Why does everyone use OSB behind drywall?

[Kattvovven]

Sounds like a typical early '90s construction.

Worse than that. Svenska bostäder.

 

[Boan]

Hello!

Are there really so few using Plyfa behind?!? It seems like OSB is the standard, but at least I consider plywood to be much stronger. Sure, it's a bit more expensive, but the difference was only about 80 SEK per sheet compared to OSB, so I didn't hesitate. We redid our walls just because they were single gypsum without insulation, and on the walls where we removed the gypsum, we placed plyfa "inside" between the studs on the side where the gypsum remained.

Råspont builds more, but has less waste so it becomes cheaper, but plywood stiffens things up as well.

 

[Eld]

I have plywood everywhere where there isn't old råspont. OSB isn't much for fastening heavy things. With plywood, you can use wood screws without any plug in all situations.

 

[Amrich]

I have plywood everywhere there is no old raw wood. OSB isn't much to screw heavy things into. With plywood, you can use wood screws without any plugs in all situations.

What do you base that statement on? That you can't hang heavy things on OSB? The difference compared to plywood isn't that big either in pull or hang direction.

There's nothing you hang in a normal villa that an OSB can't bear. Even the heaviest flat-screen TV stays up with a few screws...

Sent from my GT-S5570 using Byggahus

 

[Mikael_L]

I have plywood everywhere there's not old raw planks. OSB isn't much for fastening heavy things. With plywood, you can use wood screws without any plug in all situations.

http://beijerbygg.se/templates/BB_ByggradListItem.aspx?id=52659

And by the way, what reason is there at all to use plugs together with wood screws + wood, OSB, or plywood?
Pre-drilling can be smart though.

 

[MathiasS]

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[Boan]

hi, the difference I have noticed is the tensile strength with, for example, a 4 mm screw, try pulling one out with a crowbar from an OSB, and it goes relatively easily... but in plywood, it's significantly harder...

then I wonder how serious it is with a 2mm expansion gap... I missed it sideways, only have it underneath... but so far nothing has happened

 

[Eld]

Of course, there is never any reason to use plugs in real wood. (You shouldn't do like the previous owner of my house who put up shelves with wood screws and plastic plugs in the sheathing...) In particleboard and OSB, you might need an anchor that grips the backside if you need really high tensile strength.

For example, I wouldn't dare to fasten a folding chair with just wood screws in an OSB board. There is a much greater load on the fastenings of a folding chair than on a flat-screen TV.

 

[Johan Gunverth]

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[MathiasS]

I wouldn't, for example, dare to attach a folding chair with just wood screws in an OSB board.

You still haven't read the Beijer link with SP's tests on tensile strength, have you?

 

[Amrich]

then I wonder how serious it is with a 2mm movement joint.... I missed it laterally, I only have it underneath... but so far nothing has happened

The reason for doing so is to prevent the board from swelling when it gets more humid and causing a bulging wall. But I know several who have installed them flush and have done fine. If you've put up the boards recently, it's an advantage since we're currently in the most humid season, so the boards might be at their maximum width. It also matters somewhat how the board has been stored before installation.

 

[Amrich]

Now we have it in black and white earlier in this thread that both plyfa and OSB can handle high weight in both tensile and hanging directions.

So the ONLY question you need to ask yourself when choosing between them is whether the few kilos that favor plyfa are worth the extra cost compared to OSB. If the answer is no, you buy OSB. If the answer is yes, you buy plyfa. You don't need to take it any further than that.

The fact that some people advocate one or the other just because they have it in their walls or because their father-in-law's cousin's neighbor's brother-in-law spoke badly about the other option is actually quite irrelevant.

 

[MathiasS]

Now we have it in black and white higher up in this thread that both plyfa and OSB can withstand high weight in both tension and hanging direction.

So the ONLY question you need to ask yourself when choosing between them is whether the few kilos that favor plyfa are worth the extra money compared to OSB. If the answer is no, you buy OSB. If the answer is yes, you buy plyfa. You don't need to take it any further.

Then, the fact that some advocate for one or the other just because they have it in their walls or because their father-in-law's cousin's neighbor's brother-in-law spoke poorly of the other option is actually quite irrelevant.

Exactly. But even though the National Testing Institute performed practical tests (simulating load in kitchen cabinets), opinions still differ. If I remember the details correctly, SP even stated that all normal kitchen cabinets broke apart from the load before any of the boards (attachments) in the test failed.

 

[Eld]

Hmm... you probably shouldn't screw a folding chair into just plywood either. Mine is 40cm out from the wall and there is 15cm vertically between the screws in the wall. If it's loaded with 150 Kg at the outer edge (heavy guest or teenager jumping) the tensile force on the upper screws will be 150*40/15=400Kp. With a screw on each side, the plywood won't suffice either.

Luckily, my chair is mounted with coach screws directly into two studs.

Another advantage of plywood and tongue-and-groove is that screw holes don't wear out as much. You can mount new things in the same screw holes. This works really poorly in particle board (from personal experience) and probably not so well in OSB either (not from personal experience). I have used OSB for formwork and other temporary constructions.

 

[vectrex]

I built a bathroom over the summer. I used plywood with screw adhesive (yes, it will be a nightmare the day it needs to be demolished), then wetroom drywall/gypsum and finally tiles. I thought I reinforced properly everywhere that something would be mounted, but now it’s so frustrating that the bathtub wall that needs to be hung is ending up a cm away from the stud. Will the plywood support a glass wall?

Instinctively, it feels like it should with a couple of sturdy VVS screws, but on the other hand, it will be under quite a bit of stress. What do you think?