Foil-faced Insulation Board - Tape the seams?


J

Jay Pique

When installing foil-faced insulation board (styrofoam with shiny metal
face) are the seams supposed to be taped? I see a crew replacing
siding on a building and it doesn't look like they're taping them, and
just wondered what the "right" way to do it was.

Thanks.
JP
 
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M

marson

the only time i would tape the seams would be if i was putting it on
the warm side of a wall, using it for a vapor barrier.
 
D

DT

When installing foil-faced insulation board (styrofoam with shiny metal
face) are the seams supposed to be taped? I see a crew replacing
siding on a building and it doesn't look like they're taping them, and
just wondered what the "right" way to do it was.

Thanks.
JP
According to the Dow instructions for Tuff R, if the insulation board is
serving as the primary drainage plane behind the siding, tape the vertical
joints and z flash the horizontal joints. I've never seen anyone use z
flashing, I just tape them all with Tyvek tape, it is a lot easier to find
than Dow's building tape. If you are covering it with Tyvek or other building
wrap, that would serve as the drainage plane, no need to tape.
 
R

RicodJour

DT said:
According to the Dow instructions for Tuff R, if the insulation board is
serving as the primary drainage plane behind the siding, tape the vertical
joints and z flash the horizontal joints. I've never seen anyone use z
flashing, I just tape them all with Tyvek tape, it is a lot easier to find
than Dow's building tape. If you are covering it with Tyvek or other building
wrap, that would serve as the drainage plane, no need to tape.
Really no point in using a breathable membrane over something that
won't breathe at all.

R
 
J

Jay Pique

RicodJour said:
Really no point in using a breathable membrane over something that
won't breathe at all.
I've done a bit of reading and it looks like no Tyvek should be needed
because you're supposed to tape the seams. That said, there is a
school of thought that believes you should NOT tape the seams so that
any moisture from inside can escape. I'm not sure what I think.
Living in upstate NY makes me think I'd like to have a tightly
insulated home, so I'd button it up. Of course mold infestation isn't
something I'm really into either. Maybe I'd just prefer to have good
vapor barriers AND good insulation!

JP
 
D

DT

Really no point in using a breathable membrane over something that
won't breathe at all.

R

Correct, the only reason I mentioned it is because it was listed in an article I
read recently as one way to insure there was a complete drainage plane. I think
the information on using z flashings was from the Building Science Foundation.
Here is some information from the Dow site:


"More recently, concerns regarding bulk water intrusion into wall systems has
brought about the concept of a “weather resistive barrier”. The International
Residential Code (IRC) has developed a standard named Acceptance Criteria 71
(AC-71) for the evaluation of foam plastic sheathings as a weather resistive
barriers. Several of STYROFOAM* extruded polystyrene and polyisocyanurate
insulated sheathing recently passed certified, third-party evaluations to
qualify as "weather-resistive barriers" for residential construction. If the
foam sheathing is used as a weather-resistive barrier, the seams should be
taped."
 
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J

Jay Pique

DT said:
"More recently, concerns regarding bulk water intrusion into wall systems has
brought about the concept of a "weather resistive barrier". The International
Residential Code (IRC) has developed a standard named Acceptance Criteria 71
(AC-71) for the evaluation of foam plastic sheathings as a weather resistive
barriers. Several of STYROFOAM* extruded polystyrene and polyisocyanurate
insulated sheathing recently passed certified, third-party evaluations to
qualify as "weather-resistive barriers" for residential construction. If the
foam sheathing is used as a weather-resistive barrier, the seams should be
taped."
So the seams *should* be taped? This reminds me of when I was taught
to install Tyvek. "Grab your hammer stapler and a razor knife." Then
I later read that those seams should be properly lapped, taped and
secured with cap-nails. How about kraft-faced insulation? I was
stapling the flaps to the outside edge of the studs and overlapping
them and the more senior guy tells me to tuck them inside and staple
them to the face. (And we weren't gluing on the rock either.)

Are the directions for installation to be followed?

JP
 
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i'm gonna pass the bottom 1/8th x 1-15/16" of my 2 " iso board through the table saw so i have a tiny flap of foil to lap the next sheet for mechanical flashing when the tape fails:)
 
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I am nearing the insulation phase of my studio build. All the insulation has been purchased and is on site. The original plan was to fill the 2x6 cavities with faced R-19 fiberglass insulation and then fill the inner leaf 2x4 wall cavities with sound installation safe n sound mineral wool, which is unfaced.

My question is if I do this, then the vapor barrier faced side of R-19 ends up in the middle of the whole wall assembly, which I have read is not good. Typically, I learned that vapor barriers or retarders should be placed inside the cavity up against the surface that is warmest in winter. For me that would be up against the inner leaf OSB/Drywall sheathing. Also, I read that OSB also acts as a vapor retarder when used as interior sheathing. So if I go as planned, would I have two vapor retarders inside the wall? The faced R-19 in the middle and the OSB on the inner leaf?

My current thought is to switch the order and put the safe n sound mineral wool in the 2x6 bay cavity and then add the R-19 faced insulation so the vapor barrier in its proper place up against the inner leaf OSB sheathing.

I look forward to hearing your opinions.

Thank you and I hope all is well during this pandemic.
 
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Rigid polyurethane insulation board with two faces of metallised foil such as Celotex, is always taped.
In fact Celotex supply their own tape.
I sometimes use aluminum duct tape instead.
If one side of the board has a metallic film on one side as a moisture barrier, it makes sense to tape it.
Ask the manufacturer.
 

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