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membrane / sheathing

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sunyaer

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In Ontario building code, "membrane" and "sheathing" are used thousands of times. When we are saying membrane in every day life, it means a thin sheet, like paper or wrapping sheet, while in OBC, a sheet of "gypsum board" can be called "gypsum board membrane", see OBC SB-2 2.3.4.(1).

My questions:

1. how does building code, use OBC for example, define the meaning of "membrane"?

2. sheathing is another word having similar meaning to "membrane", how does building code, again for example in OBC, define the use of "sheathing"?
 
This is California Building Code:

MEMBRANE PENETRATION. A breach in one side of a floor-ceiling, roof-ceiling or wall assembly to accommodate an item installed into or passing through the breach.

MEMBRANE-COVERED CABLE STRUCTURE.
A nonpressurized structure in which a mast and cable system provides support and tension to the membrane weather barrier and the membrane imparts stability to the structure.

MEMBRANE-COVERED FRAME STRUCTURE.
A nonpressurized building wherein the structure is composed of a rigid framework to support a tensioned membrane which provides the weather barrier.

The typical Visqueen under a slab is a membrane. So I get the idea that a membrane is something that stops the passage of something like smoke, fire, moisture.

Sheathing is ....well sheathing. Sheathing can be part of a membrane.
 
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sunyaer said:
In Ontario building code, "membrane" and "sheathing" are used thousands of times. When we are saying membrane in every day life, it means a thin sheet, like paper or wrapping sheet, while in OBC, a sheet of "gypsum board" can be called "gypsum board membrane", see OBC SB-2 2.3.4.(1).

My questions:

1. how does building code, use OBC for example, define the meaning of "membrane"?

2. sheathing is another word having similar meaning to "membrane", how does building code, again for example in OBC, define the use of "sheathing"?
Click to expand...
1. It is contextual. For instance, in fire protection you can use a membrane based approach. In that instance it is referring to the gypsum board. Other times you are looking at the water barrier, air barrier, or vapour barrier it is a membrane as well.

2. Sheathing refers to the board product fastened to the framing members. There is both interior and exterior sheathing. Gypsum, plywood and OSB would be some examples.
 
tmurray said:
1. ... For instance, in fire protection you can use a membrane based approach. In that instance it is referring to the gypsum board. ...
Click to expand...

Can plywood, wafer board or OSB be used in membrane based approach for fire protection?
 
A membrane is a thinner material used in construction to improve a building's performance (watertightness ; temperature regulation ; wind resistant) . It often takes the form of a film or flexible material to be laid on a surface.
Typically waterproofing

Sheathing is the supporting structure that acts as a cover for the surfaces of a building. The main function of sheathing is to provide a surface where other materials can be applied to, either on either floors, roofs, or walls of structures. It also provides additional structural integrity to buildings.
Typically plywood or OSB, typically not waterproofing
 
sunyaer said:
Can plywood, wafer board or OSB be used in membrane based approach for fire protection?
Click to expand...
Membrane protection is either through Douglas fir plywood or gypsum.

There are two strategies for fire rating; membranes or assemblies.

A membrane is a single element that has the entire required fire resistance rating. See table 2.3.4.A and B for specific options

An assembly are different items which when installed together have a fire resistance rating. For example: a wall would have studs, insulation, and sheathing. each component contributes a little bit of time to an overall rating. See table 2.3.4.E for a value for studs, 2.3.4.G for insulation and 2.3.4.C for gypsum. You just add the time values of each together to get a fire resistance rating for the assembly as a whole.
 
Oh, those references are to SB-2 for the OBC. There are tables that are similar in the NBC, just numbered differently in Appendix D.
 
tmurray said:
Membrane protection is either through Douglas fir plywood or gypsum.

There are two strategies for fire rating; membranes or assemblies.

A membrane is a single element that has the entire required fire resistance rating. See table 2.3.4.A and B for specific options

An assembly are different items which when installed together have a fire resistance rating. For example: a wall would have studs, insulation, and sheathing. each component contributes a little bit of time to an overall rating. See table 2.3.4.E for a value for studs, 2.3.4.G for insulation and 2.3.4.C for gypsum. You just add the time values of each together to get a fire resistance rating for the assembly as a whole.
Click to expand...
Excellent explanation. I can't find a table for Douglas fir plywood being membrane for fire protection, where does the code say about this?
 
It's in the table for walls: 2.3.4.A. Nothing for ceilings.

The issue we've had is making sure it is actually douglas fir plywood. We've had people try to use other species of lumber and one architect even tried to swap in OSB for it.
 
Seems the context is, when the term Sheathing is used, we are talking or thinking STRUCTURE

Even though sheathing acts like a membrane (barrier) you are considering other areas like Building Science.

So it seems tome you choose the term that reflects your area of interest at the time
 
tmurray said:
Membrane protection is either through Douglas fir plywood or gypsum.

There are two strategies for fire rating; membranes or assemblies.

A membrane is a single element that has the entire required fire resistance rating. See table 2.3.4.A and B for specific options

An assembly are different items which when installed together have a fire resistance rating. For example: a wall would have studs, insulation, and sheathing. each component contributes a little bit of time to an overall rating. See table 2.3.4.E for a value for studs, 2.3.4.G for insulation and 2.3.4.C for gypsum. You just add the time values of each together to get a fire resistance rating for the assembly as a whole.
Click to expand...
IMPO
Plywood or gypsum, are Sheathing and not a membrane.
The Paint or finish would be the would membrane.
 
mark handler said:
IMPO
Plywood or gypsum, are Sheathing and not a membrane.
The Paint or finish would be the would membrane.
Click to expand...
This would not be consistent with how our code uses the term. It explicitly calls certain types of both membranes when used in certain contexts.

But normally, you would be correct.
 
Accepting UL’s usage of membrane is essential to understanding their assemblies.

Membrane Penetrations in Fire-Resistance Rated Walls - UL Code Authorities

This article focuses on membrane penetrations to protect electrical boxes in fire-resistance rated wall assemblies which are relied upon to help provide safety to life and property from fire, products of combustion, and similar hazards. In order to provide the anticipated hourly fire resistance...
code-authorities.ul.com code-authorities.ul.com
 
mark handler said:
IMPO
Plywood or gypsum, are Sheathing and not a membrane.
The Paint or finish would be the would membrane.
Click to expand...
So a Ch. 7 membrane penetration only penetrates the paint??

What on Earth are you talking about? I'm struggling with the "P" in IMPO if you don't understand what a membrane is in the code.
 
This has been said a couple of times in this thread but, when we are using the term "membrane" the context is important.

A building science engineer would say no, gypsum and plywood are not membranes. At least on their own.
A fire engineer would say yes they can be.

Neither are wrong. It is all based on context.
 
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