Concrete Kiln Pad

[firefighter ontheside]

So, I ordered an L53 and now have to get a chamber ready.  I think I have decided to build a whole new kiln and use my current one as dried limber storage.  I'm thinking of pouring a pad next to current one so I can essentially connect the two buildings.  I can then have the controls inside the storage shed.  I'm wondering if I can just pour the pad on the ground and not have to have worry about front heaving especially since the kiln building will probabky always be above freezing.  I'm wondering about insulating the floor.  Should I have insulation above the concrete?  Is heating the concrete going to be an issue if I don't?  I did some searching, but it seems the references I found were all in warmer areas.

[Southside]

One thing I have learned - the hard way - is that doing it right, and not presuming things will always be what they are intended to be, is a lot easier and cheaper than having to go back and re-do something.  Insulation is cheap, and it's a one time expense.  Energy is only going to cost more in the future. Anything I build now is super insulated.  

This winter we built a new brooder and I super insulated it, the heaters only came on for the first couple of days to get the empty room up to temperature, 85F, and ever since we have been venting excess heat that comes off the young birds with many nights in the 30's even last week.   The floor was initially framed and laid down without insulation in mind, a few days of crawling around on my back under 12", or less, of free space to put up batting, bubble board, foam, and utilities taught me the value of planning ahead.  

[YellowHammer]

I don't know about the heaving, but I put 2" foam board under my concrete pad, and the places that I didn't get real close to the edge of the framing still get cold and cause condensation on the floor which causes all sorts of problems.  

[firefighter ontheside]

So, what would you do different?  

[Larry]

Nyle calls for 2" of blue styrofoam under the slab along with perimeter insulation.  I used 1-1/2" because I had it on hand.  First load I noticed uneven drying from the top to the bottom.  Knew I had some kind of problem.  Bought a laser thermometer and saw I had a significant temperature difference between the walls/ceiling and the floor.  This was during the cold part of the year.  Decided to lay 6" of foam board on top the concrete floor and seal/cover with plywood.  This is the same amount of insulation that is in the rest of the kiln.  I also thought the air flow was slow so increased that.  Now when I start a load the temperature is a few degrees cooler on the floor and I attribute this to my heat source being close to the ceiling.  Once the temperature comes up to my preset the entire kiln will be the same no matter where I check.  Problem solved...even drying through out the load.  Of course the increased air flow probably helped.

Just my experience and not recommending anybody do it my way, but it does seem to work.  If you do insulate on top the slab it will take some space so take this into account with your wall height.

Both my kiln and shop are floating slabs with 1/2" rebar 12" on center.  No insulation under the shop floor.  Both have compacted gravel bases a couple inches above grade.  The shop has gutters/downspouts to keep the water away.  The shop is 20 years old.  No cracking or frost heave on either.  With my shop in north Missouri I did the same with the slab but used wire instead of rebar.  Never had a problem with it either.
 

[firefighter ontheside]

I feel like I'd be better off pouring concrete on a vapor barrier, no insulation under it and then build a 2x6 subfloor with foam insulation.  Then build walls on top of that.

[Larry]

My bunks for setting the stack on are 6" X 48".  I checked the compressive strength of my foam and it was strong enough I could put almost one maximum size stack on just one bunk.  So....I just laid the foam on the concrete floor and didn't use any kind of lumber sub floor.  I did put a 2 X 6 at the doors to protect the foam from damage.  On top of the foam I put 3/4" plywood which I caulked and painted the incky junk on.  On top of the plywood I put 6 - 6" X 48" bunks.

Again just what I did and seems to work fine.  Copy at your own risk.

 

[peakbagger]

FWIW there is new product called Glavel (Glass Gravel) Its made out of old glass bottles that is processed into "foamglass", the new result is what looks like crushed rock (lava rock)but its got an R value of 1.7 per inch. Foam Glass Gravel | Glavel | Lightweight Aggregate One of the uses is subslab insulation. It drains like crushed rock and is lot less prone to damage than foam. There is one factory in VT and couple of others spread arounf the country.

