1 Helpful?

Post-cure/long term off-gassing with Bayer’s Bayseal closed cell spray foam insulation (“SFI”)

I am considering having Bayer’s Bayseal closed cell spray foam insulation (“SFI”) installed in the attic and basement rim joist at my New Jersey home. I am interested in hearing thoughts on the recent concerns over off-gassing of the SFI that I have been reading about. My questions assume SFI installation gets done correctly (I have read about the improper installation problems causing odors). Anyway, the issue of concern/interest for me is long-term off-gassing AFTER a properly done SFI job. None of the information on off-gassing I have seen draws a bright line between (i) the risks of SFI off-gassing during installation/before the SFI materials cure VERSUS (ii) risks of off-gassing in the post-curing period – the long run, i.e., a few days after the SFI cures and the ensuing months and years when the home is occupied.

It makes perfect sense to me that during spraying of SFI and a few days after the cure, there will be odors and off-gassing. But it seems to me that a few days after the SFI cures, there should be a dramatic drop in off-gassing as the SFI becomes highly stable. If one were to graph off-gassing, it would seem to me there would be an asymptotic decline in off-gassing after a few days post-installation.

A webpage within this very website (i.e., gba.com) seems to confirm my belief as stated above when it says: “Polyurethane is in a lot of stuff, from foam mattresses to bowling balls. When it is fully reacted or "cured," it is stable and its chemistry is not a significant concern. However, some products, however, such as adhesives, coatings, and spray foam, react while being applied by builders or homeowners doing insulation retrofits, and continue to react for some hours afterwards, and may contain "uncured" isocyanates to which people may be exposed.”

Other sources seem to corroborate that post-cure, SFI should be highly stable/inert. With regard to SFI's main ingredient, polyurethane, Wikipedia states that "Fully reacted polyurethane polymer is chemically inert." and cites to "Health Hazards Associated with Polyurethane" from the "Journal of Occupational and Environmental Medicine (1966)". But, as cited, the article is from 1966; there has got to be more current info on off-gassing post-cure. Moreover, SFI is more than just polyurethane (SFI is also has halogenated flame retardants, etc.) so perhaps a clean bill of health on polyurethane does not equal a clean bill of health on SFI.

So, assuming a properly done SFI installation, I would like to hear comments on off-gassing and lingering chemical odors in the SFI POST-CURE PERIOD (weeks, months and years down the road). Of note, the SFI project I am contemplating on my 30 year old house which is presently insulated entirely with fiberglass is:

1. ATTIC - SFI (6”) on the floor of a vented, non-living space attic (vented via (i) vents (openings) on both gables; and (ii) a whole house fan (“HHF”) that vents through the attic and results in evacuation of attic air when the HHF is turned on (intermittent/when we feel like it); and

2. BASEMENT - SFI (2”) on the whole perimeter of the basement’s rim joist. Basement has no passive or automatic ventilation; one would have to open a window if one wanted fresh air.

3. Nothing else in the house to be changed (i.e., all other fiberglass presently in the walls to remain in the walls, etc.).

So is the concern with off-gassing (whether it be any of the ingredients in SFI or additives thereto (flame retardant additives (halogenated flame retardants in the B-side component that have been conclusively linked to birth defects and loss of fertility))), and other chemicals leaching a concern DURING install and the day or two thereafter, or are these concerns LONG-TERM, post-cure? I am already committed to leaving the home for a few days during and after installation so the question is to long term off-gassing. I thank everyone in advance for their insight and comments based on science and experience.

Asked by D S
Posted May 14, 2014 9:56 AM ET
Edited May 14, 2014 10:30 AM ET


35 Answers

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As far as I know, every case of lingering odors has involved installation errors. For more information on these problems, see Spray Foam Jobs With Lingering Odor Problems.

Builders routinely use spray-foam insulation to insulate rim joists, and the vast majority of homeowners are completely satisfied with these rim joist insulation jobs.

If you are at all worried about lingering odors, however, there is no reason to specify spray foam where its use is unnecessary. Most green builders would advise you that it makes more sense to use cellulose insulation rather than spray foam insulation to insulate an attic floor. You will get a higher R-value at a lower cost if you use cellulose rather than spray foam.

Of course, it's always a good idea to perform air-sealing work before installing cellulose on an attic floor. For more information on this topic, see Air Sealing an Attic.

Answered by Martin Holladay
Posted May 14, 2014 10:09 AM ET


Dear Martin,
Would you also suggest using cellulose insulation under the floor? Or maybe mineral wool?
Thanks a lot!

Answered by Ohad Coen
Posted May 15, 2014 2:04 PM ET
Edited May 15, 2014 2:04 PM ET.


I notice that you have already started a different thread with insulation questions:

It can be confusing for one person to scatter questions in several threads.

If your house is on piers, you can find guidance on insulating the floor assembly here:
How to Insulate a Cold Floor.

If your house is over a basement or crawl space, I recommend that you insulate the basement walls or the crawl space walls, not the floor assembly.

If you need to install insulation because your joist bays include hydronic tubing for radiant-floor heat, you can use a wide variety of insulation products. Check out these three previous threads:

Heat Transfer Plates for Radiant heat under floor joists

Reflective barrier and insulation for radiant heat

What is the best method to insulate beneath PEX pipes installed under floor joists for radiant heat?

