EPS for attic insulation
AsimM
| Posted in General Questions on
I guess it’s a “cut and cobble” question. How can EPS be used in attic insulation application for a new construction?
BTW I am in zone 6.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Asim,
EPS is not the best choice for attic insulation. Depending on the thickness of EPS you plan to use, you could either:
(a) design a high ceiling for your top floor, attach the EPS to the underside of your ceiling joists with cap nails, install furring strips (strapping) under the EPS with long screws, and then install your ceiling drywall; or
(b) Install a layer of OSB on top of your attic floor joists, followed by EPS on top of the OSB. This method may or may not require that the EPS be protected by a thermal barrier for fire safety; you'll have to check with your local building department on this matter.
Either method will require you to pay attention to air sealing and the continuity of your air barrier and your thermal layer at the perimeter of the attic.
I don't recommend cutting EPS into thin strips and inserting it between your joists.
In almost all cases, cellulose insulation will be cheaper, easier to install, and will perform better.
Labor needs to be considered just as much as the installed building products.
EPS is not labor-efficient to install in a regular stick-frame attic.
Even if the EPS you have free.
The only place where i would see EPS is as the top layer screwed on the framing after it has been filled with another loose or bat insulation ... Even then you'd probably have to cut/trim/fit alot of parts to fill up to the edges.
Still only worth it if you have the EPS for free or extremely low price.
Have a few pro quote you on loose insulation installtiong before pushing this one .
In NEW construction the best use of EPS in attics would be to put in on the exterior of the roof deck, making it a conditioned attic.
To do that without creating soggy roof sheathing from wintertime moisture accumulation in US Climate Zone 6 you need a minimum of half the total R value to be on the exterior (R25 in exterior foam, out of a total code-min R49) :
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_sec006.htm
At R4.2/inch you can get there with 6.5" of EPS, and R23 rock wool batts (or 5.5" of cut'n'cobbled EPS) between the rafters.
I am building a passive house. 2 inch of EPS screwed to bottom of truss chord. Seams taped for air tightness plus drywall screwed under that. All ceiling work done with no interior walls to interrupt air sealing. 20 inches of blown fiberglass on top of EPS. Interior walls are all non load bearing built after ceiling is complete. House walls are icf by the way. All air exchange and moisture transport happens through ventilation system or windows and doors when open. Not through wall and ceiling structures.