Posted By gioberg11 on 29 Apr 2010 07:52 AM

Hello everyone!

I am building a 15000+ sq ft house and we are using closed cell foam in the unvented attic space.   I am trying to find information on how thick the closed cell foam should be for Northeast Ohio. 

If anyone has any good links or information I would appreciate it. 

Thank you,

Brian

which town?

Medina

Closed cell foam is a lot less forgiving than open cell relative to locating roof leaks and inward-drying capacity (particularly at thicknesses of more than 2"), but with open cell you'd need an interior-side vapor retarder (retardent latex would be fine.) 

If you're combining it with sprayed fiberglass as more-insulation & thermal-barrier against ignition you can probably get away with as little as 2"making is only semi-impermeable to water vapor, which would give the roof deck reasonable drying capacity while still making it air-tight.  That would be only be ~R13 of foam though, and code-minimum is R38, which means you'd need at least ~7" of sprayed fiberglass or spray cellulose to make it work. Otherwise you're looking at a very expensive 7" minimum to make code going closed cell foam.  If you go more than code minimum on the fiber, it's best to go with proportionally more foam as well to avoid the need for interior-side vapor retarders, maximizing drying capacity at the roof deck & rafters.

If 7"+ of close cell foam is in the budget, go for it- it works from a roof-deck humidity point of view except during leak situations. Read this. (Figure your climate in Medina is most-similar to the Chicago simulations.)

Code-minimum is nothing to brag about, and with lower-cost insulations more than code-minimum may well be NPV+ in reasonable time frames, depending on what you expect to happen with heating-fuel/utility costs over the next decade or two. But anything over R60 is probably overkill, and not cost-effective if using closed-cell foam only (~10" worth!)  If done in open cell foam you could get to code minimum with there with 11", and with another 5-6" of blown fiberglass for igintion barrier you'd be at ~R60.  (IIRC you need at least 3" of properly rated blown fg to have be a code-compliant ignition barrier, but look it up to make sure, my memory isn't 100% on this one.)

Alternatively, a combination of panelized R20-R40 iso foam board with pre-laminated nailer decking on the exterior of the structural roof deck + interior sprayed cellulose or fiberglass + judcious air-sealing with foam can beat an interior side cc foam performance-wise, since it adds a thermal break over the rafters.  There are several vendors of these systems (Hunter, Atlas, et al), and come in vented or unvented nailer deck flavors.  In $/R terms it's ~2/3-3/4 the cost of spray cc foam for the material, but labor cost for installation would have to be factored in.  But it's competitive-  if the roof lines are relatively clean it's usually a better bang/buck.  If it's all dormered out with multiple &/or compound valleys etc it's not a slam-dunk.

 A 15000' house is quite the weekend-getaway shack- may I ask how many peops will be living/working there?

I build hurricane resistant houses in Florida and I use 3" of closed cell foam on the underside of the roof trusses.. Any more than this and the increased insulation value does not increase as fast as the cost. It rapidly becomes a deminishing return.
It is true that the closed cell will not let water penetrate through it. Some people think this is a terrible disadvantage. They claim that a hole in the roof will let water through and trap it in the plywood decking and the decking will rot. My experience with leaky roofs tells me that it is just as expensive to repair a 12" hole as it to repair a 1" hole. So the benefits greatly outweigh the disadvantages. The close cell foam acts as a glue that keeps the plywood "glued" to the trusses. Closed cell costs a little more than open cell but it does not have adhesive value. If
you are building a 15,000 sq ft house you won't care about the difference in cost.
Regards
Joe

Personally I prefer 9 -10" of opencell in my roof with a barrier to allow the deck to breathe. My home was completed one year ago and this very bad northeast winter kept piles of snow on my roof for the duration, I guess that means my home is well insulated. Houses always need to breathe through ridge vents and air must circulate or a sick house syndrome will develop. The only good use I've found for closed cell is basement walls. Why would anyone introduce deadly fiberglass when they are already using green materials, sort of defeats the intent.

I know your question is about foam but you will also need mechanical ventilation as that will be a tight house. make sure your mechanical contractor understands foam homes.

4" of closed cell is all that is beneficial. More of any type of insulation will not provide any additional benefits.

R values are theoretical numbers and R 39 cannot be actually achieved. Each inch of closed cell stops 85% of heat loss, so if you do the math, anything above 4" is wasted money.

There needs to be a major revamping of the coding system regarding Rvalues in order to address wind wash issues.

I love closed Cell!

My suggestion is to stay away from foam, you'll never find another leak if it happens, or any mold and mildew.
If you are looking to reduce the heat in your attic you are better of spraying a radiant barrier, it will cool your attic by 50 degrees and will cost you only 10 cents a sq ft to apply your self, and expect to pay about  50 cents a sq ft for some one else to apply this.
Take a look at www re-flectrc.com.
Hope you'll find this usefull.

