Truss Heel Blocking 6

[medeek]

I know this topic has been discussed in quite some depth in previous discussions. However, I would like to get some more input regarding raised heel trusses and what you have seen done by the truss manufacturer in your local areas with regard to supplying pre-manufactured heel blocking.

Most of the work I've done or at least seen constructed in my area tends to be non-raised heel trusses with bird blocking similar to the two examples below:

However, lately I've seen a couple jobs with fairly significant raised heels (12" - 24"). I'm not sure if this is a trend but in one case the truss plant supplied little frames for between the trusses, do you see a lot of this in your area? If the raised heel is too high then a solid 2x block is not practical in my opinion, what do you do in this case, shear panels?

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[medeek]

With an 18" heel the heel block is not practical:

Even though, structurally it is probably optimal.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[DaveAtkins]

With high heels (e.g., 24"), I have typically detailed little shear walls between the trusses.

DaveAtkins

 

[jayrod12]

I've had some really large heels where I've just provided horizontal continuous 2x4 at the top of the heel and then diagonal 2x4 extending across at least 3 trusses from top of heel to bottom.

I will admit, most people in my area just ignore the rollover of trusses entirely.

 

[KootK]

I'm stuck in a "do nothing" market too. I'm quite impressed that others are getting the little shear panels though. I long to see one in real life.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[medeek]

From a structural standpoint the entire gable wind load is transferring into the roof (maybe some ceiling) diaphragm and then through these heel blocks into the shear walls below. I think one does need to consider them. I'm always specifying A35 clips between them and the double top plate of the shearwall.

I guess they are really no different than interior shearwall shear panels other than they are usually short enough so that a block will suffice. I will probably just use the same detail with a few minor modifications when the block height exceeds some set value (ie. 14"-16").

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[jayrod12]

Oh the requirement for them is obvious. However as KootK is likely well aware, when we deviate from the local industry norm, we stop getting the phonecalls for the work.

I think most of the problem (in my area at least) is many of the existing homes from pre 1970's have essentially a 2x6 heel depth so rollover was a minor concern. And since the introduction of 12 and 14" typical heels the old engineers turn a blind eye, and the new engineers are never taught that it should matter.

 

[KootK]

Yeah, KootK is aware. This is something that I'd really like to see become a prescriptive code requirement. It puts engineers in a tough spot to have to choose between providing a real load path and staying in business. And it's not as though it's not an issue on pretty much every wood building.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[pmtrevisan1]

I have seen a couple scenarios:
1- general rule in our office is if the heal is greater than 24" and we are the project engineers we supply either blocking or small truss every 48" c/c
2- if nothing is shown on the client supplied dwgs that were sealed by a P.Eng, then we do not provide anything, but do place a disclaimer that diaphragm transfer to plates and shear wall is by project engineer.

As has been discussed above, if we were to include them as part of our package, we would calls from contractors stating that they haven't seen that before and won't put them in, couple that with the competitive market we are in, our competitors certainly don't do it so we are sort of stuck in doing what the industry does.

Cheers

paolo

 

[XR250]

Oh the requirement for them is obvious. However as KootK is likely well aware, when we deviate from the local industry norm, we stop getting the phonecalls for the work.

Ain't that the truth. I struggle with that everyday.


This is from the North Carolina code.... (see attached)

 

[BSVBD]

I'm guilty!

I've never provided any blocking or load path material from top to bottom chord.

We HAVE, on some occasions, specified the exterior, 7/16" OSB sheathing to be full height to bottom of top chord. Whenever we have parallel chord trusses that also provide a parapet, without overhang, naturally the exterior sheathing goes all the way up to top of parapet. That has GOT to account for SOME significant bracing.

I always specify an "H1" hurricane tie, which does have verticals both sides of the truss, but, i hesitate to think that that little bit of steel is the cure. It IS 2.75" of 18 gage.

I also would like to see blocking or other adequate material as a code requirement.

 

[KootK]

This is from the North Carolina code.... (see attached)

Go North Carolina! Seriously, that's bloody great.

I'm guilty!

This topic always ends up feeling like a diaphragm blocking PTSD support group.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jdgengineer]

While, we don't commonly work on high heel trusses, when we have, we specify to either provide full-height 2x blocking, pre-manufactured truss blocking or to sheath panels between trusses to form mini shearwalls.

 

[medeek]

I like what I see with NC's code but I would prefer to bring the shear panel right up to the roof diaphragm:

Thoughts?

In my opinion the venting should come secondary to the structural concerns. Pop a few small holes in the sheathing below the 2x4 shear panel top plate, but not too many that the sheathing is overly compromised.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[jdgengineer]

That is one option we use Medeek. Terry Malone's book has a good discussion on this approach.

 

[KootK]

Sheath or truss it and you're good structurally. Just need a plan for eave ventilation.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[medeek]

I'll have to open up Malone's book again, haven't looked at it for a while, that should be monthly mandatory reading.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[BSVBD]

Just need a plan for eave ventilation.

Specify the top chord proper vent. The sheathing should only go up to bottom of top chord. The proper vent will break that sheathing plane.

Trusses i typically deal with, come with only the top chord cantilevering for the pre-manufactured overhang.

The soffit is framed by the contractor and then the vented aluminum soffit is installed.

Am i missing something?

 

[mike20793]

I use the shear panel option between trusses on all my wood projects. It works well and they are pretty easy to construct. I'm actually kind of surprised that some of you are saying they would get balked at in your areas. As a warning, I've had a couple plan reviewers that will claim and that the shear panels between trusses are analogous to short shear walls and since the shear wall below is significantly longer, it triggers a vertical irregularity and a whole bunch of pain. Terry Malone agrees with them.

 

[jayrod12]

it triggers a vertical irregularity and a whole bunch of pain

Oh FFS, they should be happy anything is provided at all.

You have no idea the detailing norms around here. They'd make some engineer's skin crawl. Granted that's on the residential side of things, which thankfully my firm generally avoids except for preferred clientele.