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Posted by marson on August 8, 2006, 7:14 am
Janet wrote:
> Hi there, I'm building a 1400 sq ft two-story home in Southeast Alaska
> (cool, rainy climate) and need some advice. The house is framed with
> 2x6 (24 in. OC) walls sheathed with 1/2-in. CDX. I'll have R-21
> fiberglass batts in the wall cavities. I also plan on having
> rain-screen walls, i.e., horizontal wood siding (5/8" local hemlock)
> nailed on to 1/2" furring strips to create an air space behind the
> siding. In addition, I plan on adding 1-in. rigid foam insulation
> (unfaced extruded polystyrene, i.e., pink board) to the entire exterior
> for added insulation and a thermal break. This seems simple enough --
> there is even an article in the current issue of Fine Homebuilding
> (Aug/Sept 2006) on how to install rigid foam insulation -- however,
> there are a couple of important details left out in the article that I
> can't figure out. Mainly, how to integrate the foam panels with a
> rain-screen wall and also with window/door flashing. The article also
> doesn't explain how to integrate/install housewrap/felt when using
> unfaced rigid foam panels. I'm using 15# felt instead of Tyvek. Where
> does the felt go in the layering? Do I install the felt directly over
> the CDX as would be traditional, and then nail the foam over the felt?
> (then nail on the furring strips and finally the siding) If so, then
> the back of my airspace in the rain-screen is going to foam, not felt,
> which seems wrong. But if I put the felt over the foam panels, that
> doesn't seem right either.
>
> The FH article also skips over how to flash the windows and doors when
> using rigid foam panels. I have Certain-Teed vinyl windows. The article
> suggests furring out each rough opening (to match the thickness of the
> foam) to create a solid surface for nailing on the siding. They suggest
> you build a simple frame around each window/door opening and butt the
> foam panels against the frame to create a flush surface. However, they
> don't explain how to flash this configuration. I plan on using one of
> the flexible flashing products like Fortiflash/E-Z Seal around the
> windows and doors. These strips would traditionally be installed
> directly against the rough opening (i.e., against the CDX) but if I
> furr out the openings as suggested, then do I wrap the flashing around
> the openings and then OVER the furring strips, treating the whole unit
> as one? How do I integrate this drainage plane with my felt drainage
> plane?
>
> I guess my question comes down to -- if I want to integrate rigid foam
> panels with a rain-screen wall, how do I keep my drainage plane intact?
>
>
> Any advice on how I should assemble all of these layers would be much
> appreciated: CDX sheathing, 15# felt, 1-in. foam panels, =BD-in. furring
> strips for rainscreen, window/door flashing, windows, siding? Thanks in
> advance from a novice builder who is trying to do it right...
i would build out the windows and doors 1 1/2 inches. then wrap the
flashing over that. at the top of the window, tuck your flashing under
the building paper and bring it out over the fin. it gets complicated
if the window has a casing on the outside, since then you really ought
to have a sheet metal flashing under the building paper and over the
trim. this will have to be custom bent. in an ideal universe, i'd
want the building paper outside of the foam. but it would be hard to
attach it to the foam as a practical matter. so i guess i would put it
against the sheathing. but tape the seams with builders tape as added
insurance against water being driven into the system.
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