[Stephen1]

I agree with Larry on the foam without the framework. Years ago I finished a garage into a family room. We put down 2" SM  and then placed 5/8" plywood with biscuit joints on top. Warmest and softest floor every. Way better than walking on concrete or a wood subfloor.  He had just done a similar floor at the school cafeteria freezer he installed. Laid 4" SM blue and built the freezers on top. 

[btulloh]

Doing a Res-check can help with your design. It's a web based calculator form that the DOE offers. Actual helpful tool from our government. Go figure!

Article about doing your own res-check

You may need Don P to interpret the results though.

I ran into a big snag with Powhatan County and their new insulation requirements while planning a garage to office conversion. Fortunately my architect could deal with the details. Unfortunately there's a lot of added expense to perimeter insulate the existing slab and footers plus the interior dryall removed and the studs increased from 2x4 to 2x6!

(But . . . like Southside said, spend once for insulation, save energy forever.).

Anyway, the best way to insulate your new floor/slab may better be answered with building codes and res-checks.  I've found out that sometimes that official approach is better than my old ways.  ( Did I really say that?!?!). Also something like slab/floor insulation choice is very dependent on your local conditions, so advice needs to filtered somewhat since everyone's local conditions vary a great deal.

Good luck with the build.  Sounds like a great addition to your capabilities.

Edt/add: Personally I like your idea of putting insulation and a wood floor on top of the slab. Just my opinion though, and I am learning that decisions like that need to be checked against real data.

[YellowHammer]

Extend the slab out further than the building and insulate past the edge of the framing.

[barbender]

If you are going to frame a floor and insulate it, would the slab even be necessary?

[fluidpowerpro]

When I insulated under my pole barn slab for in floor heat, I installed 2" pink foam both under the slab, and also vertically 2' down, around the perimeter.

[YellowHammer]

If you are going to use a framed in floor, concrete insulation would not be necessary.  

[doc henderson]

I think about whether or not to have the bulk of the floor being a thermal mass or not.  It can hold the heat for when you open a door but will take longer to heat up initially.  if you want it for strength, but not as a surface to use then it can be covered and insulation on top to exclude it from being heated.  If you plan to unload and load a new load within 15 minutes, the thermal mass will get the new load going faster.  if you will occ. let the kiln set for a day between loads, the stored heat in the mass will be wasted.  you could keep the the heat on between the loads to maintain the temp of the concrete, but again some waste in energy.  you could do concrete footings to support the insulated frame.  If you plan to load with pallets and a machine, the floor will be tougher out of concrete.  you can build a framed base and pour concrete on top of the insulated base, but it will crack with flex.  so do you have interest in putting pex tubing in the floor for the poss. of radiant heat for the future?  with the size of the kiln, you will not likely need to drive a loader on the floor.  my heated floor in the basement of my shop, has thermal breaks at the edges, and then 12 inches of sand under the concrete.  it has a vapor barrier under the sand so the sand is dry and dry sand is an insulator, vs wet sand.  I have dimple board on the outside of the basement walls.  also the dimple board at the edge of the slab to separate the slab from the footing and exterior wall.  random thoughts.

[K-Guy]

The floor can be done the same way as an insulated garage floor. Be careful to only insulate to R25 or so in the walls. There is a trade off to be made in the northern states, not enough for the winter or too much for the summer.

[blackhawk]

I did an insulated floor for my L53 kiln.  I put down gravel, then 6 mil plastic, and finally 2" rigid insulation.  I also put 2" rigid insulation around the perimeter.  I have only done one load, but I was really pleased on how well the kiln held heat.  I had some 25F nights on that first load and didn't see much loss.  I have a YouTube video of what I did on the foundation.  https://youtu.be/SvoeqelX-F8

[Andries]

When I insulated under my pole barn slab for in floor heat, I installed 2" pink foam both under the slab, and also vertically 2' down, around the perimeter.

