I'm doing a project to build an energy efficient, low cost building/shop.  The whole point is to see how efficient we can get it for the least amount of capital outlay.

The building is a low cost pole barn with metal roof and siding.  The floor will be slab on grade with radiant heat.  Insulation will be 2" of high density spray-on foam for air seal and insulation.  The building is 24' wide by 40' long, 10' walls and a 4/12 roof.  There are two insulated steel doors, one 9'by8' insulated roll up and one 3'by2' double glass window.  The ceiling is open to the bottom of the roof.  About 960' floor space.

I need advice on my tubing design.  Right now my plan is;  Insulate the slab with 2" rigid foam board around the perimeter of the slab and on the bottom.  The base will be 3 to 4" of gravely/stone, vapor barrier, 2" foam board and 4" of fiber concrete.  The tubing will be placed 3' from the walls, spaced 12" apart, and stapled to the foam board.  Does this sound right?

According to my load calculations, I'm going to need 18k btus to maintain 65 degree temp with an 85 degree floor temp.  Am I in the park?

Any help would be appreciated.  This is all new to me and I have a lot to learn.

Thanks,

There is not enough information to take a ball-park stab the btu/hr heat load.

You'd need to know your design-day outdoor temp...

... the size & R values of all the doors...

...and is the roof insulation the same 2" of 2lb foam as the walls?

BTW: 2lb foam is great stuff, but when looking at per-equivalent R-value pricing it's not exactly a "low cost" R-value-leader. Your clear-wall R-value will be about R12-R14 with far more exposed surface area (& likely a much bigger design-day delta-T) than your R10 insulated 85F floor. For about the same money you could make that R20-R22 using half-pound foam, cutting your heat load considerably. (Unless you're counting on the 2lb foam to add structural strength to the building.)

The building is located in Mount Airy Maryland. We rarely get below 10 deg. The doors are 3' wide by 7", (or what ever standard height s) 2" steel with with foam core. The roll up has 2" foam panels installed as well. The entire interior will be foamed, walls, roof (underside) and gables. We are gong for the max air seal we can get. I know open cell would be cheaper, but the building is subject to high wind loads and the concern is that building movement might pull the open cell and allow air leaks. Please correct me if I'm wrong. The walls will be covered, but we hope not to have to cover the roof with anything more that a spray fire retardant. Again, I'm open for suggestions.

And thanks,

Here in the Great White North the building code calls for a minimum of R12 under the slab. This works out to 3" of expanded polystyrene. I am building a house with a heated SOG and putting in 4 inches. The additonal cost for additional insulatin is quickly made up through energy savings. More importantly I thermally isolate the slab with 3/4" blue EPS between the SOG and foundation wall.
As far as securing the heating loops to the foam use 10gax10ga 6 inch wire mesh and zip tie the tubes down. My SOG is 4 inches so clearnace is not a problem.
If you use white foam board make sure it is the type 2 not type 1 which is a lot weaker.

Maybe check with a heating equipment wholesaler for tube densities for your heating requirements...

We generally would spec a 12 inch pattern through ought the slab, 6 inch pattern on the perimeter 3 course in, 6 inches away from all walls. There is a good thread on this section
Can I heat my barn? that discuses the concept of vertical wall solar.
I like the 2 inch foam, we recommend a staple to attach to the foam board rather than a zip tie, Fast easy and works well. now you can use fiber mesh in the slab in place of steel, 1 bag per yard of concrete.
Dan

Noquarter: Your suggestion sounds very similar to my original plan, but I have since changed my tune a bit. The 4" of XPS is probably a waste of money, IF you put it everywhere. I have recently learned about a math model for slab on grade heat loss, and am now convinced that even in Fairbanks, AK, 2" of XPS in the "center" is enough (am not exactly sure what "center" means). IMHO, for my degree days (14,200): Use 3-4" around the outside of the foundation wall (including covering the edge of the slab) and at least 2" thick horizontally for two to four feet at the footer. Also use 3-4" under the slab for the first 4' (from the outside edge). Models for SOG heat loss consider only perimeter measurements, NOT sqr footage of slab. Depending on your heating degree days, maybe even 2" everywhere is enough. Dunno, but that perimeter is THE spot to grossly overkill w/ XPS if you are going to. That is my "freshly learned" two cents.

