison of the materials' relative vapor resistance.

From my sample calculations in the table below, it appears that windproofing paper (both AC350 & AC160) has a negligible vapor resistance compared to all other layers in the wall (individually). The old rule of thumb that the outside should have 5-10 times less vapor resistance than the inside is met with flying colors.

[image]

Thanks! Very surprising that it has such low vapor resistance.

So my latest decision is to proceed with the following:
1. Planks
2. Vertical 45-studs with insulation
3. Horizontal 45-studs with insulation
4. Windproof paper AC350
5. Air gap/batten 12mm (small, I know, but I really want to limit how much the wall protrudes)
6. Vertical paneling (baseboards+cover battens), painted with natural paint

So my only dilemma is which insulation to choose. Either:
1. Icell 45mm boards. About 70 SEK/m^2. Not in stock anywhere I can pick up, but can be ordered.
2. Regular glass wool. About 13 SEK/m^2. Easy to obtain.

The simplest and cheapest is glass wool. It is also non-combustible, compared to cellulose insulation where I find it somewhat unclear how fire-resistant it actually is (it is still made of newspaper). It is impregnated with borate salts and/or aluminum hydroxide, but how long does that remain in the insulation? What is the fire resistance in 10 years? As I understand it, glass wool is "naturally" fire-resistant thanks to the material.

 

[justusandersson]

I would choose stone wool over glass wool. I think glass wool is tricky regarding its ability to absorb water. Stone wool also has a higher volume weight, which is always an advantage. Besides, I find it hard to see any decisive difference between cellulose and mineral wool with the current placement.

 

[Oldboy]

I think you can assume that the fire properties/fire resistance will be there for a very long time. Probably throughout the insulation's lifetime.

 

[justusandersson]

From a fire safety perspective, the interior surfaces are more significant, as is loose furniture. A plank frame is among the best one can have from a fire point of view. The properties of the insulation are likely marginal in this context.

 

[krumbukt]

Thanks for all the responses, the wall is finished and it turned out well.

I will now start renovating the inside of the walls. Currently, there is treetex which is buckled, and the wallpaper is torn in places. I was thinking of installing vertical studs on the treetex and then OSB + drywall. Is there any point in using 45 mm studs and at the same time adding a layer of 45 mm insulation? I'm thinking it might be negative to insulate from the inside as less heat would then reach and dry out the plank frame. The alternative is to use 28x70 mm studs and just have air between the studs. Does anyone have a thought regarding this?

The wall currently consists of the following:
1. Batten and panel (22 + 22 mm)
2. Nail batten/air gap (12 mm)
3. Asfaboard (12 mm)
4. Two layers of 45 mm mineral wool insulation
5. Plank wall (about 100 mm)
6. Treetex (12 mm)

 

[Mazen]

I would skip studs and OSB and put drywall directly on the tretex.. Alternatively, if it is too uneven, tear it down and if needed (because the plank wall needs to be aligned due to large irregularities) shim OSB and then drywall ...

 

[krumbukt]

I would skip studs and OSB and attach drywall directly to the tretex.. Alternatively, if it is too uneven, tear it down, and if necessary (due to the plank wall needing alignment because of significant unevenness) shim OSB and then drywall...

Interesting. Why? I've wanted something rigid behind the drywall to avoid the risk of cracking it when I screw it up, or if in the future I want to mount something on the wall that needs to be securely fastened.

 

[Mazen]

You have the plank frame behind, and for me, tretex is quite stiff, provided there isn't a lot of air behind that makes the whole package pull in towards the plank.

It takes some force if so, and know that the screw goes through the plaster before that happens.

A standard plaster is quite hard to crack locally, and I have renovated a room with a log frame behind tretex, and sure, a few screws went through, but it wasn't a major problem.. And now, logs tend to be more uneven than standing planks.

However, if you're unsure and feel a lot of hollowness, meaning that the tretex is more or less mounted in the air. Tear it off completely.

 

[Villa1949]

I screwed drywall directly onto my Tretex walls. If I need to hang something heavy, I just screw through the drywall and Tretex into the wood frame.

 

[krumbukt]

You have a board structure behind, and for me, Tretex is quite rigid, provided there's not a lot of air behind that causes the whole package to be pulled towards the planks. It requires some force, and knowing that the screw goes through the plasterboard before it happens. A standard plasterboard is quite hard to break locally, and I've renovated a room with a timber frame behind Tretex, and sure, now and then a screw went through, but it wasn't a major problem... And now, timber is usually more uneven than standing planks.

However, if you're uncertain and feel a lot of hollow space, meaning the Tretex is more or less mounted in the air. Tear it down entirely.

Yes, the board structure is behind, and it's great for screwing in. However, it's horizontal planks, not vertical. I find it quite uneven, but it's not necessarily a problem now that I think about it. It seems unnecessary to tear away the Tretex, it does provide some insulation and maybe reduces draft risk a little. I have a couple of plasterboards, going to try screwing one up without studs and see how it goes.

I screwed plasterboard directly onto my Tretex walls. If I need to hang something heavy, I just screw through plasterboard and Tretex into the board structure.

Okay, you're starting to convince me...

But it was really the insulation question I was wondering about, if there's any point in adding 45 mm of insulation on the inside, or if it might even be negative.

 

[Oldboy]

In principle, you can insulate on the inside as well, but I think the disadvantages outweigh the benefits there.
Ideally, you want a more temperature-stable inside, which means heavy massive materials, i.e., the plank frame is good.