Paul Bogaars.

Posted By extreme on 03 May 2010 10:15 AM
My suggestion is to stay away from foam, you'll never find another leak if it happens, or any mold and mildew.
If you are looking to reduce the heat in your attic you are better of spraying a radiant barrier, it will cool your attic by 50 degrees and will cost you only 10 cents a sq ft to apply your self, and expect to pay about  50 cents a sq ft for some one else to apply this.
Take a look at www re-flectrc.com.
Hope you'll find this usefull.

Paul Bogaars.

If you read the technical data provided in your link, you will see that this radiant barrier coating is not designed to work in an unvented attic scenario if there is not an air space on one side.

There is absolutley nothing wrong with spray foam sprayed to the deck, but I would certainly suggest water testing the roof first, and plan on regular maintenance checks.

Posted By AaronB. on 01 May 2010 01:23 PM
4" of closed cell is all that is beneficial. More of any type of insulation will not provide any additional benefits.

R values are theoretical numbers and R 39 cannot be actually achieved. Each inch of closed cell stops 85% of heat loss, so if you do the math, anything above 4" is wasted money.

There needs to be a major revamping of the coding system regarding Rvalues in order to address wind wash issues.

The commonly held self-delusions of a spray foam installer, sez me.

85%  as compared to what, open air?   A tent?   A tin shack?  Half-inch OSB sheathing?

85% is a meaningless number without a baseline.

Furthermore, each successive inch of foam absolutely does NOT reduce the remaining heat loss by another 85%.  That may about right going from 0" foam on 1/2" OSB + vinyl siding to 1" of foam on the same structure.  But going from 2">>3" (no OSB or siding, just the insulation, for a best-case comparison) would be a further reduction of about ~33%,  and  getting to ~50% reduction in the 2" example would take going from 2">>4" , an additional TWO inches without achieving anything like 85% reduction.  This is verified & documented  in the ASTM C 518 testing of foam samples of differing thicknesess manufacturers use to support their R & K value claims.  (Pull a spec sheet, do the math- you don't need to dust off your 8th grade algebra to discover this.)

Clear-wall R-values higher than R39 can and are being built every day, and are verifiable.  (PassiveHouse Institute existence proofs simply wouldn't work in cold climates with 4" or even 6" of cc foam alone, yet somehow they seem to get there with R50-R60 combinations of foam & fiber.)

Any closed cell over 4" of may not be justifiable in a 10 or 15 year net-present-value analysis based on current utility & fuel pricing- it's a premium product at a premium price. (Going more than 4" in foam alone may WELL be money wasted.)  But making the economic rationale for R50 in northeast OH is possible going with lower cost materials than closed cell foam for the bulk of the R. 

WUFI modeling of cathedralized roofs performed by Building Science Corporation suggests 2" of foam may be adequate for keeping the roof deck dry if you're only going for code-minimum, using spray fiberglass or cellulose for most of the R.  Going for much higher R will require thicker foam to avoid wintertime condensation within the fiber layers.  After the first inch of cc foam, the wind-washing issues are gone, but the humidity & condensation issues remain, and it's the humidity control and the stackup with other insulating layers that then drives the minimum thickness of the foam.

Is R 50 even truly attainable, or are we throwing money at more material for no payback whatsoever?

"R" Fairy Tale: The Myth of Insulation Values

by David B. South

One of the fairy tales of our time is the "R-value." The "R-value" is touted to the American consumer to the point where it has taken a "chiseled in stone" status. The saddest part of the fairy tale is the R-value by itself is almost a worthless number.

It is impossible to define an insulation with a single number. It is imperative we know more than a single "R" number. So why do we allow the R-value fairy tale to be perpetuated? I don't know. I don't know if anybody knows. It obviously favors fiber insulation. Consider the R-value of an insulation after it has been submersed in water or with a 20 mile per hour wind blowing through it. Obviously the R-value of fiber insulations would go to zero. Under the same conditions, the solid insulations would be largely unaffected. Again R-value numbers are "funny" numbers. They are meaningless unless we know other characteristics.

None of us would ever buy a piece of property if we knew only one dimension. Suppose someone offered a property for $10,000 and told you it was a seven. You would instantly wonder if that meant seven acres, seven square feet, seven miles square, or what. You would want to know where it was -- in a swamp, on a mountain, in downtown Dallas. In other words, one number cannot accurately describe anything. The use of an R-value alone is absolutely ridiculous. Yet we have Code bodies mandating R-values of 20's or 30's or 40's. A fiber insulation having an R-value of 25 placed in a house not properly sealed will allow the wind to blow through it as if there were no insulation. Maybe the R-value is accurate in the tested material in the lab, but it is not even remotely part of the real world. We must start asking for some additional dimensions to our insulation. We need to know its resistance to air penetration, to free water, and to vapor drive. What is the R-value after it is subjected to real world conditions?

