my solar kiln project

[nrp0450]

I finally decided to go ahead and build a solar kiln. After reading all I could on here and some other sites my dad and a buddy of mine put a plan together a few weeks ago and this morning started working on it. It's going to follow the virginia tech model with a few modifications based on what pineywoods has done. It will be 14'x6'4". My buddy has some old glass windows that he's not going to use. We're going to use those for the roof (is it called glazing?).

I love reading the FF threads that show a project from start to finish so I'm going to try and do that with this. I played around with sketchup a little to get this project planned out. Here's where that's at right now. There are several things we haven't decided yet... mainly what kind of door to do. But the here's the sketchup anyway.


We have an ideal location for it right on the north edge of a hay field. So if the sun is shining it will be ready to absorb it.


This morning we cut down an ERC tree and sawed it into two 4x7s on our Woodland Mills HM126. We couldn't get 100% pink heartwood but it's pretty close. And we're going to treat them too. So hopefully they'll last a while.


I'll add to this thread as we make progress.

[thecfarm]

Sounds good. You say,hopefully they'll last a while. We built a greenhouse out of hemlock. When not in use we had the doors open to dry it out. I copied it from a guy that had used white pine for 8 years and it was still standing and looking good.

[beenthere]

And we're going to treat them too. So hopefully they'll last a while.

What do you plan to treat them with?

[nrp0450]

We'll probably treat with a diesel, linseed oil, roofing tar mix. We have some left from another project.

[LeeB]

Where are you going to use these two beams? I don't really see the need for treating unless it will be in contact with the ground.

[nrp0450]

"Beams" was the wrong term maybe. They're going to be skids that the floor joists will sit on. The skids won't be sitting on the ground. They'll be on concrete blocks. Other kilns I looked at used pressure treated lumber for the skids. That's why we're using ERC for them. But since some of it is sapwood I thought it should be treated. I'm totally new to this though. Do you not think the sapwood will rot away if it's left untreated?

[LeeB]

With it off the ground and covered by the kiln to keep it dry, not too likely to rot any time soon. However, I don't see any harm in a little insurance by coating it. Don't think you need the BLO in the mix though.

[nrp0450]

We got the beams cut to length and leveled this morning. We have shims ready if/when it settles.

[fishpharmer]

Looks good!  Your off to a good start.

[nrp0450]

I have a few questions for this great forum:
1. How do you insulate the floor on one of these? The only thing I can think of is to put some sheathing along the bottom of the joists and then insulate between the joists.
2. Should the moisture barrier (I'm thinking to use roofing felt) go on the inside of the studs or the outside? I assume it goes on the inside because that's the warm side and you don't want moisture condensing inside the walls. But I've seen several pictures of kilns with the moisture barrier on the outside of the wall. So I thought I'd double check.
3. Could I insulate with sawdust (from the sawmill)? I realize its R value will be quite a bit lower than fiberglass. But it's free. How much difference would that make in the time it takes to dry a load of sticks?

[beenthere]

nrp
Can't tell if the concrete blocks are setting on the ground, or are on concrete pads.
If on the ground, I'd turn them 90° so there is more ground contact than on edge as shown. I think they will have plenty of strength that way and will no as easily sink as time goes by.
And you will want support under each column of stickers as they go up through the stickered lumber.

Put the moisture vapor barrier on the warm side of the insulation (roofing felt isn't a vapor barrier, but is a waterproof barrier).

Dry sawdust should work fairly well as insulation.

[nrp0450]

Good idea about turning the blocks. We'll do that. They are just sitting on dirt, no pads.

We will have 3x5 joists on 24" centers. The sticker columns will go above those. This is different than the sketchup design above. I hadn't thought it through all the way when I did that design. We're doing 3x5s because we have some left from another project. DonP's beam calculation page says that's strong enough for our 48" span with 125 psf load.

Aaaah, so I should put the roofing felt on the outside and something that actually is a vapor barrier on the inside? Or do I not need the roofing felt at all? What kind of vapor barrier should I look for?

[WDH]

Vapor barrier, 6 mil polyethylene plastic.  Placed on warm side.  Cover over with 1/2 inch pressure treated plywood. 

[nrp0450]

Does it need to be pressure treated because moisture will condense on it? I'd really like to cut what I need with the sawmill and not have to buy it. If I use ERC planks would that work as well?

Do I need the roofing felt (or something else) on the outside of my studs? Or do I just nail lap siding on and call it good?

[beenthere]

You mentioned insulation...  if sawdust that will need to be sandwiched in some how. Solid boards or plywood, I'd think.

And in your application (High humidity, etc.) I too would go with treated plywood, although your ERC if heartwood should be a good substitute.

Outside, felt if needing to keep in the sawdust insulation.

[WDH]

I would use the ERC if I had it. 

[LeeB]

The sawdust will settle over time and need to be topped up a few times. You might also think about treating it with a borate solution for bug prevention and flame retarder. It will need to be dry before placing it in the walls.

