Hi, I'm a new member here with a few questions on PolyISO.

My Climate is Zone 4– Albuquerque, NM – mixed dry climate.

I was given about 1, 200 sqft of ½ thick polyisocyanurate foiled on both sides made by Celotex.

The polyisocyanurate is cut in some odd sizes, but large enough still large enough to be cut into a 2x4 16 center wall cavity. I would like to install the polyiso in between the 2x4 cavities. The home was built in the 40's or early 50's. Some walls in this home never had insulation.

I already have removed all the sheet rock and plaster on the walls and ceiling of my home to redo the electrical. ( I have lots of time to do the electrical on my own home now) .The entire home is down to the studs and the electrical work is done except the final.

So here is the run down on the exterior walls

Stucco, Lath, 15# Felt then ¾ Fiber board. 2X4 ( Actual size 1 7/8 x 3 7/8 ) .

I'm not sure really if the PolyISO should be attached to the fiberboard with glue or do I make furring strips on the studs. I know I only have so much room in this cavity maybe a little more because of the stud size. 1 7/8 x 3 7/8 . What is the best way to do this. I think I have enough polyiso to double it up to 1”

I was also thinking of filling the space extra space up with fiberglass insulation with kraft backing. Would that kraft backing be needed ? It does get cold here in the winter, but not that humid. The humidity here in the winter is about 22 % or less. But I will be running a humidifier off the furnace at about 35 % humidity in the winter. I tried to order rock wool, even slag, for the walls, but every factory told me 8 weeks out. I even said I pick the stuff up even in another state. It did not matter. So thats why I though I took polysio instead of it being thrown in the landfill.

Can polyISO bee used in framed  basements also  ,  or would blue or pick stuff be better?

Any help appreciated.

Thanks

for basements use XPS (pink or blue) boards and completely seal everything. I used great stuff cans to do that. Check buildingscience.com website they have a great PDF on this basement subject. don't use fiberglass or the like in basements. if you put foam boards in walls upstairs consider the perm rating of your wall assembly. the foil make create a vapor barrier and potentially trap moisture.....

Stucco is a reservoir for moisture- if there isn't a vented cavity between the stucco and fiberboard you may be putting the fiberboard at risk by using foil-faced goods in the wall cavities.  When the morning sun hits dew rain wetted stucco the moisture drives are pretty severe.  If there are big overhangs and no splash-back onto the stucco it might be OK, or not- it really depends, but I'm very wary of putting wood or fiberboard between a true vapor barrier and a reservoir cladding unless that moisture can be purged through a vented cavity to the exterior.  If the stucco is back vented with air between the lath & fiberboard (with at least some openings to the exterior at both top and bottom) you can cozy the iso right up against the fiberboard and it'll be fine.

Without an existing vent gap behind the stucco you might need to make one by leaving 1/4-3/8" between the fiberboard and iso, with a couple of 1/4" vent holes drilled top & bottom to the exterior in each stud bay to guarantee drying toward the exterior via convection. Ripping thin ply wood or OSB would work, or you could glue in strips of 1/4" or  3/8" XPS fan-fold  to maintain the vent space. Air seal the edges of the foam to the stud and plates with 1-part expanding foam too. If you cut the iso with a sloppy fit it's easier to get it in there, and a shot of can-foam in the edge-gap creates a very good seal- better than caulking edges of tighter fitting iso.

Yours are full-dimension 2x4 framing, and batts designed for 3.5" x 1.5" nominal studs are a half inch too wide to really fit well. Blown insulation would work better, but it's more work, and anything is WAY better than nothing.  If you have a 3/8" vent space and half inch iso you have 3" of space to accommodate a batt designed to be compressed to 3.5", so it will work better to use a low-density R11 batt than an R13 or R15 if you go that route.  The difference in whole-wall R between an compressed R11 and a compressed R13 is negligible, and the density & air retardency of an R11 compressed to 3" would be comparable to an R13 at it's intended thickness.  At the higher density when compressed to 3" the R11 batt is still performing at nearly R10, and with R3 of iso on the exterior it'll be pretty decent.

In a dry climate with a foundation well above the water table, and a foot of above grade foundation wall you can use foil-faced iso on the basement walls as long as the iso is between any framing and the concrete.  In wetter climes with higher ground moisture a foil facer might put the foundation sill at risk if there isn't sufficient drying capacity to keep the moisture content of the concrete/sill interface low, but that's not much of an issue in Albuquerque. In wetter places (or if you're near the water table) XPS would be a safer choice, unless you have a pretty good capillary break between the concrete & foundation sill, or 18"+ of exposed foundation on the exterior.

