Underslab Insulation Thoughts

Ron Schroeder

And guess what once you have trapped those air inside those bubbles they are protucted from air currents and they become the insulator the bubble wrap is the air movement protecor, why is air such a good insulator because its made up of oxygen and nitrogin that do not conduct heat but let it pass, also why forced hot air is not a good carrying medium.

Boston

Underslab Insulation

Any thoughts or comments on:

1" Rigid Board
- or -
Foil faced bubble

garage slab, boston area. Will do perimeter with the 1" rigid.

My buddy is telling me the bubble wrap is fine, but he did not use any underslab insulation in his own home.....

I would value your collective thoughts.

P>S. We installed about 1200' of climate panel in 4 man-days. You get pretty productive mid-way through the first day. Screwing it down with my autofeed gun was the slowest part once we really got the hang of it.

[Deleted User]

Thicker is better...

If you don't have dead air, you don't have resistance.

ME

Constantin

Do yourself a favor...

... bubble-wrap has it's applications, but I would not use it in our climate, as it's R-value is about 1. XPS is much better at R5/inch. I would consider insulating more around the edges, as the BOS climate is quite cold and the common clay around here is quite good at conducting heat.

PM_2

Sources

Where'd you get the graph? I get this question all the time and every time I get grief because the bubble wrap is cheaper.

Unknown

There is no comparison. Foil or tarp products under slabs in the northeast are a waste of money 90% of the time. In very few circustances when a thermal break is all you need, then it might be ok. But that is not the norm and is definitely not the norm in residential construction.

John Ruhnke

More detail please.........

Mark,

Could I have a little more detail. How thick is the xps? Is the xps Foam board? What is the difference between BFB and EPS/BFB? What is barrier or fanfold?

Thanks for the report.

JR

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Bob Forand

NRT.Rob would

you elaborate. What is the best to use in the northeast ? Where does insultarp fit into the equation ? Unfortunately this is one area I am weak in and could use pointers to understand. I do not know what all of the abrieviations are, thermal break ? Any help would be appreciated.

[Deleted User]

More details....

are forthcoming in near future articles at Contractormag.com (July, August and September)

For my friends at the wall who weren't aware, I took the initiative to compare these samples in a real world application. Was it a scientific "test"? Heck no, just a side by side "sample comparison" done with relatively accurate temperature sensing (HOBO's) devices.

#1 is TVM bubble foil bubble (approx.3/8" thick)
#2 is is TVM's bubble foil bubble bonded to 3/4" styrofoam.
#3 is Dow Pink Board 1" thick
#4 is Insul-Tarp (approximately 3/4" thick)
#5 is The Barrier (approx. 3/8" thick)
#6 is 1/2" EPS with clear plastic on one side and reflective foil on the other side.

The graph is the results of the average temperature differential between the bottom of the slab versus the top of the slab with the insulation being between during a 36 hour period of cold weather and snow.

Enough detail?

ME

Mike C_3

I have heard

that the concrete eats away at the BFB thus eliminating it's effectiveness. is this true.

And if I am reading that graph right it's saying the best insulation is actually the BFB.?

Tony_23

Wrong

BFB is the worst in the graph. The graph shows delta T from one side to the other. Higher deltaT, better insulation value.

BFB has an R-value less than 2.

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John Ruhnke

Thanks...

Mark,

Thanks a lot

very useful

JR

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Unknown

Generally up here you have either wet ground, a lot of rock, or bulletproof clay.

These are relatively high conductivity soil conditions and result in significant downward losses. As such, real insulation is needed. The only "real insulation" is rigid foam of significant thickness; 2" or so. though 1" is still more than twice as good as any tarp or roll-out product for underslabs today.

In dry, loose soil, the outer 5' perimeter of the slab and the vertical edges of the slab are the most important to insulate properly as that is where most of the loss is, and 2" of rigid foam should always be used there.

As for the center, if it's a large slab the center may be less important in the dry loose soil condition. You'll still have some downward loss, and you are adding a heck of a lot of mass to the system if you don't insulate, which complicates system control. In that case, you may be ok with low-level insulation (a thermal break) simply to decouple the slab mass from the ground mass.

I generally only see this with commercial slabs on very good sites. 90% of the time up here in the NE, full 2" of rigid foam is of great benefit under slabs.

Constantin

I agree...

... I used 2" of XPS below the slab and outside the foundation walls, and I am very happy with the results.

Brian, thicker perimeter insulation, and insulating the foundation walls from the outside in is also something to consider. See Building Science Corp. for the reasons why.

