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Community and Q&A

Hybrid Insulation Techniques

SustainablyBuilt | Posted in Energy Efficiency and Durability on

Many insulation companies in our area have begun to sell hybrid insulation systems. In a standard 2×6 wall, they will spray 1″ of closed foam inside the wall cavity and then fill the rest with cellulose. The idea is to get all the benefit of the air sealing, but then to get the rest of the R-value from the much less expensive cellulose. I can foresee many potential building science issues with this, but it’s hard to compare to anything out there.

Does anyone have experience with these systems? How do they perform? How is their durability?


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  1. gbauser-20428 | | #1

    I have used this type of approach on projects in cold climates. While I like the idea of hybrid insulation systems and fine tuning insulation for specific areas in a building or a specific application,I have concerns about the "flash and fill" method that you are describing. When I have used a similar approach, I am sure to increase the depth of the spray foam to 2 1/2-3".This depth varies depending on what climate zone you are building but it is important to have the adequate R value provided by the foam before installing the rest of the cavity fill (cellulose, fiberglass, etc..)This has direct impact on where the condensing surface will be in the assembly. I like closed cell foam for it's thermal, moisture, and air barrier qualities and I like the savings associated with filling half the cavity with foam and topping it off with cellulose.
    Many foam insulation contractors talk about "perceived R value" based on air stopping capacity and not having to completely fill the cavity with insulation. My energy raters still say R value is R value and rate a house accordingly.

  2. pbllc67 | | #2

    Jeff Medanich is spot-on with concerns about the condensing surface. The condensing surface is essentially the face of the vapor barrier-- in this case the face of the (closed-cell) foam. Warm, moisture-laden inside air will pass through the cellulose or fiberglass layers; when it touches the face of the closed-cell foam vapor barrier it had better not be cool enough to condense; otherwise there's trouble. Too little foam or too much cellulose can lead to condensation on the face of the foam.

    Joe Lstiburek has a useful report, including a formula to determine the right ratio of permeable to impermeable insulation to use for a given climate, design temparature, and inside relative humidity. It's called "Vapor Barriers and Wall Design".

    I think a lot of insulation contractors are going to create a lot of future work for the rest of us if they aren't careful about the "flash and fill" or "flash and batt" method described. It's more complicated than that, but not a lot more.


    So if I build a wall with 3/4" or even 1 1/2" foam exterior sheathing over 5" of fiberglass am I setting myself up for a major rot problem?

    I don't see how Flash and Batt is all that different from foam sheathing over fiberglass which seems to be a more readily accepted alternative. (other than the thermal bridge at the studs).

    To me the wetting potential just needs to be in balance with the drying potential and what I see as the problem here is the cellulose's limited drying potential.

    I'm just askin'...

    Not tryin' to make trouble or anything...

  4. SustainablyBuilt | | #4

    Hi Jeff! That's great you're a part of this team. Yes, we're talking about Boulder here. And your concerns are exactly what I'm referring to. I like the idea of going to at least 2" if you're going to do this. At the same time if my clients are installing an ERV, I'm hoping they'll be able to keep their humidity levels down, so condensation isn't a problem. As for energy ratings, I agree completely that we can only count R-Value as R-Value. Now, when it comes to fiberglass I have some different stories as some initial research is showing an R-19 batt wall assembly having an actual R-value of 5. Thanks for the response!

  5. homedesign | | #5

    Michael, Concerning your question above...It depends on your local climate and the humidity inside the house. The wall design chapter in Joe's Builder's Guide to(your climate) has a nice explanation.
    As our homes become more airtight the interior humidity will rise without proper ventilation.

  6. Jeff White | | #6

    Adam & Jeff,
    We don't recommend the "flash and fill" approach. I believe the goal is to build an assembly that is lower in price. When using a hybrid system, you end of doubling the effort to install. Our open cell foams R4.5 per inch can be installed as full fill and cost less than the hybrid solutions. Another problem with spraying 1" of closed cell spray foam is the application can not dialed-in 1" perfectly, so some areas might be less. If you have an area that is less than 1" you may have condensation issues just as you would with any air premeable insulation material. Closed cell foams form very tight VAPOR BARRIERS, this is not ideal in wood structures. You may trap moisture laden air or water between the closed cell foam and the exterior wall assemblies (as mentioned above). Every element in the structure follows a humidity curve (just like a 2x4).
    I like the many benefits with foam, thermal, moisture management, sustainable (lasts forever, no settling or rot/decay), air barrier, and performance. I know lots of people say cellulose does not settle over time, but its hard to believe. We just reviewed two 5 year old homes that had settling in the top 2 feet of the wall cavities.
    As Jeff mentioned above 2.5" to 3" of closed cell spray foam would be enough and I would not fill the rest of the cavity, its just not necessary and will add only a slight improvement, if you could measure it.
    On the energy raters saying an R is an R and rate accordingly, is ture, but real data shows a very different answer. The longer we promote equal performance between different materials, the longer we promote incorrect information.

  7. Riversong | | #7

    The "perceived" R-value myth is nothing but snake-oil salesmanship. Conductive heat loss is dependent on measured R-value (or calculated R-value of the as-built assembly) and nothing else. Radiant heat loss is dependent upon the emissivity of surfaces and surface temperature. Infiltrative/exfiltrative (convective) heat loss is dependent upon the air tightness of materials, assemblies and the entire thermal envelope system. They are three different and independent measurements.

