Plywood facade without air gap

[TH-huset]

Hello, I have a construction of a small house about 15 sqm where I want to keep the wall thickness as thin as possible. The most feasible option to sacrifice is the air gap.

My question is if it is possible to place 12 mm plywood directly on the studs, with wind barrier in between, without causing condensation problems.

I assume I need a diffusion-open paint so that the wood can dry outwards.

Would it help if I seal along the studs, making it completely airtight?

My last option is to glue XPS directly on the plywood and studs to create an airtight wall section similar to a sandwich panel. But I want to avoid this as I think it will be difficult to glue completely without air bubbles.

Thanks in advance!

 

[Leif i Skåne]

If you use thin strips 8-10 mm to hold the wind barrier, you naturally create an air gap and the barrier isn't glued against the 12 mm plywood board.

 

[TH-huset]

If you use thin strips 8-10 mm to hold the wind barrier, you naturally get an air gap and the barrier isn't glued against the 12 mm plywood board.

doesn't sound very dangerous with an extra 8mm per side. However, I would like to use the plywood as a load-bearing element, to be able to increase the spacing between the studs a bit. But for them to be able to do that, it feels like it should be flush against the studs. Any thoughts?

 

[Leif i Skåne]

The purpose of the strip is to prevent the cardboard from sticking to the board, allowing the surfaces to be ventilated. Always keep in mind that moisture migrates toward the coldest surface and condenses there; it must be able to be ventilated away. Normally, panel boards are positioned vertically, providing plenty of gaps for ventilation, but plywood is quite impervious to moisture migration.

 

[TH-huset]

The purpose of the strip is to prevent the cardboard from sticking to the board, allowing the surfaces to be ventilated. Always remember that moisture moves towards the coldest surface and condenses there, so it must be able to be ventilated away. Normally, you have vertical panel boards, and there are plenty of gaps for ventilation, but plywood is quite tight against moisture movement.

Okay, how can I make the facade strong enough to have some load-bearing capacity?

And what do you do with houses with plaster? There usually isn't any air gap there.

 

[Lutte]

Screw the strip properly, then glue and screw the plywood to the strip. In my world, it's the same as screwing the plywood directly to the stud. The plywood and the strip become one with the glue.

 

[TH-huset]

Screw the strip properly, then glue and screw the plywood to the strip. In my world, it's the same as screwing the plywood directly to the frame. The plywood and the strip become one with the glue.

That sounds good, I assume you need to go with vertical strips for the water to drain properly. And would it be sufficient to only have a small block right at the frame instead of all the way up along the wall?

Maybe I'll glue a block somewhere halfway up the plywood and screw an insulation screw or something similar from the outside into the XPS insulation, just so the panel doesn't bulge. How large do you think the intervals for this need to be? Every meter?

 

[Lutte]

So you are planning to have XPS on the outside of the studs and then plywood?

Looking across the pond, they use a ZIP system that has a product which is XPS glued to OSB that is coated and water-repellent.

I think it will be difficult to get any significant load-bearing capacity as everything will be hanging on your XPS.

If you absolutely have to use plywood as a façade, I would use plywood-strip-weather barrier-stud with insulation in between.

Otherwise, it is probably possible to glue XPS on plywood and inset the studs and top plates, then skip the air gap.

 

[TH-huset]

So you plan to have XPS outside the studs and then plywood?

Looking across the pond, they use the ZIP system, which has a product that is XPS glued on OSB that is coated and water-repellent.

I think it will be difficult to get any further load-bearing capacity since everything will be hanging on your XPS.

If you necessarily want to use plywood as the facade, I would go with plywood-list-wind barrier-stud with insulation in between.

Otherwise, it might be possible to glue XPS on plywood and recess studs and header and then skip the air gap.

Yes, the initial thought was to skip the air gap, but the risk is that my gluing won't be 100% tight, meaning small air bubbles where condensation might form.

But to answer the first question, I was thinking XPS between the studs, but I have quite a few studs, so it might be appropriate to fasten the plywood in XPS to avoid deflection.