A topic for debate- Closed Cell vs. Open Cell spray foam in Texas

[bmsemple1]

I am not debating the benefits of spray foam, but more the use of closed cell vs. open cell in a wall/roof cavity traditional wood construction.

We are looking to do a 2nd story addition over the garage in spray foam insulation. It is approx. 750sqft. I have a question based on the quotes I am getting. Everyone is saying no I should not do any closed cell foam in a residential application. I have asked why and the only answer cited was humidity. I realize it costs more than open cell, but I do not understand why it would generate more humidity than open cell. To me, sealing off the room/attic would potentially generate more humidity whether it was open cell or closed cell. The other argument presented to me is if the roof leaks you wouldn't know if it was closed cell. To me, this makes the opposite sense - if the roof leaks and rots then great, at least it didn't destroy the inside of my house because the closed cell protected it. Isn't that kind of the point of a roof? I would like to hear anyone else's thoughts, opinion, arguments or experiences. Personally, I was leaning toward using closed cell for the structural support it provides, but I also like the open cell for the noise reduction aspect.

 

[PCMusicGuy]

The main issue is we are in a hot climate. Your humidity will depend where you are in Texas. The type of foam you use dictates how air/moisture move.

In the typical hot/humid climates, we put our vapor barrier on the exterior of the home. Since we condition the air from the inside of the vapor barrier, you want everything within the barrier to let air and more importantly, moisture move. Otherwise, your roof sheathing could rot prematurely if enough water broke through the exterior barrier as it would be trapped between to membranes that don't allow water or air to move.

I think in the long run you would be better off using open foam if you plan to just spray the underside of the roof.

 

[chinboys]

the close cell versus open cell foam insulation debate

http://www.pentoir.com/what-is-the-...n-cell-and-closed-cell-polyurethane-foams.php

and for insect damage in foam insulation products

https://www.greenbuildingadvisor.co...able-to-tunneling-insects-like-carpenter-ants

 

[dcg9381]

I live in Texas. Both are fine.
Humidity is controlled by us running our (necessary) AC systems.
For me, it came down to R value per $.

 

[yeldogt]

IMO ... closed cell is a better product. But -- open cell is cheaper. So -- we get into a debate. Each side tries to fight it out. It comes down to .. how close can we match closed foam for a lower price ... no one ever says ... open is a better product. The say -- you don't need closed ....

Most people are very price sensitive .. so open cell has the edge. People talk about how great "foam" is. I can get this open stuff for 1/3 of the the closed .. what can possibly be the difference? Open is better ... well not so fast.

The idea that open is better because it's going to tell you that your roof is leaking -- well ...silly. It's like an HVAC guy wanting to put two AC units in your house (one in the attic) when one zoned unit will do the better job for less money.... but he tells you ... you will have a back-up with two? A back up for what ?? He makes the $$

In a cold climate you need at least 5" of open foam on a roof -- that's about the minimum to make the foam layer mostly impervious to moisture movement. Since open foam allows moisture to flow .... some can flow through the foam and condense on the underside of the sheathing.

In a warm climate this is less of a problem .. you still need enough open foam to stop air movement ...3+ inches ,,, but unless you get cold nights the need for 5' is reduced.

Inside humidity is all about -- inside water production. The more a building is air sealed -- the more it needs proper humidity control/ make up air/ fresh air control. The two foams work about the same in that regard.

I have never heard or experienced open foam being able to reduce noise more than closed.

I never use open ... I would rather do (and have done) a 2.5" layer of closed and put r13 batts on top than do = R with open.

My normal process is 4" of closed foam ... yes it costs more. But, there are no possible problems -- you have no air or water movement .. solid ..sound proof wall.

Making a building dry to the inside and outside has nothing to do with foam -- it has to do with overall construction.

There is nothing wrong with a properly installed open foam job -- in a warmer climate ....as long as the person doing it puts enough on ..knows what they are doing.

I always do closed ... stuff is amazing

 

[finn]

The installers flashed with closed and finished with open , after the builder fabricated a “proper vent” when we insulated a kitchen basement addition.

The closed flash may have been only on the basement and rim joists, though. Can’t remember.

Best of both worlds.