    While it's true that properly-installed spray foam can create an excellent air barrier (as well as offering good R-value), spraying between studs does nothing to limit thermal bridging. Mechanical penetrations in top and bottom plates can introduce vertical convection paths within the framing cavities if not sealed, and penetrations (electrical boxes, e.g.) in the interior air barrier can create channel flow of moist air in the cavities.

    The primary reason that foam installers try to sell flash and fill or minimal foam is the exhorbitant cost. A tight house with little more than energy-code minimum R-value is not going to be an efficient house, regardless of the type of insulation.

    Yes it's true that installed fiberglass has been tested as significantly less R-value than advertised. In addition, fiberglass loses R-value if it is either colder or warmer than room temperature (when it's most needed), and loses most of its R-value if air can move through it.

    Contrary to what Jim suggests, cellulose will stop most air movement, and with a good air barrier (such as air-tight drywall) creates a very effective and moisture-tolerant thermal envelope. And contrary to what Michael suggests, the drying potential of cellulose is entirely dependent upon the permeability of the interior and exterior "skins" of the thermal envelope, and cellulose has a moisture-buffering capability that few other insulation materials share. And contrary to what foam installer Jeff suggests, properly-installed dense pack cellulose (≥ 3 pcf) will not settle, since it is more than double its gravity-settled density. (Disclaimer: I am not a cellulose contractor, but I use it in all my projects).

    If you want to use foam to create an effective air barrier, then applying exterior rigid foam board as a continuous thermal break is both more effective and less costly than flash and fill.

    Northern climes require a minimum of 2" exterior foam to prevent a condensation surface, but controlling moisture migration with an effective interior vapor-permeable air barrier (such as air-tight drywall) minimizes moisture accumulation in the thermal envelope and allows drying to the interior. (By the way, the American Air Barrier Association uses drywall as the test standard for air barrier materials: ≤ 0.004 cfm/sf @75Pa)

    All parts of a moisture-tolerant thermal envelope should allow drying either to the interior or exterior, and ideally in both directions. A moisture-tolerant assembly balances wetting potential with drying potential and safe moisture-storage ability.

    An efficient and durable thermal envelope requires high R-values, low air permeance, and moderate to high vapor permeance for drying (ideally to the exterior in a heating climate and to the interior in a cooling climate).

  8. Expert Member
    Michael Maines | | #8

    My company has used "flash-and-batt" several times with excellent results. While I would prefer to wrap the exterior with foam panels, it creates too many problems for the detailed exterior trim we typically use. It is also problematic on remodels where new ties into old. We have found it cost-effective to have 2" of closed-cell sprayed into walls, and the balance of the space filled with f/g batts, with the airtight drywall approach (NO vapor barrier). We are in a cold climate, bordering on mixed humid.

    We use dense-packed cellulose about as often as flash-and-batt, for about the same price. Flash-and-batt is actually easier for the last-minute changes our clients seem to enjoy inflicting on us. The f/g cavity can be used to route new wires, etc. Dense-pack is not easy to put back together if a change is needed.

    Closed cell foam, inside or outside the shell, allows f/g to do what it's supposed to, by eliminating air leaks and insulation gaps. For the few days a year where conditions (theoretically) allow condensation on the face of the foam, the lack of a vapor barrier will allow drying to the inside.

    If you look at a house through an infared camera and see every gap and void in the insulation showing as cold spots, you will see why I don't think R-value testing is an accurate measure of performance.

  9. Wade Buler CGP, MCT | | #9

    I would only recommend the flash and fill method as discussed above if applied in our climate (Calgary), with the foam being the 1/2 pound open cell foam. As the open cell foam has a perm rating value higher than 1, it does not constitute a vapour barier, and thus condensate vapour will pass thru the foam. With the balance of the cavity being filled with fiberglass batts and poly being applied to the interior side of the studs, the wall assembly as built should have the same charastics regarding condensate as a wall cavity with only batts inside.

    The foam combined with the batts will create a much more robust air barrier and still allow for the cost savings attributed to the traditional fiberglass batts.

    I do agree that R values as advertised to not reflect a typical as built system, as the thermal bridging of wall studs is not factored into these calculations. But as building science has proven, an air tight envelope has a much higher true R value than a leaky one.

    To advocate building a leaky house so that it can dry when vapour enters the cavity, is going against the goal of building a home which consumes less energy and offers a much more comfortable environment to its inhabitants.

    A properly built high performance home with a tight air barrier and overall properly built building envelope coupled with a ERV or HRV will outperform any traditionally built home.

    The less air leakage from the house, the better. The potential for condensate in the wall cavities can be remedied by looking at the overall mechanical / ventilation system in the home and ensure it is designed properly.

  10. Riversong | | #10

    Wade Buler: "I would only recommend the flash and fill method as discussed above if applied in our climate (Calgary), with the foam being the 1/2 pound open cell foam. As the open cell foam has a perm rating value higher than 1, it does not constitute a vapour barier, and thus condensate vapour will pass thru the foam."

    In a very cold climate it is critical to hygrically isolate the sheathing from interior water vapor. This can be done with an interior vapor barrier (but that prevents drying to the interior) or with closed-cell foam thick enough to keep its inside surface above the dew point. Open-cell foam in this application will not only not have enough R-value to keep its surface above the dewpoint but will then allow water vapor to permeate through to the cold sheathing where it will condense and do all sorts of damage.

