Internal cladding, VCL, moisture induced swelling differences

Hello everyone,

Is there any practical experience with internal cladding with Skylark construction?

I have found Internal envelope and I’d like to know what are the experiences from the field trying to put up VCL membrane while sealing in on the ribs while mounting a cladding to the ribs at the same time and getting any air-tightness while doing so.

My other worry is about the materials. The construction is wood-based while I’d like to use plasterboard/drywall. These materials have different - I am not sure what the proper term is - they swell differently with the change in moisture content. Has anyone used drywall mounted directly on the ribs? Has it been longer than a year ago? Are there any cracks in the drywall?

From the risk management perspective I am thinking about not using the service ribs and instead building a somewhat freestanding front drywall using metal stud construction. From the air-tightness perspective, putting up the VCL would be supper simple - no penetrations anywhere, nice flat surface to put it on. From the perspective of different likeliness to change dimensions based on the moisture content - there would be no risk since the wall would be freestanding in bottom and top rails (corners would have dilatation spacing with flexible filling).

To summarize, I’d like to know how battle-proven is the current design of internal cladding and any thoughts on the proposed alternative.


Hi @zbynek.winkler Thanks for opening this discussion. I’ve had a bit of experience installing the VCL on a small WikiHouse build, and admit it’s a bit more fiddly than if it were a flat surface. However it didn’t seem to cause any issues with airtightness, but possibly a case of using a good quality VCL and tape. The other strategy we’re exploring is using a liquid applied VCL such as Passivepurple. over any of the joints and dogbones.
The ribs are primarily a structural device, to help resist bending in the inside panels from significant wind loads. I haven’t seen any issues related to differential movement or cracking in the drywall, and with the bowties installed the chassis is very rigid.

I like your idea of using internal metal studs to create a level surface, maybe something a bit like the metal furring system you get for suspended ceilings? I wonder if it would also be simpler to install timber battens either alongside or between gaps in the internal ribs, rather than fixing to the ribs themselves? A 32mm batten would work nicely here.
Keen to your thoughts and others who may have encountered this before. :slightly_smiling_face:

The liquid VCLs are way to expensive around here (Czechia). I can get a foil for less than 1 Eur per m2. The liquids I was able to find were for once hard to find/buy and way too expensive (10x). Using a butyl tape for the ribs where screws will go through when mounting the internal cladding would be my choice as well.

I am not afraid of movement of the construction due to an outside stress. I am more worried about different change in dimension of different materials due to change in moisture content. They say to keep dilatation space of 1mm per 1m length and expect 0.03% change in dimension for 1% change in moisture content (prospekt-egger-osb-4-top.pdf (page 18)) for this OSB4. But that is with respect to a brick construction. That’s why I am asking about a practical experience with the drywall.

The metal studs like suspended ceilings: yes, exactly. Like this, only vertical:
And you don’t need the middle connections - only top and bottom U profile.