 

[wanderer]

With all due respect I think you’re getting some pretty mixed advice here. I’m not sure I would listen to anybody that doesn’t have experience building in your area, me included. I would have some real reservations about using a product that is a vapor barrier in a space that will not be conditioned a good part of the time. I live further north and so heating is my primary concern. My house has both closed cell and open cell insulation in different areas of the house and for different reasons. Were I to do it again I would use a lot less foam and a lot more cellulose.

Hop on YouTube and check out Matt resinger. He’s in central Texas and is probably one of the most knowledgeable people about building in your area that you were likely to find. He’s very knowledgeable about energy efficiency and building envelope performance.

 

[BigWarehouse]

My take on this is that in a humid climate, indoor air should almost always be conditioned a little bit. In Texas that means A/C and dehumidifier. Keep the humidity set below 60% and you'll never have a problem. Even if you aren't going to be inside and have the A/C cranking, you can still have a dehumidifier running for not very much. It's also almost always good to have at least a little air movement, from ceiling fans and such.

Keep the place 100% air and water tight and only let it in and out through properly engineered and controlled vents. Build it like a boat!

Another thing not often talked about is closed cell foam is significantly more structural. Coat a whole building in that and it's like adding another layer of sheathing and gallons of construction adhesive!

 

[wanderer]

My take on this is that in a humid climate, indoor air should almost always be conditioned a little bit. In Texas that means A/C and dehumidifier. Keep the humidity set below 60% and you'll never have a problem. Even if you aren't going to be inside and have the A/C cranking, you can still have a dehumidifier running for not very much. It's also almost always good to have at least a little air movement, from ceiling fans and such.

Keep the place 100% air and water tight and only let it in and out through properly engineered and controlled vents. Build it like a boat!

Another thing not often talked about is closed cell foam is significantly more structural. Coat a whole building in that and it's like adding another layer of sheathing and gallons of construction adhesive!

Generally I believe that to be the case as well. If the building is going to be vapor in permeable then it should be conditioned. Some of the materials we have now are fantastic but construction techniques have not kept up and this is a real problem, especially in Spaces that will not be conditioned all the time. I see it in vacant houses all the time. My first house had plaster walls and leaky windows. The wall cavities were vented so that they would pull basement air up through the wall and into the attic. They probably leaked for 20 years and never damaged anything because the walls dried out so well. This is a really great feature so long as you never have to heat it!

 

[EricVonHa]

Closed cell = higher R-value per unit cost.

Humidity in the space is a secondary issue and can be mitigated and managed separately.

Here is an article which effectively states that open cell should not be used in attic roof joists:

https://www.energyvanguard.com/blog/high-humidity-in-a-spray-foam-attic-part-2

 

[BigWarehouse]

Closed cell = higher R-value per unit cost.

Higher R value per inch certainly, but higher R value per unit cost?

 

[75gmck25]

If you look at the firsat energyvangard link, and one of the associated links (https://www.energyvanguard.com/blog/75042/Will-Open-Cell-Spray-Foam-Insulation-Really-Rot-Your-Roof), it brings up one issue with the current code for foam insulation.

I am building a conditioned crawl space in a new addition and I'm required to circulate air through that area at 1cfm/50 square feet of crawl space. The space will have foam board underneath the gravel and on the side walls, and a moisture barrier.

However, when you build a conditioned attic there is no similar air circulation requirement, so any moisture that migrates to the attic may stay there indefinitely. I'm not sure of the exact code for foam insulation, but according to the 2nd article you cannot put air circulation in an attic area with exposed spray foam unless the foam has an ignition barrier over it. How are you supposed to reduce the moisture in that enclosed, conditioned attic?

Bruce

 

[yeldogt]

With all due respect I think you’re getting some pretty mixed advice here. I’m not sure I would listen to anybody that doesn’t have experience building in your area, me included. I would have some real reservations about using a product that is a vapor barrier in a space that will not be conditioned a good part of the time. I live further north and so heating is my primary concern. My house has both closed cell and open cell insulation in different areas of the house and for different reasons. Were I to do it again I would use a lot less foam and a lot more cellulose.