    Wade Buler: "But as building science has proven, an air tight envelope has a much higher true R value than a leaky one."

    R-value and whole-wall R-value are measures of resistance to conductive heat loss. Tightening up the house does not increase the "true R-value" except in so far as the reduction of internal convection within the insulation allows it to maintain its rated R-value.

    Wade Buler: "To advocate building a leaky house so that it can dry when vapour enters the cavity, is going against the goal of building a home which consumes less energy and offers a much more comfortable environment to its inhabitants."

    No one advocates building a house that leaks air. But a house that breathes moisture allows the thermal envelope to dry, not if but when it gets wet – as all will over the course of their useful lives. In a cold climate, the thermal envelope should be able to breathe at least to the exterior if not in both directions. In a hot climate, to the interior.

    Wade Buler: "The potential for condensate in the wall cavities can be remedied by looking at the overall mechanical / ventilation system in the home and ensure it is designed properly."

    The primary line of defense against cavity condensation is a tight, properly designed thermal envelope. The HVAC system needs to be part of the strategy of source reduction and moisture dilution. No HVAC system is going to be able to remedy a poorly designed or built envelope.

  11. Frank | | #11

    This thread is typical of the responses I am hearing when I ask my home designer, my builder, an energy expert during a blower door test, local insulators and local home inspectors - each has their own opinion with very little consensus among the group. Needless to say, I am confused as hell.
    I am building a 2000 sq ' home with conditioned basement, radiant, HRV, platform construction, conventional framing in the Seattle, WA area. I would like to do the flash n' bib but am concerned about the condensation threat inside the wall cavity...perhaps the blown in batt is the way to go - better air infiltration control, and better human factors control for the insulator - the vapor retarder will actually contact the sheathing and wallboard in the vaulted space. For my climate, does anyone have a reasonable recommendation? thanks

  12. Riversong | | #12


    Yes, there are at least as many opinions as there are insulation options. Some can be dismissed because of obvious conflict of interest, other's have to be weighed based upon the knowledge, experience and credibility of each "expert".

    IECC recommends only R-13 walls for your climate zone, so you can get away with almost any option. But since you're in a marine environment, drying is critical. Since you have a lot more HDD than CDD and little sunshine, drying to the exterior is more important. For that reason, I would advise against closed cell foam. BIBS is probably a good option, as it offers good R-value and good air resistance. Do not use an interior vapor barrier, but make sure the drywall is air-sealed as well.

    If it helps you in discerning the credibility of my advice, I have been designing and building super-insulated homes for 30 years, and I teach hygro-thermal engineering and building science.

  13. Jayson | | #13

    We recently had an energy audit performed by both utility companies here on Cape Cod and they both came up with the same (or very similar) plan. However, their plan could only be 30% implemented as the insulation contractor was refusing to perform all the requested action items due to concern for condensation or loss of R-value.

    One of specific concern is our attic. Both auditors wanted dense packing. However, our walk-up attic (which will be finished in the future) is decked and has 10" of batt laid between the engineered I-beams. The decking is tongue and groove, so not easy to remove. The insulator did provide a $15,000 quote to hot roof our attic, as an alternative (which is too much for us to invest with too far out a payback). To further complicate our issue, we have our 2nd story air handler and duct work running through the attic (above the decking).

    If I were to be so ambitious to rip up the decking and want to spray closed-cell cellulose, would we flash and batt (reusing the 10" fiberglass, as I have a few extra inches between it and the underside of the decking) or remove the fiberglass and just spray the foam? I know I have thermal loss through the ceiling penetrations into the attic from the HVAC ducts and mechanical penetrations through the top plates in the walls.

    Any suggestions you can lend for our climate is appreciated? Thanks for the help.

  14. Riversong | | #14


    "Dense pack" is recycled shredded newspapers (cellulose) with borate fire retardant, blown in at a minimum 3 pcf density, it is not a closed-cell foam. The auditors probably recommended cellulose because it is more cost-effective than spray foam and blocks much of the exfiltration through the ceiling, unlike fiberglass (though penetrations should be foamed first with a can of Great Stuff or equivalent).

    But, if you plan to finish and condition the attic in the future, then you may have no choice but to "hot roof" the attic unless there is enough headroom to build the framing down to make space for roof venting and dense-pack cellulose (basically turning your rafters into parallel-chord trusses). And, with HVAC in the attic, you'd be better off moving the thermal envelope and air barrier to the roofline.

  15. Jayson | | #15


    Thanks for the quick reply and catching my explanation error. If I move the thermal envelop to the roofline, would a flash and batt situation work there or can I use closed cell foam (the insulator was pushing 6" - 8" of Icynene). I obviously would have to cover the eave and ridge vents and install a ventilation system.

    By chance we don't finish the attic (it was to be a future home theatre and not really necessary), is there an option you would recommend?

    Thanks again for the help.

  16. Frank | | #16

    thank you Robert for your response...I've heard similar recommendations from Home Inspectors - fellows who see how houses wear in the NW climate. One said even to avoid the bibs... as eventual water infiltration combined with a bibs application will make remediation a messy job. Seems a bit too skeptical.