The outdoor humidity level in winter is irrelevant- it's the outdoor TEMPERATURE and the INDOOR HUMIDITY that determines whether the sheathing will load up with moisture.  The dew point of 70F 35% RH air is about 40F, so any susceptible materials in the assembly that dwell at 40F or lower for weeks on end over the winter have the potential for moisture accumulation to rot levels if it can't dry quickly when warmer weather returns.  The mean temp for December-January in Albuquerque is about 36-37F, so it only takes a modest vapor retarder on the interior to protect the fiberboard from wintertime vapor drives even if you didn't have the foil facers, but it does mean you want the interior to be truly air-tight, since far more moisture can be transmitted into the walls through a square inch of air leakage than a whole wall of vapor diffusion through 3-5 perm paint.  

With R3 iso and R10 fiber the interior facer the interior facer only drops below the ~40F dew point of the interior air when it's below freezing outside, so the amount of condensation occurring inside the cavity will be limited & short-lived, but it would still occur with some regularity in winter.  If you doubled it up to 1"  R6 iso/R8 fiber you'd get very limited wintertime condensing hours in the cavity, since with a 70F/35%RH interior condensation on the interior facer would then only occur when it's below ~18F (which happens to be the 99% heating design temp for Albuquerque. )  This is an extremely safe level that would not require the gypsum to be air-tight, and is well worth considering.  (If you can't find R8 batts, splitting unfaced R19 batts works fine for 2.5" cavities.)

To use foam board in basements requires either a fire-rated facer (like Dow Tuff-R polyiso) or a recognized ignition barrier (half-inch gypsum works.) The flash point and melting point of polystyrene is much lower than polyiso, so I suspect it would take a fairly hefty facer to get it to pass the various fire tests with an EPS core. I'd be very surprised if any foil-faced EPS would come anywhere near meeting the required fire ratings.

The R-value of half-inch EPS is pretty low (~R2), but that can be nearly doubled if you used 1x furring through-screwed to the foundation to keep it in place, and give a mechanically secure mounting for the gypsum ignition barrier. But any place that gets down to +7F would do well to take the foundation up to R10 or higher, which you could do by adding an interior w/batts, but with only R2 on the exterior you'd be prone to wintertime condensation on the foil facer and moldy studs. (R5 exterior foam would probably get you there safely though, if this is a climate where +7F is the all-winter-low most years.) A 2x3 studwall w/R8 econobatts would probably be OK with only R2 foam from a condensation point of view. Fire-rated iso at 1.5" would hit ~R10 at less thickness than the half-inch EPS + furring + gypsum solution that delivers only ~R3.5.

If the house has sill gaskets between the concrete & foundation sills or 18" of exposed above grade exterior it'll be fine, but just because it doesn't have bulk-moisture issues doesn't mean it won't wick ground moisture. With bare concrete facing the basement quite a bit of moisture can pass through the foundation without even a hint of efflorescence, but when you put up a foil vapor barrier the moisture content of the concrete WILL rise (even in NM)- it's only a matter of how much it will rise.

OK,I'm back been working on this house.

I removed a section of the exterior wall ( stucco) only because I was installing a exterior electrical outlet. There is no back venting with the stucco as far as I can tell. It seems to be a total sandwich. Stucco, 3/4” , Portland- 1.5” under the stucco, lath, 15# felt, Then fiberboard. That is one very thick dense heavy stucco job they did ( 1947 )

I did some actual temperature wall tests with my hvac meter , I could not measure that much humidity, because there was not much in the wall cavities for this time of the year.

I did three different test configurations with insulation on closed 2x4 wall cavities on the hottest side of the home. I used my Alnor Hvac meter.

The average temperature of the outside stucco wall was about 130 deg, the outside temp was 96 degrees. The first test I done was with PolyISO on the fiber, with R13 Kraft sealed and closed to the 2x4 . Studs. I sealed the edges of the kraft paper with glue and foil tape and let it set over night. Test #2 Regular R13-nothing else and sealed as above. Test-3 Rock wool (Rocksul) I also took temps on the fiberboard inside sealed 2x4 wall cavities.

The room temperature was set to 78 degrees with the AC . Temps were taken at the hottest part of the day about 5pm in NM . Time 24 hours.

