OSB panels for the attic "required", yet extra charge?

As already said on page 1: OSB boards need a transverse battens underneath so that air can circulate. Then OSB is no problem after drying for 1 year. Once the attic is dry and ventilated (wedges between the overlapping foils), nothing can happen anymore. If the real vapor barrier of the house (viewed from above under the insulation) is tight, no moisture can get into the attic at all.

then it fits for us

That’s why we deliberately installed rough-sawn boards instead of OSB panels. OSB acts like a vapor barrier.

The approach of the construction contractor here seems strange to me. Coming up with this at the last minute is outrageous. I strongly suspect: Someone wants to play games here, someone wants to make quick money, because as already said here: The price is just astounding.

I now assume that what is meant here is that the panels in the attic are for the floor covering.

I don’t know how the house is built. With a cold roof and insulation in the upper floor ceiling: OSB is not an option at all. In that case, rough-sawn boards must go on cross battens. Otherwise, there will be mold. With a warm roof, you can use OSB. Since this will only be a storage room in a 1.5-story building (like in our case), the solution with rough-sawn boards on cross battens is quite charming anyway. With a cold roof, laid with a large gap. With a warm roof, with a small gap, or you get tongue and groove boards later. That doesn’t cost much and the hauling is manageable.

With a proper house construction and statics: The roof purlin/roof beams/upper floor ceiling provide stability. The bit of OSB on the floor doesn’t affect the statics here, that would be an ultra-mega-joke in a bag—if the floor covering of a roof knee wall influenced the house’s statics, I’ve never heard of such a thing (Well, it does contribute somewhat, but if the house is constructed so that it gets critical because a few OSB panels are missing... oh oh oh, what kind of house is that???). I believe they really want to cheat you spectacularly here. Some people don’t even use that space; they don’t need a floor covering up there at all.

My advice: They should keep that stuff with your developer and find a really dumb person who buys that at such a price and believes such a story at all.

As for the structural relevance, as I said, I have serious doubts. That would be a joke-wobble-pudding house if the statics depended on a few OSB panels. If that is nevertheless given by calculation, you really shouldn’t have to pay for that in a turnkey deal.

Best regards

Thorsten

As I said, I have enormous doubts about the static relevance. It would be a joke-wobbly-pudding structure if the statics depended on a few OSB boards. If it is actually verified by calculation, you really don't have to pay anything for that in a turnkey project.

That's exactly what I thought when I first read it, that he can only hope that they want to fool him. The carpenter from the construction company, who was there because of the slight mold, said that the beams are deliberately always chosen at least one size larger than necessary, so that, for example, in the case of slight mold infestation, you can easily remove something without someone immediately complaining about the statics.

The only thing I could imagine would be stiffening... to be fair, no one knows the structural engineering of the client. It is somewhat strange, however.

The only thing I could imagine would be stiffening...

Hmm.

With (rattling) OSB boards (probably still without tongue and groove) screwed onto cross battens on the floor of the knee wall, 5 cm lower lies the purlin/upper floor ceiling, above that the roof structure/knee wall. I wouldn't immediately understand how this additional construction should absorb forces and moments in any significant way. 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 building. Not a few totally ridiculous floor boards.

Of course: It also stiffens to some extent - but if that would influence the statics even a little, someone would already have made a substantial error in the calculation of this building. Honestly - that's my opinion.

Maybe one built a house like this in 1728, but certainly not anymore today.....Never, in my opinion the original poster is being completely screwed over by his builder.

Stiffening panel - that’s nothing funny, but a normal part in structural engineering. I have 24mm panels - there’s absolutely nothing floppy about that...

OSB always has tongue and groove, doesn’t it? We installed ESB instead of shiplap - more stable than shiplap, also lets water vapor through and I just wanted to.

By the way, we only have just under 40 sqm in the attic with about 110 sqm of house floor area - and no townhouse either.