Structural Insulated Panels for Kiln Construction?

      The foam and skins used in some "SIP" panels may not tolerate the high temperatures in a wood drying kiln. May 13, 2009

The use of stress-skin panels (foam panels with 1/2" OSB applied to both sides) seems like an intelligent way of assembling a small (1500-3000 bf) dry kiln. Has anyone else used this method and does anyone have a Midwestern source for these panels? They are normally produced to order for homes and such.

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
A kiln is much hotter than a home, so I would be concerned about thermal degradation, especially in the insulation. A kiln is more humid, with acetic vapors at times, than a home, so I would be concerned about moisture degradation, especially with OSB. I am not sure if it would be easy to seal the interior and keep moisture out of the panel.

From the original questioner:
I just finished reviewing the FAQ sections on Nova and Northland's websites and it appears that Nova uses this exact method and then covers the inside with aluminum and the outside with galvanized steel. Northland's isn't quite as clear but it does sound like their chambers are the same material. I understand the concerns mentioned but I have to think, based on these two manufacturers, that the structures have proven themselves.

From contributor S:
Although it may seem logical that a small lumber kiln is generally going to be much hotter than a home, this may not be true for closed attic spaces. A closed attic space in hot climate like Texas or Arizona could get very hot and while ventilation of these spaces is a design element. I'd have to believe that the stress skin panels would be able to withstand ventilation blockage, power failures and the like. There should be plenty of "extra" designed into the stress skin panels to take the heat. There is a panel manufacturer in Tennessee that has a price list, look for general panel corp in Google.

A 4x9 R-38 panel with moisture resistant drywall is about $150 plus freight. You could pencil out the numbers for a stick built r-38 wall and see what you get. I have a feeling the pre-fab panel will be about the same or lower because of the high cost of insulation materials if you buy retail. Ask them what kind of heat their panels can take.

From contributor L:
We have a number of customers who have used stress skin panels. Some have stood up well and some have failed. Kilns that operate below 125F seem to be okay but the white EPS, that they often use, does shrink when it gets warm. We found that happening about 160F when we tested several panels a number of years ago. Also EPS (expanded polystyrene-white foam made by expanding beads) does hold a lot more water than closed cell foam. That degrades the insulation value. And that starts breaking down the OSB. Also these panels are usually glued together and the in the internal expansion and contraction in a kiln, usually breaks down the glue. These problems usually don't show up for a few years so you should get 3-5 years of good use. If you can find someone that foams the panels in place with urethane (yellow) foam and they use not less than 2.2 #/cubic foot density, you could have a better shot at lasting.

From the original questioner:
Thanks. Those are definitely good questions to ask. Since this a relatively small kiln, my plan is to build it within another building and further reduce the costs of heating it since that building is kept at 55-65 all winter.

From contributor S:
That sounds like a really good plan. If the stress skin panels aren't providing any real structural function, like holding up the roof, you should be able to use cheaper panels. I like the idea of having an aluminum skin on the inside, and maybe seal that real good with spray can foam to keep the moisture out of the panel insulation. If you can get away with a panel that has OSB on one side only, you can get a 4x9 r-38 for about $100.

From Gene Wengert, forum technical advisor:
Stressed skin panels would not be used in an attic, so they would not be subject to a lot of heat in a home. Why not just use a 2x6 frame wall with plywood? That would be cheaper and also would give more insulation and could be vapor-proofed. The insulation is the issue in this case, and not the wood, as contributor L confirmed. The insulation in such a panel is not designed for high heat. OSB does not stand up well to moisture and heat, except for a rare instance. In a kiln, the OSB would be repeatedly hot and moist. I am not sure if you can adequately seal the inside without exceptional effort. Why even use OSB, as this engineered material, design for stress, is not needed in this application?

From the original questioner:
Gene, the idea of using these very efficient panels was spurred on upon learning that this panelized construction is what Nova and Northland are using. Maybe it isn't any better but it certainly warrants consideration. A couple of nice things about the panels are they are very rigid and flat, and when attaching interior or exterior covering, stud location is not an issue. Again, I do understand the concerns with heat and moisture and will do more research.

From contributor G:
Actually SIP are often used for the roof, the reason is that they are excellent for spans. A lot of log homes have them for the roof for that reason. So you may find a design that the roof is separated from the living space. I would think the challenge would be to keep the OSB happy, if you could do that the SIP should be fine. It has been my experience that these systems are very air tight, that may be a bigger help to hold the heat in than you would think. I have an 800 square foot apartment that is heated with two 1,500 watt heaters, that is like two hair dryers to heat a good size apartment.

From Gene Wengert, forum technical advisor:
I just checked Northland Kilns site and they state that they use .032" thick, white painted, stucco embossed, aluminum inside and out, and permanently bonded to a 6" foam core. Nova, for their small kilns, uses polyurethane insulation with aluminum inside and embossed steel outside. Neither uses OSB. I would also assume that the insulation that they both use is able to withstand 160 F.

From the original questioner:
From Nova:
Q: What materials does Nova Dry Kiln use for the chamber walls?
A: The end loading kilns use a pre-insulated polyethylene aluminum panel that interlocks in place. The front loading chambers use SIP (Structural Insulated Panel) that is connected using wood splines. The SIP consists of OSB (Oriented Strand Board) with a treated UL Classified EPS (Expanded Polystyrene) rigid core. The inside of the chamber is lined with sheets of aluminum and the exterior has galvanized sheet metal.

From Gene Wengert, forum technical advisor:
According to ASTM C578, EPS insulation is limited to 165 F.

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