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Type C Gypsum Board
- Thread starter Plumb-bob
- Start date
Type X is the commonly used 5/8-in fire rated gypsum.
Type C is also a fire rated gypsum product, occasionally referred to as an improved Type X. This is because Type C has additional glass fiber reinforcement and minerals that expand during exposure. The expansive minerals help to offset the shrinkage resulting from the desiccation of the gypsum. Type C can be sourced in 1/2-in or 5/8-in.
Another note... ASTM C1396, Standard Specification for Gypsum Board, only has regular and special fire-resistant (Type X) designations. Type C is not defined by ASTM, but is a designation from the manufacturer's who utilize the designation as part of proprietary UL assemblies.
So in a way, all Type C is Type X, but not all Type X is Type C.
Type C is also a fire rated gypsum product, occasionally referred to as an improved Type X. This is because Type C has additional glass fiber reinforcement and minerals that expand during exposure. The expansive minerals help to offset the shrinkage resulting from the desiccation of the gypsum. Type C can be sourced in 1/2-in or 5/8-in.
Another note... ASTM C1396, Standard Specification for Gypsum Board, only has regular and special fire-resistant (Type X) designations. Type C is not defined by ASTM, but is a designation from the manufacturer's who utilize the designation as part of proprietary UL assemblies.
So in a way, all Type C is Type X, but not all Type X is Type C.
Oh, and Type C does not correspond to 'Ceilings'.
I was told that a number of times, and but in my understanding this is false. Given that ceilings have a greater heat exposure during fires and assembly testing, Type C can perform better than conventional Type X in floor/roof/ceiling assemblies. Therefore, more often that is where it is located. However, there are both wall and ceiling assemblies that will specify Type C GWB.
I was told that a number of times, and but in my understanding this is false. Given that ceilings have a greater heat exposure during fires and assembly testing, Type C can perform better than conventional Type X in floor/roof/ceiling assemblies. Therefore, more often that is where it is located. However, there are both wall and ceiling assemblies that will specify Type C GWB.
Thanks for this, very helpful.
Paul Sweet
Sawhorse
Type X is generic, but Type C is usually proprietary, so you have to use the same brand Type C that the UL or other rating specifies.
Inspector Gadget
Registered User
There are a small number of listings that allow one layer of 1/2" type C to be used to provide a 45-minute rating instead of one layer of 5/8" type X on a ceiling. These are proprietary, and last I recall there are only 10 of them or some such.
1/2" type C can be considered as having the same or better properties as 1/2" type X, and can be used instead of any assembly calling for 1/2" type X. 5/8" type C (which, IRRC, I have never seen in the wild) can be used where plans cal for 5/8" type X. You can use type C instead of Type X in appendix D or ULC assemblies. Any of the drywall manufacturers can provide you with an official document attesting to this.
The issue is that there are *very* few assemblies with Type C. That said, several ULC listings will allow three layers of 5/8" type C on open-web joists and insulative material to meet a 2-hour FRR for ceiling/floor assemblies. It's the only way I've seen to achieve 2Hr rating with a combustible floor joist.... Certainteed has one for sure, and I think Georgia-Pacific (Or USG. At home, too lazy to surf while off work.)
Do you allow ULC assemblies in a pt9 building without field review by an architect? I would be comfortable with an arch spec'ing the ULC assembly, and reviewing its install, as they are so specific. But for pt9 I try to stick to the assemblies in the fire and sound tables, or appendix D.
Inspector Gadget
Registered User
Yes.
9.10.3.1. Fire-Resistance and Fire-Protection Ratings
1) Where a fire-resistance rating or a fire-protection rating is required in this Section for an element of a building, such rating shall be determined in conformance with
a) the test methods described in Part 3,
b) the calculation method presented in Appendix D, or
c) the construction specifications presented in Tables 9.10.3.1.-A and 9.10.3.1.-B.
3.1.7.1. Determination of Ratings
1) Except as permitted by Sentence (2) and Articles 3.1.7.2. and 3.6.3.5., the rating of a material, assembly of materials or a structural member that is required to have a fire-resistance rating, shall be determined on the basis of the results of tests conducted in conformance with CAN/ULC-S101, “Fire Endurance Tests of Building Construction and Materials.”
2) A material, assembly of materials or a structural member is permitted to be assigned a fire-resistance rating on the basis of Appendix D.
Conclusion: Any ULC-tested assembly is allowable in a part 9 building without engineers or architects being involved.
It should be noted the inverse is NOT true. I cannot accept assemblies in 9.10.3.1-A/B to be used in Part 3 construction.
Good answer thanks.
tmurray
SAWHORSE
The key is making sure that they are adhering to the listing. It can be a little restrictive, so the Part 9 tables and Appendix D are a little more common due to their flexibility.