Allowable stories?

[Sifu]

I drive by a job not in my jurisdiction everyday that has me puzzled. It is a wood frame, 5 story R2. In researching how they might have allowed 5 stories I came across a design on the internet for one. I can't figure out how a type V can be done with 5 stories but the one I found on the internet is a type III, wood frame. That brings up another question, which is the definition for noncombustible. Type III requires noncombustible exterior walls. So does this mean the wood frame walls are considered noncombustible by the use of a fire wall assembly? I am under the impression that a rated wall is rated for time, and that at some point it will fail, so it is ultimately combustible. I have seen code change proposals for the definition to noncombustible but none that have been approved.

 

[Sifu]

I have found the test criteria, ASTM E 136. So a wall assembly would have to meet the test criteria, and it would then be a noncombustible wall. Has anyone seen a wood wall assembly, studs, zipwall etc. that meets this test? I assume that is the only way this would work but if there is another way please inform me.

 

[Francis Vineyard]

Type 3 permits FRTW within the exterior wall assembly and would appear to be Type 5 during construction.

 

[cda]

The first floor is also wood ??

And are apartment units?

 

[Sifu]

Yes the first floor is wood, the exterior sheathing is zip wall, not FRTW unless that is a new product. Even so, is FRTW as part of a wall assembly a tested ASTM E136 assembly? The building is either R1 or R2, either way the story limit for type V is 4 (sprinkler increase). I am trying to learn how this building could be a type III since that is the only way you could exceed the 4 story type V limit. I assume greater minds than mine have already addressed this so I just want to know how.

 

[mark handler]

Factors That Influence Design

Species of Lumber

Grade of Lumber

Moisture Content and Wood Shrinkage

Condition of Seasoning

Vertical Displacement (Shrinkage) IBC §2303.7 in Multi-Level Wood Framing

Location of Shear Walls

Support of Floor Joists

Seismic and Wind Height Limitation

Fire and Life Safety

Building Type – IIIA

Type III construction requires the exterior walls to be constructed with noncombustible materials.

As an exception to using noncombustible construction, §602.3 of the IBC states that fire retardant-treated wood (FRTW) framing complying with IBC §2303.2 is permitted for exterior wall assemblies with ratings of two hours or less, basically allowing wood-frame construction for many structures where noncombustible materials would otherwise be required.

 

[cda]

City missed it?? And when they find out, will make them take a floor off??

1st floor is for apartment units?

http://evstudio.com/3-story-vs-4-story-vs-5-story-apartments/

 

[cda]

Check starting about page 3::

http://www.rethinkwood.com/sites/default/files/Multi-Story-Wood-Construction.pdf

 

[Sifu]

So if the framing and sheathing are FRTW then allowed as a type III. I do not know the materials for sure so I guess that could be the answer.

 

[steveray]

Never seen Zip as FRTW...but Mark gave you the section that (potentially) allows it

 

[mtlogcabin]

I can't figure out how a type V can be done with 5 stories

Designers used to bring dirt and landscaping in around the 1st level and create a level below grade by code definition to avoid sprinklers in 3 story R occupancy buildings. Did they do something similar to get what looks like a 5 story wood building but would actually be 4 under the building code?

 

[sshiffermiller]

A colleague of mine and I were just discussing this yesterday. Developers where I live and work are all about "5-story wood" framed structures (out of town developers...). Student housing in particular... There have been at least 4 projects in the last two years that made it happen. One with 5-stories of wood framed construction over a 1-story concrete plinth. One with 5-stories straight from the ground up. Our code officials seem to allow it under IBC 2009 as Type-IIIA (recently adopted 2012 but wouldn't apply to any of those projects). Our local structural engineers are a bit more weary...

 

[Paul Sweet]

I believe that a NFPA 13R sprinkler system is limited to 4 stories, so it would have to have a full NFPA 13 sprinkler system.

 

[Builder Bob]

510.4 Parking beneath Group R.

Where a maximum one story above grade plane Group S-2 parking garage, enclosed or open, or combination thereof, of Type I construction or open of Type IV construction, with grade entrance, is provided under a building of Group R, the number of stories to be used in determining the minimum type of construction shall be measured from the floor above such a parking area. The floor assembly between the parking garage and the Group R above shall comply with the type of construction required for the parking garage and shall also provide a fire-resistance rating not less than the mixed occupancy separation required in Section 508.4.

 

[Keystone]

Also, see link for American Wood Council PDF's.

http://www.awc.org/codes-standards/buildingcodes/ccwd

 

[ADAguy]

Bob,
If I read you correctly then if I have 4 stories of wood over a two story podium, 1st floor mixed use (office and parking), then the 2nd floor use (medical offices) would have to be of 3hr construction?

 

[Builder Bob]

Nope - that section specifies S-2 parking only or a combination thereof - one story above grade.