# Enclosure under stairs 1009.5.3  (IBC 2006)



## Leo (Sep 8, 2011)

I have a two story type V-B construction building with B-occupancy.

I am allowed unenclosed stairs.

I have one unenclosed stairway in U-shape.

I have a storage area under one run of stairs and under the stair mid-level landing.

the next run passed over two adjacent small offices.

I have the storage area with 1-hour rated walls with fire rated doors.

The stair soffit under the mid-level landing is similar to a floor/ceiling assembly so is easy to rate for 1-hour.

The reviewer does not agree with just applying two layes 5/8 type x board to the bottom of the stairs as this

is not a the same as a floor/ceiling assembly. E.g. I need to double up with 2x4 framing, osb or ply on top with 2 layes type 'x' board.

A little difficult to construct with the osb or ply on top but is is doable. (although not necessary in my view)

In addition the reviewer wants to fire rate the walls and ceilings of the two adjacent offices because one run of the stairs crosses these two rooms. The Code Commentary specifically mentions that the concern is regarding storage under the stairs. The code also mentions "useable space" under stairs. I believe what the reviewer is requesting is not the intend of this code requirement.

Imagine a small section of stairs crossing a large office area, you would have to rate all the walls, ceilings and doors?

Also, if I have within the fire rated wall of the storage area a wood post (4x6) to support the stair opening trimmers.

Of course the reviewer classifies these as columns and need to be independently rated from the wall.

E.g. I need to wrap the posts.....note: there is no tested system for wood column fire rating.


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## Codegeek (Sep 8, 2011)

Have you tried utilizing Table 721.2.1.4(2) which assigns a time for materials?  Two layers of 5/8 Type X gets you 80 minutes according to the Table.

The code language says "enclosures under stairways".  Technically if the offices are under the stairs the reviewer has an argument.  I believe the intent is to protect any adjacent areas from the potential that multiple combustibles create when piled into a storage area.


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## Leo (Sep 8, 2011)

Correct me if I am wrong, but I think Table 721.2.1.4(2) applies to wall finishes applied to cast in place or precast concrete walls.

Table 721.6.2(1) is similar, but only applies to walls where framing members are at 16" o.c.

Using this table for floor/ceiling assemblies requires an upper membrane.

And if you have a column (wood post) within a caculated rated wall assembly, do you still require individual "wrapping" fire rating of this column?

You mentioned yourself that the intent is to protect from cumbustibles piled in storage, these two areas in question are offices.

The other staiway is in small lobby area that leads into a corrodor....the reviewer did not ask me to rate this small lobby and corridor because for obvious reasons it is not intended for storage.


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## Codegeek (Sep 8, 2011)

Thanks Leo, I used the wrong Table and you are correct, it is for application to framing members.  :banghd

Yes, it is to protect combustibles from the storage to the adjacent areas when they are all located under the stairs.

"The walls and soffits within enclosed _usable spaces_ under enclosed and unenclosed stairways shall be protected by 1-hour fire-resistance-rated construction or the fire-resistance rating of the stairway enclosure, whichever is greater."


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## atomahutna (Sep 8, 2011)

Wow, good luck.  I think just about any engineer will tell you that's a post, not a column, but it sounds like that argument would require some serious wrangling.

In any case, individual column protection in 704.2 only applies "where columns ARE REQUIRED to be fire-resistance rated".  In 5B construction, the primary structural frame (column) is required to have a rating of zip, zero, nada. (table 601)


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## texasbo (Sep 8, 2011)

I think you have encountered a competent plans examiner. Look, whether it is overkill or not, the code says (1009.5.3, 2006 IBC) "walls and soffits within enclosed usable space under enclosed and unenclosed stairways...". It says nothing about storage. You have enclosed usable space under the stairs. Is it necessary? Maybe, maybe not. Is it required by code? I think so. In my opinion, strictly by code, he's correct.


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## Paul Sweet (Sep 9, 2011)

Try GA FC-5406.  (5407, 5408 & 4490 are similar) The double layer of 5/8" type X gypsum board ceiling provides one hour fire resistance protection for framing, including trusses.

http://www.gypsum.org/pdf/GA-600-09_Print_7_Megs.pdf


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## Leo (Sep 9, 2011)

Thanks for suggestion the GA Manual.

The floor/ceiling is not really a problem. Applying this to the stair soffit is a problem.

Same for the wood posts within the rated wall assembly which could be a problem.

I believe is is no different than any other framing member within the wall assembly like double or tripple jack studs with

lintels at openings. This reviewer considers these wood posts as being columns, and want them individually fire rated.

As for the office space under the stairs, yes I know the code says "useable" space. The Code Commentary does specifically refer to storage so it is

my belief that it is the intent of the code to provide fire protection for storage uses under stairs.


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## TJacobs (Sep 10, 2011)

I look at this scenario the same as if it was enclosed.  If the openings would be allowed in an enclosed stair then they should be allowed under an unenclosed stair.  The storage room would not be allowed in an enclosed stair so it should not be permitted under the stair, protected or not.  An office would be allowed so I would allow it unprotected.


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## texasbo (Sep 11, 2011)

Leo said:
			
		

> This reviewer considers these wood posts as being columns, and want them individually fire rated.As for the office space under the stairs, yes I know the code says "useable" space. The Code Commentary does specifically refer to storage so it is
> 
> my belief that it is the intent of the code to provide fire protection for storage uses under stairs.


I disagree with the interpretation of rating the columns individually. The code says walls and soffits shall be rated. It doesn't even say they shall be fire barriers. I think it's a stretch to require wood framing members to be individually protected in this case.

As for the offices, the code says usable space. If you have usable space under the stairs, regardless of how it's used, the code requires protection.  Again, I'll not comment on the practicality, but only on the letter of the code.


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## peach (Sep 11, 2011)

you're protecting the means of egress (stairs) from whatever may be stored beneath them.  Kind of destroys the appearance of the open stairs (but so does the appearance of all the junk stored underneath).


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## DRP (Sep 11, 2011)

Isn't a solid 8x8 timber column considered to be protected?


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