    You mentioned, "... Do not use an interior vapor barrier, but make sure the drywall is air-sealed as well." Do you mean avoid these applications ...
    "Depending on the climate, additional water vapor control may also be specified. These often include polyethylene plastic sheeting, faced fiberglass insulation, foil-backed wallboard, or an interior "vapor barrier" paint."


    "The logical series of sealing and detailing steps pioneered by the Canadians in the Airtight Drywall Approach (ADA) and Simple Caulk and Seal (SCS) is usually less expensive, simpler, and more effective than more commonly used polyethylene sheeting techniques."

    thannks, Frank


  17. Riversong | | #17

    I obviously would have to cover the eave and ridge vents and install a ventilation system.

    Either you're still confused or I am. If you close off the roof venting with spray foam then the attic becomes conditioned space and attic ventilation is incompatible with that. Perhaps you mean to include the attic in a whole-house ventilation system (which is a good idea once you sufficiently tighten up the envelope).

    Closed-cell foam would offer the most R-value in whatever space, but code calls for R-38 ceilings and you're not likely going to be able to achieve that without building down your roof. With a closed-cell "hot roof" it's imperative that the roofing material can breathe to the outside for drying any leakage. Open-cell foam or open cell flash and batt at least allows some drying downward and shows roof leaks after a while.

    The least costly and most effective retrofit would be to seal any obvious penetrations with a can of spray foam and add some cellulose on top of the fiberglass to increase R-value and control exfiltration. Also seal all duct joints with duct mastic or foil-butyl tape and insulate ducts well.

  18. Riversong | | #18


    It's not just that air sealing is simpler, less expensive and more effective than poly vapor barriers, it's that a true vapor barrier (plastic or foil) is as likely to trap moisture as it is to prevent its intrusion. Air sealing is a must, and then you can use a 1 perm vapor retarder (like latex v.r. primer) on the drywall to meet code requirements. There is a significant difference between a vapor barrier and a vapor retarder.

  19. Brett Moyer | | #19

    I'm confused on your stance on open-cell flash and batt applications. In comment 17 you state, "open-cell foam or open cell flash and batt at least allows some drying downward and shows roof leaks after a while," yet in comment 10 you are clearly against open-cell flash and batt-- "Open-cell foam in this application will not only not have enough R-value to keep its surface above the dewpoint but will then allow water vapor to permeate through to the cold sheathing where it will condense and do all sorts of damage."
    Yes, you were talking about a wall application in one comment and a roof application in the other, but I don't see a difference. I think the moisture that "permeates" through the foam to the cold sheathing is a concern in walls AND in roofs.

  20. Riversong | | #20


    If you're confused, it's because you're no paying attention. My first comment was about open cell foam in a very cold climate (Calgary), the second was a generic comment about open cell in a roof compared to closed cell. I do not advocate spray foam in any climate, though in some renovation scenarios it may be a reasonable option. But one needs to consider the VOC off-gassing that has forced some homeowners to move out of their homes and the inadequacy of R-value or moisture protection in many applications.

  21. GBA Editor
    Martin Holladay | | #21

    I agree with your point. Like you, I'm uncertain what Robert meant by "open cell flash and batt."

    Lest anyone be tempted, it's important to clarify: all flash-and-batt proponents I have talked to emphasize that the technique is only used with closed-cell foam, so (as far as I know) there is no such thing as "open cell flash and batt."

  22. Richard | | #22

    I don't sell SIPs, but doesn't the use of SIPs eliminate most of this debate.
    I have done enough remodels to see mositure damaged walls from all framing systems.

  23. Expert Member
    Michael Maines | | #23

    Martin, Owens Corning's "EnergyComplete" system could be described as a flash and batt system, and it uses open cell foam: It's not what we usually think of as flash and batt, and I'm dubious about their air sealing claims at such minimal thickness.

    Richard, I've seen moisture damage from SIPs, and it's very difficult to repair. They come with their own set of debatable traits.

  24. GBA Editor
    Martin Holladay | | #24

    I think you are mistaken. The spray foam used in the EnergyComplete system is very dense -- denser even than closed-cell (2-pound) foam. It has a density of 7 to 8 pounds per cubic foot, so it is about 4 times denser than closed-cell foam. Open-cell foam has a density of only 1/2 pound per cubic foot.

  25. Expert Member
    Michael Maines | | #25

    Martin, I was going by OC's website. See #7 under "System" here:

    Under "Performance" they list the R-value at 3.2/in, even less than 1/2lb foam.

    There are a lot of slippery answers on their FAQ section, including comparison to "Polyurethane" foams, which makes it sound like their product is not polyurethane based. I don't have any first-hand experience with it though.

  26. GBA Editor
    Martin Holladay | | #26

    I can see the source of your confusion. I think that Owens Corning could do a much better job with their literature, so that the answers to these questions weren't so mysterious.

    The source of my information was Dwight Shuler, OC's technical manager for foam products and fiberglass insulation, who I spoke with on the telephone today. He described the spray foam as more of an air-sealing product than an insulation product. "We don't make any R-value claims for the product," he told me -- which is consistent with its density (it's dense) and the fact that it is applied only 3/8 inch thick.

    I'm not sure why they call it an "open-cell" foam -- probably because it is applied in a very thin layer, and therefore may allow for some drying.