ScottMP

and yet

Me's graph shows the Insultarp as tie for second ?
If I remember this was taking from a snowmelt job. I am not questioning that 2" is the best for the job but I think the jury is still on how bad insultarp is.

Scott

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Scott Gregg

What a great thread!

My thoughts on this are more rational and might or might not be correct. First ME, thank you so much for performing this study! It makes some really great points in a part of the trade that is lacking in data and knowledge.

This is how I am looking at it starting with a few basic premises: You need the thermal brake. Something is ALWAYS better than nothing. There is ratio somewhere where the material cost/benefits/labor to install costs all meet to make one product or another the right choice for a project.

These are some of my random thoughts on heat transfer. R-Value is really more accurate in determining the heat transfer through surfaces including the infiltration of air. Moisture infiltration would play a major role in the conditioning needs of a space. If R-values are so great, why don’t we have fiberglass coffee cups? Glass/ceramic coffee mugs are not as good insulators as thinner foam coffee cups.

Here are some random thoughts on insulation: Air is not a very great insulator and all the bubble wrap stuff is essentially just trapped air. Of the foam products, the rigid board is subject to breaking. There is a compromised insulation value at the breaks, and certainly no moisture barrier at the seams or break points. EPS foam products that are flexible in nature and that form a waterproof barrier and an airtight seal theoretically would offer a better mousetrap. Air filters are made of…fiberglass. Put beer in a foam-insulated cooler full of ice and sit it in the sun on Friday. It will still have ice in it Monday morning in many cases. Coolers with the flip over tops (Playmate style) that do not have insulated lids and allow more air infiltration do not work as well as coolers with a tight fitting insulated top. Notice nobody makes a cooler that uses bubble wrap, or air chambers. They all use foam, and they all work pretty well. The tighter the cooler, the better they work.

Homer Simpson was right! “Beer. The cause and solution to all of life’s problems.”

On a job blue board foam can be a nightmare to use. It’s slow to install compared to other products and if it is windy forget it. You still need a vapor barrier below it and it tends to break up in spots. The foam products that have lower perm rates (Better moisture barrier) also offer some radon shielding benefits and can be used without the need for the poly moisture barrier since they off a better barrier anyway. This saves labor, money and time also.

If I can install a product that is almost 100% moisture proof, comes in rolls, goes down in less than 1/3 the time and still gives adequate insulation, that narrows it down to 2 products for me. The only thing left to look at is cost and ease of installation between those products.

Personally I think The Barrier has a better Perm rate since its virtually water proof and it’s the easiest and fastest to install. As for the insulating properties, it is certainly good enough and the cost is about the same as 2” Blue board without all the headaches that come with blue board.

Guys I’m all ears. Mark, thanks again for the study and I’ll be looking forward to reading it!

Mike Kraft_2

slab insulating

ME,

Nothing on slab sheild? Low -E company.IMO 2" extruded poly styrene for thermal break has its place in a slab,but conditions need to warrant application.Such as water table and ledge.In a "typical"resy install with frost wall /edge protection a R3 can suffice.

Been awhile so enlighten me master cylinder

cheese

hook me up with a link to your articles ME

Ron Schroeder

Air is not a very great insulator and all the bubble wrap stuff

I hate to disagre but air is a great insulator the trick is to stop air movement and that is just what insulation does is stop air movement of trapped air in most cases.

ScottMP

CHEESE ....

How ya been Man ??

Badger, Badger, Badger


Scott

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Tony_23

air movement

under a slab ???

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Tony_23

Hi Mike

I agree. I pretty much go with R-5. Seen too many slabs incapable of keeping up w/o the flywheel of some warm earth when applicable.

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Ron Schroeder

Tony

if there is no air movement under the slab then all the more reason all insulation woulds work better however I suspect that fiberglass batt insulation would loose it air hold ability once the slab was poured last statement said with tongue firmly planted in cheek

Tony_23

Ha Ha

BB has TWO air bubbles. Blueboard has HUNDREDS. It's not the air movement you're stopping, it's the insulative air you've trapped and placed there to slow heat.

BTW, fiberglass doesn't stop air movement, even at full loft in a wall or ceiling.

I don't think I could stand it if I saw someone use FG under a slab

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Constantin

Hmmm...

Insulation is supposed to stop heat transfer, something that typically happens in three modes: radiative, convective, and conductive.

What XPS and other insulations of that type do, is minimize convective losses by having very, very small bubbles in them. Radiative losses are usually a non-issue below slabs, the primary mode of loss there, I would suspect, is conductive in the case of XPS and like insulations. Here, XPS works so well because the bazillions of thin walls (i.e. it is not a solid hunk of plastic resin) lengthen the path that heat has to take (while being a very bad conductor due to material and thinness), further increasing the insulative value.