The R-value is a fictitious number supposed to indicate a material's ability to resist heat loss. It is derived by taking the "k" value of a product and dividing it into the number one. The "k" value is the actual measurement of heat transferred through a specific material.


Test to Determine the R-Value

The test used to produce the "k" value is an ASTM test. This ASTM test was designed by a committee to give us measurement values that hopefully would be meaningful. A major part of the problem lies in the design of the test. The test favors the fiber insulations -- fiberglass, rock wool, and cellulose fiber. Very little input went into the test for the solid insulations, such as foam glass, cork, expanded polystyrene or urethane foam.

The test does not account for air movement (wind) or any amount of moisture (water vapor). In other words, the test used to create the R-value is a test in non-real-world conditions. For instance, fiberglass is generally assigned an R-value of approximately 3.5. It will only achieve that R-value if tested in an absolute zero wind and zero moisture environment. Zero wind and zero moisture are not real-world. Our houses leak air, all our buildings leak air, and they often leak water. Water vapor from the atmosphere, showers, cooking, breathing, etc. constantly moves back and forth through the walls and ceilings. If an attic is not properly ventilated, the water vapor from inside a house will very quickly semi-saturate the insulation above the ceiling. Even small amounts of moisture will cause a dramatic drop in fiber insulation's R-value -- as much as 50 percent or more.


Vapor Barriers

We are told, with very good reason, that insulation should have a vapor barrier on the warm side. Which is the warm side of the wall of a house? Obviously, it changes from summer to winter -- even from day to night. If it is 20 F below zero outside, the inside of an occupied house is certainly the warm side. During the summer months, when the sun is shining, very obviously the warm side is the outside. Sometimes the novice will try to put vapor barriers on both sides of the insulation. Vapor barriers on both sides of fiber insulation generally prove to be disastrous. It seems the vapor barriers will stop most of the moisture but not all. Small amounts of moisture will move into the fiber insulation between the two vapor barriers and be trapped. It will accumulate as the temperature swings back and forth. This accumulation can become a huge problem. We have re-insulated a number of potato storage's which originally were insulated with fiberglass having a vapor barrier on both sides. Within a year or two the insulation would completely fail to insulate. The moisture would get trapped between the vapor barriers and saturate the fiberglass insulation to the point of holding buckets of water. Fiber insulation needs ventilation on one side; therefore, the vapor barrier should go on the side where it will do the most good.



We understand air penetration through the wall of the house. In some homes when the wind blows, we often can feel it. But what most people, including many engineers, do not realize is that there are very serious convection currents that occur within the fiber insulations. These convection currents rotate vast amounts of air. The air currents are not fast enough to feel or even measure with any but the most sensitive instruments. Nevertheless, the air is constantly carrying heat from the underside of the pile of fibers to the top side, letting it escape. If we seal off the air movement, we generally seal in water vapor. The additional water often will condense (this now becomes a source of water for rotting of the structure). The water, as a vapor or condensation, will seriously decrease the insulation value -- the R-value. The only way to deal with a fiber insulation is to ventilate. But to ventilate means moving air which also decreases the R-value.


Air Penetration

The filter medium for most furnace filters is fiberglass -- the same spun fiberglass used as insulation. Fiberglass is used for an air filter because it has less impedance to the air flow, and it is cheap. In other words, the air flows through it very readily. It is ironic how we wrap our house in a furnace filter that will strain the bugs out of the wind as it blows through the house. There are tremendous air currents that blow through the walls of a typical home. As a demonstration, hold a lit candle near an electrical outlet on an outside wall when the wind is blowing. The average home with all its doors and windows closed has a combination of air leaks equal to the size of an open door. Even if we do a perfect job of installing the fiber insulation in our house and bring the air infiltration very close to zero from one side of the wall to the other, we still do not stop the air from moving through the insulation itself vertically both in the ceiling and the walls.

The best known solid insulation is expanded polystyrene. Other solid insulations include cork, foam glass and polyisocyanate or polyisocyanurate board stock. The latter two being variations of urethane foam. Each of these insulations are ideally suited for many uses. Foam glass has been used for years on hot and cold tanks, especially in places where vapor drive is a problem. Cork is of course a very old standby often used in freezer applications. EPS or expanded polystyrene is seemingly used everywhere from throw away drinking cups and food containers to perimeter foundation insulation, masonry insulations, and more. Urethane board stock is becoming the standard for roof insulation, especially for hot mopped roofs. It is also widely used for exterior sheathing on many of the new houses. The R-value of the urethane board stock is of course better than any of the other solid insulations. All of the solid insulations will perform far better than fiber insulations whenever there is wind or moisture involved.