Test -1 The polyISO \ R-13 kraft. Temp measured in middle of R13bat.( poking a hole in the kraft. ) 89 degrees. Temp drop is 42 deg from exterior 130 degree.
Humidity in the wall cavity was 9 percent.

Temp- on fiberboard between and between the PolyISO 99 deg,

Test-2 , Normal R13 \ Kraft. Temperature measured in the middle of the2x4 wall cavity 113 degrees. Hum- 15 percent. Temperature drop was 17 degrees from 130 degrees.

Temp on the fiberboard 119 degrees.

Test-3 ,Rock-Wool, Roxsul. R15. I used 5/8 drywall , because that is what's going on the wall anyway. Roxsul was installed with no vapor retarder, The Drywall was sealed at the edges very tight with heavy foil tape. Temperature measured in the middle of the wall cavity,108 degrees. ( drilled hole at an angel through the dry wall) The temp drop was 22 degrees from 130 degress. measured from the center of the rock-wool humidity was 11 percent in the 2x4 cavity.

Temp on the fiberboard. 126 Degrees. This is strange, I'm not sure why there is a temperature increase on the interior fiberboard. It seems to have an oven effect with rock-wool.

I like the poly-ISO but the wall need to breath both ways in this climate. The Perm on the polyiso is 0.003 it's almost a barrier.

I did find R 15, but I don think there will much difference from R-13 from my test. I was thinking about using R-13, the add ½ XPS to the interior wall studs with ½ or 5/8 rock. I have not test this yet but that is my goal by the end of the week. The perm for ½ xps is 1.1 if the facer is removed it's 2.0 to 2.5 according to OC.

You guys are great here. I did so much research in the last 7 days my eyes hurt.

A perm rating on a foil facer of 0.003 isn't almost a barrier- it IS a barrier- lower permeance than 6 mil polyethylene sheeting.

But that doesn't much matter if you're putting a vented cavity between the iso and the stucco/lath/felt/fiberboard sandwich to allow the fiberboard to dry to the exterior. (A vented cavity is always "breathing" to the exterior side, big time, but the facer blocks summertime moisture from finding it's way into the air conditioned interior to condense. )

The relative humidity of the air in the fiber layer is irrelevant- it's the DEW POINT (absolute humidity) that counts. It's only a problem when the dew point of the cavity air is above the temp of the drywall (in summer) or the inner face of the iso (in winter.) With a foil facer on one side of the cavity and kraft facer on the other the absolute humidity won't change much over a weeks time, but it can and will shift over a month or two as the average vapor pressure changes seasonally. A kraft facer on the interior would still allow the assembly to "breathe" water vapor slowly to the interior in warmer weather, and since the foil facer of the iso isn't much affected by condensation in winter the assembly isn't compromised as long as it isn't condensing so much moisture in winter that it runs down to the bottom plate of the studwall and puddles. But with a kraft facer on the interior slowing moisture transfer from the interior there isn't much risk of that happening. In summer the higher average temps of the fiber layer will drive any moisture accumulated in winter through the kraft paper for most of the spring/summer/fall hours, and the foil facers of the iso block moisture from being driven into the fiber-side from the stucco.

Walls don't need to "breathe", but moisture susceptible materials need to be able dry. A foil facer isn't necessarily a disaster as long as it's place properly within the stackup for the climate.

With half-inch XPS on the inside of the stackup and only the #15 felt for an exterior vapor retarder you could end up taking on enough summertime moisture into the cavity to cause issues if you are cooling the place with air conditioning. The higher-risk areas would be anywhere the walls get direct sun, driving moisture out of the stucco. Even under the best of conditions you'd want that to be 2 layers of 15lb felt, and 2-perm+ XPS.

Putting the XPS between the drywall and gypsum gives a pretty good boost to the whole-wall R though, raising it from ~ R9-10 to R12-ish.

Dana1. , thanks for you replay and insight. The west side of house is where I tested and it's all direct sunlight. The interior is refrigerated to 4 tons.

RE: " With half-inch XPS on the inside of the stack up and only the #15 felt for an exterior vapor retarder you could end up taking on enough summertime moisture into the cavity to cause issues if you are cooling the place with air conditioning. The higher-risk areas would be anywhere the walls get direct sun, driving moisture out of the stucco. Even under the best of conditions you'd want that to be 2 layers of 15lb felt, and 2-perm+ XPS. "

When the Rains come at mid July until mid September, that is the highest humidity. always in the neighborhood above 50 to 90 percent in those months. 