Half pound foam is pretty flexible, and is a perfect air-barrier, if not a great vapor retarder (but at 5" thick, it's a class-III vapor retarder at ~10 perms.)  But the steel panel is a vapor barrier(!)  With half-pound foamed over the steel's seams it's "as-good-as..."   If a class-II or better vapor retarder is needed it can be spray-painted with vapor retardent latex, but in MD's climate, it's probably not necessary, and may be counterproductive.  If flexed to the point where it actually cracks it means your  steel has already been permanently deformed.

Whether you need 2lb foam as structural reinforcement for hurricane-type wind loading is another issue- it adds considerable rigidity and structural integrity to the building.  Whereas half-pound foam can be though of as glue & sealant, 2 lb foam on steel can be thought of as a structural panel.  If that's a factor/requirement in your project, go with it.  But you might price out going with 1-1.5" on the walls for rigidity and  3" on the roof  (for ~R20), adding 2-3" of cellulose between the foam and the interior wall covering to bring the R value to at least R15.

BTW: You're probably required by code to put a thermal barrier (not fire retarder) between the rest of the space and the roof.  The issue with spray foams is less about flame spread than it its about voluminous toxic smoke when heated, and fire retarders won't stop it from smoking.  Exceptions to the thermal barrier rules are generally only made for attics & crawl spaces, and then only when there's no air-communication between those areas and the rest of the interior of the building, (no open plumbing wiring chases, no ignition sources, etc.) and still may require a lower spec. thermal-barrier covering.  Many foams already have flame-retardent mixed in to address flame spread issues, but they all still smoke when heated.  An open sprayed ceiling with sprayed on fire retardent probably doesn't meet the exceptions.  Still, check local code (most installers know where the local exceptions may differ)  See:

http://www.sprayfoam.org/index.php?page_id=241

scroll down to "Thermal Barriers and Ignition Barriers Unconfused"

jklingel...thanks for the input. I have looked at the studies saying insulation is most required at the perimeters, unfortunately the building code here requires R12 under the entire slab. I agree 4" is not worth it for the entire slab. I may consider 4" (or greater)tickness 2' from the building edge and the rest 3". (My top of slab is 27" above grade that is why I am going for the extra thickness.).

sorry for going off-topic a bit but arcamm may find this dialogue useful...

Any info is helpful and appreciated. My project is work space and not living space so the code issues are not as critical. If money were no object, I would go better on the insulation. But we just want to build a low cost space (less than $50/sqft) that can be warmed and will not cost a fortune to to warm it. The no-tubing zone (3' from the walls) is for equipment/cabinit placement, areas where we will drill the floor for anchoring.

Is there any recomendations for somebody or a web site that could help me with the tubing layout? Nothing that is high cost, just some coaching to make sure I'm on the right track.

We provide a free lay out with purchase of pipe. If you need a full blown heat loss we charge. That said most applications like your shop with a 2 inch rigid foam and a 4 inch slab will be fairly standard. We generally will design running the entire slab with pipe, even under cabinets, pipe is the least of the cost, we are looking for heat mass. If there is to be equipment located, columns, interior walls it is best to provide a area of avoidance by at least 6 inches horizontally for wall, 18 inches diameter for post and point loads. Typically these type of loads will have a footing pathing directly through to solid base (no insulation).
As I understand there is a point of diminishing return on R value, not to say more is not better but the most effective values are in the initial portions of insulation applied. Meaning the 2 inch rigid foam is a great choice, R value 11, anything more becomes expensive for gained insulation value.
A concept though I have never done the math would be to place a concrete barrier foil (smoke & miror's I know but it has its place as a product) under the 2 inch rigid dow board, in that aplication the radiaton value would have effective operation "airspace" and is a cost effective product.
Have a look at this site, the curtian wall on the left side of the building suports 30 solar colectors in 3 X10 groups, Heating 8,000 sq ft boiler back up Nova Scotia, $1,000.00 anual fuel bill, Glycol system, turns of in summer no drain down, same glycol since comissioning in 2002,
http://www.thermo-dynamics.com/
Dan

How exactly would "concrete barrier foil" have an "airspace" by putting it under the rest of the insulation? Are you suddenly levitating the whole building up a few inches because of the foil?