Answered by Martin Holladay
Posted May 15, 2014 2:31 PM ET


FYI: EPA considering action on certain chemicals associated with spray foam insulation, such as MDI & related polyisocyanurates


Answered by Terry Sopher Sr
Posted May 15, 2014 4:42 PM ET


This is the original questioner, DS, responding to Terry Sopher, Sr. who posted Answer #4. Terry, you seem to have missed the point of my question. The issue is SFI pre-cure versus post-cure dangers from off gassing. Certainly there are SFI pre-cure (during installation) dangers, but I could not find evidence of SFI post-cure dangers. SFI post-cure (long term) dangers, if any, is my issue. The EPA webpage you linked to says nothing about post-cure, but only discusses risk pre-cure. The EPA webpage says, "but EPA is concerned about potential health effects that may result from exposures to the consumer or self-employed worker while using products containing UNCURED (unreacted) MDI and its related polyisocyanates (e.g., spray-applied foam sealants, adhesives, and coatings) or incidental exposures to the general population while such products are used in or around buildings including homes or schools." (emphasis mine). The EPA is speaking of pre-cure (during installation) times, not post-cure, post-install. Regardless, thank you for your input.

Answered by D S
Posted May 21, 2014 4:30 PM ET


FWIW: Closed cell BaySeal is blown with HFC245fa, which has a global warming potential (GWP) of about 1000x CO2, whereas the open cell version (like most open cell) is blown with water:


The 2" shot on the band joists is not going to be a crime against the planet, but 6" on the attic floor probably is- it will probably never recoup the GWP impact of the blowing agent in the reduced energy use over the life of the building when going with that much foam.

It doesn't take anything like 6" of foam to air-seal an attic floor, and there are much cheaper lower impact methods of getting higher R values there. Some amount of spray foam for air-sealing may make sense there, but unless it's a cracked/crazed plaster & lath ceiling below, it won't take a full coverage to air seal it. (Even a 1" flash shot of closed cell would be good enough if it's too tough to air seal otherwise.)

Answered by Dana Dorsett
Posted May 22, 2014 3:11 PM ET


This is DS, the original poster of the original 5-14-14 question, updating the original question with a request for input with regard to the following. This website: http://sprayfoamdangers.com/tag/epa/ which seems to be the anti-SFI "blog" of a concerned mom, asserts, "Spray foam also off-gases a toxic soup of other known carcinogens, endocrine disruptors, ect ect. [ sic]" I am not overly concerned by statements from someone who does not even know that the correct abbreviation for et cetera is "etc.", but is there any evidence for concerned mom's allegation in the case of properly-installed closed cell SFI?

Answered by D S
Posted Oct 9, 2014 3:07 PM ET


The rate of off gassing and your ventilation rates are what determines the your exposure/concentration.

Even geniuses make typos- wouldn't use that as a measure of credibility.

Download the MSDS pages for the product in question, and do some online research on the toxicity or other bioactivity of the potential offgassing, and at what concentrations. There are nasty materials in all sorts of things we use daily, but the dose & response doesn't necessarily rise to clinical illness. The dyes and binders of newsprint ink can be unhealthy, but not easily absorbed when dry. Should we be worried about the offgassing in cellulose insulation too? (Some people are, but it's mostly about some of the fire retardents used.) SFAIK there haven't been clinical cases where long term exposure to outgassing polyurethane insulation at the extremely low doses you would find in a home where it was A. properly installed and B . the house is properly ventilated. But that's not to say there is zero tail-end risk associated with SPF.

There is evidence of occupational exposures to some of those chemicals causing health issues. The foam installers and chemical manufacturing workers may carry some risk.

If there is a general health issue with houses with polyurethane insulation the problem is nowhere near the order of magnitude of experienced with urea formaldehyde foams offgassing back in the 1970s. Some of those houses had to be condemned, but many are still standing, with the foam still there (though pretty much completely outgassed, decades later.)

Answered by Dana Dorsett
Posted Oct 9, 2014 5:51 PM ET


In my opinion, I have an impression "D S" is not a concerned individual, rather a troll for industry hoping to stir the bee hive.

D S if you were a concerned citizen, builder or architect you would read what the concerned Mom has on her blog as she is personally living the life of a spray foam victim. If you take pleasure in insulting the author for her own personal experiences your not seeking truth. The concerned Mom has one of the most truthful and informative web pages out there about SPFI and the people who have been personally affected.

If I'm wrong about you and your seriously considering any SPFI product, your seeking answers in the wrong forum. You should be asking these questions of the chemical provider directly and from your selected installer. Almost all SPFI chemicals have hidden proprietary ingredients of which they will never disclose to you or I. With that said you ned to draw the line as to what you consider safe and what your willing to risk.

Here's your warning from the EPA......

and a warning from CPSC on properly installed SPFI's amines....(the unknown)

Answered by Richard Beyer
Posted Oct 9, 2014 10:56 PM ET


I am a home owner looking into the same issues as DS. I am considering applying spray foam insulation to a basement level bedroom area. I framed for it but then became aware of the concerns many seem to be registering about long term offgassing. I am surprised by the lack of direct answers to DS's inquiry.

Do we or do we not have clear indication that spray foam insulation, properly applied does not offgass toxically?

Dana, your answer in post number 8 is the most direct. But your advice to "Download the MSDS pages for the product in question, and do some online research on the toxicity or other bioactivity of the potential offgassing, and at what concentrations" is a tall order for an ordinary consumer who may not even have yet selected a particular product, who is not knowledgeable about its chemical makeup and who has little way of drawing comparisons on the amounts of each particular chemical involved to those listed in MSDS pages. If there is a real question about toxicity, we need to know it.

