Virginia Tech solar kiln build - modified a bit. I have questions…

I'm planning a solar kiln. I need advice on support for the rear of the kiln above where the doors will go. I want a clear door opening of about 16'4".

First, my assumptions. I want to be able to dry up to 16' long, or have two 8' stacks next to each other (end to end). I want to be able to dry slabs up to 60" wide. I'll have about 4' of internal height at the shallow side of the kiln. Most of my stacks will be 4' wide. If maxed out, (with one stack, 16' long, 4' wide and 4' high, 4/4 lumber, with 1" spacers, with 4X4's at the bottom of the stack as bunks, it will hold roughly 1500bf. I'll be drying mostly hardwoods, and I'm not in a hurry.

I'm considering a footprint of 17'4" x 6'8". The front (framing height, exterior) will be approx 4'7" and the rear will be 9'. This creates about a 35° slope of the roof. My latitude here is 30.22°N.

For the area above the doors, I'm considering a rectangular (floor type) truss as pictured. My goal is to not have any sagging of the framing down on the doors. I would gusset the meeting points of the truss members with 1/2" ply both sides.

What do you think? Is a truss overkill? My "get 'er done" dad suggested just using a couple 2X8's, 17'1 long with 1/2 ply between them, with vertical supports up to the upper framing members. Any other advice or suggestions?

Attachment 351235

Why not use a micro lam beam and studs?

Because that just oozes of costing a whole lot more money.

I think that the truss should be plenty fine, especially gussetted on both sides with some ply. It wouldn't hurt to use 3/4" ply while you're at it, unless you already have the 1/2" and don't have to go buy it.

What kinds of doors are you installing? With 2 outswing doors at 8'x9' , they are going to be pretty large and need some serious hinges. What will they be sheathed with? Just curious as you may want to think about installing some type of extra bracing/strength to the jacks/studs around the door to keep them plumb for the long term. Of course, you'd want to do this in such a way that wouldn't encroach on your clear space from the full width and height of the opening, but something to think about.

Post pics when you get it built!

The doors will be more like 5'6" tall by 8' wide. I'm now wondering if bottom-hinged doors, doubling as ramps might not be a bad idea.

Or maybe I'll just make them removable so I can load/unload with a set of forks?

Inside the kiln, I'll use a sheet material. Outside the framing, I'll apply 3.5" of rigid polyiso, then wrap that with 1x4 strapping, then probably metal siding.

Still in the design phase!! Thank you for your comments and questions!

For doors, how 'bout rolling barn doors? The tracks would extend off one side of the building by 8'. Both doors would roll out there when you're loading a 16'-wide stack.

That's tempting, but sealing would be more difficult.

What do y'all think about the 12" fan on this page:

https://www.mcmaster.com/#1915k81/=15ulqgz

I'm thinking 3 of them. There aren't any specs for CFM in the Virginia Tech design. Kind of expensive. I've read stories of the plastic fans melting though.

Being able to load and unload the kiln with a tractor with forks or a forklift is critical.

This is the type fan in the Nyle L53 dehumidification kiln unit. They are designed to operate in the kiln environment, put out 850 CFM, and are half the cost. I added 4 additional fans of this type in my kiln and they been running 85% of the time since then for 3 years with excellent performance.

https://www.carltonbates.com/Axial-F...115V-AC-125W-8

Hi Todd. I built three VT type solar kilns last year to augment the one that I already have. Two of them are 20' wide (external), and one is 14'. As I recall they are around 6'8" deep in order to accommodate lumber stacks that are 40" - 48" wide. It's a good idea to have at least 8" - 12" extra on each side, so that you have maneuvering room to get your boards / planks in. I've found that the 20' external footprint (19' or so inside, and around 18' inside the door opening) is adequate for lumber that is 16'6" long or two stacks of 8'3". I would not want it any narrower because of the problems that I have with getting 16' lumber in and out of my 18' wide VT kiln.

I fabricated a truss for the door header, and also glued / screwed plywood to the outside to strengthen it even more. So far no sagging. I did this because my previous 18 footer with the typical double 2 x 12+ OSB header tends to sag a bit in the middle and pinches the doors.

Some height was added in my modification to the VT design in order to allow me to put 2K bd ft of 4/4 oak in each of the 20 footers. My Nyle kiln stacks are 40" - 48" deep and I wanted to be able to fork the same stacks into either the solar or DH kilns, and the original VT design required 5' stacks in order to make the targeted bd ft amount. As I recall the "rule of thumb" for 4/4 oak is 10 bd ft per sq. ft of collector, and my collector is 10' x 20' on the 20 footers.

My original kiln uses single wall corrugated panels, with the three new ones I sourced an 8mm clear double wall polycarbonite panel from Greenhouse Megastore. Member MattJ did an analysis on single versus double wall panels for solar kilns on the Forestry Forum a couple of years back and the double wall panels provided significantly better performance.

I heartily concur with Danny about the benefits of being able to load / unload with forks.

I use the inexpensive 20" box fans in mine (4 in the 20 footers, 3 in the 14 footer). They are good for 3 years or so here in NC, and have very low power consumption.

Here is a pic of my new ones during framing.

Attachment 351401

Subscribing because I've got two solar kiln builds coming up, but I have been toying with the idea of powering the fan on direct solar. Figure a solar panel will spin the fan when temperatures are at their highest. The added benefit of not having to keep the kiln near a wired powered source is appealing too. And there's that other thing....you know....it is all solar :)

Anyone done this?

Over on forestry forum, Piney Woods uses a room dehumidifier to collect the moisture inside the kiln. Any of you guys tried that?

Scott, in your image, is that one of your doors on the ground there in front? Then you are going with two doors on the 20' kiln? Got any more pics, perhaps with a larger image size?

Thanks! (I too decided to go 20' wide. Good suggestion.)

Quote:

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Originally Posted by Todd Burch

Scott, in your image, is that one of your doors on the ground there in front? Then you are going with two doors on the 20' kiln? Got any more pics, perhaps with a larger image size?

Thanks! (I too decided to go 20' wide. Good suggestion.)

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Yes, that was one of the doors. We used triple 2 x 4's on each side, and singles on top and bottom, and then studded out on 16" centers. Exterior plywood was glued and nailed for additional rigidity (matter of fact, we did that on the entire exterior - not just the doors).

Inside of the doors has a tensioning cable and turnbuckle running from the top above the hinge to the bottom where the doors meet. The entire interiors (including the bottom) are spray foamed with about 3" - 4" of closed cell spray foam. Coupled with the double pane green house panels, I'm seeing up to a 40 degree temperature increase above ambient. The actual temp varies from 10 degrees to 40 degrees depending upon the MC% of the load and how much cooling effect that is taking place as the air passes over the lumber.

I can't speak to the engineering of the truss design. If you're putting vents up there, will that interfere? On my kiln, I used two 2x12's with 1/2 plywood glued and nailed together. I haven't had any sag. I also used barn door hardware to create bifold doors. I estimate I've got at least 500 lbs. of doors hanging there. But the truss design is appealing because getting that back wall lifted up was interesting for two people and no heavy equipment.

Also, be sure to give yourself enough length on the building, especially if using a forklift. I'd go at least 18', maybe a bit more if you're planning on two stacks of 8' footers +/-. With the bifold doors I lose a good 3' of loading/unloading space but it's not an issue for my application. Also, the ratio of solar collector to kiln space is something you'll want to watch.

Bifold doors open:

http://www.sawmillcreek.org/attachme...777907&thumb=1

Complete build thread with plans here: http://www.sawmillcreek.org/showthre...-doors-(walls)