  27. Expert Member
    Michael Maines | | #27

    There are more answers on OC's website but they're hard to find:

    The problem is that our common terms "open cell" and "closed cell" are shorthand for polyurethane foam in 1/2lb and 2lb densities. The Owens Corning product is a latex-based foam, with a perm rating of 40. Definitely vapor permeable.

  28. Expert Member
    Michael Maines | | #28

    Martin, it's interesting that Mr. Shuler (thanks for making that call, btw) would claim that they don't make any R-value claims, when it's posted on the document I linked to above and elsewhere on OC's website that their product has an R-value of 3.2/in.

    At least it's low R-value means that we don't have to consider it in the 1/2lb vs. 2lb polyurethane foam debate....

  29. GBA Editor
    Martin Holladay | | #29

    Thanks for the useful link. As an example of the inadequate job that Owens Corning is doing with their technical literature, consider this sentence from the linked document: "However, it does have an R-value of 3.2 and can be used behind electrical boxes as insulation."

    The statement is meaningless without specifying the thickness of the sample they are discussing. Presumably, they mean R-3.2 per inch — but without a thickness measurement, we're all left in the dark.

  30. Expert Member
    Michael Maines | | #30

    Martin, on this page they are clear, "R-3.2 per inch." The whole sheet does read like the marketing people got hold of it after the tech guys wrote it.

    I'm intrigued by the idea of the permanently flexible latex foam as drywall gasket though. With fully air-sealed framing cavities, fiberglass could actually perform adequately. The addition of exterior foam would keep the delta T to a minumum, reducing convective looping.

  31. GBA Editor
    Martin Holladay | | #31

    I agree. The system shows a lot of promise. My criticism is not a criticism of the system — just a criticism of the clarity of the marketing materials.

  32. Frank | | #32

    Have you looked at OC's Energy Complete System?

    As a one-time homebuilder wrestling with new terms like convection, conduction, radiation, diffusion, heating days v cooling days, permeable/retarder/barrier, 2.5 ACH @ 50 pa, ERV v HRV...I'm certainly attracted to OC's Air Sealing Claim + Insulation performance.

    2000 Sq ft home + basement, Thermal Envelope main floor and second floor, Cathedral ceilings - scissor trusses in attic, Seisco 18 KW microboiloer closed radiant system, HRV - Seattle, Wa.

  33. Danny Kelly | | #33

    The main reasons open cell foam is not a great canidate for a flash and batt are - It is almost impossible to spray a 1" layer of open cell - it expands too quickly and even if you could it would not do you any good because it is only an air barrier when it is 3" thick. It could be used in a very cold climate when trying to reach a very high R-Value but does make sense to combine it other products anywhere else.

  34. Frank | | #34

    Are you referring to OCs Energy Complete System foam which they use for air sealing (ref 26 above)...or is your comment directed at open cell foam in general (used in a flash-n-batt application)? thanks, Frank

  35. Frank | | #35


    If an Insulation contractor was to use closed cell foam with the same methodology as the OC energy complete system latex foam (as an air sealant), would it yield the same results? (OC Energy Complete is offered by few contractors...most fellows will spray closed cell foam however).


  36. Riversong | | #36


    Owens Corning's Energy Complete system is intended as a cheaper and lower-tech alternative to flash and batt or flash and fill that allows the use of the dreaded Pink Stuff while eliminating some of its liabilities. It's ironic that OC's comparison chart for various insulating approaches shows that fiberglass batts alone are the worst performers by a mile (but they're cheap).

    Latex foam has the advantage of being toolable and paintable (must be painted if it's exposed to the exterior), has low expansion and is water cleanable.

    But, it's highly flammable, produces flammable heavier than air fumes during application, requires personal protective equipment during installation, is highly vapor permeable and absorbs water. It has less adhesion than other foams and, like all latex, will shrink over time.

    Other than being an improvement over plain fiberglass, it's mostly more hype from the Pink Panther.

  37. Frank | | #37

    ...darn Robert - I thought I was looking at the mac-daddy of air seal/insulation systems with Energy Complete.
    Well then, let me ask the same to you as I posed to Martin...if I was to shoot closed cell foam as prescribed by Energy Complete to address air infiltration and drywall sealing (ref application, use a blown-n-bib for stud bays (NOT flash-n-bib in the stud bays - I need drying to the exterior for my marine environment), a latex vapor retarder primer on my drywall to address diffusion, properly size and balance my HRV for 2 adults and 2 rowdy toddlers, further ventilate in bathrooms and kitchen (short rigid ducting vented outside)...wouldn't I be putting together a solid program (92.3% solution)? Cheers, enjoy your posts...

  38. Riversong | | #38


    Is this new construction? If so, what stage of construction are you at?

    Closed cell foam cannot be applied to most of the surfaces listed in OCEC, since they are expanding foams not surface treatments.

    What EC is trying to do is an easier method of the Air-Tight Drywall Approach (, except they fail to address electrical boxes which are a major source of air leakage.

    If you haven't yet framed the house, I would recommend the ADA system using either EPDM gaskets ( or Tremco acoustical sealant. If it's already framed and sheathed, then the alternative though less effective "simple caulk and seal" uses caulks and sealants to do the same as shown in the Energy Complete system.

    But, in either system, don't forget the Lessco polypans ( behind all electrical boxes in insulated walls and ceilings.