Most of the solid insulations are placed as sheets or board stock. They suffer from one very common problem. They generally don't fit tight enough to prevent air infiltration. It does not matters how thick these board stocks are if the wind gets behind it. We see this often in masonry construction where board stock is used between a brick and a block wall. Unless the board stock is actually physically glued to the block wall air will infiltrate behind it. In this case as the air flows through the weep holes in the brick and around the insulation it is rendered virtually useless. Great care must be exercised in placing the solid insulations. The brick ties need to be fitted at the joints and then sealed to prevent air flow behind the insulation.

The only commonly used solid insulation that absolutely protects itself from air infiltration is the spray-in-place polyurethane. When it is properly placed between two studs or against the concrete block wall or wherever, the bonding of the spray plus the expansion of the material in place will effect a total seal. This total seal is almost impossible to overestimate. In my opinion most of the heat loss in the walls of the home have to do with the seal rather than the insulation.

For physical reasons, heat does not conduct horizontally nearly as well as it does vertically. Therefore, if there were no insulation in the walls of the homes, but an absolute airtight seal, there would not necessarily be a huge difference in the heat loss. This would not be the case if the insulation was missing from the ceiling. Air infiltration can most effectively be stopped with spray-in-place polyurethane. It is the only material (properly applied) that will fill in the corners, the cripples, the double studs, bottom plates, top plates, etc. The R-value of a material is of no interest or consequence if air can get past it.


Anecdotes

During the 1970s my firm insulated a bunch of new homes in the Snake River Valley of Idaho with 1.25 inches of spray-in-place polyurethane foam in the walls. In 1970 the popular number for the R-value of one inch of urethane foam was 9.09 per inch. Using this value, we were putting an R of 1.25 x 9.09 = 11.36 in the walls. This was much less than the R = 16 claimed by the fiberglass insulators. Today, using the charts from an ASHRAE book, we would only be able to claim an R-value for the 1.25 inches of 7.5 to 9. Neither of these numbers make for a very big R-value. The reality is that the people for whom we insulated their homes invariably would thank us for the savings in their heat bills. They would tell us their heating bill was half of their neighbor's. They felt as if they saved the cost of the polyurethane in one, or at most two, years. This is anecdotal evidence, I know, but anecdotal evidence is also compelling and very real in our world. Most of these customers were savvy people. They would not have paid the extra to get the urethane insulation if it had not been better.

About mid 1975 I received a call from a division manager of one of the major fiberglass insulation manufacturers. The caller asked, "I understand that you are spraying polyurethane in the walls of homes?" I told him that was true. He was calling because we were cutting into the fiberglass insulation sales in our area. He asked, "How can you do it?"

I knew what he meant. He wanted to know how I could look somebody in the eye and sell them a more expensive insulation than the cheap old fiberglass. I told him the way I did it is with a spray gun. Of course, that wasn't the answer he wanted. He wanted to know how I could not feel guilty. I told him of insulating one of two nearly identical houses built side by side. We insulated the walls of one with 1.25 inches of urethane. The other house was insulated with full thick fiberglass batts put in place by a reputable installer. Not only did we use only 1.25 inches of urethane as the total wall insulation, but we had the builder leave off the insulated sheathing. At the end of the first winter, the urethane insulated home had a heating bill half of their neighbor's. I know that is not terribly scientific, but it is very real. I am not sure he was convinced, but it should be noted that same company jumped into the urethane foam supply business the next year.

One and a quarter inch of polyurethane sprayed properly in the wall of a house will prevent more heat loss than all the fiber insulation that can be crammed in the walls -- even up to an eight inch thickness. Not only does it provide better insulation, but it provides significant additional strength to the house.

One of my early clients was Brent. I had insulated several potato storages for Brent. He knew what spray-in-place urethane insulation could do. When he decided to build his new, very large, very fancy new home, he asked me to come insulate it. I told him I would be delighted. The builder pitched a fit. He "didn't need any of that spray-in-place urethane in his buildings. He made his buildings tight, and fiberglass was just as good."

Brent explained to the builder, "I know who is going to insulate the building. It is not as definite as to who is going to be the contractor. You can make up your mind. We are going to have the urethane insulation and you build the building, or we are going to have the urethane insulation, and I will have someone else build the building." It didn't take the contractor long to decide he wanted to use urethane insulation.

It was amazing to me how it worked out. We sprayed a lot of foam in Brent's house, and it cost him quite a bit of money because it was such a large home. Always after when I would meet him, he would tell me his heat bill was less than any of his rent houses or homes of anybody else he knew. And his home was two or three times larger. Also, the builder started having me insulate most of his new custom built houses. He told me he would explain to his clients the best insulation was the spray-in-place urethane. It would cost a little more, but it was by far the best. Most of the owners opted for the urethane. Never have I had a customer tell me that he did not save money by using the urethane spray-in-place insulation. You can spend all the time you want with R-values and "k" factors, and "prove" on paper there is no way the urethane can do the insulation job that the fiberglass will. In the real world, I can assure anyone there is no way fiber insulation can be as effective as spray-in-place urethane -- not even close.

