Dry Kiln Construction

[pine]

This kiln design topic has been discussed in several threads but here is a question that I have not seen an answer to. 

I have a set of plans for a Nyle kiln that I like in general but feel are not exactly what I want to build. 

The plans use a 2x4 construction wall, skinned with either sheathing or 1/2 inch CDX on the outside wall then an airspace of 1.5" then 2" non-foil faced Celotex to fill the 2x4 space, then the inside of the frame wall skinned with 2" foil faced Celotex then 6 mil poly with 1/2 inch CDX.  R value by my calculations is R-20 not accounting for the air, the poly, and the CDX. (minimal at best)

I do not understand the  1.5 inch air space.  It seems to have more value if insulated instead of air space.  Could use 1.5 inch Celotex but I thought about bumping up to 2x6 walls.  With the price of Celotex I wondered if I kept the original 4 inch Celotex design placement but with the extra space from using 2x6 instead of 2x4 walls, I could put in less expensive fiberglass and get an R13 bump to the R20 from the Celotex for very little incremental cost.
I have read about the negatives of fiberglass in a kiln due to moisture but with it being on the outside of the wall behind 4 inches of Celotex and a vapor poly wall I wonder if it would be OK to use in the design.

Also what is the rational/advantage of the foil faced Celotex on the inside wall and non foil faced on the internal Celetox if anyone knows?

Thanks

[Tom the Sawyer]

I have the same set of plans from Nyle and also questioned the air space, it may have something to do with moisture, not just insulation value.   

I bought the 200M model and the book that comes with the unit differs a bit in the construction details.  It specifies 2x4 construction for the walls, floor and ceiling (??).  They call for blue or pink Styrofoam (extruded polystyrene) friction fit between the studs.  Then they specify that the interior face of the studs be covered with 1" Celotex Thermax (or, better, two overlapped 1/2" layers).  That seems like a lot less insulation that in the plans they distribute. 
smiley_confused

I wonder if it makes that much difference.  To some extent, the more insulation the better but there is a point of diminishing returns on the construction investment.

[GeneWengert-WoodDoc]

The foil creates a vapor barrier.  With foil, you need polyethylene sheeting, which is actually better.

I suggest a 2x6 wall using rigid styrofoam boards for insulation (blue board).  The original plan was when energy, including electrical, was cheap...to cheap to pay for extra stud size and insulation.  It is not cheap today.  But it was so cheap that thin insulation was ok.

Air space does give some insulation value.

For various building materials, see http://en.wikipedia.org/wiki/R-value_(insulation)

We need to use an insulation that will not sag if it gets wet and also will not absorb water.

[pine]

The foil creates a vapor barrier.  With foil, you need polyethylene sheeting, which is actually better.

I suggest a 2x6 wall using rigid styrofoam boards for insulation (blue board).  The original plan was when energy, including electrical, was cheap...to cheap to pay for extra stud size and insulation.  It is not cheap today.  But it was so cheap that thin insulation was ok.

Air space does give some insulation value.

For various building materials, see http://en.wikipedia.org/wiki/R-value_(insulation)

We need to use an insulation that will not sag if it gets wet and also will not absorb water.

Gene
So the design is basically an old one and that is why it seems a bit light weight.
 
Is there really much difference between the blue and pink (FOAMULAR 150 extruded polystyrene (XPS)) rigid foam insulation?  I think Celotex is a brand name for an older polystyrene but have not been able to compare it directly to the blue or pink XPS.  I have read that Styrofoam is to be avoided at all costs and I think the blue board is a polystyrene (not styrofoam) just like the pink but do not know what the difference beyond color is. 

Is using fiberglass batts in the outer 4 inches of the stud with the 4 inches of rigid board and poly film sheeting vapor barrier and taped boards acceptable or will there be moisture infiltration that will cause it to sag no matter what one does in the kiln wall? 
Since the styrofoam is not recommended in the kiln wall because of the heat issues I would presume that even with 4 inches of XPS then the styrofoam outside of that it would still result in a heat degradation problem?

