[jlhaslip]

the 2x sub fascia is dependent on nails but inserting the block reduces the dependency.
I can see this being a far superior method and remind everyone that 'code' is a minimum standard.
this would certainly exceed code.

Another method we use around here, which is a code enhancement, is to nail lengths of 3/8" OSB to the bottom of the top web of Wood I joists used as rafters in order to maintain the air space all the way up the cathedral ceilings when using them as rafters. No question that the insulation doesn't block the airway. Leave a space of a couple inches between sheets and use 4 foot lengths allows lots of places for the insulation to vent into the cold airway.
Never had a callback for condensation where this method is used.
It also spaces the I-joists and helps keep them straight.

 

[Morning Wood]

I block whenever possible. I haven't worked with trusses in ages. I run my blocking different than framerman though. I rip the roof pitch on the top of the blocking leaving a 1 1/2" vent space and install the blocking flush with the outside of the top plate. The blocking is installed on edge plumb. I then run the wall sheathing up onto the blocking (yes it is notched around the rafters) and nail it off to the blocking. works just like hurricane ties only better. Lately I've been thinking about cutting all my rafter tails off flush with the outside of the plate then blocking and sheathing. there are serious air sealing issues with rafter tails when building unvented roofs.

 

[Burns-Built]

We have never used blocking, nor have i seen any builder use it here in Pa. But based on the dialogue of everyone else i can see how it would be code ++.

The 2x fascia will keep everything from rolling combined with the nailed off sheathing. But that block would certainly make the system stronger IMO.

Never done it that way but I just might consider it now that it's been brought to the table.

Great thread! :thumbsup:

 

[Winchester]

Ive never blocked ether but i agree with the 2x rough fascia.. it keeps everything from rolling not that its going anywhere anyways IMO its toenailed and nailed to the cealing joists

Block at the bearing points where the bearing actually takes place would be more effective, but it's probably already overkill anyway.:laughing:

I like the idea and will do it this summer when I'm building a new home :thumbup:

I already confessed in another thread, I have an expensive addiction to overbuilding...

 

[Tinstaafl]

tin, that is a gross exaggeration of what the blocking does. We are not talking about just one sheet. If I laid 20 2x4's, nailed (not tacked) the osb, and then took the leap, you would see little to no reaction.

Yup, it is. :thumbsup:

But the principle is there. Keep in mind that blocking is neither required nor recommended for itty-bitty rafters; only the honkin' big ones. Granted, you'd have to have a pretty big lard-butt to knock over 20 2x12's that way, but it would certainly be more likely, no?

I'm not a crusader for the practice--I agree with others that most probably, in most situations, a properly nailed 2x fascia would be quite sufficient. The exaggeration was just to illustrate the principle. :thumbsup:

 

[Kgmz]

Now imagine you are in 100 mile plus wind design zone, and it is pushing on the gable end of the roof.

If you ever really read a engineers calcs for this, it is a little ridiculous. They actually have to calc if a 100 mile plus wind can turn a house over, pull or push the roof off, etc.

OK, here are a couple of links for you about this lateral load.

http://www.nibs.org/client/assets/files/bssc/Chapter6final.pdf

http://www.cbs.state.or.us/bcd/committees/10ossc/20090610_ho/Submitted_by_Rice_061009.pdf

 

[Kgmz]

Forgot to add:

 

[Timuhler]

Forgot to add:

We used to use those vents, but we've been framing closed soffits for awhile. They were about $1/piece

 

[Gene Laratonda]

I know this is a year later, but I just found it on a Google search.

Funny how the same names popup for some really detailed answers. Thanks for the images Tim.

I was just doing some bedtime reading through the 2009 International Residential Code and came across this.

R602.3 Design and construction. Exterior walls of wood-frame construction shall be designed and constructed in accordance with the provisions of this chapter and Figures R602.3(1) and R602.3.(2) or in accordance with AF&PA's NDS.

Figure R602.3(1)...

1. Blocking between joists or rafters to top plate, toe nail 3-8d (2 1/ 2" x 0.113")
2. Ceiling joists to plate, toe nail 3-8d (2 1/ 2" x 0.113")
3. Ceilingjoists not attached to parallel rafter, laps over partitions,
   3-10d
4. Collar tie rafter, face nail or 1 1/ 4" X 20 gage ridge strap 3-10d (3" x 0.128")
5. Rafter to plate, toe nail 2-16d (3 1/ 2" x 0.135")
6. Roof rafters to ridge, valley or hip rafters:
   toe nail 4-16d (3 1/ 2" x 0.135")
   face nail 3-16d (3 1/ 2" x 0.135")

Hope this helps someone else.

 

[JustaFramer]

H1 & H2 & the A35 are all very common stick or truss.

Now don't forget the Simpson LS series of hardware. Had to put LS70's on vented birdblocks on a trussed roof every bay or other. We also had to nail the bird block from the sheathing. Which was becoming the norm. However that was the year they changed the venting requirements so the 3 hole vent block became a 4 hole vent block. Ended up having to use non tico rated nails :shifty: The blocks couldn't handle the nailing other wise.

Then that same year on a stick frame had to put LS90's on every rafter that connected with a ridge, hip or valley.

 

[woodworkbykirk]

when i was starting out we did it on one job. the elder said it was required to keep the rafters from twisting, i thought the sheathing would resist that he said no. it was the first and last time ive done it though, we block off the end with either a batt of insulation or cardboard but we still leave the airspace for flow though

 

[jumbocactar]

never seen one without, i had one boss who required that the blocks were toenailed to the plate, maybe overkill.

 

[jamesdc]

I've never seen a house without bird blocks. Then again I live in so cal, so everyone has open soffits and exposed blocks. I've always just ripped the top edge to the roof pitch and face nailed through each opposing rafter with a couple of 12's then stick an a35 in the center.

 

[PaulPrice]

we must have some lax codes here, i've never seen blocking .... although we do get pretty crazy with hardware when you get close to the water

 

[txgencon]

I've never seen blocking here with boxed (closed) cornices. I have seen it on open rafters but they call it "bird blocking". I've recently gotten a couple of bids for trusses for a project. In the list of "accessories" one of the suppliers listed Simpson HM9's. The Simpson catalog lists them for Seismic applications. A note alongside their recommendation states "facilitates locating and fastening".

 

[Dirtywhiteboy]

then stick an a35 in the center.

You a35 the bird block down??