bearing on cantilevers

[darcar]

Can anyone direct me to a section in the 2006 or 2009 IRC where it addresses roof load transfering bearing to a cantilevered floor joist?

A person wants to enclose an existing deck with windows. The roof system will be a shed type roof that has bearing on the outermost part of the room, in which the floor joists are cantilevered 18".

 

[mark handler]

What Seismic Design Category?

CHAPTER 3 is filled with restrictions for SDC of C, D and E

 

[darcar]

sorry... A

 

[imhotep]

Can anyone direct me to a section in the 2006 or 2009 IRC where it addresses roof load transfering bearing to a cantilevered floor joist?A person wants to enclose an existing deck with windows. The roof system will be a shed type roof that has bearing on the outermost part of the room, in which the floor joists are cantilevered 18".

It sounds like the person wants to convert an exterior deck to a living space. I don't believe there is a prescriptive solution in the IRC. R301.1 would have you looking for how both gravity and lateral loads are resolved. If walls and a roof are added then braced wall panels per 602 are required.

Chase that down and you come to R301.2.2.2.5 Irregular buildings. Prescriptive construction as regulated by this code shall not be used for irregular structures located in Seismic Design Categories C, D0, D1 and D2. Irregular portions of structures shall be designed in accordance with accepted engineering practice to the extent the irregular features affect the performance of the remaining structural system. When the forces associated with the irregularity are resisted by a structural system designed in accordance with accepted engineering practice, design of the remainder of the building shall be permitted using the provisions of this code. A building or portion of a building shall be considered to be irregular when one or more of the following conditions occur:

1. When exterior shear wall lines or braced wall panels are not in one plane vertically from the foundation to the uppermost story in which they are required.

 

[permitguy]

Seismic concerns aside, is there anything that prohibits roof loads being transferred to prescriptively cantilevered floor joists? Cantilevering floor joists beyond a basement wall seems pretty common. If you can do that, then what is being described in the OP seems pretty tame. Thoughts?

 

[rktect 1]

Table 502.3.3(1) and 502.3.3(2)

But I think there would be other issues here. You need a DP for this one.

 

[Papio Bldg Dept]

1. When exterior shear wall lines or braced wall panels are not in one plane vertically from the foundation to the uppermost story in which they are required.

We are dealing with the same issue. Typically we require engineering when nominal lumber floor joists are used (but are currently evaluating a pre-engineered detail for limited deck spans). I-joists typically have a pre-engineered installation detail for bearing decks on cantilevers. Enclosing decks is a whole other animal as imhotep indicated.

 

[rogerpa]

Not enough information given. What are the existing floor joist (of the dwelling) and what is the width (depth) of the existing building? Porch? Eve or gable? Roof trusses or rafters? Not only do you need to pick up 1/2 the new roof load, you also have to pick up 1/2 the new floor load. Sounds to me like R104.11 applies.

R502.3.3 Floor cantilevers. Floor cantilever spans shall not exceed the nominal depth of the wood floor joist. Floor cantilevers constructed in accordance with Table R502.3.3(1) shall be permitted when supporting a light-frame bearing wall and roof only. Floor cantilevers supporting an exterior balcony are permitted to be constructed in accordance with Table R502.3.3(2).

R301.1.3 Engineered design. When a building of otherwise conventional construction contains structural elements exceeding the limits of Section R301 or otherwise not conforming to this code, these elements shall be designed in accordance with accepted engineering practice....

Not necessarily a RDP.

 

[Papio Bldg Dept]

Seismic concerns aside, is there anything that prohibits roof loads being transferred to prescriptively cantilevered floor joists? Cantilevering floor joists beyond a basement wall seems pretty common. If you can do that, then what is being described in the OP seems pretty tame. Thoughts?

One of the issues we see is that the rim joist on the cantilevered section is not designed to carry a ledger load for a deck, joist spacing is not designed for additional loading, hangers are typically installed to not accomodate additional loads on cantilevers, and blocking is not installed correctly at the foundation line...and yet we hear, "we have been doing this for twenty years and never had a failure yet."

 

[permitguy]

Given the state of the existing deck being compliant, I could design this prescriptively without an engineer. Whether the plans examiner would wimp out and require one anyway is another story . . .

If the homeowner is hell-bent on some feature that falls outside the prescriptive code, then that's a different story. We'd need to know more about the project to say for sure.

 

[steveray]

PG and Darcar.....From the 2009 IRC....see #2

R602.10.7 Braced wall panel support. Braced wall panel support shall be provided as follows:

1. Cantilevered floor joists, supporting braced wall lines, shall comply with Section R502.3.3. Solid blocking shall be provided at the nearest bearing wall location. In Seismic Design Categories A, B and C, where the cantilever is not more than 24 inches (610 mm), a full height rim joist instead of solid blocking shall be provided.

2. Elevated post or pier foundations supporting braced wall panels shall be designed in accordance with accepted engineering practice.

3. Masonry stem walls with a length of 48 inches (1220 mm) or less supporting braced wall panels shall be reinforced in accordance with Figure R602.10.7. Masonry stem walls with a length greater than 48 inches (1220 mm) supporting braced wall panels shall be constructed in accordance with Section R403.1 Braced wall panels constructed in accordance with Sections R602.10.3.2 and R602.10.3.3 shall not be attached to masonry stem walls.

Rooms on decks (post and pier) require a DP!

 

[permitguy]

Thanks for the clarification on support of the BWPs - I stand corrected!

So I can do it in the '06, I'm screwed in the '09 unless I run the BWPs to a trench footing or similar, but I might be able to do it in the '12 if I ignore 602.10 and use 602.12 instead (where allowed)? And I thought things were getting out of hand with elevator lobbies in the IBC!

This makes me glad I came to the fire service.

 

[Francis Vineyard]

Not forthright as steveray reference to the 2009 sections but R602.10.8 and R404.1.5.1 in the 2006 prescribes all exterior load bearing walls and braced wall panels be on continuous footings. Covered decks without walls may require bracing for uplift R802.11

Limited experienced with RDP's either opt to go with continuous foundations and take advantage to enclose the space below or simply used every method of bracing in the 2009 along with every bracket applicable from Simpson.

(permitguy why did Virginia delete sections 708.14.1 through 708.14.2.11?)

 

[NH09]

There is some reference to cantilevers supporting exterior walls in the Wood frame construction manual (2001 edition),although I am unclear if referencing this manual under the following section is allowed. At the very least it should be able to give you some guidance:

R502.2 Design and construction.

Floors shall be designed and constructed in accordance with the provisions of this chapter, Figure R502.2 and Sections R317 and R318 or in accordance with AF&PA/NDS.