Richard Beyer's comments questioning the integrity of DS's thoughtful research are inappropriate. His references are about flame retardants which are just one set of the chemicals in question. His second reference concludes Health-based exposure limits are not available for consumers, and occupational exposure limits are not yet established for the majority of amine catalysts used in SPF.... In the past two years, CPSC staff, along with other members of the Federal Working Group on SPF10, have met with members of the American Chemistry Council who have provided exposure data on some high- and low-pressure SPF systems. However, staff and other federal partners are not satisfied with the robustness of this data." It recommends further study.,

So, I ask: if there is any updated knowledge about long term offgassing from spray foam insulation and I ask if you at Green Building Advisor consider this product to be inert after correct application and safe or if you think there may be cause for concern about long term harmful chemical exposure.Health-based exposure limits are not available for consumers, and occupational exposure limits are not yet established for the majority of amine catalysts used in SPF. Also, using occupational exposure limits for the general population may not be protective due to factors, such as sensitive populations and exposure duration differences. In the past two years, CPSC staff, along with other members of the Federal Working Group on SPF10, have met with members of the American Chemistry Council who have provided exposure data on some high- and low-pressure SPF systems. However, staff and other federal partners are not satisfied with the robustness of this data. Put another way, would you put your child in a partially below grade bedroom insulated with spray foam insulation?

DL, I would like to learn what you concluded as well.

Thank you for your guidance with this issue.


Answered by Chris Campbell
Posted Jun 10, 2016 2:06 PM ET


Q. "Do we or do we not have clear indication that spray foam insulation, properly applied does not offgass toxically?"

A. We do not have any clear indication that spray foam insulation, properly applied, off-gases toxically. Toxicity has been shown for lead and asbestos, but not for properly installed and cured spray foam.

Improperly installed and cured spray foam has been known to emit a loathsome odor, and some homeowners with smelly foam have medical symptoms.

Answered by Martin Holladay
Posted Jun 10, 2016 2:28 PM ET
Edited Jun 11, 2016 5:09 AM ET.


I apologize that in my inquiry above, I inadvertently re pasted into the bottom of my inquiry the quote I had referenced earlier - sorry.
Chris Campbell

Answered by Chris Campbell
Posted Jun 10, 2016 11:15 PM ET


Thank you for your direct reply. How troubled should we be that hundreds of thousands of people are using SPF product to insulate living spaces? As stated above, there are many products with toxic chemicals in them that we trust are inert. Knowing that there are concerns, would you sleep in a space insulated with spray foam insulation? Would you put it in your home?

Thank you.

Answered by Chris Campbell
Posted Jun 10, 2016 11:23 PM ET


Martin, I apologize but in rereading your reply, Im not totally clear what you mean: you say "we do not" when I ask if we have clear indication that spf insulation does NOT offgas. But you then say "Toxicity has not been shown for it the way it has for lead and aesbestos."

So is the conclusion we just dont know? Is there any further discernment?

Thanks again.


Answered by Chris Campbell
Posted Jun 10, 2016 11:36 PM ET


Yes, I have slept in spaces insulated with spray foam insulation.

Answered by Martin Holladay
Posted Jun 11, 2016 5:09 AM ET


I haven't seen any evidence that cured spray foam, properly installed, is toxic. The "lingering odor" cases are very rare, and all of them involve foam that was not properly installed.

If the risk associated with the installation of spray foam worries you, don't specify spray foam.

Answered by Martin Holladay
Posted Jun 11, 2016 5:12 AM ET



If spray foam was clearly the best way to make an excellent envelope at a reasonable cost, we would try to persuade you to put aside your concerns and use it. But most of the time there are options that are equally effective and less expensive anyway. GBA is generally helpful and enthusiastic about helping people figure out alternatives, and I'd encourage you to post a new question if you want help with any particular application.

Personally, I like to avoid spray foam even though I don't worry about the long term exposure issues when it cures properly. My reasons for avoiding it are three. One is the high global warming potential of the blowing agent used in closed cell foam. Another is the rare jobs that go wrong and have lingering odors and sometimes health impacts because the foam doesn't cure right. ( I know that they are very rare, but they seem to be nightmares when they do happen.) And finally, it's expensive, and there are other more effective ways to save energy that I'd like to spend my money on instead.

Answered by Charlie Sullivan
Posted Jun 11, 2016 1:53 PM ET


The spray foam industry has done a great job in marketing their product as the superior way to insulate over batts or anything else. When building we had installers recommend only a couple inches of closed cell because anything over that is overkill. Plus they scare the consumer because batts are less effective due to air infiltration (which I guess is partly true) and prone to mold. I don't know why I posted this...it just seems like installers of foam are very aggressive and make outlandish claims to scare the consumer. As a consumer it's hard to filter out what's true and what isn't in this industry.

Answered by Mel Tillyard
Posted Jun 12, 2016 2:18 PM ET
Edited Jun 12, 2016 2:19 PM ET.


What other options are there to spray foam where I need to insulate an attic roof that is a living space below? This attic has very complex dormers and hips and valleys making it very difficult to vent at the ridge and it has brand new roof. I have the ceiling removed now and tried putting 1" thick xps foam board that has radiant foil attached to one side foil facing up with a 1" airspace made using ripped osb spacers between the foam and roof deck. We fit it as tight as we could between the rafters then installed fiberglass batts up against the foam board with kraft vapor barrier facing down. I just began installing drywall last week and noticed that on very hot sunny days after we had cloudy overcast days the peaks of all the highest dormers are wet on the kraft paper. I pulled the batts back and the fiberglass is dry and so is the foam board above it. Only the kraft paper vapor barrier is getting soaking wet and only on certain sunny days. If I turn on some large fans facing up the paper drys very quickly. I am concerned if I continue and drywall the ceilings this problem will continue to happen inside the cavity and rot my roof deck since there are no vents and the moisture will be trapped inside molding the drywall and everything else. So other than spray foam what else could I do in this situation? I have read other threads on the site about condensation on cathedral ceilings and no I have no recessed can lights only a few 4in boxes will be on ceiling for the light fixtures that I plan to caulk and seal around the drywall cutouts as best as possible. Thanks!