Foil-faced bubble-wrap fails the under-slab test in many respects, as was borne out by a Canadian home lending study. Slabs with bubble-wrap resulted in higher bills and all the other headaches that a non-insulated hydronic system are known for.

That there was not a great ΔT in Mark's testing between various brands of insulation may also have to do with local soil conditions. The need for insulation in well-drained, sandy conditions is usually lower than in wet, clay-like conditions. The latter conducts heat very well due to the high water content and the "solid" nature of clay, whereas well-drained sand will have thousands of small air-pockets.

I will have to read his report (congrats Mark!) to see what conditions he was dealing with.

Unknown

Are you keeping the slab at 50 degrees? Or, whatever your local ground temp is?

If not, this is not "warm earth" and it's not contributing to your space, it's drawing heat out of the slab. Heat goes from hot to cold, always. It may be a lower temperature differential than the space to the air, but it's still colder than your slab and therefor is NOT contributing to your heating.

Insulation resists this heat transfer from hot to cold. R-5 may be "enough", but R-10 will always be better. Twice as good, in fact, halving your losses. I've done my share of R-5 when needed, in basements or the centers of large slabs, but perimeters and edges should not receive lesser insulation at the very least.

Unknown

Scott, blueboard can break, sure. However, you're throwing a whole lot of stuff out here that is basically irrelevant.

We are talking about insulation. If you need a vapor barrier, then install a vapor barrier. If you want ease of install, I understand. But the first and foremost concern is not how good of a vapor barrier your insulation is, or how easy it is to install the insulation, but HOW GOOD OF AN INSULATOR IS IT? That's why we call it... INSULATION.

If you have cracks, those are small areas of imperfection compared to the vast majority of the slab that is consistently covered in R-value. If 1/100th of your slab is not insulated due to cracks, then you have reduced your effective overall insulation by a similarly very, very small amount. In short, broken rigid foam is a non-issue, just like a couple of holes in a vapor barrier is a non-issue; total coverage area is still huge compared to the imperfections and the imperfections only reduce performance relative to the total surface area of the imperfections.

CERTAINLY a few cracks does not reduce an R10 slab insulation to the R1.65 of "the barrier".

1.65 is certainly better than nothing. However, it is not GOOD insulation. If you are in a site that really only needs a thermal break, so be it. Most jobs could use more. I know you installers want this easy install option to be a good answer, but seriously, it's not in most cases, no matter how attractive its other properties seem.

Full-thickness Rigid foam does what it is supposed to do; insulate, and it does it far better. Deal with the other issues seperately if you have to.

Constantin

Hear Hear!

Tu-Tuff is a great vapor barrier, I'm not convinced that Insultarp or the other bubble-wraps come close in terms of toughness, puncture resistance, etc.

Tony_23

Bruce

I think you missed my point. Blueboard has HUNDREDS of air bubbles, you just can't see them. Double bubble has TWO. As far as stopping the air movement under a slab, WHAT AIR MOVEMENT ?????

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Tony_23

you read too much

into what I wrote. I meant center slab at R-5, not edges. And if the earth under my center is warmer than the air in the space, it takes less heat than the air in the space. Insulation works on DeltaT also, right ?

ie. Garage kept at 60F with a 75F slab. If the earth under that slab gets to 60, just in the top foot, and the load of the building goes up because of extreme temps outside, dropping the room temp to 58, which way will the heat flow fastest ? Will R-5 be better than R-10 at that point ? The slab temp also dropped 2F because it's already maxed.



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Unknown

In the case you just put forward, a two degree reduction in a 15 degree delta T (75 slab to 60 earth, then 73 slab to 60 earth) would reduce your downward transfer by 2/15ths, or 13.3%. R10 insulation would have cut it in half over an R5, and would have kept it cut in half the other 99.9999% of the time you are running the slab as well. If you assume the ground is kept cooler with better insulation, you're still ahead of the game.

Until the SLAB ITSELF is at or below earth temperature, you are simply losing heat downward faster than you need to. And if your slab is at or below earth temperature, maybe it shouldn't be heated or insulated at all; just tighten up the envelope and let the earth maintain it directly.

I'd say if you're worried the slab might not keep up, more insulation is helpful, not less.

Tony_23

The case I looked at

The slab could not keep up, always. The outdoor temp was 5-20 below ODT for three straight days and the slab was under-tubed but had R-10. I have to believe that a warmer earth under it would've helped some, at least during the day. If the btu loss is higher into the space than below the slab, then it stands to reason that warmer underslab temps will give some flywheel effect. BTW, the slab lost much more than 2deg, as did the garage. 140F water to the slab continuously. I know, the problem was lack of tube, but a little flywheel would've buffered it.