I'm seeing that done over here for heated concrete floors. . . with a slight difference. The perimeter foam is placed on a 45° angle away from the slab and about a foot under grade. It leads surface water away and traps ground warmth under the concrete. 
They're referred to as "frost wings".
.
For FFOTS and his MO location, that might be a bit much, but us glaciated types do all sorts of weird things to conserve those btu's.

[barbender]

And to keep the frost from lifting the corner of our building up a foot😁

[Andries]

That is a great little video on the kiln pad concrete detailing, @blackhawk 
They are a lot of work but the info conveyed in 10 minutes is incredible.
Thanks to you and all the FF members that go to the time and trouble to make YT videos. 

[firefighter ontheside]

Thanks for the great input guys.  Lots to think about and decide on.

[barbender]

I'm really leaning towards building a kiln with an elevated wood floor. Redi-mix has gotten so expensive I'm going to avoid it wherever possible. Same thing with a mill building, I'm thinking something along the lines of @PASawyer building. 

[Tom K]

Extruded polystyren insulation (XPS, blue or pink board) comes in different PSI rating as well, typically 15 psi or 25 psi. It is better to use 25 psi or higher if you put any under your slab. Don't use polyiso or expanded polystyrene insulation below grade as they will both absorb moisture. 

I would also use the 25 psi to insulate above your slab. You can run the numbers based on your expected kiln volume and wood weight to see if you can eliminate the framing in the floor. Using a 1/2" plywood stiffener on edge would also give you more compressive strength while not creating as much thermal short circuiting.

[firefighter ontheside]

Well, my current drying shed/kiln is built on an elevated platform on piers.  I was wanting to do this one on a slab for simplicity, but perhaps I should just do a platform again.

[doc henderson]

how big are you planning?

[Larry]

The first solar kiln I built 29 years ago was supported by the butt end of old poles.



I sold the farm a few years ago and the new owners were using it as some kind of green house.

I used 6" fiberglass batts for insulation in the floor.  I didn't have much crawlspace so I put the batts in from the top, than the floor followed by the rest of the kiln.  It was a pita keeping the batts dry from frequent showers while I got the rest built.

I just now got to thinking and that solar kiln held almost the exact same amount of wood as my new L53.  Never had any trouble with the floor.

[Don P]

15 psi x 144 si/sf=2160 lbs per square foot capacity on the 15 psi foam. You probably don't need the high density. I typically assume the soil is only good for 2000 psf.

[firefighter ontheside]

I'm thinking 11' wide inside and 7' or 8' deep inside.  It wouldn't hurt my feelings if I never mill another 10' log, but I hate to limit myself especially if someone wanted to pay for kiln service.

[Tom K]

15 psi x 144 si/sf=2160 lbs per square foot capacity on the 15 psi foam. You probably don't need the high density. I typically assume the soil is only good for 2000 psf.

HERE, presumptive allowable bearing capacity is 2000 psf, most of out soils are good for 2500-3500 psf. Regardless, I wouldn't put 15 psi under a slab as it's just not good practice, and not recommended by the foam manufacturers. 25 psi foam isn't really anything special and is available at most if not all big box stores.

I was more mentioning the foam rating so FF could run the numbers and figure out he probably didn't need a frame if he did over slab insulation.

FF, why the hate for 10'+ logs? In the shop I would much rather have 10-12' lumber then 8'. I'll be following along to see what design you end up going with.

[blackhawk]

For reference, the concrete pad for my kiln was 14' x 9'.  I did a monolithic slab with 18" deep footers around the perimeter.  I poured in September 2022 and had around $1000 in the foundation.  This includes concrete, gravel, 6 mil plastic, and rebar.  I did all the labor myself.  

On the foam, I used 25 psi and would not use anything less.  In my area, there wasn't a choice anyway as 25 psi foam is all that is stocked.

[firefighter ontheside]

I found these on FB and thought they were interesting and perhaps useful for something.  