Concrete "barrier foil" has NO place as insulation, this has been proven over, and over, and over again in study after study, and making any claim to the contrary is, at best, extremely misleading.

Reflective barriers have a place. That place is definitely not under concrete. Please never let those words cross your fingers into a keyboard again!

Rob you are so correct. FOIL and Reflective has NO place underground however THE BARRIER is a recycled EPS foam rolled Not a reflective, Not a foil. The Barrier X5 is 1 1/4 inches of highly compressed EPS FOAM with heavy duty poly laminated, it has patented self seaming taped edges.


AGree Reflective Barriers have a place. Not under concrete. that is why the BARRIER is the under concrete insulation!

I'll 2nd (or 3rd) that.

Reflective foils are useful when used in conjunction with fiberglass,  (which is translucent to infra-red), not with XPS (which is opaque to infra-red), and not at all when in contact with the underside of the concrete (since in full contact the heat transfer becomes 100% conducted, 0% radiated, 0% convected.)

So, if you're suspending the slab so's you can insulate with fiberglass batting, go for it! :-)   Otherwise, stick with the tried & true XPS.

so does that mean a radiant barrier is needed with fiberglass???

recent topics convinced me that in a staple up system with aluminum plates require no radiant barrier just insulation with r value?

should use a radiant barrier with fiberglass-- some concerns are mold growth.

who boy,
I knew I'd solicit some response there with this concept, and after all we are working with moving targets across the country. Remember I did say of foil first (smoke & mirror's I know but it has its place as a product)
First Rob, air space I realize this is a push but Dow board has an air component to it, the resistance is derived by encapsulating air in there chemical process, When you look at Thermax you see a similar process to what I am leaning towards in concept. The foil is attached to both sides of a air infused substance. Foil then provides reflective value, Concrete barrierfoil is designed for earth contact so logic would follow that as a foim additive membrane it will enhance a 2 inch rigid foam. How much ?????? I do not know, remember concept first.
The Barrier has the same problem as bubble foil bubble though not as extreme, they rely on K value, however a 3/8 inch of poly styrene is not much more resistance for conductive heat transfer than Bubble foil bubble, I agree it is better but by what?
I am 100% supporter behind 2 inch rigid as proper, What I am addressing is enhancement of the vapor barrier and what value is gained $ for $. here is a link to the barrier PDF
http://www.blueridgecompany.com/documents/rFOIL_CBF_TDS.pdf
dismiss the R-3.8 claim, think purely on what is knownTEMPERATURE RANGE* ASTM C411 -50°F to 180°F
FIRE RATING ASTM E84 CLASS 2 / CLASS B
EMISSIVITY ASTM C1371 43%
REFLECTIVITY ASTM E 903 57%
THERMAL RESISTANCE ASTM C236
(MODIFIED) R-3.8
WATER VAPOR PERM. ASTM E96 <0.01 Perms
PUNCTURE RESISTANCE ASTM D751 85 psi
COMPRESSIVE STRENGTH -- 140 psi
DEFLECTION ASTM 1621 <10% under 0.5 psi
LINEAR SHRINKAGE ASTM D1204 None
FLEXIBILITY CAN/CGSB – 51.33 - M89 No Cracking
RESISTANCE TO
FUNGI/BACTERIA ASTM C1338 No Growth
METHANE & RADON
PERMEABILITY -- Impermeable
I have to get back to work but(cautiously) look forward to the response on this thought.
Dan

I'll make this simple. If the foil touches something that is not clear or invisible to radiant energy... like foam, concrete, or most materials on the planet... it is absolutely useless as insulation. It requires an actual air space. Not air trapped in an opaque rigid foam board. That's like saying there is air over the concrete, or even in the concrete and therefor putting a mirror under the concrete should let you see your face on the floor. In short, it's ridiculous.