[WDH]

The nyle plans say that you can use fiberglass batt insulation between the studs if you cover the studs on the inside with a layer of the rigid polystyrene, and then a layer of the foil backed polyisocryanulate rigid foam (celotex is one brand), along with a 6 mil polyethylene vapor barrier, then a 1/2" treated plywood interior.  All joints and nail/screw holes need to be sealed with high temp silicone. 

I actually taped the joints on the polyisocryanulate foil backed foam with aluminum tape like that used to seal heating and cooling ducts.  With a 2x6 wall with R-19 fiberglass insulation, then 2" of the pink polystyrene rigid foam, then 1/2" of the polyisocryanulate foil backed rigid foam, the walls and ceiling will have a R-value of at least 32.

For the R-value, the fiberglass is much cheaper in the stud walls than the rigid foam.  You just have to cover the studs on the inside with the rigid foam and the foil backed stuff along with the additional poly vapor barrier.  For me, the biggest expense in building my kiln chamber was in the insulation, especially the pink rigid foam (or blue or green depending on where you buy it) and the foil backed stuff.  A 4x8 sheet of the 2" polystyrene foam is $35, and that gets you R-10.  To get R-30, you need 3 sheets.  That is where the fiberglass in the stud walls will save you big money. 
[/quote]

[pine]

The nyle plans say that you can use fiberglass batt insulation between the studs if you cover the studs on the inside with a layer of the rigid polystyrene, and then a layer of the foil backed polyisocryanulate rigid foam (celotex is one brand), along with a 6 mil polyethylene vapor barrier, then a 1/2" treated plywood interior.  All joints and nail/screw holes need to be sealed with high temp silicone. 

I actually taped the joints on the polyisocryanulate foil backed foam with aluminum tape like that used to seal heating and cooling ducts.  With a 2x6 wall with R-19 fiberglass insulation, then 2" of the pink polystyrene rigid foam, then 1/2" of the polyisocryanulate foil backed rigid foam, the walls and ceiling will have a R-value of at least 32.

For the R-value, the fiberglass is much cheaper in the stud walls than the rigid foam.  You just have to cover the studs on the inside with the rigid foam and the foil backed stuff along with the additional poly vapor barrier.  For me, the biggest expense in building my kiln chamber was in the insulation, especially the pink rigid foam (or blue or green depending on where you buy it) and the foil backed stuff.  A 4x8 sheet of the 2" polystyrene foam is $35, and that gets you R-10.  To get R-30, you need 3 sheets.  That is where the fiberglass in the stud walls will save you big money. 

[/quote]

That is where my question came from.  Since you have done basically exactly what I have been thinking have you seen any moisture contamination of the fiberglass batts or with them sealed you can't really tell.  I guess I should not complain as the 2 " XPS is only $30 a board in my area vs your areas $35.

[WDH]

I have only been running my kiln for 3 months, so I do not have enough experience so far to say if the method I followed is proven effective.  But, I did follow the Nyle plans to a Tee.  There is no free moisture in the interior of my kiln chamber at any time, and the aluminum roofing paint used to coat the interior has always been dry to the touch.  So, I not believe that the fiberglass in the stud walls has been compromised and has sagged, given all the protection from the 2" rigid foam, the 1/2" foil backed foam, the poly vapor barrier, all joints and nail/screw holes sealed with silicon, the 1/2" treated plywood coated with fibered aluminum roofing paint.  However, I have a small chamber, only 9.5' by 11.5' inside dimensions.  A larger, commercial chamber might not work as effectively if built the way that I built mine.

I actually have more problems with the kiln over-heating, requiring me to open the vents, than I have with not enough insulation.  When you drive up the temperature to sterilize the load, the extra insulation will really come into play.   

[GeneWengert-WoodDoc]

The foil creates a vapor barrier.  With foil, you need polyethylene sheeting, which is actually better.

I suggest a 2x6 wall using rigid polystryrene boards for insulation (blue board).  The original plan was when energy, including electrical, was cheap...to cheap to pay for extra stud size and insulation.  It is not cheap today.  But it was so cheap that thin insulation was ok.

Air space does give some insulation value.

For various building materials, see http://en.wikipedia.org/wiki/R-value_(insulation)

We need to use an insulation that will not sag if it gets wet and also will not absorb water.

Polystyrene is correct.