Exposed wood trusses for 30min rated floor

[Ryan Schultz]

We're designing a full sprinklered 3 story Type VB R-2 Occupancy.

We're using wood trusses and tossing around an idea of exposing the floor trusses.

Per the exception at 711.2.4.3, the floor needs a 30min rating.

Do you feeling, that although we'd have to apply some type of intumescent paint for the trusses (to achieve the 30min rating) and a more augmented acoustical floor assemble above the substrate of the floor, it it would, at the very least, be a wash, cost-wise, relative to the standard approach of drywall and metal channel under the trusses and batt insulation in the cavities?

 

[steveray]

I would think the intumescent and acoustic would be more expensive....But if you really like the look...

 

[ICE]

420.3 Horizontal separation. Floor assemblies separating dwelling units in the same buildings, floor assemblies separating sleeping units in the same building and floor assemblies separating dwelling or sleeping units from other occupancies contiguous to them in the same building shall be constructed as horizontal assemblies in accordance with Section 711.

711.2.4.3 Dwelling units and sleeping units. Horizontal assemblies serving as dwelling or sleeping unit separations in accordance with Section 420.3 shall be not less than 1-hour fire-resistance-rated construction.


Exception: Horizontal assemblies separating dwelling units and sleeping units shall be not less than 1/2- hour fire-resistance-rated construction in a building of Type IIB, IIIB and VB construction, where the building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.

Rated means what? To my way of thinking rated means that it was tested and given a rating by a NRTL that is accredited for that type of evaluation. Is the paint and truss that you suggest a rated assembly for a 30 minute floor?

While I am not educated enough to know much about this, trusses and fire don't get along well at all. It's like the trusses weren't even there.

 

[cda]

You may also have some added sprinkler design issues

 

[RLGA]

There is no tested assembly for an intumescent coating applied to wood members that provides a fire-resistance rating per ASTM E 119/UL 263. There are, however, intumescent products for wood that improves the rating per ASTM E 84/UL 723, but that does not provide the required 30-min. separation between dwelling units.

Also, you don’t state if the sprinkler system is an NFPA 13 or 13R system. If using an NFPA 13R system, you cannot reduce the required separation between dwelling units.

 

[tmurray]

As RLGA stated, intumescents generally in an of themselves have an hourly rating. They usually just form part of a rated assembly.

 

[Sifu]

Also, after the intumescent coating on I joist issues I would really be careful.

https://www.denverpost.com/2017/08/17/colorado-formaldehyde-fume-floor-joists-lawsuit/

https://www.fdazar.com/new-home-buyers-battle-formaldehyde-problem-from-weyerhaeuser-joists/

 

[classicT]

Also, after the intumescent coating on I joist issues I would really be careful.

https://www.denverpost.com/2017/08/17/colorado-formaldehyde-fume-floor-joists-lawsuit/

https://www.fdazar.com/new-home-buyers-battle-formaldehyde-problem-from-weyerhaeuser-joists/

This seems a bit suspect. Formaldehyde is typically used as a disinfectant or its derivatives as thermo-setting resins for adhesives. While some intumescent coatings use urea-formaldehyde as an adhesive compound, why was this used on I-joists in SFD construction where fire-rated assemblies would not be required?

 

[steveray]

This seems a bit suspect. Formaldehyde is typically used as a disinfectant or its derivatives as thermo-setting resins for adhesives. While some intumescent coatings use urea-formaldehyde as an adhesive compound, why was this used on I-joists in SFD construction where fire-rated assemblies would not be required?

Because they are required....Or sprinklers in some cases....

 

[classicT]

Because they are required....Or sprinklers in some cases....

But why was it required? In SFD construction, I have yet to see a requirement for a fire-rated floor assembly. Requirements for sprinklers are typically driven by ability for fire department to fight the fire; a rated floor may (if other opening protectives are used) compartmentalize a fire, but does not provide anywhere near the equivalent protection of sprinklers.

 

[JBI]

But why was it required? In SFD construction, I have yet to see a requirement for a fire-rated floor assembly. Requirements for sprinklers are typically driven by ability for fire department to fight the fire; a rated floor may (if other opening protectives are used) compartmentalize a fire, but does not provide anywhere near the equivalent protection of sprinklers.

2015 IRC requires fire protection of floors. See R302.13.(See also R501.3 in the 2012 IRC)

 

[classicT]

2015 IRC requires fire protection of floors. See R302.13.(See also R501.3 in the 2012 IRC)

Agreed, fire protection is required, but fire-rated is not.

 

[JBI]

Agreed, fire protection is required, but fire-rated is not.

Ty J, correct, but the OP was about an R-2 occupancy, not an IRC application and not a SFD...

 

[classicT]

Ty J, correct, but the OP was about an R-2 occupancy, not an IRC application and not a SFD...

Understood, I was responding to Sifu's post with the links, which were related to SFD's.

 

[Sifu]

Apologies, my post was not in reference to any particular occupancy or use, but just the product which started showing up as a response to IRC 501.3 (2012) by some national builders. My understanding is that the off-gassing of the applied barrier into the environment is suspected to have caused health problems, which led to my alert for leaving something like that exposed. Obviously, anybody is free to make their own choices, but if, as the designer, the choice was put in front of me I would be considering this aspect of it.