 

[firefighter ontheside]

also found this


 

[KenMac]

also found this

This looks like walk-in cooler or freezer wall panels and may or may not be good in heated spaces. I did think I was wrong once, but was mistaken..............

[firefighter ontheside]

  @Tom K I cut a lot of live edge stuff.  10' long 8/4 slabs are so heavy.  I broke my tractor loader on a very large 10' log.  It just doesn't seem that 10' logs are great for me.  That being said, I have decided to go ahead and build the kiln to allow 10' lumber.

[Stephen1]

If you going to build 11' you might as well go for a 13' so you can load 12' lumber, or slabs. 
I get lots of call for 12' very few for 16' 

[firefighter ontheside]

I can only mill 10' 6" long at max.

[Don P]

Remember door swing/thickness and being out of level so you are going though the door diagonal to the door a bit. And I can't nail the landing the way I used to, in my fondest memory. Just make sure you can wiggle in. I wish we had gone 22'  :D

[GAB]

I can only mill 10' 6" long at max.

Bed extensions, last I heard, are still available.
GAB

[Larry]

It wouldn't hurt my feelings if I never mill another 10' log, but I hate to limit myself especially if someone wanted to pay for kiln service.

I feel the same way for a variety of reasons.  About all I saw is hardwood grade lumber.  It is always easier to get high grade (FAS) out of 8' logs especially if I buck the tree.  With only one length of log it is easier to fit the load in the kiln and block the empty space on the sides.  It's easier to surface shorter boards in my smallish shop.  Makes measuring and storage easier when time to sell boards.  Most of all shorter boards are LIGHTER which is pretty important when jointing and planing....and the boards get heavier every year!

I did make my kiln 12' wide but would have been most happy with 11'.  The last two loads through it were 10/4 live edge walnut and 8/4 grade walnut all 10' plus long.  I can only lift one end of the live edge stuff.
 

[Tom K]

 @Tom K I cut a lot of live edge stuff.  10' long 8/4 slabs are so heavy.  I broke my tractor loader on a very large 10' log.  It just doesn't seem that 10' logs are great for me.  That being said, I have decided to go ahead and build the kiln to allow 10' lumber.

Thanks for the reply. That makes a lot of sense if you deal with a lot of live edge and 8/4 stuff.

Most of what I cut is 4/4 hardwood that I plan to keep in the 8-12' range, and for my own use. I always get frustrated in the shop when I need a whack of 30-32" or 48" pieces and 8' boards don't work well allowing for some waste.

Those 3" IMP panels in your first link would make some decent walls. Being that thick you would not need any intermediate support. Depending on the manufacturer they should have a R value around R-25 with an EPS core. While not right, I have seen those used as roof panels as well with just caulking the panel joints.

[K-Guy]

I'm probably repeating myself but this is very important.

Whatever insulation you are looking at, remember to check the heat rating on it. Some insulation is only good for cooling and breaks down at higher temperatures.

[firefighter ontheside]

Thanks Stan and others.  I will definitely confirm the temp rating before I buy something.  I would think anything that could be used in a roof will be fairly high rated to be able to take the summer heat.  A lot of the used foam stuff I see is stuff that has come out of commercial roof systems.

[scsmith42]

I'm probably repeating myself but this is very important.

Whatever insulation you are looking at, remember to check the heat rating on it. Some insulation is only good for cooling and breaks down at higher temperatures.

Yes, but...... how much heat will insulation see below a concrete pad?  
I can see where temp rating for the walls and ceiling inside a kiln would be critical, but seems to me that the slab will be a giant thermal heat sink and the insulation under the slab will not see that high of a temp.

[Tom K]

Yes, thanks for the reminder again Stan. We do use these panels a lot in cooler buildings, and we have also used them as bulkheads above oven lines. Without knowing the manufacturer it's going to be hard to nail down a solid temp rating. I would think the IMP's would be able to hold up much better to the heat then a prefab cooler panel. I doubt those are, but some IMP's are also fire rated.

[Tom K]

I'm probably repeating myself but this is very important.