  39. Frank | | #39


    Yes, new construction. I am currently framing (1st floor/walls complete w/ 1/2" cdx , 2nd floor joists in place).
    That being said, I'm unable to put a gasket on the top plate of my first floor but could do the same on the second floor. Do you have a suggestion as what to prioritize for maximum air sealing (or rather minimal air infliltration) at this point...I've let the horse out of the barn...

  40. Riversong | | #40


    The top and bottom of the building are the most important places to air seal. You can use construction adhesive (such as PL Premium urethane) to seal the framing from that point upwards, and get a foam gun and a half dozen cans of PurFil or other ozone-friendly low-expansion foam to seal the sill and band joist and any exposed sheathing joints as well as mechanical penetrations and around doors and windows.

    I would get the Lessco boxes and make sure the drywallers caulk the top and bottom plate edges, door and window openings and Lessco flanges as they hang the rock. Make sure the interior air barrier is continuous from wall to upper ceiling, with special attention to attic kneewalls, cantilevered floor joists and any hatches into unconditioned space.

    If you're using a pull-down attic stair, the only one worth using is this ( insulated and air-tight unit. No ceiling light cans in the insulated ceiling, and make sure to seal around chimneys and plumbing or radon vents where they penetrate the thermal envelope. I use a roof flashing for the plumbing stack at the ceiling level and metal flashing and mortar fire/air stops around masonry chimneys.

  41. Frank | | #41

    Great Stuff Robert ~ family and I appreciate how to sound proof the kids' rooms!

  42. Frank | | #42

    we've discussed the interior of the envelope. One of the products I'm considering for the exterior that touts superior weather/air seal properties while still allowing 50 perms of breathability to the exterior is Wrapshield by . Any comments on this product?

  43. joe | | #43

    OK, here is the way it is i have dont insulation for many years, if fiberglass touches either the plywood wall or any other material is loses its R-value, thats it in a nut shield. Also use your common since if you use foam and fibergalss togther you are setting yourself up for a major problem down the road. I have seen where this has actually rotted the floor away from the wall, sorry people its the true, Now if you properly install cellulose with someone who has year of experience, you can go up and touch the cellilose and it will fill only damp let set for the week and your will be ready for sheetrock. Now if its in a lower under ground you need to let it dry for at least 2 weeks. I know all about flash and batt and i have actually test that have been done at Oakridge National Lab. And again if the fiberglass touches plywood or any other matter it will lose its R value have the test to prove it.

  44. Riversong | | #44

    if fiberglass touches either the plywood wall or any other material is loses its R-value

    This statement has no basis in either hygro-thermal physics or fact.

    This writer seems to have as little comprehension of thermo-dynamics and building science as he does of the English language.

  45. Keith bollman | | #45

    Hi folks, I recently had my second floor reinsulated as it never was completed from 20 years ago. I live in Vemont - Here is my situation and what I elected to have done. 2X12 rafters 2X6 collar ties. Pre existing soffit to gable vent . My insulator installed used closed cell foam to seal all air infiltrations at soffit where pre existing soffit ventilation was generated then instatlled 1" foal faced ridgid insulation and used 3/4" stapping to hold insulation up and act as fasteners for drywall. All joints were taped with foil tape.I then installed and taped ceiling with 1/2" drywall. My insulater they blew in high density cellulous in rafter bays and 2' on ceiling. Prior to blowing in insulation all ceiling and wall penetrations such as outlets and light boxes were foam sealed. I having been a general contractor for 20 years (which of course explains my unfished house) was very sceptical of this insulation approach. I had planned to either foam entirerly or stay with conventional insulation and soffit to ridge ventilation techniques. My insulator convinced me against my better judgement that this was the way to go. everthing he told me when i questioned him about this aproach made sense at the time and maybe still does. So my questions .... Is this a good technique? Also more importantly it seems as if i am experiencing negative pressure issues now, how do I find out if i am correct and what can / should i do to solve problem? FYI The reason I think i may be experiencing negative pressure is that I can now smell creasote from time to time and I have not been running heat of any type. This is something i have never smelt before the insulation project was completed. I plan to question my insulator ( very nice your gentleman) but would appreciate imput from anyone who has it. Thanks Keith

  46. Riversong | | #46


    If you have a new question to bring to the forum, you're far better off starting a new thread than by piggy-backing on an ancient one.

    What do you mean "reinsulate"? Was the attic floor already insulated and air-sealed?

    What could you possibly mean by "used closed cell foam", since such foam is sprayed in place and cannot be re-used. Or do you mean pieces of rigid foam board that were sealed in place with canned foam?

    Why in the world would use drywall and then cut holes to insulated rather than blowing through the foam board, sealing the holes and then drywalling over (which is how this is done)?

    Do you have creosoted sills in your house that could possible be a source of a "creosote" smell? Creosote is a banned carcinogen and has no place in a residential structure.

    If the contractor used sprayed foam, the smell you're noticing may be the chemical odor of the foam if it was not properly installed at the right mix and the right temperature at the appropriate thickness.

  47. GBA Editor
    Martin Holladay | | #47

    The insulation method used by your contractor -- dense-packed cellulose in unvented rafter bays -- is fairly common in Vermont but is controversial and may be risky. It would have been safer to include ventilation between the top of the insulation and the roof sheathing.