I may have found a solution, but I'm not sure if it still would work. The top plate of the entire western wall of this home sits below the vented parapets ( the roof is low sloped) .. It's a very small air space that spans under the entire roof deck. There is about 12" air space between top plates and the roof deck. I was thinking of maybe drilling a 1/4" to 1/2" hole though the top plate into each cavity for a backup type of venting. or maybe make a path for venting though center of the studs directed to a central point in on the top plate. ( just like if your running wire though the studs) Ie. drill 1/2 hole horizontal though a number of wall cavities then drill 1/2 to 3/4" inch holes at few points in the top plate every so many feet. I know I can only use 1/3 of a stud for drilling a hole. Thats the building code where I'm at, it also cover this in the NEC.

  The above plan would be for the XPS on the interior side of the studs. (  I could pull the plastic off the xps to get a 2.0 perm according to OC.  I'm not sure how this would effect the dew point by drilling  horizontally into the stud in addition to the top plate. The rest of the house is framed in 2x8 and 2x10. It's this west wall that heats up the entire house in the summer, while in the winter the reverse, it's worse if it's windy.  The west wall is about 65 feet lenght in that section of the house.  There is Low E glass on all the new windows, in addition I'm having some awnings made. This is a tough battle .

Again forget about "percent humidity"- it's only half a number when stated without the associated temperature it's relative to. Only dew point relative to the building material temp matters.  A 90% humidity at 60F (dew point = 57F ) during the early morning hours of a July day that hits 90F outside isn't very humid compared to a reading of 60% humidity at 85F in the afternoon (dew point = 70F).  Dew points of 57F are pretty dry and comfortable independent of the outdoor temp, dew points of 70F are pretty damned sticky, whether it's 80F out or 100F.

It can rain at 90F from thunderheads even when the dew point of the air near the ground is 60F, with a very low relative humidity. While rain splash-back can affect the moisture content of stucco, the stucco takes on significant moisture from dew quite independently of rain.  When the exterior of the house drops below the dew point of the outdoor air, the stucco takes on moisture.  When the sun hits it, that moisture is released at high intensity bursts, some of which gets through the felt and into the fiberboard.  On a clear night the exterior walls can drop several degrees below the outdoor temperature and hit the dew point via radiational cooling.  (This can happen any day of the year in your location.)  You'll see it fairly readily on composite shingle roofs as visible dampeness at dawn, since the moisture isn't absorbed. The same thing is happening with tile roofs & stucco siding but it's not visible- these materials wick the moisture in rather than leaving it on the surface, storing it until driven off by heat (or more slowly by evaporation on the shaded sides.)  East and south faces are more susceptible to high vapor drives than north sides, but west sides are not immune.

Dew points tend to track the daily temperature averages, and the daily low temperatures tend to fall to near the dew point, which is why places with clear air and radiational cooling get huge daily swings in temp.  Pull down a years worth of temp & dew point for Albuquerque and you'll see that even though June is pretty warm compared to it's dew points the highest humidity months are July & August, which are the highest average temperature months, but the average dew point for September isn't dramatically higher than the June dry period, but the average daily low is lower:

http://weatherspark.com/#!dashboard...20nm%20USA

If you build a cavity with the iso and vent it to the roof deck venting that'll probably work, but you need to make the fiber-layer air-tight.

Awnings don't do anything for mitigating gains from west facing windows.  Low-E glass does, and low-E storm windows are a fraction of the cost of replacement windows, and often offer BETTER performance than low cost replacement windows. (A low E storm over any double-pane outperforms a clear-glass triple-pane and many argon-filled low-E double-pane window.)  But nothing beats an insulated exterior shutter or shade for rejecting those gains.  Awnings can work well on the south side though, where the solar angle is much higher.

Bringing the interior side XPS up to 2 perms won't change the dew point of the cavity air much, but it allows any moisture that gets in to leave reasonbly quickly.  The mid-winter average temps are ~40F, so you won't accumulate much winter moisture in the cavity.  Interior side vapor retarders are designed to protect the exterior sheathing from soaking up moisture when it's below the dew point of the interior air, but with foil faced iso in the cavity that simply won't happen.  With the iso in place the key thing is to back-ventilate the sheathing to the outdoors to relieve any moisture absorbed during the high intensity bursts of moisture drive that occurs when the sun hits the stucco.