Re: OSB thickness under metal roof

[peg_688]

7/16 th's is used a lot for metal , that being said 5/8" would be better. IMO.

  If sheet goods have to be used.

  #1: Would be 5/8" CDX.

  #2: 1/2" CDX.

  #3: 5/8" OSB.

  #4: 1/2"OSB.

But for metal why not skip sheet it? 1x4 or 6 common fir , spaced 2 1/2" (8 penny nail the long way) . Or even purlin style,  2' OC.  The roof would breath / vent better.

 BTW ,   your on your own,  if your waitin for me      

[glenn-k]

I agree with PEG -- I like it purlin style.

Did it on my garage.

[jraabe]

5/8" CDX will be an excellent roof deck. With 30# felt down you should be ready for anything short of Katrina.

[glenn-k]

Sounds like good reasons - any of the above will work -- Hope all goes well.

[Bouncer]

I used 7/16 under my metal roof and it was was fine.
Kevin

[Jared]

I agree with PEG -- I like it purlin style.

Did it on my garage.

And that'd be enough to keep the weather out? Are there any drawbacks to doing it that way?
Jared

[glenn-k]

As mentioned above - not the sound deadening effect.  You would not have as much diaphragm bracing but the screwed in sheeting should still be plenty.  Most sheeting will support 4' purlin spacing - if you go on 2' centers you have doubled that.

Also mentioned -air flow would be better with purlins .

Cost should be much less.

There are some trade offs.

The sheeting if installed properly should keep the weather out either way.  There is still as much room for insulation between joists also.

[Micky]

Our local lumber yard had 15/32 osb versus 7/16.  They recommended this for the roof sheathing.  I think they did some stuff the make that extra 1/32" matter.  The lumber yard said the 7/16 is not rated for 24" rafter spacing.  Maybe they just wanted to sell more $, but it appears to work well.  I used 7/16" for the walls.

I used a roofing product called Titanium UDL instead of the felt.  I was very happy with this because it was more tear resistant.  http://interwrap.com/Titanium-UDL/titanium-index.html  I would suggest this if you are planning on having it uncovered for a while.  

[peg_688]

7/16" OSB or 1/2"CDX  "H " clips are used between the truss spacing . So folks dbl up on the "H" clips on OBS.

 Ya want thicker OSB just leave it out in the rain, 7/16 " will be 1/2 " over night , in two days it'll be 5/8" a week ya got 3/4" a month full 1"   Of course in two months ya gota basic straw / powder mix of worth less crap/  OSB , not much different than when ya started.

"H" clip :

[jraabe]

H clips support the edges of the non-T&G panels between supports. You may not need them with 5/8" material.

[Rover]

I agree with John; used as clips between non T&G panels.

[Amanda_931]

Plywood as well as OSB needs space between panels.  

Pretty sure they used plywood on my roof in Nashville--not everybody understood the concept of allowing for expansion in wet weather.  Not me, I didn't get up on the roof during that project.  I'm afraid it was the friend who was later shot dead by a couple of off-duty sheriff's deputies.

[peg_688]

The "H "clips provide more support / make the two edges work together between the rafters/ truss's . They also do space the sheet goods , be they plwood or OSB slighty. [highlight]The main purpose is additional support. [/highlight] Less flexing / seperating / working of the sheet goods at the seams.

With the 5/8" plywood and a metal roof I would still use the H clips [highlight]unless [/highlight]your rafter / truss spacing is 16 " OC.   You did not state what the spacing is / was I don't think . If it is 24" OC use one H clip between each truss centered in the space , by eye , no need to measure / stress on exact center.

 G/L PEG