Kiln framing

[AnthonyW]

To maximize insulation, minimize wood (and thus weight). I was thinking of using I-beam joints for the wall studs. Any tried this? Done this? I was thinking it would be OK since each I-beam is made with a 2x3 on each side. I would just need to span the top end of the I-beam to catch both 2x3s to support the roof.

[Tree Dan]

Im not sure what your doing here.
Is it a enginered joist that your useing for the wall stud?
Or are you putting stud together with 3 pieces? ???

[AnthonyW]

I was thinking of using an off-the-shelf 2x8 I-beam joist as a wall stud. It would provide extra depth for more insulation while also reducing the amount of in-wall wood thus allowing more insulation per inch of width in the wall.

I was looking at the joists. The top and and bottom chords appear to be 2x3s with a piece of 1/2" OSB between them. I was thinking if a 2x4 is acceptible as a wall stud, then why not a pair of 2x3s? Plus the plywood in between. For a top plate, I would use one regular 2x8 thereby tying together all of the 2x3 chords.

[WDH]

I built my kiln chamber with 2x6 walls filled with fiberglass batt insulation with the inside covered with 4x8 sheets of the 2" polystyrene rigid foam board, and over that, 1/2" sheets of the foil backed rigid foam insulation, then a vapor barrier, then all that covered with 1/2" treated plywood.

My problem is not that there is not enough insulation; it is that there is more heat produced by the compressor and fan motors, and I have to dump heat to keep the temps at the right level.  So, my concern with your plan is that it may be over-kill. 

[AnthonyW]

Good concern. I was thinking of a solar kiln (sorry that was starting in the OP). In essence, you have the same amount of insulation I was planning 6" fiber glass plus 2" rigid = 8" of insulation. I was also thinking of the 1/2" foil backed sheets with the seam tape to act as the vapor barrier then 1/2" exterior plywood over that to finish the inside.

It's probably easier to have to dump heat that try to create (or capture it) though.

[WDH]

In my opinion, you still need to add heavy mil polyethylene plastic over the 1/2" foil backed foam, in between the foil backed foam and the treated 1/2" plywood.  A pretty simple, but aggravating step. 

[69bronco]

Seems like a lot of expense in materials and insulation when you have a 1/64" of plastic where the heat rises to

[willmyers0169]

The I-beams you're talking about are not meant for vertical load, engineered for horizontal only.  Given the weight of a VT kiln is not that much, they may work.  But factor in snow load and high winds it would be a risk I would not take. 

[AnthonyW]

The I-beams you're talking about are not meant for vertical load, engineered for horizontal only.  Given the weight of a VT kiln is not that much, they may work.  But factor in snow load and high winds it would be a risk I would not take.

That I understand. I saw an article about split wall framing where the wall was made of an inner and an outer stud, not touching, with insulation in between. I think this is very similar. Instead on a 2x6 wall with 1 1/2" of heat conducting wood, there is only 1/2 of heat conducting wood. I'm not counting on the plywood insert as more than a tie between the two 2x3s. You can frame a wall with a single 2x4, would not two 2x3s be stronger than a single 2x4?

[GeneWengert-WoodDoc]

A wall stud has a load that is compressing the stud.  So, the compression strength is basically the cross sectional area.  However, as the stud gets smaller, it is more prone to buckling.  So, several smaller is not always better.  The VT kiln is indeed "over built" so the walls are much stronger than required.  The reason for the over building is that we need rather straight walls and not wavy walls.

[Chop Shop]

How is two 2x3s and some osb lighter than one 2x6 or 2x8?