Hip Roof Design

[jimtheengineer10]

Attached is a sketch and a roof plan that a client sent me and the contractor wants to stick build it. It is a 26' wide x 20' addition. The snow load here is 55 psf.

Do you see any issues with it?

 

[jimtheengineer10]

Here is the roof plan

 

[DaveAtkins]

All members need to be checked of course, but conceptually it appears you have all of the ridge beams you need to support the various sloping rafters.

I think this roof would be a lot easier to design and build if you used roof trusses. They do hips, gables, etc. all the time.

DaveAtkins

 

[msquared48]

Could get away with a few fewer members in reality, but what he shows conceptually will work. Just have to verify the member sizes and delineate the connectors.

Mike McCann, PE, SE (WA)

 

[XR250]

The ridges seem a little light for that load and span. Make sure you check deflection.

 

[jimtheengineer10]

Are there special connections required at the ridge or where the rafters meet the 2x10 wood beam and/or exterior walls?

Our area is required to install hurricane ties where the rafters meet the exterior walls but is there some other connection required?

 

[DaveAtkins]

You must check each member for the appropriate load combinations. Almost certainly there will be a load combination which results in uplift at the connections.

DaveAtkins

 

[rlflower]

I agree with XR250 and I would stress the importance of the deflection consideration. A minor amount of deflection may not be a structural concern but can be a serious detriment as far as your client is concerned. If the deflection of the ridge is readily visible, that can become a problem.

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

 

[msquared48]

That is where the induced extra rigidity of the roof diaphragm, further affected by the roof pitch used, that will reduce the actual deflection calculated. Hard to quantify. Just have to be conservative.

Mike McCann, PE, SE (WA)

 

[XR250]

That is where the induced extra rigidity of the roof diaphragm, further affected by the roof pitch used, that will reduce the actual deflection calculated. Hard to quantify. Just have to be conservative.

Yup, seen plenty of big vaulted roofs - gable and hip that have no intentional support and are not sagging at all.
Then again, I have seen plenty that are pushing the walls out.