R-value tables are truly part of the "Fairy Tale." They show the solid and the fiber insulations side by side, implying they can be compared. The fact is, without taking installation conditions into account, comparisons are meaningless. Spray-in-place urethane foam provides its own vapor barrier, water barrier, and wind barrier. None of the other insulations are as effective without special care taken at installation. The fiber insulations must be protected from wind, water and water vapor. Again the tables need a second table to state installation conditions.


Consider the following anecdotes:

Meadow Gold Company was going to build a freezer in Idaho Falls, Idaho. Chet, the plant manager was a good friend of the local Butler dealer. The local Butler dealer and I had become good friends. A Butler building does not lend itself very well to a freezer if you are going to insulate the freezer with expanded polystyrene. So the three of us got together and planned a freezer that would accommodate the needs of Meadow Gold yet be built of a Butler building and be properly insulated. This was in my first year of spraying polyurethane foam, and at that time I believed all the literature and knew what we were doing was going to be just right. It turned out even better. The then current R-value table showed one inch of urethane equal to 2.5 inches of expanded polystyrene. So, I suggested we spray the metal building with four inches of urethane to replace the 10 inches of expanded polystyrene normally used by Meadow Gold for freezers.

Meadow Gold Company was going to build a freezer in Idaho Falls, Idaho. Chet, the plant manager was a good friend of the local Butler dealer. The local Butler dealer and I had become good friends. A Butler building does not lend itself very well to a freezer if you are going to insulate the freezer with expanded polystyrene. So the three of us got together and planned a freezer that would accommodate the needs of Meadow Gold yet be built of a Butler building and be properly insulated. This was in my first year of spraying polyurethane foam, and at that time I believed all the literature and knew what we were doing was going to be just right. It turned out even better. The then current R-value table showed one inch of urethane equal to 2.5 inches of expanded polystyrene. So, I suggested we spray the metal building with four inches of urethane to replace the 10 inches of expanded polystyrene normally used by Meadow Gold for freezers.

Chet considered one alternative to his predicament was to turn one of the older freezers that had been used as a cooler back into a freezer. Then maybe he could make a cooler out of the new building with the just the one compressor. It was not a satisfactory arrangement, but it maybe could work. The other thing Chet kept telling us was that he would know as soon as he turned on the freezer equipment whether or not the building would work. When I pressed him, he said that normally it takes five days to bring a freezer down to 10 F below zero -- needed for ice cream. When he turned on the new freezer, with only the one compressor, the temperature dropped to 18F degrees below zero by the second morning. They had their freezer. It ran the entire summer using only the single compressor.

A few weeks after start up of the freezer, I was visited by a Meadow Gold engineer from Chicago. He wanted to know exactly what we had done to insulate the freezer. One compressor should not be able to hold the temperature as it was doing. I explained to him exactly what we had done. He seemed satisfied and he left. A few weeks later he showed up again with his boss. We went to the plant and verified with an ice pick the thickness of the foam. It was indeed four inches in the walls and five inches in the ceiling. Here again they reiterated that the building should not be operating as it was. What they were telling me was that even though I had used one inch of urethane to replace 2.5 inches of expanded polystyrene, the building was still requiring only 50 percent of the normal compressor power for cooling. As you can imagine, the experience made me a lot more bold, and I used the information to sell more freezer insulation jobs.

One of our largest freezer insulation projects was a sixty thousand square foot freezer at Clearfield, Utah. I was able to talk the general contractor into letting us insulate with spray-in-place polyurethane foam the brand-new all-concrete freezer he was building. This building was the 12th in a chain of freezers. My friend Bob, the contractor, had taken it upon himself to make the switch from the ten inches of expanded polystyrene to four inches of urethane with a fifth inch on the roof. The building was built with tilt up concrete insulated on the interior side of the concrete with spray-in-place urethane. We then sprayed on a three-fourths of an inch thick layer of plaster as the thermal barrier. Over the pre-stressed concrete roof panels, we put five inches of spray-in-place urethane and then covered it with hot tar and rock. (This is an old CPR-specification).

I was on the job the last day. As we finished up the owner showed up. He had expected to see ten inches of expanded polystyrene, and here was four inches of urethane. I told him he would like the four inches of urethane as it would be even better than the expanded polystyrene, based on my previous experience. He told me he was sicker than a dog because he felt like there was no way that could be true. It was too late for him to do anything about it. If he could have, he would have changed the contract instantly, but he was stuck and felt stuck.

They had 12 other similar size freezers, except the others were insulated with expanded polystyrene. The normal way of operating them was to use three large compressor assemblies. Two of the compressors would be needed all summer to keep the building cold, and the third one would be a standby unit, in case one of the other two had problems.