[pineywoods]

Put a full width door or doors across the back side..Build a laminated beam across the rear opening..Your back will thank you when you stack and unstack boards..Especially if you have a fork lift or tractor fel.

[nrp0450]

I've read that about treating the sawdust with borate. But didn't see many details. Can we use borax? How do we treat it?

Unfortunately we don't have a fork lift or FEL.

Another question: is the facing on regular fiberglass insulation a vapor barrier? I'm wondering if it would really save any money to use sawdust if I need to buy a vapor barrier and borate to use it. Regular insulation may be the same price and less work. Does anyone know if the facing is a moisture barrier?

[thecfarm]

My brother bought an old house and sawdust was used on the attic floor. I would not want to use sawdust. That stuff has to be dry and you are going to enclose it too.At my brothers house they MIGHT of stired the sawdust around some,since it was in the open.

[GeneWengert-WoodDoc]

Regarding the floor insulation, it is best to put a solid layer of wood on the bottom outside of the floor to prevent rodents or insects from entering.  Treated plywood is best. 

The cost of insulation is small, especially when factored over ten years.  Use a closed cell insulation product and not fiberglass.  The reason is that if you accidentally get a hole or leak, the fiberglass will quickly lose its insulation vale, will sag, etc.  aw dust is not a good idea, as others have mentioned.  For a solar heated kiln to work best, you need to keep as much heat as possible inside the chamber, so insulate floor and walls well.

The plywood on the inside should be exterior adhesive, but treatment is not needed as the environment will be quite dry.

Although the vapor barrier is on the warm side, you should also have a vapor barrier in the soil under the kiln to prevent high MCs and the risk of decay or insects.  Then, you would have the air space between the soil and the bottom of the kiln.

[nrp0450]

OK, a layer of wood underneath the joists is what I'll do. I think I'll do ERC boards though (1/2" maybe). It would be too painful to buy wood when I have a sawmill. I'm thinking we'll nail the joists and rim joists together, flip the frame upside down, nail/screw on the ERC boards, flip it back right side up, nail it to the skids, put the insulation in and add the decking. Is that the best way to do it?

I'm too much of a newbie to understand some of the terms. Is closed cell insulation the foam panel type? I looked at those the other day at Lowe's and the thickest I saw was 2". Do I just stack enough of them to get the right overall thickness? Do I need to use closed cell insulation in the walls too or is fiberglass ok there?

[WDH]

Go to the Nyle website, go to Resources, and you will find plans for how to build and insulate a kiln chamber.  You can use fiberglass insulation if you cover the inside of the chamber with at least 1" of closed cell foam insulation (Extruded polystyrene) and 1/2" of foil backed insulation (polyisocryanurate).  In the chamber that I am building for a Nyle L53 kiln, I am using 9" of R-30 fiberglass insulation between the 2x6 studs, 2" of pink Owens-Corning closed cell insulation over the studs, 1/2" of R-Max foil backed foam panels over that, then a 6 mil polyethylene plastic vapor barrier over the foil backed insulation, then covering the inside with 1/2" treated CDX plywood.  Seal the foil backed insulation over all joints and screw/nail holes with silicone caulk and aluminum tape like that used to connect and seal heating and cooling ducts.  Then paint the entire inside with fibered aluminum roof coating paint.  The chamber has to be water tight. 

[pine]

I would ensure that the seams are very well sealed on the vapor barrier.  A vapor barrier that has leaks at the seams works somewhat but the losses that you have will significantly decrease effectiveness.

[GeneWengert-WoodDoc]

In theory, you can use fiberglass using the techniques that WDH has given, but because in the real world a wall is never perfectly sealed from the inside moisture, or over time will get a hole in it, moisture from a nail hole, poor construction, mouse, errant piece of lumber, moisture from the wet soil at the bottom of the wall or in a floor, warped plywood, driving rain, heat that makes the vapor barrier brittle and full of cracks, (electrical boxes or plumbing in a house), or some other way, it is best to avoid any insulation that can absorb water.  Hence, closed cell, meaning that it will not absorb water, even if the water is present, is best for all insulation.  I have seen too many solar kilns with wet insulation to suggest fiberglass.

Most panel insulation products are closed cell, especially the polystyrene or similar types.  Some boards are fiber products and do not work well in this application.  Dow Styrofoam (R) brand of rigid foam insulation is perfect in this case.  Check out a u-tube video...
youtube.com/watch?v=1VpBhY36krg‎

For the bottom, you could use hardware cloth (wire mesh with 1/4" grid) to hold the insulation and keep out most critters.  It might be shepaer and just as effective as plywood.

If you need 4", then use 2 sheets that are 2" each.  Around here, the boards are often blue in color.

Incidentally, for a wall or floor, always make sure that you do not seal both inside and outside as this will trap the water.  We need the outside to be quite breathable just in case some water does get in the wall.

In a kiln that gets quite hot, some of the foam insulations will melt.  So, for a durable installation, use insulation that is not sensitive to temperatures of 150 F or so.