will mold grow on PolyIso?

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Author Message Jerome J. Lazar, CCS, CDT, CSI, SCIP Senior Member Username: lazarcitec Post Number: 2058 Registered: 05-2003 Posted on Wednesday, September 11, 2019 - 11:04 am:    One of my clients has indicated aluminum faced Polyiso for insulating a concrete block exterior wall. My experience in South Florida: moisture moves from the hot exterior to the cold interior, condensation occurs on the foil facing because the moisture can not move through it. Once this happens, the moisture is trapped in the wall, the moisture degrades the insulation and causes mold to grow. Could polyiso be degraded by the moisture allowing mold to grow? Phil Kabza Senior Member Username: phil_kabza Post Number: 636 Registered: 12-2002 Posted on Wednesday, September 11, 2019 - 02:42 pm:    Polyiso by itself does not offer any organic material that would provide food for mold growth (although a suppose some facers and adhesives might). That said, I've had the long term understanding (ie., hearsay) that polyurethane insulation is subject to performance loss in a moist environment like a wall cavity. We've never used it in cavity applications. Extruded polystyrene (XPS) has long been the staple product for cavity insulation. Now rigid mineral wool board is also being used in cavities as its thermal performance isn't affected by moisture; as it is non-combustible, it offers advantages in certain designs. Jerome J. Lazar, CCS, CDT, CSI, SCIP Senior Member Username: lazarcitec Post Number: 2059 Registered: 05-2003 Posted on Wednesday, September 11, 2019 - 02:48 pm:    No cavities Phil, insulation will be installed between furring over CBS, I too prefer extruded polystyrene, I am not fond of foil faced since the foil becomes a vapor barrier. Marc Chavez Senior Member Username: mchavez Post Number: 524 Registered: 07-2002 Posted on Wednesday, September 11, 2019 - 03:08 pm:    remember it is not just the material. a totally inert material (insulation) covered in dust (dirt, various organic particles etc) is an issue. When it gets wet the dust=food so ... food + water + spore = mold. Although I LOVE mineral wool I'd go with extruded or polyiso and try to keep it clean (within reason) prior to placement. that I believe will be just about the best you can do. my 2 cents Greta Eckhardt Senior Member Username: gretaeckhardt Post Number: 110 Registered: 08-2013 Posted on Wednesday, September 11, 2019 - 03:31 pm:    Question: Is the foil-faced polyiso insulation going to be applied to the interior face of the CMU, or to the exterior face with some sort of cladding installed over it? There are many variables that would control where the dewpoint would occur and whether or not the insulation could dry out if it did experience condensation. The best thing would be for the insulation to be outside the CMU, with a vapor-permeable air barrier applied to the exterior surface of the CMU and the insulation installed with foil-facing to the exterior so it can limit the amount of moisture that enters the insulation from the ambient hot, humid air. In this case of course, cladding would be needed as the first line of defense against rain. Ronald L. Geren, FCSI Lifetime Member, AIA, CCS, CCCA, CSC, SCIP Senior Member Username: specman Post Number: 1565 Registered: 03-2003 Posted on Wednesday, September 11, 2019 - 04:35 pm:    Greta nailed it. Ron Geren, FCSI Lifetime Member, AIA, CCS, CCCA, CSC, SCIP Phil Kabza Senior Member Username: phil_kabza Post Number: 637 Registered: 12-2002 Posted on Wednesday, September 11, 2019 - 05:31 pm:    Welcome to Florida. Jerome, the installation you describe occurs all the time in Central Florida, usually with furring strips overlaid and shot or Tapconed through the polyiso and into the CMUs. The question is whether the exterior moist air is lowered to dew point at the location of the foil facer. Ask your insulation manufacturer rep to run the numbers for your location; I don't think it will occur very often under your southern Florida temperature circumstances. BTW your residents will likely have lousy cell phone performance living inside a foil-lined box. anon (Unregistered Guest) Unregistered guest Posted on Wednesday, September 11, 2019 - 05:31 pm:    Jerome, you are correct- in South Florida hot humid air moves from the exterior toward the interior, via air transport (holes) and diffusion, and if the interior is air conditioned, cold surfaces are subject to condensation when in contact with moisture from the exterior. The easiest and most effective way to prevent this is applying a vapor-IMPERMABLE air barrier coating to the exterior CMU surface. If the CMU is meant to be exposed to the exterior in the completed work, a vapor-impermeable paint is what you want. If covered with insulation and/or cladding, then you have any number of vapor-impermeable air barrier products to choose from - I recommend a fluid-applied product. Once you have a vapor-impermeable air barrier on the exterior surface of the CMU (make sure this is tied in with your air barrier at the roof and at the base of the building), no moisture-laden air can get to the cold surfaces on the interior -minimizing/preventing condensation potential. If the outside face of the CMU itself is cold, not a problem either, because the hot, humid exterior air will condense on the exterior coating/air barrier material on the CMU and harmlessly roll down and away from the exterior enclosure of the building. You do not want a vapor permeable membrane on the outside face of the CMU, not in South Florida. That will allow vapor drive through the wall assembly via diffusion, and will then condense on any cold surface inside the wall assembly, and that is what will cause mold growth - on any surface (as Marc correctly points out). Greta Eckhardt Senior Member Username: gretaeckhardt Post Number: 111 Registered: 08-2013 Posted on Thursday, September 12, 2019 - 08:08 am:    Anon - I agree with everything you wrote, but would like to explain one thing. I mentioned a vapor-permeable, air barrier membrane on the exterior face of the CMU for the condition where the insulation is then installed on the exterior over that membrane and has a sealed, vapor-impermeable foil-facing on the exterior side. Personally, I think that locating the insulation outside the CMU is best, since any condensation that might occur could be drained or dried to the exterior. But that would require a cladding to protect the insulation, which maybe is not what the Owner had in mind. Your explanation assumes that the insulation is installed on the interior face of the CMU. In that case, I do agree that an air and vapor barrier would be needed on the exterior face of the CMU. Foil facing should be avoided on the insulation. Either way, an air barrier on the exterior face of the CMU should go a long way in preventing moisture-laden air from infiltrating to cold surfaces, since the CMU is not an air barrier itself.