About a year later, I received a phone call from one of the managers. He asked me if I had time to insulate another sixty thousand square foot freezer in Clearfield, Utah. I assured him we had the time, the inclination, and the excitement to do it, but I thought the owner wanted nothing to do with urethane foam insulation. The manager explained to me that not only had the Clearfield freezer operated better than any other freezer in their line, it had operated for less than half the costs of any others. They were adding another sixty thousand square feet without adding more compressors. The compressor power available to them because of the urethane insulation efficiency allowed them to do it. The building had run very nicely through the hot part of the summer with just one compressor. Now they would be able to run two buildings off of two compressors and still have a spare.

Again, this is anecdotal evidence, but let me assure you that you will get the same results if you do the same thing as we have. I have insulated too many buildings now to know that this will happen in every case. Never can you use an R-value from a fiber insulation and compare it to the R-value of a foam insulation. Nor can you use the R-value of a foam insulation if it is in sheet form and compare it to the R-value of the foam insulation if it is spray-in-place. Spray-in-place polyurethane is an absolute minimum of three to ten times as effective as any other insulation available today.

During the late 1970s, the FTC went after the urethane foam suppliers for misleading advertising especially with regard to fire claims. A consent decree followed. It destroyed a tremendous amount of confidence in the use of urethane. Up to that point, Commonwealth Edison would give Gold Medallion approval for homes insulated with 1.25 inches of spray-in-place urethane in the side walls of masonry constructed homes. True, that was anecdotal evidence, but also true, it worked. Much work was done in the early 1970s using a 1.25 inches urethane as a replacement for wall insulation in a home. Not only did it replace the wall insulation, it also replaced the exterior sheathing. The buildings are stronger and better insulated when sprayed with the 1.25 inches of urethane.

Understanding the two purposes of insulation gives a standard to measure the insulations:

I. Heat loss

There is a little understood part about insulation that needs to be covered. There is a substantial difference between insulation for temperature control and insulation for heat loss control. For instance, the graph (below) shows the heat loss control of the spray-in-place urethane foam insulation. Any insulation will have a similar graph but with thicker amounts of insulation. This graph points out that more insulation is not necessarily cost effective. There is a point where more insulation is pointless from a total heat loss perspective.

The graph shows that 70% of heat loss from conductance is stopped by a one inch thickness of spray-in-place urethane foam. Remember we are going to stop nearly 100% of the heat loss from air infiltration with the first one-fourth of an inch of urethane foam. The second inch of spray-in-place urethane stops about 90% of the heat loss and the third inch 95% and so forth.

Thermal Diffusivity and Heat Sinks

It should be noted that when the urethane is used on the exterior of a heat sink, such as concrete, the actual effective R-value is approximately doubled. This is why with the Monolithic Dome, we are able to calculate effective R-values in excess of 60. A heat sink is any substance capable of storing large amounts of heat. Most commonly we think of concrete, brick, water, adobe and earth as heat sink materials used in building. The property of a heat sink to act as an insulation is called thermal diffusivity.

The simple explanation for the way it works is: As the temperature of the atmosphere cycles from cold to hot to cold to hot the heat sink absorbs or gives up heat. But because the heat sink can absorb so much heat it never catches up with the full range of the cycle. Therefore, the temperature of the heat sink tends to average. Large heat sinks will average over many days, weeks or even months.

An example is the adobe hacienda with its 2 to 6 foot thick walls. By the time the adobe walls begin to absorb the daytime heat it is night time and the same heat then escapes into the cooler night. Therefore the temperature would average. Because the mass of the adobe is so large the temperature averages over periods of months. Adobe acts as an insulation even though adobe has a minimal "R" value.

You can see from the graph that urethane thicknesses beyond four or five inches is practically immaterial. We use three inches for most of our construction. Two inches will do a very superior job. We have insulated many metal buildings with one inch of urethane and the drop in heat loss is absolutely dramatic. Obviously the first quarter inch takes care of the wind blowing through the cracks. (It usually takes an inch to be sure the cracks are all filled.) The balance of the inch adds the thermal protection.

II. Surface temperature control

Surface temperature control is the second reason for insulation. In many cases it is the most important reason for the insulation. I noticed this phenomena first while insulating potato storages.

We had various customers ask us to insulate the buildings anywhere from two to five inches of urethane. The buildings insulated with two inches would hold the temperatures of the potatoes properly, just as well as the buildings insulated with five inches. The difference came in the condensation. Potato storages are kept up at very high humidity levels. The buildings with the two inches of urethane would have far more condensation than those with An engineer from the Upjohn company explained this to me. He stated that thicker insulation is absolutely necessary to maintain higher interior surface temperatures. One and a half inches of urethane on the walls and ceiling of a potato storage would control the heat loss from the building, but it took a minimum of three inches of urethane to control the interior surface temperature. Four inches was even better. With five inches the difference is practically negligible. The only place where we have felt the need for five inches of urethane was insulating the roof or ceiling of a sub-zero freezer.

