Why does everyone use OSB behind drywall?

[Huddingebo]

30 minutes of fire insulation with double plasterboard. Felt good in a kitchen. 3 layers of plasterboard are A60 and are used in some flammable environments.

But with today's commonly open floor plans, it might matter less if the entire ground floor doesn't have double plasterboard.
However, it does become more soundproofed between the rooms.

 

[Stefan1972]

Doubtful if it can even be measured......An overheated kitchen interior doesn't care about double drywall in that way. The heat ignites what's behind anyway. Separating fire compartments otherwise has a bit different purposes. It can be about saving 2/3 of a row from burning down instead of everything.

 

[Mikael_L]

I believe that fire compartments in apartment buildings mainly exist to give people in adjacent apartments a chance to escape and/or be rescued by emergency services.

Secondly, it is to reduce the spread so there is a chance to save parts of the building.

I agree with the rather pointless idea of having double plasterboard for fire protection on just certain walls here and there inside a fire compartment. It’s almost useless unless you have created a complete fire compartment, i.e., IE30 or IE60 or something, for all walls, ceilings, floors, and doors.

 

[MathiasS]

I believe that fire compartments in apartment buildings mainly exist to give people in adjacent apartments a chance to get out and/or be rescued by the emergency services.

Secondly, it is to reduce the spread so there is a chance to save parts of the building.

I agree about the rather pointless use of double plasterboard for fire protection on just certain walls here and there inside a fire compartment. It does almost no good until you create a complete fire compartment, i.e., IE30 or IE60 or something, for all walls, ceilings, floors, and doors.

The times I've seen row houses on fire, which unfortunately have occurred a couple of times around here in recent years, the fire has spread via the attic and roof, and the fire brigade has had to fill all the apartments with water anyway. So it's probably exactly as you say. It gives people a little more time to get out.

 

[Mikael_L]

That is mostly due to outdated lax norms for fire protection.

When those townhouses were built, it only required fire separation in walls between apartments, there were no requirements for the attic space (there was no apartment above). That's why entire rows of townhouses burn down today, when the fire brigade arrives 5 minutes after the alarm, the fire is already in the attic over every part of the townhouse, making it impossible to save any part of the townhouse, at least not without water damage equivalent to total destruction.

Nowadays, many rows of townhouses are being retrofitted with fire separation walls in attics.

 

[Daniel 109]

It also happens that there are firewalls in the attic. But that they fail at the eaves or due to perforations for later installations.

 

[Jochi]

30 minutes of fire insulation with double gypsum. Felt good in a kitchen. 3 layers of gypsum is A60 and is used in some fire hazardous environments.

Also good with a non-combustible board under the cabinets where the stove fan is located.

 

[Daniel 109]

What benefit would it provide?

 

[Eld]

Surely the spread is a bit slower anyway. It can save the house.

It requires fire doors that close automatically for it to make any difference at all.

 

[Mikael_L]

It's important to stop fire gases, to keep them contained within the fire compartment. Yes, the development of heat should also be kept inside the fire compartment, but if fire gases spread further, the other factors don't matter as much anymore.

So yes, fire compartment boundaries in all 6 directions, as well as fire doors and sealed penetrations and all that. This isn't something that can be done half-heartedly; if you do it inadequately, you might as well not do it at all.

 

[Daniel 109]

There I don't agree. Even a regular interior door stops a fire surprisingly well. Also, fairly tight penetrations without proper fireproofing are much better than large holes.

 

[pacman42]

The goal is to stop fire gases, to keep them inside the fire compartment. Yes, the heat development should also be kept inside the fire compartment, but if the fire gases spread, the other aspects no longer matter as much.

So yes, fire compartment boundaries in all 6 directions, as well as fire doors and sealed penetrations and all that. This isn’t something that can be done half-heartedly; otherwise, you don’t need to do anything at all.

There is an example of this at Liseberg in Gothenburg...

For regular houses, the floor is often not as important. Since heat rises, they last longer.

And as @Daniel 109 points out, regular doors provide good protection as long as they are closed. They reduce the spread of smoke and decrease the initial strength of the fire by reducing oxygen supply.

Moreover, if the wall doesn’t catch fire quickly, it’s difficult for the fire to spread laterally, it spreads upwards, which thus delays the lateral spread.

Everything you do is beneficial, the question is what the goal is.

 

[Nytt_användarnamn_2024_12]

A regular interior door does not stop any fire gases; anyone who believes it does is simply ignorant about construction or fires.

 

[Krille4]

A standard interior door doesn't stop any fire gases, anyone who thinks that simply doesn't know anything about construction or fires..

But a closed interior door is still better than an open interior door, isn't it?

/Krille

 

[Daniel 109]

A regular interior door does not stop any fire gases, anyone who thinks so simply knows nothing about construction or fires..

Yes, it stops a lot of fire gases.