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

 

[rdubs]

I agree with medeek - bringing the shear panel up to the roof diaphragm allows additional nailing where the roof sheathing uplift is the highest. Drill round holes to get the appropriate ventilation area.

 

[KootK]

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.

FFS indeed. Now jayrod and I will be yet another step behind the state of the art.

Technically, those widdle shear wall panels need to be able to resist vertical shear or T/C on their sides to be in equilibrium. And, in many instances, you get that by fastening each panel to the last vertical of the truss such that vertical shear is passed across the truss from one panel to the next. Where that is the case, I would very much argue that the panels are just an extension of the primary shear wall rather than a whack of new, short shear walls. I guess, by the book, you'd still need to connect the mini-wall boundary studs at the far ends to the boundary studs of the primary shear wall. I would not want to be the first to specify that in my domain.

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]

If you don't bring the shear panels up to the roof diaphragm then the top chords of the truss are being loaded in shear, I suppose it all works itself out somehow since I haven't seen any failure of roof from this but the load path seems more convoluted. I suppose one could always do something like this:

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

http://www.medeek.com

 

[jdgengineer]

I would not want to be the first to specify that in my domain.

We do just that...

 

[medeek]

Sorry forgot to post the image:

I don't know that this is really any better than my first shear panel but at least it positions the vent holes up high out of the way of the insulation and it gives a solid nailing surface for the sheathing to the vent blocks. It does get us back to using the A35 clips though, so back to messing around with hardware.

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

http://www.medeek.com

 

[dik]

The high heel height allows more insulation with ventilation between the roof sheathing and the top of the insulation. Normally just a matter of securing the outside wall sheeting to the higher heel and carrying it down the wall to anchor it. A higher heel also permits a greater anchorage of the roof truss system.

Dik

 

[KootK]

We do just that...

Beautiful. You're living my dream man! Got one for when the walls terminate at a location where it's not an exterior corner? When I imagine it in my head, it's hard to get the edge of the nearest truss heel panel thing to line up with your boundary studs below.

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]

Looking at it now I see that one could probably nail up through the shear panel top plate into the vent block with about four 16d nails and probably not have to use the A35 clips, not sure why I didn't see this before. Looking at it in 3D helps sometimes.

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

http://www.medeek.com

 

[DaveAtkins]

medeek,

Your illustrations are really cool!

You should write a book. It could be called, "Blocking Between Truss Heels and Other Things Contractors Don't Want to Do."

DaveAtkins

 

[kipfoot]

It's not just NC that calls for this. The tar heal state followed the IRC (international residential code). This is the adopted residential code throughout the US, I think, in localities large and small.

R602.10.6.2

 

[nac521]

That blocking requirement isn't isolated to just NC. The same prescriptive wall bracing provisions are in the IRC2009 R602.10.6.2 for heel depths greater than 9 1/4".

 

[medeek]

I use SketchUp for conceptual stuff, I used to draw a lot of hand sketches but I find SketchUp is much quicker for many things. All of my 2D drawings are in AutoCAD but I prefer 3D when I'm trying to visualize a specific construct, it helps things pop out that you sometimes miss with a 2D sketch or drawing. I've managed to cobble together a couple of extensions for SketchUp which allows me to quickly generate roof, floor and foundation geometry (I use a third party plugin for wall framing), so in almost less than a minute I can usually create a fairly realistic model of just about any residential framing or structural issue. I've used a lot of 3D softwares (AutoCAD, SolidWorks, Catia, Chief Architect, etc...) and I can safely say that SketchUp beats them all hands down when it comes to speed and simplicity.

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

http://www.medeek.com

 

[medeek]

The high heel height allows more insulation with ventilation between the roof sheathing and the top of the insulation. Normally just a matter of securing the outside wall sheeting to the higher heel and carrying it down the wall to anchor it. A higher heel also permits a greater anchorage of the roof truss system.

If the wall sheathing extends up over the raised heel without a break then yes this is a major advantage to the roof construction as far as uplift and even truss overturning, the question is do most contractors do this or do they just break the sheathing at the top plate and then patch on more sheathing at the raised heel?

That is why I like my 2nd option with the heel block on top of the shear panel. This allows the contractor to terminate the sheathing at the underside of the top chord of the truss, the sheathing is continuous up the entire wall and over the raised heel. The heel block then provides an uninterrupted load path to the roof diaphragm. I don't see the validity in those shear panels with an air gap between their top plate and the roof sheathing, load cannot be transferred through thin air.

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

http://www.medeek.com

 

[jayrod12]

do they just break the sheathing at the top plate and then patch on more sheathing at the raised heel?

since walls are generally 8'-1 1/8" or 9'-1 1/8" this is less of an issue than you think. They start the sheathing at the sill plate on the foundation wall, span it over the floor system, and then up the wall. It usually means the 8' mark from the bottom of the sheathing ends up being a foot or two below the top plates. The good home builders alternate whether the infill piece is at the top or bottom.

 

[medeek]

The problem with my first shear panel option shown is that the contractor would have to notch around the top chords of the truss, too much hassle and then you are still left with having to punch holes in the sheathing for the ventilation and its hard to control how big these holes may be so the shear panels are probably compromised.

The downside of Option #2 is that you have both shear panels and heel blocks to install, but I don't supposed you would need the shear panels every truss bay, just over the identified shear walls and maybe every other bay where no shear walls are present, I guess it really depends on how conservative you want to be.

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

http://www.medeek.com

 

[CBSE]

Manufactured truss blocking is about the easiest and least expensive thing you can specify for anything over a 10-12" heel. Specify it with a bevel at the top so you get good edge nailing. For shear walls, you can give the truss manufacturer the lateral load each block needs to be designed for (keep it simple). They will build the block to resist the load. You do however need to resolve over-turning forces on the block. Usually you can get away with toe-bailing the block to the trusses, sometimes you need A34's or A35's.

I will Post a detail later.

IF you aren't supplying blocking, how are you justifying your load transfer.

 

[jayrod12]

IF you aren't supplying blocking, how are you justifying your load transfer.

Hopes and prayers mostly