ᐅ Timber frame builder replaces OSB with gypsum fiberboards – are they equivalent?

Hello everyone!

After months of searching for timber frame house manufacturers offering reliable wall constructions, I finally chose one from Bavaria. I also adopted the mantra that “OSB is a universal solution” because it is ecological, more or less breathable, very rigid, load-bearing, sound-absorbing, and so on.

Now, due to material shortages and price increases, the builder has informed us that as an alternative, they plan to use gypsum fiber boards instead of OSB. This would be cost-neutral for us and technically advantageous. Until now, gypsum was intended as a single layer in addition to the OSB board. Now, the entire wall will be constructed using gypsum fiber boards.

I doubt that gypsum fiber boards, due to their material properties, can be an equivalent or even superior replacement for OSB.

What is your opinion?

Reltaw2021 schrieb:

I have also heard the mantra that "OSB is a universal solution" because it is ecological, more or less breathable,

Well, it certainly is not a universal solution – ecological? My architect and builder deliberately avoid it because it’s not that environmentally friendly. Breathable? How is an inanimate object supposed to breathe?
There are many materials you can use to brace a timber stud wall; you’re not limited to OSB.
What does the exact wall assembly look like? What does the structural engineer say?

Hello Daniel!

There are certainly much more breathable building materials than OSB, no question. The structural engineer hasn’t commented yet, but is likely to approve the construction since he works for the same company that commissioned this alternative sheathing.

What’s important to me is your assessment: For bracing, you can use many materials besides OSB. I understand from you that gypsum fiber boards are one of these materials.

"Breathable" does not apply to OSB at all. The material is installed the other way around using tongue and groove with glued joints to create an airtight layer.

The interesting question for me here would be: if there is no OSB anymore, what then serves as the airtight layer? Double-layered drywall certainly does not.

Instead of drywall, gypsum fiberboards should be used. He corrected that in the text. For example, Fermacell Vapor can be used here to create a windproof layer.

As far as I know, gypsum fiber boards are not as load-bearing as OSB boards. This means that when installing tall cabinets and kitchen units, this must be taken into account or there are limitations.