    Here's one possible explanation for your creosote smell: the insulation work reduced your home's air leakage rate. So your home is tighter than ever. I'm guessing that you have a variety of exhaust appliances -- perhaps a bath fan, a clothes dryer, a range hood, and maybe a water heater. These appliances put your house at negative pressure. The makeup air is coming down your chimney, and you are smelling creosote, even when you have no fire in your stove or fireplace. (That's the smell of your chimney flue.)

  48. Riversong | | #48

    Of course, it would be the chimney (assuming you're burning wood) - I didn't think of that.

    But tightening up the roof should have reduced the negative pressure in the lower floors, since there'd be less air escaping at the top. If you're wood-burning appliance is upstairs, though, it might now be in the negative or neutral pressure zone and be more easily influenced by the draft from exhaust fans.

    You need to give us a lot more information about your house if you want an appropriate assessment.

  49. KEITH BOLLMAN | | #49

    Robert & Martin – First thanks for your speedy replies, I was in a big hurry in my earlier post and was obviously not clear of my situation.

    Robert, to answer your questions…

    The floor was not insulated; I had previously insulated the rafters with fiberglass and proper vent (the older white Styrofoam type) which I never liked. The area was left unfinished other than that & was not occupied. As I now intended to complete the second floor I wanted to investigate better ways to insulate and consider either improving ventilation or possibly eliminating it by using foam. FYI I have eight gable front dormers so as you can imagine proper ventilation was a bit tricky to achieve. The closed cell foam was used only in the new insulating process I had decided on, and was used to aid in sealing air flow from soffit vents previously in place. My existing ventilation was achieved through use of continuous vents in soffit with proper vent to attic and gable vents in both main gables. I always felt soffit to ridge was the best way to ventilate so was unhappy with what existed. As far as the new technique used, first all existing fiberglass was removed. Second all existing penetrations from soffit were blocked by means of ridged dams and closed cell foam which was spayed over entire ridged blocks and to seal areas which left small air gaps ( obviously insulator was not going to scribe blocks, especially since he planned to foam, the blocks were to stop foam and cellulous from flowing into sofffits. After all soffits were blocked 1” foal faced ridged insulation was installed from eave connections to collar tie/ rafter joint. The foil faced insulation was held in place on the slopes with plastic washer type nails and only enough nails were used to hold the foil faced in place until strapping could be applied perpendicular to rafters, this served a couple of purposes, First to hold foil faced insulation up as the insulator was to later blow high density cellulous in rafter bays so the washer head nails would not hold pressure of cellulous. Second purpose was to act as nailing for drywall to be later installed only after insulation was totally completed. The one exception was to be the ceiling, that area the insulator wanted dry walled and taped so that once rafter bays were filled he could then cover the horizontal bays of the collar ties. Prior to blowing cellulous insulation all electrical or other penetrations especially in ceiling were foam sealed , also the washer nail heads and ridged insulation joints were taped with foal tape. Hope that makes sense.

    No creosote sills only source of creosote is wood stove and not much either as I burn exclusively kiln dried firewood or clean & check chimney regular. I am a 20 year fireman so often chimney gets checked from cleanout twice a week.

    As to you comment of the smell possibly being the foam, I will have to check that possibility but it sure smells like creosote to me. Interesting also that the smell comes and goes and I expect is more prevalent during certain barometric situations.

    Martin, I agree with every comment you have made 100%! The question is if this, as we both suspects the case, now what? Mechanical ventilation, I never thought this could happen to me I used to laugh at houses with no ventilation now I worry about my families health even more than my house and probably both are at major risk. Thoughts? Stove is not in use this year and is on first floor.

    Thanks again

  50. GBA Editor
    Martin Holladay | | #50

    If you have evidence that my analysis is correct, then you need to either:
    1. Install a new wood stove with ducted outdoor combustion air, or
    2. Crack a window to allow fresh makeup air to enter your house when you are operating any exhaust appliance, or
    3. Install a balanced ventilation system (for example, an ERV or HRV) or a supply-only ventilation system.

  51. Riversong | | #51


    If your chimney has no rain cap, then it will smell like creosote every time it rains.

    If you have no whole-house ventilation, then you must install that. No modern house is livable without both point-source moisture removal (baths and kitchens and possibly laundry) and whole house ventilation to meet ASHRAE 62.2 standards.

  52. KEITH BOLLMAN | | #52

    Robert, Martin

    I thought I posted yesterday but did not see my reply, not sure what happened.

    Is it possible that the creasote smell is a result of abnormal barimetric pressure? The reason I ask is that the smell was previlant for 3 or 4 days mostly in evenings and I have not noticed the smell in at least a week. I also have been using ( I think ) more fresh air as in the last week I have started running my furnace in the evenings as well as all normal year round items.

    Recommendations of reasonable cost whole house ventilation systems would be appeciated!

    I have point source moisture for all items mentioned.

    I had thoughts of installing a chimney cap , can't hurt.


  53. GBA Editor
    Martin Holladay | | #53

    I don't know if you have a range hood, but range hood fans are the usual culprit when it comes to pulling makeup air down a chimney. Some range hood fans are rated at 600 or 800 cfm -- they move way too much air for a tight house.

    Here's more information on designing and installing a ventilation system:
    Designing a Good Ventilation System

  54. Riversong | | #54


    As I'm sure you've noticed, when barometric pressure is low smoke stays close to the ground because there isn't as much density difference between the smoke and the air. The same will be true of the warm air trying to escape your chimney - it will rise faster on high pressure days and have trouble getting velocity on low pressure days.

