Overhead Insulation - Tape?

[K2]

I'm wondering if anyone knows what the name of the product is that I see in most insulation pictures where batts are put overhead?

It looks like a plastic sheet, but I'm pretty sure it's adhesive, maybe like white duct tape in large sheets?

Any thoughts?

[Dana]

You mean goods like the ProPink Complete Fabric or Certainteed Optima blowing mesh, or do you means something MemBrain vapor retarder?



http://garsideinsulation.com/images/new-pic-05.jpg

None of it is self-adhesive, but which is the right product depends a lot on your water-vapor control requirements (which will vary with climate.) Assuming the Delridge Valley you're in is the neighborhood in Seattle, you'll want an interior-side permeance of less than 1 perm, provided there is space above the insulation vented to the outdoor air. Far more important than mere vapor diffusion the assembly needs to be air-tight to avoid mold conditions in/above the insulation layer. A layer of housewrap (Tyvek, et al) can be made air-tight, but will be highly vapor-permeable. Vapor diffusion can be adjusted by the choice of paint, if this will be a finished ceiling. A square inch of air leak cross-section is worht a whole house ceiling's worth of vapor diffusion in terms of volume of water transported. Moisture can get IN to an assembly any number of ways, but dries primarily by vapor diffusion. (In attics & roofs in heating dominated climates it also dries via ventilation to the exterior, but that can be a two-edged sword, as the stack effect of a ventilated attic with air leaks to conditioned space pulls more humid interior air into the attic while sucking heat out of the place.) MemBrain is a vapor retarder, ProPink Complete fabric is air & vapor permeable as is the Optima blowing blanket, and need separate vapor retarders (like the plastic sheeting in the picture- sorry about the image size.)

Or, if you mean something else, find me a web-picture.

[K2]

Dana,
Thanks for the reply! It is in fact in Seattle, and it gets a bit trickier as this ceiling is the basement ceiling (i.e. underneath the subfloor). And my joist spacing is 6x6's on 36" centers. The basement, for the indefinite future, will not be heated, but my main floor is heated (hyrdronic radiant) and I need to get something in place before winter so I don't go broke.

Basically i'm looking for something to hold the batts in place between the 36" span, so maybe a staple up propink fabric could be the solution. The more I look at the pictures online it does look like the batt face stapled to the studs. Obviously this won't work in my scenario.

I'll see if I can find a good picture that illustrates what I was imagining...
Thanks,
Kurt