Answered by Brian Tober
Posted Jun 14, 2016 10:11 AM ET


@Brian. You probably should start a new thread for this discussion.

In the meantime, a few questions:

- Where are you located?
- Is the living space on another floor or is it in the attic?
- Is the attic ventilated or not ventilated?
- Does the attic have additional insulation other than what you described in your post?
- What is the depth of the space you have insulated with foam and fiberglass?
- What is the R value of the fiberglass batts?
- Is the space you are describing conditioned (HVAC)?

Answered by Steve Knapp CZ 3A Georgia
Posted Jun 14, 2016 3:31 PM ET
Edited Jun 14, 2016 3:40 PM ET.


If the kraft facing is getting damp, I imagine that your attic is air conditioned and the kraft facing is cold. It's possible that your roof sheathing is damp, and the sun is driving the moisture inwards. The moisture condenses on the first cold surface it encounters (the kraft facing).

This type of "vented" roof assembly won't work unless each rafter bay has a ventilation inlet (usually a soffit vent) and a ventilation outlet (usually a ridge vent). For the type of roof you are describing -- one with "very complex dormers and hips and valleys" -- the vented approach isn't possible. You need an unvented insulated roof assembly (one that either uses spray foam on the underside of the roof sheathing, or rigid foam above the roof sheathing).

For more information on your options, see How to Build an Insulated Cathedral Ceiling.

Answered by Martin Holladay
Posted Jun 14, 2016 3:46 PM ET


Hi Steve Knapp;
I am in NJ few blocks from the beach 07740 zip code. The 2nd floor is an apartment with the roof is the ceiling it is a old house almost 100yrs old. The house never had any insulation on 1st or 2nd floors and had plaster and lath walls. House was flooded with 16 in of water on 1st floor in Sandy so I removed all plaster and lath on both floors so I could at least insulate with fiberglass and put in drywall to clean up the walls that had many lumps and cracks etc. The roof is very unique some areas have deep 9 in rafters and other sections have 2x6 rafters and 5 smaller dormers have 2x4 rafters. I used 1in foam in all deeper areas and 1/2" foam on the 2x4 rafters. The fiberglass is owens corning R-21 where it would fit and R-15 in the 4in dormers. I shimmed the rafters deeper so all the foam has the 1in airspace between the decking. There is no attic space to vent as the attic is entirely living space and always has been but like I said was never insulated in the history of the bldg. we owned it since 1964. It had hot water heat with cast iron rads but I am replacing them with fintube baseboard. If I can resolve the wet fiberglass vapor barrier issue I plan to install a mini-split for a/c it was previously only window a/c's. Thanks for any advice.

Answered by Brian Tober
Posted Jun 14, 2016 4:01 PM ET


PS right now there is no drywall in the 2nd floor nor any a/c or heat. I was about to close it up when i noticed the wetness so now at a standstill with my project. A drywall guy said I should tear off all the kraft paper that I created two vapor barriers with the foam above.

Answered by Brian Tober
Posted Jun 14, 2016 4:16 PM ET


Your drywall guy is wrong. Read my previous response (Comment #21).

Answered by Martin Holladay
Posted Jun 14, 2016 4:19 PM ET


"I have the ceiling removed now and tried putting 1" thick xps foam board that has radiant foil attached to one side foil facing up with a 1" airspace made using ripped osb spacers between the foam and roof deck."


"The fiberglass is owens corning R-21 where it would fit and R-15 in the 4in dormers."

You have a true vapor barrier (the foil-clad foam) on the exterior side of the insulation stackup, with an insufficient fraction of foam-R for dew point control for your location (US climate zone 4A.) In your climate the foam-R would need to be a minimum of 30% of the total to avoid moisture accumulation in the fiber over the winter. The R15 prescriptive in Chapter 8 assumes a code-min R49 total:


That may or may not be related to the moisture cycling you're seeing now, but it's a mistake that's best corrected before you end up with rotting rafters. Rather than a vented assembly, 2" of closed cell polyurethane (~R12) against the roof deck would allow you to install as much as R28 in fiber under the foam layer without risk of moisture accumulation. An alternative would be to fill the cavities completely with open cell foam and install 2 mil nylon (Certainteed MemBrain) as the vapor retarder behind the ceiling gypsum, which is low-permeance in the winter, but becomes vapor open when the sun is driving moisture out of the roof deck, which allows the assembly to dry quickly while still dramatically reducing the rate of moisture accumulation when the roof deck is cold.

Replacing the cast iron rads with fin tube is almost always a mistake. If you haven't already scrapped them analyze the system before moving forward.

Without the thermal mass of the greater water volume plus that of the cast iron it'll end up short-cycling the boiler unless you put sufficient fin tube per zone that it can deliver the full boiler output into that zone. At a 180F high temp on the boiler the fin tube delivers ~ 500 BTU/hr per running foot. Even with a tiny 2-plate 50,000 BTU/hr-in , 42,000 BTU/hr-out boiler that takes 85' of baseboard per zone to balance perfectly, and if you don't have at least 55' per zone it's at risk of short-cycling the boiler into low efficiency and higher maintenance, shorter lifespan. If the boiler is even bigger than that relative to the zone radiation, the problem becomes even bigger.

With the thermal mass of the rads to work with there is considerable forgiveness, since even when the zone is under-radiated relative to the boiler output the thermal mass and high/low settings on the boiler define a minimum burn time, for fewer, longer, and higher efficiency burns. If you're installing a condensing boiler the extremely low thermal mass and of fin tube becomes an even bigger short-cycling problem when running the system at temperatures low enough for condensing, since at temps low enough to get the benefit the fin tube emits only half (or less) the BTU rate than at an entering water temp of 180F.





