rafters without blocking

[sharbin]

So my contractor installed all the rafters without installing any blocking. When I told him about that he said that blocking will not allow enough ventilation to the roof even if he notched it (I told him about the notch as per the 1 1/2 plan).

Any advise?

Thanks

[Jochen]

I'm not 100% sure about what kind of blocking your are talking. The one at the bottom of the rafters? Yes that would be necessary and should be a pretty standard practise. I can't see any problems with that when properly notched.

Jochen

[PEG688]

 Around here (earthquake country) we have to block to meet code.

Back in RI way back in the 70's we never blocked between rafters.

IF you don't have to pass the IRC (International Residential Code)  and your soffits are going to be enclosed I personnel wouldn't have a problem with no anti -rotation blocks , also called Bird blocks ( open soffit's the blocks have holes bored thru them with soffit screen to keep critters / birds etc out) Vent blocking is another name , all the same block , just different nomenclature.


  So does that make sense? In other words "It depends".     


Bad picture of standard vented bird block ,

 

These blocks are short of the top of the rafter so they vent over the top of the block we used a continous soffit vent in a enclsoed soffit situation here.

 



Edited to add the second photo which I forgot to insert   

[sharbin]

yes Jochen, these are the rafter anti-rotation blocks that Peg688 described. I also read in most of the books (3 of them) that blocking is essential.

So would the OSB sheathing be playing the role of rafter anti-rotation?

[PEG688]

So would the OSB sheathing be playing the role of rafter anti-rotation?

Yes , the rafters and joist , I assume are side by side and both are toe nailed down to the top plate. You'll also MTL be adding a Simpson H 2.5 hurricane tie to the top plate and the rafters.

Then on top of the rafters your roof sheathing.

  All that being said today anti-rotation blocks are required by code.


BUT thousands of stick framed building have been framed without and still stand today.


NOW on a truss roof where you have one 1 1/2" truss separated , generally , 24"OC , the blocks play a bigger role.

This is common sense looking at this, in a rafter /  joist case you have 3" of wood in contact with the top plate and (assumed common practice of nailing) you have 4 EA. 16 d nails holding that wood in place. Above that, about 8"  above,  after the birds mouth is cut,  you have sheathing properly nailed down .

On top of that you have a birds mouth cut on your rafter that is a good fit , and providing more surface area and  a sort of locking in joint to rotation.

So with a  properly  stick framed roof following normal / good building practice you have more strenght right out of the gate.   


  BUT back to code , it does NOT necessarily  follow common sense , it provides for poor building practice , and Simpson connectors to provide ALL required strenght , sheer , and nailing.


 

   

[alcowboy]

I am a bit confused on this. The block is at the top plate of the wall, right? And shorter than the rafter to offer a gap? what about venting up the roof line to the roof ridge? How do you handle that?

[glenn kangiser]

If you are insulating between the rafters, there are channels - plastic? - that some use to keep the insulation down a bit and leave a vent channel.

[PEG688]

   #1: I am a bit confused on this.

   #2:The block is at the top plate of the wall, right?

   #3:  And shorter than the rafter to offer a gap?

   #4: what about venting up the roof line to the roof ridge?

   #5:  How do you handle that?

  #1: Two different situations in those photo's. The first one is set-up for open soffits. The second is for enclosed soffits.

  #2: Yes the first one is square to / or off the rafter. The second one is plumb with the wall below.

#3: Only in option #2 , the first photo the block is place square to the rafter and covers the whole area , the block is bored with three holes , thats where the air goes in and up the underside of the roof sheathing.

#4: That where the "channels " Glenn mentioned go , they can be plastic , card board , or other material.

     

Link : http://www.insulationsolutions.com/products/bafflo/information.html

#5: You need to provide a vent either at the ridge with a core-a-vent product , or use multiple roof jacks / roof vents to promote air flow from the soffit and out the ridge or roof vents.

[alcowboy]

Ok that makes sense. I guess what is confusing me is in the fact of "open rafters". I am looking at 20x30 1-1/2 story plans with on-site built trusses. I would like to plan on having "cathedral ceiling" if possible with exposed beams; however, if this would be a more expensive endeavor what would be the best course for me to take? I do want to insulate the house well because it would cut down on heating/cooling costs.

[sharbin]

I did the cathedral ceiling look on 20 feet and loft on 10 feet and used 2x10 rafters (not trusses) with 4x8 rough lumber beams every 4 feet on the open ceiling part tying the walls together (http://countryplans.com/smf/index.php?topic=4637.40). More cost, yes but not huge difference.

Ok that makes sense. I guess what is confusing me is in the fact of "open rafters". I am looking at 20x30 1-1/2 story plans with on-site built trusses. I would like to plan on having "cathedral ceiling" if possible with exposed beams; however, if this would be a more expensive endeavor what would be the best course for me to take? I do want to insulate the house well because it would cut down on heating/cooling costs.

[PEG688]

I am looking at 20x30 1-1/2 story plans with on-site built trusses. I would like to plan on having "cathedral ceiling" if possible with exposed beams; however, if this would be a more expensive endeavor what would be the best course for me to take?

There are many options , but basically you could use the baffles all the way up with the exact truss John has in that plan I'm NOT sure how much space he allowed for insulation , BUT the baffle COULD be used from the plate line to the ridge with a ridge vent and you get what ever insulation in the bay that space will allow.

Talk to a insulation contractor in your area , they carry or can get , higher density insulation than "the big box guys " have so your R value can be increased . The other beauty is that "generally" a insulator can sell , sometimes , you the insulation AND the labor for pennies more per square Ft. than your cost of the insulation only. He'll also provide the baffle that you may not be able to purchase as well.

Worth a few phone calls , you'll,  at least, get a education on insulation. 

G/L PEG