ᐅ OSB Boards for the Attic "Required," Yet Additional Charges?

Payday schrieb:
As mentioned on page 1: OSB panels need a cross battens underneath to allow air circulation. Then OSB is no problem after drying for 1 year. Once the attic is dry and properly ventilated (wedges placed between overlapping membranes), nothing can happen. If the actual vapor barrier of the house (viewed from above, below the insulation) is airtight, no moisture can enter the attic.

Then it should be fine for us.

Musketier schrieb:
We specifically chose not to use OSB boards but rather tongue-and-groove boarding. OSB acts as a vapor barrier.

The builder’s approach seems strange to me. To bring this up at the last minute is quite unreasonable. My blunt suspicion is that someone is trying to take advantage and make quick money, especially since, as mentioned before, the price is amazing.

I assume this refers to the boards used for the floor in the attic.

I don’t know how the house is constructed. For a cold roof with insulation in the top-floor ceiling: OSB is definitely not suitable. In this case, tongue-and-groove boards laid across battens are required to avoid mold. For a warm roof, OSB can be used. Since this space is going to be just a storage room (like in our case) in a one-and-a-half-story house, the solution with tongue-and-groove boarding on cross battens is quite practical. For a cold roof, it is laid with a large gap, while for a warm roof, a small gap or tongue-and-groove joints can be added later. This doesn’t cost much, and the effort to transport the boards is manageable.

In a proper house construction with correct structural calculations, the stability comes from the ridge beam/rafters/top floor ceiling. A few OSB boards on the floor do not affect structural stability; that would be a huge joke if the floor covering on a roof knee wall affected the building’s stability. I have never heard of such a case (Well, there is some contribution, but if the house is designed so critically that missing some OSB boards causes issues... oh no, what kind of house is that?). I think they are really trying to fool you here. Some people don’t even use any floor covering up there and don’t need it.

My advice: Your builder should keep the material and find someone really naive willing to pay that price and believe such a story.

As for structural relevance, as I said, I have serious doubts. It would be a flimsy, wobbly structure if its stability depended on a few OSB boards. If it is truly required by calculation, you shouldn’t have to pay anything extra for it in a turnkey contract.

Best regards

Thorsten

T21150 schrieb:

As I said, I have serious doubts about the structural relevance. It would be a joke of a shaky, wobbly building if the structural integrity depended on a few OSB panels. If it is indeed verified by calculations, you really shouldn’t have to pay anything extra for it as part of the turnkey construction.

That’s exactly what I thought when I first read it—that he can only hope they are trying to fool him. The carpenter from the construction company, who was there because of minor mold, said that the beams are deliberately chosen at least one size larger than necessary, so that, for example, in case of slight mold infestation you can remove some material without anyone immediately complaining about structural issues.

The only thing I could imagine would be bracing... to be fair, no one knows the builder’s structural calculations.
However, it does seem a bit odd.

BeHaElJa schrieb:
The only thing I could imagine would be bracing...

Hmm.

With (rattling) OSB boards (probably without tongue and groove) screwed onto cross battens on the floor of the knee wall, 5 cm (2 inches) below lies the purlin/upper floor ceiling, and above that the roof structure/knee wall. I wouldn't immediately understand how this additional construction could significantly absorb forces and moments. That would be a construction miracle. No: the forces and moments are absorbed by the roof structure, the purlin/upper floor ceiling, and the walls, and transferred into the overall building. Not a few rather flimsy floor panels.

Of course: this also provides some stiffening to a certain extent—but if that had any real impact on the structural calculations, someone must have already made a major mistake in the design of this building. Honestly—that’s my opinion.

Maybe in 1728 someone built a house like that, but certainly not today... Never. In my view, the original poster is being completely misled by their builder.

Shear wall – this is not something funny, but a normal element in structural engineering. I have 24mm (1 inch) panels – there is absolutely nothing flimsy about them...

OSB always has tongue and groove, right? We installed ESB instead of tongue and groove boarding – more stable than tongue and groove, allows water vapor to pass through, and I simply preferred it.

By the way, we only have just under 40 square meters (430 square feet) in the attic space with a house footprint of about 110 square meters (1,185 square feet) – and it's definitely not a townhouse.