The following is clipped from a draft blog-bit I was considering as an addendum to the boiler sizing blog sketching out the napkin-math for analyzing systems with cast iron radiation:
---------------------- begin clipped rough draft addendum

To analyze the cast iron you need to estimate three numbers:

1: The total square feet of equivalent direct radiation. (see: http://www.columbiaheatingsupply.com/page_images/Sizing%20Cast%20Iron%20... )

2: The total water mass/volume in the system, including the distribution plumbing and radiators. (For half inch copper it's about 1 gallon (8.34lbs) of water per 100' of pipe. )

3: The thermal mass of the cast iron in the system.

In an ideal system the ratio of the output of the boiler at minimum fire will be less than 50 BTU/hr per square foot EDR. At 70 BTU/hr per foot the thermal mass of the system may keep it from short-cycling and still run at reasonable efficiency but it won't magically turn it into a right-sized boiler that modulates.

You may have to look up the water volumes and shipping weight of new radiators of similar size & shape to figure out the water volumes. The relevant number for both is the weight/mass. The specific heat of water is 1 BTU/lb per degree-F, the specific heat of cast iron is 0.11 BTU/lb per degree-F. (http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html ) So to convert the mass of the iron to water-thermal-mass equivalent, multiply it by 0.11, and add it to the water mass.

As an example case, say you have a zone with a half dozen Sunrad or Burnham Radiant type radiators (http://www.republicsupplyco.com/SpecSheets/radiator-baseboardlit.pdf ) that add up to 225 running inches, and have 80' of total supply & return plumbing, all half-inch. According to Burnham's specs there is 1 square foot EDR per running inch, and 0.15 gallons per every 2.25" section, which is comparable to the OCS Cast Ray (http://ocsind.com/wp-content/uploads/2016/03/15981-OCS-Catalog.Updated15... ). Shipping weight on the Cast Ray is 5.1lbs per 2.25 section, so we'll use 5lbs/section as iron weight as a ball-park figure.

Plumbing water mass: 80' of pipe /100' per gallon is 0.8 gallons, x 8.34 = 6.7 lbs.

Radiator water mass: 225"/2.25" per section is 100 sections, x 0.15 gallons/section = 15 gallons, x 8.34lbs/gallon= 125 lbs.

Radiator cast iron thermal mass: 100 sections x 5 lbs/section is 500lbs of radiator, x 0.11 = 55 lbs water-equivalent.

Total thermal mass: 6.7 + 125 + 55= 187 lbs of water-equivalent.

Total sq.ft. EDR: 225" x 1 sqft/inch= 225 square feet EDR.

Ideally the boiler's min-fire output would be under 50 BTU/ft-EDR, which would be 225' x 50= 11,250 BTU/hr, in which case you'd be able to run at mid-90s combustion efficiency continuously, without cycling the boiler on/off. If that's the case the boiler is sized reasonably for the radiation, and you should be able to tweak the system to get it to run high

But let's say it's a Navien NCB 240, which has a min-fire input of 18,000 BTU/hr, and at 95% efficiency would be delivering 0.95 x 18,000= 17,100 BTU/hr. (That would be a ratio of 17,100/225' = 76 BTU/hr per foot EDR.) The rads are only emitting 11,250 BTU/hr which means there is (17,100 - 11,250=) 5850 BTU/hr of excess going into the system. When that happens the temperature will rise until the boiler's internal controls sense that it's over the outdoor reset setpoint and quench the burner, and wait for the rads to emit enough that the temperature drops back into the right range before re-firing the burner. 

A typical mod-con will have somewhere between a 5F and 10F difference in temp between the burner-off and refire, and this is where the thermal mass of the system comes into play. It takes 1 BTU to raise the temp of a pound of water 1 degree F, 5 BTU/lb to raise it 5F. So the BTUs to raise the 187lb thermal mass of the system 5 F is then 5F x 187lbs= 935 BTU. At the min-fire excess of 5850 BTU/hr that takes about 935/5850= 0.16 hours, or 9.6 minutes.

That is plenty long, not even close to a short-cycling situation, and would be plenty of radiation + mass to get 95% efficiency out of it. But you can see that as radiation EDR shrinks, the excess BTU is more, and the thermal mass less, and with much less radiator than that the minimum burn times would shrink an order of magnitude. You need burn times of at least 3 minutes and fewer than 5 burns an hour to be in the "reasonable" range. If it looks like 10 burns/hr or more at min-fire it's going to take a toll on equipment longevity and efficiency.

If you run this napkin analysis on your system and it's close, be sure add in the water volume and iron mass of the boiler as well.

---------------------- end clipped draft piece.

So, what are YOUR boiler's input & DOE output BTU?

How many zones?

How much radiation (sq. ft. EDR or fin-tube baseboard) on each zone?

