Greetings,

QUOTE> Yes you do want insulation against the roof deck, the roof deck will not rot out, drywall is not required in any of the conditioned space.

Apparently you are not a builder. You tell all he people who had insulation in contact with the sheathing that their replacement costs were just in their minds. Also if there is a small air space between the insulation and deck you run the risk of air flow contacting the insulation. The only way you could use insulation against the deck is if you could eliminate condensation. and, you can't do that. You can even have condensation problems with foam. I have a sips house and the moisture passed thru the rafters and condensates on the inner side of the sheathing, Cause the osb panel to warp up. My situation was corrected when I installed a RB on the inside using furring strips and wood pads to obtain the necessary air spaces. The RB acted as a VB even though it was perforated.

When working with a customer, even on a standard house, I give very specific instruction on air control in the attic including specifying ridge vent manufacturer and Bird block air gap size.

MOST builders don't have the slightest idea on how to properly vent an attic.

The reason for the drywall is to act as a:
1 air barrier. You are going to have air pressure differences and there should be some type of semi rigid or rigid barrier.
2 fire barrier. ( I should have said fire rated drywall not MR).

Now you could use HD RB from Superior Insulation Co, San Demis, Ca, but you would have to tape the seams. Class A fire rating.

rbisys1; yes I am a builder and am licensed in your state (LA. LIC. # CL.0033845 (commercial GC)) It is perfectly acceptable to insulate against the the roof deck in hot - humid climates, it is not a good idea in the northern cold climates.Your air and fire barrier is on your ceiling lid, you don't need a second one in the attic, it is simply dead air space If you are a buider too I am wondering why you are looking for advice on a forum? If you have a SIPs house why do you have rafters?

Greetings,

Not looking. I'm a RB insulator/ dist. of 35 yrs, semi retired.

Considering how much condensation I've seen summer time I hope you'll excuse my concern. If I was in your area I still wouldn't want insulation contacting the sheathing as I'm a firm believer in RV/ soffit venting.

Sips still have internal framing, at least the one have does, 2x6s. What else would you call them? They're functioning as a rafter.

The only reason we bought this house was because we needed a house immediately and it was the only one that didn't have FG. I wouldn't have another one.

Posted By rbisys1 on 22 Sep 2011 12:14 AM
Greetings,

Not looking. I'm a RB insulator/ dist. of 35 yrs, semi retired.

Considering how much condensation I've seen summer time I hope you'll excuse my concern. If I was in your area I still wouldn't want insulation contacting the sheathing as I'm a firm believer in RV/ soffit venting.

Sips still have internal framing, at least the one have does, 2x6s. What else would you call them? They're functioning as a rafter.

The only reason we bought this house was because we needed a house immediately and it was the only one that didn't have FG. I wouldn't have another one.

They are a spline not a rafter, and it is an older style if it is a 2x6 not commonly used anymore, a solid 2x6 spline is a source of thermal transfer. The sips we use have no splines at all, are solid foam to foam contact and have no thermal transfer at joint