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Should we use fiberglass blue board?

drpepper | Posted in Green Products and Materials on

We are building a really tight home… It will be net zero and LEED Platinum. Our architect and builder have different views on whether to use the fiberglass blueboard or not (one says it retards mold, but the other says that it’s a non-issue and will cost us an extra $10K unnecessarily). Would love to get your opinion and reasoning. Thank you!


  1. GBA Editor
    Martin Holladay | | #1

    Please clarify your question. "Blueboard" has many meanings. To some, it means blue polystyrene foam, also known as Dow Styrofoam (XPS). To others, it means moisture-resistant drywall. To others, it means rock lath for use under plaster.

    I suspect you are talking about a drywall substitute with a fiberglass facing instead of a paper facing -- but it's best to ask.

  2. Riversong | | #2

    If you're referring to GP DensGuard fiberglass-faced backer board, that's designed for tile installations in wet environments such as showers.

    If your "tight" house is going to be so humid as to require mold-resistant wallboard throughout, then fire your designer and builder or be prepared to wear a wetsuit and SCUBA tank in the house..

  3. Expert Member
    ARMANDO COBO | | #3

    What’s your location or climate zone? Are you using Dow's SIS panel (Structural), XPS Styrofoam or what? What’s the perm rating of that particular board? What cavity insulation are you using? Do you want the wall to dry to the outside or the inside? Do you plan to control your interior humidity or not? What type of moisture management details is your Architect providing you with? etc, etc. In other words, there is so much more to that question before it can be answered.
    In any case, you most do a Dew-Point analysis for your wall assembly, indoor relative humidity, indoor and out door temperatures. Your Architect or an ME should be able to answer all those questions. Any good product use in a wrong manner, wrong application or bad installation will create problems for you. You are doing right getting those answers upfront.

  4. drpepper | | #4

    It's the glass matt fiberglass faced interior wall board. Our architect recommends using it but understand that it is not in-expensive. If you need to limit the use of it he would next only use it in bathroom and the basement or at the very least in the bathrooms. It has a surface that mold can’t grow on. Thanks again for your responses.

  5. Riversong | | #5


    Which one - there are several. The new USG Humitek panels, for instance, are not mold-proof (nothing is), but merely mold-resistant.

    This is from their data sheet:

    "In independent lab tests per ASTM D3273-00 “Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an environmental Chamber,” the average panel score was 8. This means the risk of mold and mildew growth on the panel is minimized."

    "This ASTM lab test may not accurately represent the mold and mildew performance of building materials in actual end use. Given unsuitable project conditions during storage, installation and after completion, any building material can be overwhelmed by mold and mildew. To manage the growth of mold and mildew, the best and most cost-effective strategy is to eliminate water exposure to building products during storage, installation and after completion of the building. This can be accomplished by using good design and construction practices."

  6. GBA Editor
    Martin Holladay | | #6

    It makes sense for basements and bathrooms. Elsewhere, your drywall should certainly not be damp enough to grow mold. If your house is that damp, something is seriously wrong -- and I don't mean your choice of drywall.

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