Answered by Dana Dorsett
Posted Jun 14, 2016 4:59 PM ET


Scrapped the cast iron rads already. They were all different sizes and shapes in every room of this house, probably were salvaged over the years from other houses. They also took up a lot of floor space and caused problems placing furniture in the rooms like sofas and beds. The first floor which flooded the rads had all rusted within days of Sandy and had to be removed and placed outdoors to tear up the flooring and subflooring. Flood insurance would only pay me to clean them and repaint them but since the storm hit in end of October they ended up spending that winter outside in the yard getting rained and snowed on and totally turned to rusted junk by springtime. Flood insurance does not pay for any type of storage trailers or Pods or anything similar. So I junked them all then decided to do 2nd floor reno after making huge mess tearing out plaster on 1st floor. The heat and hot water for each apartment is Takagi TK-Jr units one dedicated for the heat and one dedicated for domestic for each apartment. They are not condensing units but they are modulating. I had them in before Sandy hooked to the cast iron with a filter on the returns that had a flush valve at the bottom of clear filters so I would occasionally open and blow out rust to protect the Takagi's. I had home runned every radiator with 1/2" oxy barrier pex to a manifold and the heat worked fine with this layout before Sandy. Now I plan to use Hydrotherm baseboard from Lowe's and also home run each section via the manifolds so each room of each apt has a home run same as the rads previously had. I decided to tear out the pex that was run to the rads after seeing a lot of rust on the inside of the pex and put in all new 1/2" oxy pex for the baseboard. I can set the dip swithes on the Takagi for 120, 140, 160, 180 as needed to dial in the temp that seems to work best once I'm back running again but this time with insulated walls on both floors. The code you quote of R49 is required in new construction but NJ has a Rehab subcode that addresses existing buildings and it says you can or should do as best as you can within the limitations of the building being worked on. So I have limited rafter depth in the 2x4 dormers its not possible to get R45 nor in the 2x6 areas either.

Answered by Brian Tober
Posted Jun 14, 2016 5:37 PM ET


IIRC the min-fire output of a TK-JR is about 15,000 BTU/hr. At an EWT of 180F that balances at ~15,000/500 = 30' of baseboard per zone. As long as each zone has 30' of baseboard it'll be fine.

If you want to run it at a lower temp than 180F you'll need more baseboard. If you try to micro-zone it with 8-10' sticks of baseboard per zone it'll trash a TK-JR pretty quickly unless you add buffer tanks.

I don't expect you to hit R49, but no matter what you still need to observe the minimum 30% of total R being closed cell foam, or it'll be prone to mold & rot conditions.

For the 2x4 sections it only takes an inch of closed cell polyurethane (R6) and a compressed R13 (=R10 @ 2.5") would be fine, since R6 would be ~37% of the total R. For the deeper-raftered sections it'll take 2" (R12). Where the rafters are fully 9" deep that would leave 7" for the fiber, which is fine. Compressing an R25 into 7" yields about R24, and at 2" the R12 foam would still be over 30% of the ~R36 total R.


Answered by Dana Dorsett
Posted Jun 14, 2016 6:06 PM ET


Thanks for the input I have received regarding spray foam insulation offgassing. I hear that you do not find a problem with offgassing from correctly applied spray foam insulation. I hear from Martin that we have no clear indication that spray foam insulation does NOT offgas, but that we have no evidence that it does, the way we know about toxicity of lead and aesbestos. I read that ASTM is currently trying to develop standards for measuring offgassing from spray foam insulation. So I suspect that correctly applied, it is inert, but I think the matter is still under examination.

I hear that if toxicity is a concern, I should consider other forms of insulation. So Id like your advice about that.

My space is partially below grade, with cement slab walls. I live in New England so there are big swings of cold and hot, and moisture can be an issue. So I had planned to use spray foam and framed for it, using some 2x3 framing on one wall to save space. I hope not to have to tear that framing down.

Is there an alternative form of insulation that would be good for below grade, that provides as good R value but does not require more depth of thickness than spray foam?

Again, thanks.

Answered by Chris Campbell
Posted Jun 15, 2016 1:06 AM ET


You may find there is some odor with the spray foam, but it probably won't be an issue when covered with drywall. When framing my basement area, I went with 1.5 inch metal studs to increase the usable space and mitigate any risk of moisture related problems. The metal also makes for straighter walls. Just be sure to include blocking for any heavy objects you plan to attach to the wall.

Answered by Steve Knapp CZ 3A Georgia
Posted Jun 15, 2016 8:03 AM ET


Chris: A continuous inch of rigid foam trapped to the concrete by your 2x3 studwall, compressing R13s in to the cavities gets you to code-min performance in New England without using spray foam.

You can't put the studs in direct contact with the concrete without significant rot risk. You have both the ground moisture to deal with, as well as the fact that the below-grade concrete will be below the summertime air dew points if the studwall cavities are insulated. But an inch of rigid foam will provide a capillary break against ground moisture, and will keep the foam/fiber interface and stud edges above the wintertime air dew points, which keeps the studs at a sufficiently low moisture content year round. An inch of foam under the bottom plate makes sense too (for the same reasons.)

Use foil faced polyiso against the walls, and EPS under the stud plates, both of which are blown with low environmental impact pentane, whereas XPS is blown with HFCs with extreme 100 year global warming issues, and drops to the performance of EPS over a handful of decades as the HFCs leak out.

Answered by D Dorsett
Posted Jun 15, 2016 9:31 AM ET


Thanks Dana and Martin! The foil faced foam board has info printed on it claiming a R value with the air space of 3/4" min so I used 1" air space against the roof, then the fiberglass under it as I explained. I just got 4 small relative humidity sensors on ebay that have wired probe with small digital displays. They were very inexpensive and shipped from china. When I opened the envelope they all were on showing 57% RH. I placed 2 above the foam in the 1" space between roof and foil and they went to 34% then placed the other two in the 2x4 dormer areas slipping probe between the drywall and kraft paper at the peak (drywall is not taped or finished yet in the areas we rocked so far). Those went up to 86% then when I turned on some fans they dropped to 59%. So my theory is the moisture is interior RH that is trying to go up to the hotter area above the foam but gets stuck at the kraft vapor barrier and converts to water. This is happening now in NJ on the first few hot sunny days we had in high 80's outside and it is hot and humid in the 2nd floor where we are working. There does not seem to be a cold surface for condensation formation as it is very hot inside the bldg and outside and this happens in the afternoon around 1-2 pm, not in the evenings or mornings when I would expect it to happen as the roof cools off. So I understand that you recommend spray foam as the only fix but its not in the budget so I am considering taking out the fiberglass and stacking up more layers of foam at the highest sections 1 foot wide each side of the peaks and can foaming around it (this only appears at the highest peaks a few inches on each side).Or other option is to not insulate roof at all just drywall it with 5/8" or would that be more problematic for moisture? The house never had any insulation anywhere until I started this project so it would be back to square one but with drywall instead of plaster ceilings.