Hop on YouTube and check out Matt resinger. He’s in central Texas and is probably one of the most knowledgeable people about building in your area that you were likely to find. He’s very knowledgeable about energy efficiency and building envelope performance.

Matt has some interesting videos -- but he is also all over the map on what he uses. I get that he likes to use new products ... but, care should be given when mixing things up. I also don't like it when people move to start making money of of showcasing products.

Almost every insulation will retard air movement and vapor -- most people don't understand how important air movement is. People fixate on "R" w/o understanding that "R"only works w/o air movement.

The nice thing about closed cell is the VB is now at the sheathing -- the building will dry to each side with the inert foam in the middle -- be it wall or roof. I like to use plywood as any small leak will have less effect should there be damage.

Cellulose typically requires some other form of VB -- although the wet product with adhesive is IMO a very good foam product ... because it stops air movement.

Foam with the zip system -- I see a problem with this. You now have two VB w/ osb stuck in the middle. The OSB can't dry to either side if it somehow gets moist.

Inside air needs to be managed with any system -- it's why plastic is such a problem. Plastic traps moisture ..

 

[BigWarehouse]

How are you supposed to reduce the moisture in that enclosed, conditioned attic?

Dehumidifier.

Also just because code doesn't require air circulation, doesn't mean you can't use it. If the attic is "conditioned", there must be something up there conditioning it.

 

[yeldogt]

If you look at the firsat energyvangard link, and one of the associated links (https://www.energyvanguard.com/blog/75042/Will-Open-Cell-Spray-Foam-Insulation-Really-Rot-Your-Roof), it brings up one issue with the current code for foam insulation.

I am building a conditioned crawl space in a new addition and I'm required to circulate air through that area at 1cfm/50 square feet of crawl space. The space will have foam board underneath the gravel and on the side walls, and a moisture barrier.

However, when you build a conditioned attic there is no similar air circulation requirement, so any moisture that migrates to the attic may stay there indefinitely. I'm not sure of the exact code for foam insulation, but according to the 2nd article you cannot put air circulation in an attic area with exposed spray foam unless the foam has an ignition barrier over it. How are you supposed to reduce the moisture in that enclosed, conditioned attic?

Bruce

They have some interesting articles -- the whole group. It's also important to understand that they have evolved over the years.

Martin's big issue with closed foam was the blowing agents -- not the end result or it's performance. Much of his alternatives had a basis is finding an alternative to foams blowing agent.


I have been using closed cell on my projects since the early 90's -- I always do sealed attics and crawl spaces. Early on the closed attic was done because of all the HVAC units installed in vented uninsulated attics -- it's such a dumb idea ..and still being done! Not the closed attic .. putting HVAC in an unconditioned space.

A sealed attic with HVAC --- no issue with stagnate air as the equipment leaks so much .... but I have never had a problem with an empty one either. I also never VB the top floor ceiling.

Building codes often counter each other -- I had a major house fire. The closed foam saved the structure --- The flash over point of closed foam is so high as to be irrelevant IMO

I can't do it in my current project .. but -- a thin layer of foam internally to isolate the sleeping areas of some homes would be easy and stop smoke travel. It's the smoke that kills ....

In some areas -- painting the foam is the answer -- to make the code officer happy.... but they never worry about the crawl. The problem is the confusing codes .. not the foam. I have run into the same issues -- you need to positively condition the crawl .. well ...... why not the attic. They never ave an answer?

I think much of this comes down to history -- we have lots of history regarding nasty crawl spaces .... the fact that it's caused by open venting to the outside ..well that's forgotten. There are also many nasty vented attics

 

[Viper98912]

I'm not super knowledgeable in this, but,

In my last house in Georgia which was new construction, they put (I think) closed cell foam all across the roof joists in the attic. The HVAC was also mounted in the attic as well.

Whether it was slightly chilly in January or miserably hot and humid in August, my attic always stayed at a very dry 70 degrees or so. It was incredible to go up there and it was just barely less comfortable than the rest of the house.

My energy bill was also the same as my previous home, even though the previous home was 1k sqft and this one was 3k.

Nonetheless, if anyone is on the fence, I highly recommend doing it (correctly, of course).