Whatever insulation you are looking at, remember to check the heat rating on it. Some insulation is only good for cooling and breaks down at higher temperatures.

Yes, but...... how much heat will insulation see below a concrete pad?  
I can see where temp rating for the walls and ceiling inside a kiln would be critical, but seems to me that the slab will be a giant thermal heat sink and the insulation under the slab will not see that high of a temp.

These other types of insulation would not be used below grade, or at least I hope not. I was assuming FF was looking at different options for walls/roof, which is where Stan's comment is applicable.

Under slab really needs to be XPS, which the IPM's or other sandwich panels are not.

Unless I'm not following along right, which could also be a possibility.....

[K-Guy]

how much heat will insulation see below a concrete pad

I'm talking about insulated panels or insulation out of coolers mainly that might be used for wall and ceiling insulation. For the pad you are probably correct.

[firefighter ontheside]

My L53 has shipped, but I do not have a tracking number yet.  I assume it will be here early next week.

[firefighter ontheside]

Well, the L53 will be here tomorrow it seems.  I've been trying to get the tracking number from Nyle, but they were having trouble finding it.  Got a call from the shipper today.  It will be here tomorrow.

[Larry]

My Nyle came on a lift gate truck.  We didn't use it, I just meant the driver on the road and pushed the pallet off the truck into the back of my pickup.  Its not all that heavy.

[firefighter ontheside]

Yeah, the shipper said its on a pallet and weighs about 150lbs and that the driver would need help offloading it.  I will probably just take the tractor down to the road and pick it up with the forks.  I need to boxblade my driveway anyway from the recent rains we've had.  Maybe the truck will show up while I'm out doing that.

[Don P]

We've been doing shipper tag over a neighbors dust collector that he has had supposedly coming for a week. I finally had to go get the loader back yesterday and have them deliver the box it to the building supply. I'm not in the loop but how can you miss by a week? (somebody lost something  :D). It's another one, I doubt it weighs 200 lbs but it is a big box.

[firefighter ontheside]

I ended up meeting the delivery truck in town in a parking lot.  I back up behind his truck and he was able to just lower his lift gate right down on my flatbed and roll it onto my truck.  Worked great for both of us.  His tractor trailer would not have done well on my road.


 

[jpassardi]

FFOTS: Bear in mind - the used flat roof insulation isn't necessarily closed cell and can take on water. Because of this it may not be the best choice for under slab due to groundwater & condensation.
Congrats on the new Nyle unit. I'm interested to see how you like it.

[firefighter ontheside]

Yeah, I don't think I'm gonna use any of those panels that I posted.  It's tempting, but I'm going to pretty well follow the Nyle plan with 2" poly iso foam.  Also, I've give up the idea of building on a slab.  I will likely hang floor joists off of my current kiln/shed and then make some piers to carry the other end of 2x10x8 joists.  I will sheet the bottom of the floor with something...not sure what yet.  I will cut foam to fit in between joists and then 3/4" plywood.

[jpassardi]

 Just thinking: if you laid your floor joists 90 degrees to the long door opening, you could set casters (on top of the plywood) directly above the joists and roll in the stack after bringing it in with forks. Those joists would need to be well supported, maybe worth doubling them also.

[firefighter ontheside]

My joists will definitely be running that direction.  

[TBrown99]

Are recommended r-values for ceiling, walls, & floor in the NE noted anywhere?

The floor can be done the same way as an insulated garage floor. Be careful to only insulate to R25 or so in the walls. There is a trade off to be made in the northern states, not enough for the winter or too much for the summer.

[beenthere]

NE meaning Nebraska, or northeast US ?

Your location in your profile would help with answers.   ;) ;)

[K-Guy]

The R-values are not in the manual but it gives the amount and type of insulation to use. For the floor you want a standard insulated pad. L53 manual link below.

https://www.nyledrykilns.com/wp-content/uploads/2023/10/NDK-L53-Manual-Rev-2023.02.pdf