Answered by Brian Tober
Posted Jun 15, 2016 10:04 AM ET


The RH is "Relative Humidity", relative to the temperature. The temperature is not the same on each side of the foam. To count the air space as R2.8 requires that the air be extremely still, and completely horizontal to inhibit convection, and only when the roof deck being hotter than the interior. That does not help your wintertime dew point considerations at all, since in winter the foil facer is warmer than the roof deck, and convection breaks up the still air film performance. Allowing for even another R1 would be generous, and not conservative enough from a dew point risk perspective. To be conservative, give the air films + foil facer about an R0.3 for total average wintertime performance.

The R3.85/inch indicates that it's 1lb density Type-I EPS, which is it's performance when the average temp through the foam is 75F. When the average temp through the foam is 40F it's performace rises to about R4.15. With 1" of foam the average temp through the foam in your location will be slightly above that, so for dew point control don't count on more than R4.0 for the foam, plus the R0.3 for the foil + air films gives R4.3, which is sufficient dew point control for up to a maximum of R10 of fiber below it. That's fine for the 2x4 section, where even with full dimension 2x4s (rather than milled 2x4s that are nominally 3.5" deep), since compressing a batt into the remaining 2" woul still be less than R10. But it's a problem for R13 or R15s in a 2x6 rafter bay.

If you stack another inch on it, the average temp through the inner inch will be warmer still, and the foil offers no value, so all it R3.9 for every subsquent inch. At 2" you would have about R4.3 + R3.9 = R8.2, which is sufficient dew point control for up to a maximum of R19 of fiber, which is again fine for the 2 x 6 rafter bays, but a problem for the 9" deep sections, with 7" of space for fiber.

Stacking the EPS 3 layers deep there would be fine though, since you would have R4.3 + R3.9 + R3.9= R12.1 which is good enough for up to R28 of fiber. The remaining 6" of space, which is enough space to compress an R25 fiberglass batt (or doubled-up R13s if that's cheaper & more available) which would deliver about R22 performance for the fiber layer.

For layering the EPS, cut it ~1/2" narrower than the available width, and tack it to the original layer with small dabs of foam board construction adhesive (or thin double sided tape) then use can-foam to fill the 1/4" gaps at the edges for a tight seal to the rafters. It doesn't matter if the additional EPS has facers or not, whatever is cheapest is the "right" foam to use. Even unfaced Type-I EPS is usually under 5 perms @ 1" thickness, and even if some tiny amount of moisture accumulates in the layers EPS it's performance isn't much affected, nor is it damaged. The only way significant moisture can accumulate would be if the foam layering is not tightly air sealed at the edges.

Answered by Dana Dorsett
Posted Jun 15, 2016 11:39 AM ET
Edited Jun 15, 2016 11:42 AM ET.


This is DS, the original questioner from May 14, 2014 writing. I have been meaning to give an update/epilogue to my research on closed-cell Spray Foam Insulation (“SFI”) off-gassing, and Chris Campbell’s June 10, 2016 post (post #10) has prompted me to finally write this.

As should be clear from my several previous posts, I understood that potentially-harmful gasses were created and dispersed during SFI installation. My concern was long-term off-gassing since I and my family would be living in the home. My summary of findings is this: I am extremely happy with the SFI, there is no odor whatsoever, and my research (and common sense) indicate that (as Martin Holladay has noted several times) properly-installed SFI should be inert and odorless. I believe it to be that and entirely safe – even safer that fiberglass or other insulation materials. I had the SFI installed in the fall of 2014, and have now lived with it through six full seasons (including two winters), and am very satisfied with the results, the cure of the ice damming and mice issues, and several other unanticipated fringe benefits as described below.

By way of background, I had three motives in getting SFI: 1) stopping ice damming; 2) getting rid of field mice in my attic and basement; and 3) saving a little money. Also of note, I listed these three rationales in order of importance to me. Yes, saving money was the least of my motives. Solving the ice damming was my primary motive. Getting rid of the field mice was going to be an extra bonus that helped me rationalize the cost of SFI. Saving money on fuel (and less wear and tear on the HVAC units) would be the icing on the cake, but it was the least important issue for me (my winter fuel bills never exceeded $350). Also, one of the typical rationales of homeowners, “making the house more comfortable,” was not a motive of mine at all since my house, built in 1980, was already quite comfortable (not drafty or anything as far as I could tell).

ICE DAMMING: I had a problem with ice damming nearly every winter. Water was dripping into the house and ice damming could cost tens of thousands of dollars’ worth of damage I had read. Heat was escaping through my old, fiberglass insulation and causing this problem. In addition to ice damming, I had icicles anywhere from 2’ to 5’ hanging from my gutters. Clearly I had a freeze-thaw cycle going on which was causing ice damming as well as the hazard of heavy, dangerous icicles hanging all over the house, including over entrance ways.

MICE: I also had field mice in the attic and basement (as does nearly every house in the rural area where I live). We never had a mouse in the living space, but the attic and basement were concerns. The scratching and other noises coming from the attic during the night drove my wife crazy. Our neighbors, who do not have SFI, still complain of the critter noise problem they have and how they can’t sleep at night. In addition to the noise, critters in the house pose a health hazard and can potentially damage wires and other infrastructure. I figured SFI would incidentally solve this issue.

SAVINGS: As stated above, saving money was the lowest of my motivations, so much so as to not be a motive at all.

