insulation question.

[rabbidrabbit]

OK,

Someone has to know about this...

Doing a remodel and have removed the previous roof structure and replaced it with sissor trusses 16 inches on center.  I have a total area of about 1000 sq ft and I'm trying to make sure I'm making the right insulation decision.  My plan is to push up unfaced r38 bats between the trusses then have the drywall crew lay up the drywall.  Is this the best plan?  Should I be using faced bats?  Is there any real advantage to foil as a radiant barrier?  Any other ideas or tips?

[eagl]

Isn't the backing also a vapor barrier?  My attic in texas was filled with 1.5 ft of blown insulation and it worked ok I guess...

[parker00]

You will need a vapor barrier of some kind. If it doesn't have paper then buy some plastic to put up but don't do both as you can trap the moisture in between the two.

[rabbidrabbit]

doesn't the primed and painted drywall act as a vapor barrier?

[A_Clown]

was in an attic of a home, but this attic wasn't the kind you could use for a room of any sort. Strictly crawl space, and room for HVAC and electrical stuff.

The insulation we used was Bats that were completely sealed in plastic. I really enjoyed working with this stuff because the plastic held the fiberglass in, which made the handling much more pleasant, and it also served as the only needed moisture barrier.

It sounds to me like you have the more traditional style attic, like from the book "Toys in the attic" I am pretty sure all you should need would be the paper backed insulation. Can you ask a competant sales person at your local supply house? Or perhaps consult a local "Building Code" book? I know building codes vary frm area to area.

[rabbidrabbit]

well..  made my way down to home depot and the bats cost about 4 times as much as the blown in stuff so now I'm leaning towards getting the rental machine and hiring some sap to spray while I feed after the drywall goes in.  

The roof is a sissor truss so no one is going up there after the insulation goes down.

[A_Clown]

Check the R ratings and make sure that blowing in material will give you the insulation you are wanting. I'm pretty sure the bats are more efficient-

[parker00]

Originally posted by rabbidrabbit
doesn't the primed and painted drywall act as a vapor barrier?

I'm pretty sure it doesn't but can't say for certain. If it was closed on both sides, like outside walls, you would need a vapor barrier but hell it sounds like you would be better off just spraying it in. Put in like 1 1/2 feet and make sure all your vents are open and clear when you're done. Home Depot or Lowes will usually let you use the machine for free if you buy like 10 or more bags of insulation, at least they do in Kansas City.

[MrRiplEy[H]]

Any wall which faces large differences in temperature is prone to condensation. That's why you need to install a vapor block to the outside walls.

Now depending on the insulation you use you either use plastic and bottle up the house (bad) or you use paper together with an organic insulator. Wood based insulations breathe and let the humidity pass without getting wet.

A breathing house is the best recipe for a healthy home.