External insulation with wood fiber boards on OSB boards

Hello everyone. I need some advice. We renovated an old house. We removed the entire upper floor and rebuilt it with a timber frame construction. Insulation wool was installed between the beams. Outside, I wanted to have the insulation and plastering done by a specialist company. They wanted me to cover the timber studs outside with OSB. Now they were supposed to insulate and plaster, but the person from the company responsible said that since OSB is on, they cannot attach wood fiber boards. We have now obtained a second opinion, and they say we should remove the OSB boards. The window sills and roller shutters are already installed. I don’t know if I can remove the boards. They were nailed on. Now my question: Can I leave the OSB on, and can insulation be applied on it so that it can be plastered?

Attached is a photo of the house. Here you can see the current status.

Now they should insulate and plaster, but the person from the company responsible for this asked why OSB is on it. He said he cannot attach wood fiber boards on that.

He should please explain a) why not and b) how he intends to fix the boards. If he wants to glue and finds the wood too smooth, there will be some kind of primer available to pretreat it. I would consider tearing off the OSB boards nonsense.

"They probably *could* do it, but it's unusual. The reason is probably that the installed OSB is diffusion-tight. Normally, the wood fiber insulation boards are placed directly on the rafters. Between the rafters is insulation, and BELOW THAT the diffusion-tight layer. If wood fiber insulation boards are placed on the OSB (is there insulation under the OSB?), moisture will enter in the wrong place, leading to mold and other serious problems. Since this involves a specialist company, they would even be liable for consequential damages, even if you sign that they should do it that way. Of course, this is only my 'layman’s opinion,' as always without guarantee.

Quintessence: dismantle the OSB in good weather, then immediately put the wood fiber insulation boards on it. Alternatively, make the OSB diffusion-open (or there is another reason for it -> ask).

Why did this happen in the first place? Presumably due to lack of communication between the client and the executing trade!"

I don't get it. The insulation boards are now put on the outside and then the diffusion-open plaster goes on them. Isn't that normal? I'm not an expert in timber construction, but that's how I know it.

Normally, the wood fiber insulation boards are placed directly on the rafters. Between the rafters insulation and BELOW that the diffusion-tight layer. If now wood fiber insulation boards are placed on the OSB (is there insulation under the OSB?)

What do you mean by "rafters" and "below"? – we are not talking about a roof, but an exterior wall.