The barrier has no such problem because it does NOT rely on reflectivity. Their misleading marketing practices aside regarding K-value (which are exactly as bad as the reflective guys), they are in fact actually rigid foam. 3/8" of polystyrene is approximately two and a half times the apparent R value of foil-bubble products, IF you count the dirt, concrete, and crushed stone in the foil-bubble products R-value. If you add those items into the barrier's R value too, it would beat it by even more.

the larger Barrier thicknesses are commensurately better of course. They don't yet have a 2" thick variety but the 1-1/4" might be feasible for some and would be so far in excess of any foil-bubble product you wouldn't even put them in the same league.

What can you gain, having confirmed that bubble foil "insulation" can't reflect "heat" when placed under (and in direct contact with) the slab? It was not designed nor specified for sub-slab systems.

As for blankets of any kind; what is the long term aged 'R' value and compressive resistance for these marginal products?

XPS, boring perhaps, but a real confirmed value.



http://www.xpsa.com/comm/belowgrade/index.html

"Needed", not exactly.  It will improve the performance of the fiberglass by an effective R5-R6 or so (best case.)  But it can be labor intensive to install perfectly, and it's usually cheaper/easier overall to just add effective-R by using thicker &/or denser fiberglass ("cathedral ceiling" batts).

The standard-density R19 batts in most common use in staple-ups only perform to about R12-R13 due to radiant losses, but that's usually "good enough".  The total losses vary quite a bit depending on the water temp used.   Lower water temp==lower delta-T across the insulation==lower heat loss.   A 180F water staple-up over an unheated 40F uninsulated crawl space needs considerably more insulating value (and will derive more benefit from a radiant barrier) than 110F water above a heated/conditioned 68F room.  When in doubt, go with thicker/denser batts.  If there isn't sufficient space for thicker batts, adding a radiant barrier still does SOME good- even on the cold side of the batting!

When using radiant barrier on the cold side of batting, be sure that it's a vapor-permeable type.  Vapor permeable aluminized polyester with micro-holes is available from several vendors.  Aluminized bubble-pack may give you another R1-R2 over the aluminized polyester, but runs the potential of creating a moisture trap if installed on the cold side.  But if it's inside of conditioned space I wouldn't worry too much about it unless you live in a humid climate with high summertime relative humidity and don't air-condtion the place.

But under slabs? Forget about it!

OK, I stepped in it here,
First I am on the phone to TVM in the AM to confirm the ASTM code they used for there certification, then we have 2 products with the same ASTM lab, Both Barrier and TVM rely on ASTM. Can we trust ASTM, are they bias?
I will report what I find.

As I said earlier, I am a firm believer in 2 inch rigid Dow foam,Blue, pink grey, your choice, this over 6 mill plastic, staple the pipe down, rebar, wire or fiber mesh in a 4 inch slab and your doing it right. I have done this many times.

Barrier, yes better than TVM, 2 x cost also. The 1 1/4 cost prohibitive? use Dow board at least you can use staples.

TVM alone, well better than nothing, how much? I do not know. I agree if the slab could be levitated well I suspect it would work better, a lot... not likely.
Using TVM bubble foil bubble as an alternate to 6 mill plastic under 2 inch rigid, that was in essence the question i posed, mind you I did not provide the answer, Just the question.

In my personal home where the radiant as 1 1/2 light weight on platform I have crawl space 18 inches over dirt I have 2x10 joist, stuffed with insulation. I blanketed from the underside 4 foot foil bubble foil. I suppose it adds to the overall performance of the building, I know when I work under the house I do not have a head full of fiberglass insulation, spiders and mice. Sooo... my point, these products are relatively inexpensive and have a lot of applications,
It just might add to the ability to enhance the 2 inch rigid foam........ A foam enhancement product.
But, I have no science. I might sugest we create a test, perhaps using an electric coil as heat source and several modles.
Dan