 

[75gmck25]

The use of the term "conditioned" space is confusing because it does not always mean there is something providing conditioned air to the space. The definitions are not consistent across various organizations and industries.

However, back to the question of whether spray foam is a good idea for the attic. When I used foamboard to insulate my basement walls I was told that it needed a fire/heat barrier over it because it was in an occupied area and foam was flammable. If it had been fiberglass or rock wool insulation I could have left the stud bays uncovered. Are there any special requirements or conditions for fire/heat barriers if you use foam in an attic?

Bruce

 

[yeldogt]

The use of the term "conditioned" space is confusing because it does not always mean there is something providing conditioned air to the space. The definitions are not consistent across various organizations and industries.

However, back to the question of whether spray foam is a good idea for the attic. When I used foamboard to insulate my basement walls I was told that it needed a fire/heat barrier over it because it was in an occupied area and foam was flammable. If it had been fiberglass or rock wool insulation I could have left the stud bays uncovered. Are there any special requirements or conditions for fire/heat barriers if you use foam in an attic?

Bruce

Years ago I sprayed the second floor of an attached garage -- walk up steps. Never covered it and was never required as the garage/ house had a block firewall. It was an unoccupied space .. I have no idea how that would be treated today.

Same with most attic spaces in modern homes ... they are unoccupied spaces. I have never needed to do anything.

A basement is an occupied space -- some foam board is very flammable. That's a different situation IMO.

Your discussion is now something that comes up --- what's a conditioned space. And does an attic need active conditioning.

With a crawl space I think it's prudent to have active conditioning in many climate areas -- cool moist air will naturally fall ..

 

[DC73]

Texas is a large area. We have 5 different climate zones (Zone 2 humid, Zone 2 dry, Zone 3 humid, Zone 3 dry, Zone 4). What is right for one zone might not be right for another.

I can tell you that out here in West Texas, closed cell foam is rarely installed because open cell foam is cheaper and does the job needed.

Closed cell foam is much more of a vapor barrier and is the foam of choice in very cold climates. It may also be the foam of choice for the humid areas of Texas but I'd want to hear from the experts and would post the question on the Q&A forum of GreenBuildingAdvisor.com.

I have asked why and the only answer cited was humidity.

Closed cell foam will do a better job of keeping humidity out of the home. It will also do a better job of keeping humidity inside the home so proper sizing of air conditioning and dehumidifiers is important.


I agree with your assessment on roof leaks and the structural support.


Since the closed cell foam is also a pretty good vapor barrier, it will help keep the garage fumes and and odors out of the living space.


DC

 

[kj_mustang]

Unvented attic space with closed cell foam at the roof and hvac supply lines in the attic will probably get a little leakage out the ducts and help with conditioning the space. I would put a small supply and return into the attic space anyway. I think the codes are behind the times. They make you use ridiculously thick amounts of foam to meet the R values of the building code when foam far exceeds fiberglass insulation products in other ways. Studies have shown once you exceed a certain thickness of closed cell foam it doesn't really help to add more.

 

[DC73]

They make you use ridiculously thick amounts of foam to meet the R values of the building code when foam far exceeds fiberglass insulation products in other ways. Studies have shown once you exceed a certain thickness of closed cell foam it doesn't really help to add more.

R-value is r-value. Spray foam installers started fudging the debate because spray foam can't compete with more conventional insulation on price.

Heat is transferred by one of three methods - conduction, convection, & radiation. R-value stops heat transfer by conduction. If you need R30, you need R30, regardless of insulation type. Air sealing stops heat transfer by convection. Spray foam provides both r-value and air sealing.

What the spray foam industry has basically done is to compare the cumulative conductive and convective heat transfer of spray foam to only the conductive heat transfer of conventional insulation. It's not apples to apples.

While there have been several studies that show once you achieve proper R-value, adding more insulation is of little benefit, there are no studies that suggest adding enough insulation to get to code minimum is not effective.

I like spray foam. It's a superior insulation to fiberglass in a lot of ways but it's more costly. But, to fairly compare the cost of spray foam to other insulation materials also requires that you factor in the cost of proper air sealing when using non-foam insulation. That air sealing adds to the cost and closes the gap in price. And that's the point the spray foam industry needs to make instead of overstating the performance of foam.

