Solar kiln framing questions

I'm making this solar kiln.
https://pubs.ext.vt.edu/420/420-030/420-030_pdf.pdf
My kiln is smaller, 8' X 4'. I haven't done much framing in my life, so I'm a little at sea, although it looks pretty straightforward. But I do have t wo questions.
On page 9 of these plans -- North wall frame and doors -- the plans call fo r a 2x8 across the frame. I have two questions. 1) Since I am making a smal ler version, will a 2 X 6 do for this piece? (I have one handy. That's why I'm asking. And 2), are there two 2X8s in this plan fastened together. The reason I'm wondering is that if there is just 1, I'm not sure how the doors close flush.
Sorry for the rookie questions, but I'm trying to avoid getting bogged down with mistakes.
Any other advice appreciated as well.
Thanks,
Mike
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On Sat, 16 Jul 2016 14:45:40 -0700 (PDT), Michael

I would think a 2x6 would be plenty since yours is half the span. There should be two, here. With 2x4 walls, I put a piece of 1/2" ply between them That gives 2 X 1.5" + 1/2" = the width of a 2x4. Then a crapload of nails pounded both directions through the assembly.

This really isn't a woodworking question but since it's a kiln. ;-)

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On Saturday, July 16, 2016 at 7:37:28 PM UTC-5, snipped-for-privacy@attt.bizz wrote:

e two questions.

maller version, will a 2 X 6 do for this piece? (I have one handy. That's w hy I'm asking. And 2), are there two 2X8s in this plan fastened together. T he reason I'm wondering is that if there is just 1, I'm not sure how the do ors close flush.

Thanks for the information! Much appreciated.
Mike
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On Sun, 17 Jul 2016 04:22:04 -0700 (PDT), Michael

Forgot: Glue the plywood between the 2x6s, too. It'll be *plenty* strong.

You're welcome.
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On 7/16/2016 5:45 PM, Michael wrote:

What to size the floor joists depends on the span, the type of wood, the weight it is expected to hold. You can calculate it yourself here:
http://www.awc.org/codes-standards/calculators-software/spancalc
Myself, I often find these calculators are over cautious, particularly when if it fails, all that happens is a pile of lumber falls a few inches to the ground. Myself, I'd use the 2x6's, in fact, looking at the picture, the joists are sitting on the ground, so you could use 2x4's if you wanted. (Make the floor joists out of PT lumber, rated for ground contact, if sitting on the ground.)
For the doors, they don't have to be the same thickness as the framing? I'd make them out of 2x4's half lapped joints, t-111 skins, or whatever your siding material is, and let the skins overlap the fame a bit for stops.
--
Jack
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