I Joists for solar kiln floor?

[Brad_bb]

I'm planning to build 2 solar kilns.  Found a good deal on some lightly used TJI's.  Will they fall apart more quickly?  I'm planning to put the kilns on concrete or gravel.  Trying to save some money, but if the osb center section will not hold up outdoors as well as regular construction lumber.... then I'll nix the idea.  They would be about 30% of the cost of new 2x8's.  I'd have to buy construction lumber as I only have Ash hardwood logs.  Or should I go for Ash 2x8's even though it will be heavier?

[barbender]

They usually have a better glue in the I joists than regular osb, I think. I still wouldn't want them somewhere that they would be subjected to a lot of moisture/humidity. 

[Don P]

I wouldn't do it Brad, too much possibility of moisture. Same glue specs in the web IIRC. I'd opt for the ash but I would SOAK it in borate, then dry and use. My partner just called, we need to pick up more roof coating for our DH under construction. It's covering about a sheet and a half per gallon.

[WDH]

I laid some treated 2x4's flat on the foundation 16" on centers and built the joist floor for my DH kiln on top of that.  Treated with disodium octaborate tetrahydrate (DOT) and kept dry, the ash would outlive you. 

[GeneWengert-WoodDoc]

It only takes a few settings for these products to loose integrity.  So, it would be prudent to use something else...PT SYP is ideal, except that the kiln will likely not last 35 years, so this would be overkill.

[Brad_bb]

Ok, I'll nix the I joists.  With the 2x8 joists though, I'm thinking some blocking in the floor would help stiffen it up and share floorload? 

@GeneWengert-WoodDoc , in the virgina tech plans, it lists six 4x4 x8' treated pieces.  I can't see what these are for?

Additionally, I'm considering making a timber frame for the bottom that I can get my forks under to lift and move it if needed.  Anyone else do this?  If so, how did it work out?  Not sure how much the kiln will weigh empty?

[GeneWengert-WoodDoc]

I am not sure why Brian used 4x4.  In most cases, treated 2x8 16" to 24" oc will be more than adequate, especially if they are well supported with blocking above the ground or concrete slab.  Air flow underneath will keep the floor dry, although pressure treated plywood for the floor might be a reasonable idea.

[Brad_bb]

2x8 treated floor joists are listed and shown on the floor deck plan, but in the materials list there are six treated 4x4 x 8'  listed.  They don't appear in any of the wall or floor design pictures, so I'm not sure what they are intended for? Ok, I just looked at the plans online and could barely make out in one of the color photos, it looks like the 4x4's are used on the very bottom under the floor joists to either keep the joists off the ground or to be able to move the kiln with a forklift? It looks like they used 8 of them through and not 6.  @GeneWengert-WoodDoc