Engineering Assistance

[zigmark]

I have a proposed design for a full hip roof system on a 30'-0" square residential structure above the third floor level. The proposal employs Glue-Lam Beams as the hip rafters from each corner that meet at the peek and then 2x12 jack rafters to infill the roof. The design does not include any ceiling joists or rafter ties and is fully vaulted with the single joist rafter construction. There is not a column beneath the peek and no interior load bearing walls.

My questions are regarding the outward force resisting capabilities of this methodology. Does it work?

2012 IRC

2012 IBC

135 V-ultimate

25 psf Ground Snow

Exposure D

Seismic D2

Thanks for any help here-

ZIG

 

[mjesse]

As a Code prescribed method , No.

With an engineered design, Maybe. The beam connections are the key to the puzzle

 

[mark handler]

Done it with bolted connections, top and bottom.

Also done it with wood wrapped steel tubes.

 

[MASSDRIVER]

There is a diaphragm solution as well. It involves strapping and anchoring the corners of the hips on to the other so they can't expand away from each other. It's great fun.

Brent.

 

[JBI]

Not prescriptive, but could likely be designed.

 

[Mark K]

An engineer needs to consider the horizontal thrust and deflection. If done right there is no reason it can't work but to do it right may mean some changes are needed.

 

[steveray]

Agree with engineered solution

 

[Paul Sweet]

It can be made to work with a tension ring at the perimeter. This has to be engineered; there is no prescriptive solution for this.

 

[zigmark]

Thank you all for confirming my position. The engineer has now provided a few changes including details and supporting calculations to address the issue. Initially the design ignored this completely and when questioned the response was that it was a prescriptive application. It obviously is not prescriptive and we are moving on with the design provided.

Thanks,

ZIG

 

[BSSTG]

Greetings,

I love these questions here in Texas. Requires engineering per state law for anything over 22'. Lams too, they're an engineered beam anyway. Makes life simpler.

BS