Blocking Along Wood Framed Hip

[marinaman]

I have a question regarding what you guys do at wood framed hips.

If you've got rectangular building with typical gabled roof at the middle of the plan and a hipped roof at each end, and the roof is framed with trusses, where the plywood decking terminates at the hip, do you guys detail blocking along that hip intersection of the plywood or do you take that as typical framing that is expected to be installed simply as "good framing"?

When an architect wants hip ridge vents, that further complicates providing blocking at the hip, because the plywood must be cut back from the hip to allow for airflow thru the vent.

How do you guys detail this......or do you detail that at all?

 

[msquared48]

At the hip, due to the longer span of the plywood there, I typically install blocking, but at the ridge, if the diaphragm shears allow for an unblocked diaphragm, would omit it.

In the case where the diaphragm happens to be stressed there to the point of needing blocking, I have put a row of blocking on each side of the ridge with a small opening in between to allow for venting. 1 to 2" seems to work, and the trusses can handle that.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[spats]

Since the plywood usually changes span direction at the hip, I don't know how you could justify not using blocking.

 

[marinaman]

My question is not whether or not blocking is needed. My question is do you specifically detail it or leave it to the framer?

 

[msquared48]

I detail it.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

The plywood changing direction is a good point, but at a hip, depending on the location of the hipmaster truss, which is usually 8 feet from the endwall(but can vary), the change will not occur until after the hipmaster. This means there be a mix of directions of the plywood along the hip at each side.

The blocking really is needed.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[marinaman]

I include a note on my drawings that essentially states what is said in IBC 2308.10.8.1.......which is that panel end joints shall occur over framing members. In the case of a hip created with stepping trusses before transitioning to 90 degree turned jack trusses, this note would cover supporting the plywood panel at the cut back hip....but I agree.....I believe I will need to add a detail that covers hip blocking so that it is not missed by the framer.

You'd think a framer would have enough sense to frame that blocking automatically. Seems like common sense to me.

 

[ToadJones]

Well, most of the hips I framed with trusses had a girder truss about 8-10' off the wall as M^2 stated with monos going from the girder truss to the outside wall.
The trusses running parallel to the girder truss going up to the ridge were usually had the top chord dropped in elevation to allow for 2x's to be laid on their side as purlins so that the plywood could be run the same direction up the whole roof. I always requested this type of truss where it would work because it also made for a better system IMO.
These purlins made it very easy because you could run one right up the hip and it eliminated having to cut individual blocks which are usually a nasty compound miter and difficult to install.

 

[ToadJones]

Here is a link for an image of the drop-hip truss configuration I am trying to explain....only we were never provided the panel as a frame...we framed it ourselves....great system. Sorry about the long link

http://www.google.com/imgres?imgurl...tgQe-2JGDDQ&page=1&ndsp=24&ved=1t:429,r:2,s:0

 

[ToadJones]

if you get your truss guy to do this, you can eliminate your nasty blocking.
I used 3 o4 truss manufacturers routinely and all of them were able to provide the trusses like this when i asked.