Underground housing - surface temperature control vs. heat loss control.

Most underground housing is in trouble from mold and mildew growth. The cause is not enough insulation to control interior surface temperatures. Rarely is there a problem with total heat loss. Water vapor condenses on the surface allowing mold to grow. Mold makes people sick. The only solution is lots of insulation for temperature control and ignore total heat loss.

My experience is that R-value tables can be used as indicators. They need modifications to make them equal to real world conditions. There needs to be allowances made. They must show equivalents. These equivalents will be more like one inch of spray-in-place urethane equal to four inches of fiberglass in a normal installation. Footnotes to the table will need to define degradation of insulations in real world conditions. Only then will the "R-value" Fairy Tale become a real world success story.

I'd read that folksy treatise AGES ago, but I'm sure it's still available online from multiple sources. It's full of cute anectdotes, but I'll take the word of the Building Science and Oak Ridge Nat'l Lab testers over his charming but unsubstantiated anecdotes. He makes some reasonable statements about the faults of low density fiberglass (an easy straw-man to beat down) relative to closed cell foam, but that's about it.

The issues surrounding the inadequacy of ASTM C 518 testing on low-density fiberglass have been well studied since the 1980s, and the models with combined foam/fiber system are now well substantiated, and confirmed by whole-assembly and whole building testing from those slobs at Oak Ridge Nat'l Labs, who obviously don't know NEARLY as much about the real world as David B. South. But in the real world, even solely fiberglass-insulated buildings can and are being built with full air-barriers & air-tight construction methods these days. Closed cell foam is not the only air-barrier or vapor retarder out there, nor necessarily the most cost-effective method of achieving those ends.

Like I said, after the first inch, the infiltration loss issue is off the table and it's all about R. (and drifting R over temperature).

Flash & fill works. Exterior foam board + cavity fill also works. R50 is only "throwing your money away" if you pay too much for it (like doing R50 all in closed cell foam). R50 combinations of foam/fiber have a positive lifecycle NPV (if not a 10 year NPV+) in placed like OH when using lower-cost material to fill out the R value, even in situations when R36 in closed-cell foam is net-negative in 25year time frames. If taken on early in the process as a whole-house design basis, the ability to drop to smaller mechanical systems can make the payback terms even shorter.

David B. doesn't mention that closed cell foam loses R at high delta-Ts whereas even open-blow 1.8lb density cellulose is fairly R-stable (and 3.0lb+ density even more so), and doesn't fully address the vapor trapping issues that can arise in real-world assemblies with closed cell foam, or it's relatively low thermal mass, etc. Rather he continually harps on his low-density fiberglass straw man, the insulation everyone loves to hate. Convection within the fiber layers in combined insulation systems is still an issue, but it's been dramatically reduced with new-skool sprayed fiberglass or even high density fg batts, and is inconsequential with cellulose at any standard density.

And his bit about closed cell foam on underground assemblies has to be taken under close advisement when trying to apply it to YOUR house. Below grade foundation walls need to be able to dry toward the interior via vapor diffusion, or the capillary drive upward can create problems. Anything over 2" of cc foam on a foundation wall of a stud-framed house could be detrimental to both the foundation and the foundation sill, since it forces ground moisture higher in the foundation resulting in efflorescence & spalling on the exterior of the above grade portion of the house, as well as sill rot.

Don't get be wrong- I LIKE foam, I USE foam, but your assertions regarding what is/is-not possible or economic in the real world regarding foam and other insulation types, just aren't aren't true in the real world, nor are your assertions about it's 85%/inch heat loss stop. Ya gotta give us something better than David B.s folksy soapbox ditty to substantiate it. He is not a disinterested party, and the bit quoted is at least 20 years behind the time. (I understand he's re-published his book with updates- haven't read it, nor am I going to buy it, but it's out there.)

Below grade foundation walls need to be able to dry toward the interior via vapor diffusion, or the capillary drive upward can create problems. Anything over 2" of cc foam on a foundation wall of a stud-framed house could be detrimental to both the foundation and the foundation sill, since it forces ground moisture higher in the foundation resulting in efflorescence & spalling on the exterior of the above grade portion of the house, as well as sill rot.

Dana1,

In my area we often build foundation walls with concrete block on top of a poured concrete reinforced footer.

Are you saying that one should not use more than 2" of closed cell polyurethane foam on the "exterior" of a foundation wall for a wood stud home?  For example, between the concrete block and brick.