    The least expensive whole house ventilation system is a 24-hour programmable timer on one or more bathroom exhaust fans (assuming you have quiet, efficient and quality fans). If your house is leaky enough, you can get away without make-up air inlets. If not, then you will need to install a half dozen passive inlets (like the Aldes Airlet 100) in bedrooms and living spaces.

    I would definitely get that chimney cap, as rain will dissolve the creosote lining the chimney and wash it down. A screened cap also keeps birds and squirrels out.

  55. Earthcore SIPS | | #55


    Have you checked out a product called rstud.
    It is a thermally broken framing member that has a high r value.
    The rstud eliminates thermal bridging due to the stud and allows for a higher performing wall assembly.
    You can visit the website by searching on rstud or insulated lumber.


  56. Alicia | | #56

    I am building a new home outside of Athens, Georgia. Obviously this is in a far different climate than the ones you all have discussed earlier (Calgary, Seattle, and such). My very helpful builder has gone through a number of different insulation scenarios with me. My aim is not only to get the best energy efficiency my budget will allow, but also to control for moisture. I currently live in an 80-year-old house built on a combination cellar and crawl space. Because of moisture issues here, I am maybe a bit paranoid about creating similar problems in this new house. All this to say, I have looked at everything from vented crawl space and attic with fiber glass batts throughout to unvented and conditioned c-s and attic using closed-cell spray foam. Many of the comments I've read here are making me wonder if spray foam may be overkill for the climate here as well as an invitation for moisture. I would be so grateful for any wisdom you experts can bring to my situation. Whenever we dry out from the recent snow we've had, then they'll be pouring the foundation, so I still have time to decide. Thanks for your help!

  57. Alicia | | #57

    PS- What brought me to this site was that one of the more recent options presented was the closed -cell foam flashing in the attic with cellulose. I am assuming if I did this it would mean a vented attic. The air handler for the upstairs will be in the attic, so I wasn't sure if it would be better to make that a conditioned space or not.

  58. GBA Editor
    Martin Holladay | | #58

    1. It would be best to locate your air handler inside your home's conditioned space.

    2. There is nothing about spray foam insulation that makes it likely to contribute to moisture problems.

    A home with cellulose insulation can have moisture problems, or be free from moisture problems. A home with spray foam insulation can have moisture problems, or be free from moisture problems.

    If you want a home without moisture problems, you need a good design and good details. This takes "whole house" thinking. It's more complicated than just choosing one type of insulation.

  59. Alicia | | #59


    Thanks for your response.

    So, it would be better to have the air handler in an upstairs closet (there is a very large one off of the office in this house) than in the attic?

    I understand your point about a whole-house strategy in planning the insulation and overall efficiency of the house. At least, I understand the general concept. I don't, however, know enough about specifics of good design of a house to know where to begin in making the insulation decisions. I have read in this series and have heard from local insulation installers that the most important areas would be the crawl space and attic. For that reason, I considered doing spray foam and unvented spaces for both (with the air handler in mind for the attic especially having heard that it's better to put them in conditioned spaces). I guess I just want to make a wise decision, both energy-wise and budget-wise. What would you say would be my best next step in making a whole-house plan for efficiency?

  60. GBA Editor
    Martin Holladay | | #60

    If you feel confident that you understand the building science concepts that affect moisture in homes, you can, of course, design these details yourself.

    If you are unsure of your own ability to tackle the task, it's best to find a designer or a builder you can trust.

    Assuming that you want your air handler to be within the home's conditioned space -- and I think that's a good idea -- then your air handler can be in your sealed crawl space, in an equipment room on either floor, or in a conditioned attic.

    In your climate, I think an unvented sealed crawl space makes much more sense than a vented crawl space.

  61. Alicia | | #61


    Thanks again for responding. I am particularly grateful for the opinion on the crawl space.

    In truth, I feel more than confident that I DON'T understand the building science concepts that affect moisture in homes well enough to design these details myself. My builder is very competent, but he has had more experience with more traditional types of insulation and vented c-s and attic than with others. What type of designer should I consult? I confess I don't even know the title of the type of designer I would need to consult.

    Thanks for your patience in taking on my questions. I'm sure everyone who normally contributes to this exchange is far more knowledegable and well-versed on the topics at hand. I, on the other hand, have only recently started thinking about any of this b/c of building this house. Naturally, though, I want to do it right. Thanks again for all your help!

  62. GBA Editor
    Martin Holladay | | #62

    I know of three resources in Georgia you might want to contact or look into:

    1. Southface Energy Institute
    241 Pine Street
    Atlanta, GA 30308

    Check out their Web site. I think they offer educational events and have educational resources.

    2. Carl Seville, a GBA Advisor, lives in Decatur, GA, and sometimes works as a consultant. I think you can contact him at info [at] sevilleconsulting [dot] com .

    3. Allison Bailes also lives in Decatur, GA, and sometimes works as a consultant. I think you can contact him at abailes [at] energyvanguard [dot] com .

  63. Alicia | | #63

    Thanks, Martin!! I will check out these leads. I so appreciate your help.

  64. user-509810 | | #64

    Hi Martin: Do you have any resources for my area? Washington DC region

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