Determine the rating of an existing floor

[Ryan Schultz]

I have an existing floor that is very similar to a 2hr UL G515 floor assembly. The only difference is instead of metal furring, there is Wood 1x2's - 10" o.c.
How do a determine the hourly rating of this floor? I know about chapter 721 and 722, but what I can gather there's no area that talks about wood furring.

 

[mtlogcabin]

Have you looked at
RESOURCE A
GUIDELINES ON FIRE RATINGS OF
ARCHAIC MATERIALS AND ASSEMBLIES in the back of the IEBC

 

[classicT]

Are you sure that it was rated? What was the original construction type too?

 

[Ryan Schultz]

From what I can gather, the original construction was probably a 2A.

It's a 3 story building with exterior brick, and steel beams and steel joists--most of which are encased in plaster w/ metal lath.

---

Unfortunately the Resource A Guidelines on Fire Ratings of Archaic Materials and Assemblies doesn't seem to address it either.

 

[classicT]

II-A with wood furring strips?

I'm sorry, but if it were my rodeo, there is no way I would accept the continued use of this as a rated assembly if it has wood furring in a non-combustible construction type building. The wood furring should never have been permitted (IBC Section 603), so trying to justify its continued use for fire rated construction is a reach in my book.

I would need something from the legacy code under which the building was built that justified the use of wood furring for me to change that opinion. And I just don't believe that you will find that. I have a feeling that you are looking at a non-conformity that was missed at original construction.

 

[mtlogcabin]

Will it work as a Type III B construction type building

 

[steveray]

603.1 Allowable materials. Combustible materials shall be
permitted in buildings of Type I or II construction in the following
applications and in accordance with Sections 603.1.1
through 603.1.3:

18. Nailing or furring strips as permitted by Section 803.13.

803.13.1 Direct attachment and furred construction.
Where walls and ceilings are required by any provision in
this code to be of fire-resistance-rated or noncombustible
construction, the interior finish material shall be applied
directly against such construction or to furring strips not
exceeding 13/4 inches (44 mm), applied directly against
such surfaces.
803.13.1.1 Furred construction. If the interior finish
material is applied to furring strips, the intervening
spaces between such furring strips shall comply with
one of the following:

Maybe.....

 

[classicT]

603.1 Allowable materials. Combustible materials shall be
permitted in buildings of Type I or II construction in the following
applications and in accordance with Sections 603.1.1
through 603.1.3:

18. Nailing or furring strips as permitted by Section 803.13.

803.13.1 Direct attachment and furred construction.
Where walls and ceilings are required by any provision in
this code to be of fire-resistance-rated or noncombustible
construction, the interior finish material shall be applied
directly against such construction or to furring strips not
exceeding 13/4 inches (44 mm), applied directly against
such surfaces.
803.13.1.1 Furred construction. If the interior finish
material is applied to furring strips, the intervening
spaces between such furring strips shall comply with
one of the following:

Maybe.....

From the 2018.... I don't see how it would meet either of the (3) options. Does not appear to be filled, and fire blocking every 8-ft in each direction seems unlikely.

803.15.1.1 Furred Construction​

If the interior finish material is applied to furring strips, the intervening spaces between such furring strips shall comply with one of the following:​

1. Be filled with material that is inorganic or noncombustible.
2. Be filled with material that meets the requirements of a Class A material in accordance with Section 803.1.1 or 803.1.2.
3. Be fireblocked at not greater than 8 feet (2438 mm) in every direction in accordance with Section 718.

Exception: Compliance with Item 1, 2 or 3 is not required where the materials used to create the concealed space are noncombustible.​

 

[steveray]

If is full of insulation that might work....

 

[redeyedfly]

If is full of insulation that might work....

Nope. You can't add insulation to a horizontal UL assembly unless it is listed in the assy. Also, what he is showing is not an interior finish, it is part of a fire rated assembly.

I think your best bet is an engineering judgement. It might be hard to find a fire engineer who will write the judgement you want. The owner may have to pay to replace the gyp membrane with steel furring.

 

[steveray]

Nope. You can't add insulation to a horizontal UL assembly unless it is listed in the assy. Also, what he is showing is not an interior finish, it is part of a fire rated assembly.

I think your best bet is an engineering judgement. It might be hard to find a fire engineer who will write the judgement you want. The owner may have to pay to replace the gyp membrane with steel furring.

You can add insulation,(although not for 2hr.) but you may have to add drywall:

17. Blanket Insulation

Unless specifically described in the individual designs, the addition of insulation in the concealed space between the ceiling membrane and the floor or roof structure may reduce the hourly rating of an assembly by causing premature disruption of the ceiling membrane and/or higher temperatures on structural components under fire-exposure conditions.

Insulation in G500, L500, M500 and P500 Series Designs — For 1-hour-rated G500, L500, M500 and P500 Series assemblies, fiberglass insulation, either loose-fill, or faced or unfaced batts or blankets may be added to the plenum or joist space above the gypsum board, provided an additional layer of gypsum board is added to the assembly.

I was speaking strictly to construction type question with wood furring...

I would agree with the EJ if you can't find a proper listing...

 

[ccollings]

my humble opinion is that you rip out the existing drywall and the wood furring strips and redo the ceiling so that it complies with G515. Without knowing the details of your project, i'm assuming that you need a 2 hr floor rating? I'm also assuming that your dealing with a plain drywall ceiling and that it's not ornamental and needs to be preserved? if it's just a plain drywall ceiling, rip it down, rebuild it so that it complies with an approved system and move on.
you may be able to add metal furring and another layer of drywall so that your system becomes a hybrid of G515 & L505 and you'd have to sell it to the AHJ but i still think the best bet is to rip it down and do it right. heaven forbid that there ever be a fire but if there is and you find yourself in the witness seat, it's better to say that you followed a tested and approved system than saying that you left a deficiency in place and put a bandaid on a turd and hoped for the best. it's one thing if the floor/ ceiling was compliant at the time it was built, but from the other comments it sounds like it was never compliant and should never have been built that way.