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In process of utilizing 5/8″ fiberglass shell for a small building

timboyle | Posted in Energy Efficiency and Durability on

Is wrapping in EPS or XPS advisable; should foil surface (vapor barrier) face inward to building or outward to ambient? Is Ceramic Paint a viable alternative since Fiberglass Shell is a homogeneous structure. Electrical and plumbing to be installed on interior side of shell. if so referral to independent (i.e ASTM) applicable studies is appreciated…Thank you, Tim

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  1. GBA Editor
    Martin Holladay | | #1

    Tim,
    I'm having a hard time visualizing what you are talking about, but it sounds similar to a fiberglass boat. Is that what you are talking about? Something like a geodesic dome, built like a fiberglass boat?

    You don't mention your climate zone, but in almost every climate, it makes sense to install insulation. Green builders usually avoid the use of XPS, because XPS is manufactured with a blowing agent that has a high global warming potential. If your building will have flat walls or a flat ceiling, I suppose you could use EPS. If your fiberglass shell is curved, then spray foam insulation makes more sense.

    A fiberglass shell -- assuming that it looks like the type of fiberglass used for boat-building or bathtubs -- is a vapor barrier, so you don't need an additional vapor barrier. If there is a vapor barrier facing on your EPS, it can face any way you want.

    Products described as "ceramic paint" or "insulating paint" cannot substitute for insulation. Marketers of these products often make false claims; in general, these marketers are involved in fraud. For more information, see ‘Insulating’ Paint Merchants Dupe Gullible Homeowners.

  2. timboyle | | #2

    Martin...thank you for your timely response. A partial clarification...in the main, it is a fiberglass shell much like that of a structurally sound enclosed boat; however, it is a prototype (and thus I cannot expand much beyond this ---for the present---)and secondary elements of the conceptual design called for utilizing and re-purposing existing units finished on interior side only. Thus, elements of the main structure (has finished gel-coat exterior side only) will be insulated on the interior side; while other secondary units will be insulated on the exterior side and then skinned with fiberglass sheets, and/or gel coat. The resulting R Factor will be lower than desired since maintaining overall 2" plus wall thickness controls the outcome. Passive heating/cooling measures are under review as well; thus,the interest in viability of ceramic coatings. As in boat construction, breathing walls are essential...and we will do our best to provide egress for water that accesses the wall cavity. On one 65' yacht that I was involved with the Owner (way ahead of his time) demanded no toe kicks or wall base molding, opting rather for a minor base shoe, and a 3 '' high screened opening immediately above the shoe and a parallel 1/2" opening at the paneled wall/ ceiling joint line. All exposed vapor cavity wall material (i.e insulation) was sealed top & bottom; thus the cavity allowed the denser exterior wall sweat to run down the wall while the vapor cavity upward counter air flow aided in removing/drying the resident moisture. Years later, there was still no mold on that boat and the interior air maintained a fresh affect. So. we are thinking this may be the wall option on the prototype. Again Martin, thanks for your answers AND COMMENTS. We welcome your expertise as we continue with this exciting project.and ultimately introducing you the finished structure.... Tim

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