DC

 

[yeldogt]

R-value is r-value. Spray foam installers started fudging the debate because spray foam can't compete with more conventional insulation on price.

Heat is transferred by one of three methods - conduction, convection, & radiation. R-value stops heat transfer by conduction. If you need R30, you need R30, regardless of insulation type. Air sealing stops heat transfer by convection. Spray foam provides both r-value and air sealing.

What the spray foam industry has basically done is to compare the cumulative conductive and convective heat transfer of spray foam to only the conductive heat transfer of convention insulation. It's not apples to apples.

While there have been several studies that show once you achieve proper R-value, adding more insulation is of little benefit, there are no studies that suggest adding enough insulation to get to code minimum is not effective.

I like spray foam. It's a superior insulation to fiberglass in a lot of ways but it's more costly. But, to fairly compare the cost of spray foam to other insulation materials also requires that you factor in the cost of proper air sealing when using non-foam insulation. That air sealing adds to the cost and closes the gap in price. And that's the point the spray foam industry needs to make instead of overstating the performance of foam.

DC

I have a little different take. The needed R values are based on fiberglass insulation in a static state. You are not getting that R value in the real world -- you are getting that in the real world with foam because it's stopping both air movement ..and radiation.

I have felt the radiation --- there is no comparison between 2" of foam and r19 fiberglass on a roof deck.

Foam is more money .. the industry tries all manner of ways to get you to buy. Correct. And the OP's Open /Closed debate

I do 4" of foam --- that's R28 .... it can be 0 or 100 -- the inside foam is room temp .. even on a roof.

 

[DC73]

. . . you are getting that in the real world with foam because it's stopping both air movement ..and radiation.

Air seal with fiberglass insulation and you'll have a comparable product.

There are some weird physics going on whereby fiberglass gets de-rated at certain temperatures and if air can flow through. But, r-value is a rating based on how well insulation materials block the flow of heat transfer due to conduction. R-value has nothing to do with air sealing. Some foam manufactures want you to believe otherwise as they advertise "effective r-value" which is nothing more than a composite of r-value and the blocking of heat transfer due to convection.

To stop heat transfer via radiation really requires a reflective surface. None of the conventional insulations including foam do much to stop radiation. In practice, it is rarely cost effective to install radiant barriers as the majority of the heat transfer occurs through conduction and convection. Once you've achieved proper air sealing and proper r-value the payback just isn't there for most radiant barriers, especially in a retrofit situation. It could make sense to install roof decking with a built in radiant barrier if the cost increase was very marginal. It could also make sense in a DIY application if the material cost was low enough.

DC

 

[yeldogt]

Air seal with fiberglass insulation and you'll have a comparable product.

There are some weird physics going on whereby fiberglass gets de-rated at certain temperatures and if air can flow through. But, r-value is a rating based on how well insulation materials block the flow of heat transfer due to conduction. R-value has nothing to do with air sealing. Some foam manufactures want you to believe otherwise as they advertise "effective r-value" which is nothing more than a composite of r-value and the blocking of heat transfer due to convection.

To stop heat transfer via radiation really requires a reflective surface. None of the conventional insulations including foam do much to stop radiation. In practice, it is rarely cost effective to install radiant barriers as the majority of the heat transfer occurs through conduction and convection. Once you've achieved proper air sealing and proper r-value the payback just isn't there for most radiant barriers, especially in a retrofit situation. It could make sense to install roof decking with a built in radiant barrier if the cost increase was very marginal. It could also make sense in a DIY application if the material cost was low enough.

DC

That's my point -- the codes are based on fiberglass R .. and they are testing with no air. In the real world = leaking with fiberglass.

I'm not talking about reflective barrier ... sorry.

Maybe using terms of my own making --- I have had the opportunity to stand inside identical houses one with foam and the other with fiberglass. In an attic w/ foam you don't get the heat coming through the roof assembly. I'm not talking about feeling the assembly with your hand ... I'm talking about the suns radiation through the assembly.

It's dramatic.

The same with cold -- even on a thick roof were the R of the fiberglass is greater vs the 4" of foam.

I normally pay for a bit over 4"