Posted By Alton on 03 May 2010 04:18 PM

Below grade foundation walls need to be able to dry toward the interior via vapor diffusion, or the capillary drive upward can create problems. Anything over 2" of cc foam on a foundation wall of a stud-framed house could be detrimental to both the foundation and the foundation sill, since it forces ground moisture higher in the foundation resulting in efflorescence & spalling on the exterior of the above grade portion of the house, as well as sill rot.

Dana1,

In my area we often build foundation walls with concrete block on top of a poured concrete reinforced footer.

Are you saying that one should not use more than 2" of closed cell polyurethane foam on the "exterior" of a foundation wall for a wood stud home?  For example, between the concrete block and brick.

I suppose I should have been clearer- I was referring to cc SPF on the interior side of the foundation (a common but sometimes problematic retrofit in my neck of the woods) being an issue. On an exterior wall the SPF won't wick ground moisture into the wall readily, and as long as only permeable & semi-permeable materials are used between the block and the conditioned space all remains well- any moisture finding it's way into the block can dry toward the interior rather than get wicked up to the sill.  XPS can be used here as well, and may be more cost-effective than SPF depending on how the labor costs break down.

A capillary break between the footing and block wall is also a good idea, to limit ground moisture paths from below causing efflorescence near the bottom of the interior side of the block wall.   In a brick & block cavity wall, 2" (or more) of SPF on the block wall extending below grade would be a  good thing.  Soil type and drainage affects how important the capillary break issue is.  Spray-applied concrete sealers are probably "good enough" in cases where it's well drained sandy soil  and the footing 10s of feet above the water table, but in others 10 mil poly continuous with the vapor retarder under the basement slab might be called for.

If there's a good capillary break between the top of the foundation & the sill,  the sill is protected.  In instances where foundations are having exterior-side efflorescence or spalling issues, a layer of sacrificial parging can be applied.  Around here, most older homes have no sill gasketing at all, and when 2lb foam in a continuous interior layer from band-joist to slab as insulation, the thicker it is, the more sill-rot and spalling issue they have. But if permeable EPS or fiber-faced is is used along with spray foam as an air-sealer these problems rarely happen, but it may make sense to use vapor-retardent paints at the top down to ~1 foot below the sill in the coldest areas.  If open cell SPF is used instead of closed cell, or only 1-2" of closed cell it's usually fine.

Similarly, closed cell cavity fill & rim-joist insulation without a good capillary break between sill & foundation can trap moisture at the sill in some cases.  It's great stuff, but you have to think about where you apply it, especially when going more than 2".  (I know, I know, "Two inches is all you'll ever need- why would you throw good money away on more than that?" ;-) )

Dana1,

Thank you again.  That helps my understanding.

On my home I used open cell foam under the floor and not on the concrete block foundation wall.  Next time, I would probably use closed cell foam instead of open cell under the floor.

By the way, additives such as XYPEX are available to plug capillaries in concrete.  This type of additive is very useful for basement walls but the additive must be included in the concrete mix.  It is not an add-on treatment.

Posted By Alton on 03 May 2010 05:56 PM

Dana1,

Thank you again.  That helps my understanding.

On my home I used open cell foam under the floor and not on the concrete block foundation wall.  Next time, I would probably use closed cell foam instead of open cell under the floor.

By the way, additives such as XYPEX are available to plug capillaries in concrete.  This type of additive is very useful for basement walls but the additive must be included in the concrete mix.  It is not an add-on treatment.

If the foundation walls are insulated and the basement well sealed from air infiltration, depending on your subsoil temp you may be better off either

A: Leaving the floor uninsulated, which earth-couples the building from a heating/cooling point of view, using the subsoil for thermal mass

or

B: Put XPS/EPS under the slab, which couples the house to the thermal mass of the foundtation & slab.

Closed cell foam between the first-floor and basement shouldn't cause problems, but it does mean you have to control their humidity separately.  If the capillary breaks are already taken care of (good call on the Xypex), and are vapor semi-impermeable (2" of cc foam) the basement won't appear like much of a latent load on the AC, and the extra thermal mass may trump the slightly higher heat loss from the insulated above-grade portion of the foundation.  Subsoil temps between 60-70F can make for better annual efficiency going earth coupled than insulated-floor, which IIRC includes much of the non-mountainous south. See this, and this for a guesstimate of what your subsoil temp might be.

It's great stuff, but you have to think about where you apply it, especially when going more than 2". (I know, I know, "Two inches is all you'll ever need- why would you throw good money away on more than that?" ;-) )

Who says that you only need two inches?

Thanks for everyone's reply.
I am going to give you the final specs I've decided on. If anyone has additional thoughts please let me know.

Interior Basement Stud walls : 2" closed cell foam (includes rim joist)
Stud walls on 1st and 2nd floor: 5" open cell foam
Attic floor above garage: 6" open cell foam
Unvented Attic: 3' closed cell foam with ignition barrier (ERV in attic)
Basement walls below grade have 2' foam board already

Thanks again

Brian