blocking on roof

dogneck · November 05, 2008, 11:23:11 AM

I'm building a 14x24 with a slope roof. Almost flat. The roof joists are 2x10 on 16' centers. I have it covered with 0bs sheathing and a metal roof on top.
The soffits are metal flat on the underside with a facia board on the outside.

Looking at the plans- it shows blocking and says (to hold the insulation). I didn't put any blocking in.

Question: Is this like floor blocking, is it necessary to prevent twisting. From what I see a lot of the truss roofs do not have any blocking. do I need to place blocking between the roof joists and if so, what spacing?

harry51 · November 05, 2008, 12:02:40 PM

Are the joists 14' long? If that's the case, a block about halfway might not be a bad idea. The osb nailed to the top edge of the joists will stabilize them to some degree, but not as much as blocking would. Did you put a moisture barrier of some kind between the osb and the metal roofing? I'm wondering if sweating on the underside of the metal could lead to problems over time?

November 05, 2008, 01:12:11 PM

Quote from: dogneck on November 05, 2008, 11:23:11 AM

Looking at the plans- it shows blocking and says (to hold the insulation). I didn't put any blocking in.

Is this blocking located at the wall line between the rafters? That's what I think it is. This would be to help keep the rafters from rotating out of place while the roof was being constructed. It also keeps birds, bats and the like from entering the attic space from the soffit area if the soffits are open. It also keeps the insulation from over flowing into the soffit where it is not needed or wanted.

dogneck · November 05, 2008, 03:49:30 PM

The soffits are completely enclosed. The roof is already one. If I put the blocking in (as the plan shows) -- yes it is right above the walls. The rafters didn't rotate out of place when the osb was nailed on.
Just don't know if they would rotate now. (completely nailed from osb into the rafter. ) No other support- no simpsons or anything, just nailed into the top plate of the 2x4 wall.

Metal roof- I have builders felt on the osb. then the metal. I will put in faced insulation and it will vent from the soffits to the soffits. 2x10 rafters and will use maybe a r19. the r30 or 35 is too thick and leaves no space for the venting. They make a pink R30C. (the c means catheral, and it is for 2x10 rafters and is about 8 1/2 inch thick.) But nobody around here has the R30C.
Thanks.

PEG688 · November 05, 2008, 08:27:43 PM

Dog,,, Mtn D is right the blocks MAIN job is anti -rotation , but not JUST during construction. The code sez you need them , BUT IF your not in a earthquake zone or a high wind area , IMO , you'll be fine without them IF your soffits are enclosed.

That row of blocks can, and are commonly called bird blocks , vented blocking , anti-rotational block , and maybe even more different names for the same exact row of blocking.

I'd forget about them UNLESS you are in the areas mentioned above , or IF you need to pass a IRC inspection.

November 05, 2008, 10:12:41 PM

dogneck what did you actually work out for the venting on your roof. It was up in the air ( no pun intended) the last time I had heard from you.

dogneck · November 06, 2008, 07:44:27 AM

I gave up. The lower wall has full length soffits. It will vent to the higher wall, I'll leave a channel between the insulation and the osb. The higher wall has a full length soffit- so it will shoot right out. Now, on the section that abutts the house (12 of the 24 ft length). It has no vent. I'm going to drill some holes in the rafters so that (hopefully) it will side vent to the other and go out the soffit. If I get any indication that this won't work, then I'm goin to put in two roof vents.

Redoverfarm · November 06, 2008, 05:41:33 PM

Not real sure about that venting option. Hot air rises which is the natural venting process. Will it go sideways

. I did this on a couple headers for the fireplace and have done it on some dormers at the house . These areas are relatively small and I firgure with the build-up of hot air it should vent the most of it just by the pressure the hot air exerts from the natural process. Can't never remember the technical term

.

Don't give up you have gone so far.

John

dogneck · November 07, 2008, 07:57:35 AM

If I find to have problems, then I might just cut a slot the whole length and build a box on top of it and vent it out that way. I didn't do the metal roof, the roofer said it would be oK. I didn't really believe him, but I wanted to get a roof on before winter. I probably should have just waited till spring. Now I'm at the wiring and I will get someone to do that. I have no idea on what price range it should cost. Here is what they would have to do. Run 30' conduit on outside of house(they will use the main breaker box- said it had space). the whole basement is drywalled so they will run it back outside the house. Install breaker box in the 14x24 addition. Wire for the following: three overhead lights, two overhead fans. On wall switch. Five outlets. One exterior outlet. One exterior light on switch. Install a PTAC (motel type) heat pump i'm buying it and it is not in the price). I'm waiting on a price, but don't know if this is like a one day electric wiring job or two. The smaller breaker box and the boxes, wire and switches ( $500?? at most) Labor- $500
should this be near $1000? or $600 or $2000- hopefully not more.

I just have no idea.