Off to dinner now.

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Unknown

Tony, warmer earth would have helped. But if they had cut their downward insulation in half to get the earth warmer.. well, how helpful is that? Unless the half cut in insulation yielded half the delta-T they would have otherwise, you're losing ground (erm, no pun intended).

You're also ignoring the cost of that flywheel during regular operation.

Pipe the slab properly and insulate it

Ron Schroeder

Tony

see Scotts post above my first one, the first sentence in mine was his comment in his fourth paragraph that I was respondint to, I think you and I are aruging the same point maybe different angle

Scott Gregg

I guess one of my points

was that foam is a better insulator than fiberglass or Double bubble. Let's see. What is it again that most air filters are made out of?

Seems to me that just a body of air is a poor insulator. Air changes temperature very easily. Look how poor a job it does in conveying BTU's. Why is that? Because it gives them up so freely. You have to stop the movement/transfer of air which foam does. Stop moisture transfer/infiltration and you get another benefit.

Ron Schroeder

Scott

""Most insulation materials work by trapping pockets of air, which is an excellent insulator. Fiberglass does this by creating air pockets between spun glass fibers, and foam insulation contains air bubbles. Similarly, double pane windows work by trapping air between the panes.""
http://tva.apogee.net/res/reinrva.asp

The better insulator just do a better job of keeping air from moving through the insulation, I don't know the answer but what would 2inches of double bubble be compaired to 2 inches of foam That is where the rubber meets the road, I would not expect one layer of bubble to come near 2 inches of foam but inch to inch would be more telling

Tony_23

Yes

I believe you're right

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Tony_23

Improper piping

That's usually the problem I see on underperforming systems. This particular one had 1/2" PEX on 12" c-c, 8" concrete, R-10 under slab and edges. Garage got to 42F
Poor guy couldn't shovel coal fast enough. I'm guessing the guy who designed the floor and walked away got a nice phone call

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Unknown

You could max out floor output with a system like that (though that's a huge flywheel there) with little trouble. That sounds like a bad construction job on the garage, not a bad radiant install (though he does have a large flywheel there with 8" concrete..)?

Glen

the canuck point of view.

more is better - but cost analysis need to be done too.

here's a bit of info -

Unknown

standards

ME,

I like your tests that do show us true results. My fear is we again are looking at "acts like" results.
I just can not stand the claims of the foil and bubble and foam people any more. The "acts like R-12" that they publish/advertise is rubbish.

What we need are national standards and to have standard tests to give us a true set of standard published results. There are currently no less then 6 bubble foil bubble manufactures on the market that call on me every 4-8 weeks. Of these I only know of one that has true ASHREA published R-values.

Why is it that we, the radiant industry, finally are having to have the "show down at OK coral?" Why are the insulation manufactures like Insultarp, Low-E, etc not making and testing to standards. Why are the manufactures not paying for their own R&D? My fear is because they are all “smoke and mirrors” and would be better suited being wrapped around a beer bottle then they are for under a radiant floor.

Now, lets add to that the fact that all of these insulation manufactures make your worst wholesaler look like a Greek God. I love the fact that as a wholesaler I can make a 40K investment in their product, make sales calls, handle the material, inventory the wrap and have it ready for pick up or deliver it to the job site.... and then the manufacture sells my contractor at a price LESS THEN MY STOCKING PRICE and ships to the contractor full freight allowed. This antic alone has made me VERY SOUR to the entire bubble/foam insulation industry.

As a system designer and supplier this is all very frustrating. I am very close to saying that all bubble wrap is created equal.... that they are all just useless crap. Bubble, foil, foam, tarp, whatever. Add to this all of the stories I get about cracked slabs due to improper insulation, bug & termite infestation, how a house collapsed because of the underslab insulation rotting out..... phew.

OK, I'm done ranting. Thanks ME for all your work. Maybe this will wake a few people up to start making STANDARDS... but I doubt it.

wheels

Martin Lunde, PE

below slab insulation

Critical properties that are required for below slab insulation include:

Long term resistance to moisture and soil chemistry
Long term adequate structural bearing capacity without excessive settling (questionable with either bubble pack or tarps)
Long term, non degrading R value (questionable with bubble pack and some urethanes)
Ease of radiant tubing installation
Radiant barriers are only effective if an adequate air space is provided in front of the radiant barrier (not available under slab)

For all of the above reasons I only allow 2" blue board (or its equivalent) on our projects - proven long term results without problems. In my opinion, the other options are very questionable as to their long term performance.