PROCESS: I removed all the fiberglass from the attic and the rim joist of the basement. I also vacuumed the entire attic and rim joist (in order to get rid of any debris, mouse droppings, etc.). I then had 6 inches of closed-cell SFI installed on the attic floor and the entire basement rim joist.

RESULTS: In all, I am very happy with the SFI. Not one single icicle on my house these past two winters. The other neighbors had 5' icicles by contrast, as did I before the SFI was installed. Post-SFI installation, I had no ice damming at all, and, of course, no ice dam leaks whatsoever. No more mice in the attic or basement (the mice must have been entering near various points of the rim joist in the basement and making their way up to the attic through cavities in the inner walls of the house). Our heating bills also went down, and the second floor HVAC works much more efficiently now because the SFI in the attic stopped all the leaks where the duct work met the exchanges in the ceiling, and the first floor HVAC is more efficient too since all the gaps in the basement got sealed up. The conditioned air coming out of all vents is actually now noticeably more forceful (more CFM due to the reduction in air leakage). And with air convection and air loss during the old fiberglass days, it is not hard to fathom that the HVAC was circulating air containing unhealthy fiberglass particles. There was no SFI odor in the house after a few days post-installation, and to this day, no odor at all from the SFI. I have been in the attic on several hot days. Many materials, when they get very warm/hot, give off an odor that might not be detectable at regular temperatures. Indeed, the fiberglass in the hot attic had a slight odor that probably resulted from the formaldehyde in the fiberglass. As such, SFI having no odor in the hot attic is a good indicator of how stable it is and that it does not off-gas. As noted, a good part of SFI is polyurethane. My original post observed that “Fully reacted polyurethane polymer is chemically inert." It makes sense that both the polyurethane as well as anything suspended in it (such as any deleterious material), would remain highly stable. Anything in the polyurethane would remain “trapped” in the polyurethane, unable to off-gas. In all, there is no SFI odor at all. My research confirmed Martin Holladay’s conclusion – SFI odors occurred in instances where SFI installation was done incorrectly. We had no issues. Indeed, the SFI has reduced the odors in the house (see below reference to the rim joist odor problem that SFI solved). Anecdotally, we seem to be healthier and breather easier in the house now. The house is less dusty. We believe the SFI has significantly reduced air borne particles, obviously airborne fiberglass, mold, mildew, dust, and allergens. We are very pleased.

One major benefit of sealing the basement rim joist with SFI has been a tremendous reduction/elimination of the musty odor in the basement. My theory is two-fold: First, prior to the rim joist being sealed, the first floor HVAC return was pulling musty air into the basement through the outer, fiberglass-filled walls of the house, down toward the rim joist and into the HVAC return. Now, with the rim joist sealed, that suction action no longer happens. Second, with the rim joist sealed, the basement is a much more air-tight space. As such, the dehumidifier can accomplish a lot more and isn't always playing catch up due to constant outside air infiltration. The hygrometer in my basement proves this point as it has shown summertime relative humidity at levels much lower than ever before achieved pre-SFI installation (I have tracked the basement's humidity for 7 years now – pre-SFI and post-SFI installation).

Lastly, and this may sound strange, but the SFI applied to the attic floor (which is also the second floor ceiling) has made the 2nd floor ceiling very strong. The house was built in 1980 before using screws to secure sheet rock was popular. As such, nails were used, and in my opinion, insufficient nails were used to secure the sheet rock (as tested by tapping in a variety of areas). The ceiling was quite flat (no warping or other issues), but it always nagged me that the sheet rocking wasn’t done right (in my opinion). The 6” layer of SFI on the attic floor, though, essentially bonded the entire ceiling to the joists and the ceiling is incredible strong. The SFI (closed cell) is so strong, you can walk on it in the attic with no risk of falling through to the living space. A fringe benefit of the SFI installation.

The SFI has accomplished everything I hoped it would and a lot more. There is no odor post-installation, and we are very pleased with it.

Answered by D S
Posted Jun 15, 2016 3:35 PM ET


It should come as no surprise that 6" of 2lb polyurethane makes the ceiling very rigid and very strong. Even 2" would be noticeably stiffer, and 3" under roof decks is considered structural in hurricane zones. Any 2lb density foam is walkable without breaking at 6" at typical joist/truss spacings.

The theory that the musty basement issue was all about air being pulled down toward the rim joists isn't well founded- it's really the outdoor air infiltration, and the average temperatures in the basement. Ideally the whole basement wall would have been insulated, not just the band joists. With the basement being insulated the surfaces are warmer, above the dew point of the air, whereas with an uninsulated foundation the air films near the walls are cooler, and extremely high relative humidity. Being more air tight helps reduce the load on the dehumidifier, sure, but even at a higher average relative humidity in the basement than previously the musty smell issue is mitigated by warmer wall surfaces, and lower RH in the near-wall air films

If the mechanical dehumidifcation had previously been unable to keep the basement under 65% RH and now can, that's great, but there isn't much benefit to taking it a LOT lower than that- 60% is usually fine with insulated basement walls, and will use a lot less annual power than pulling it down to 50% or lower.

If only it were true that "...Anything in the polyurethane would remain “trapped” in the polyurethane..." The HFC245fa surely isn't. Outgassing HFCs are a greenhouse gas problem, if not a human health problem. Using some amount for air sealing or vapor retardency control as-need is one thing, but 6" on the attic floor opposite of "green building" by most reckoning.

At the attic floor using open cell foam (10-11" to hit the same R value) would have been just fine in a NJ climate and comes without the HFC burden. It uses less than half the polymer to boot, and would also have been cheaper. Putting closed cell foam on the basement walls where its low vapor retardency actually BUYS you something makes far more sense than on an attic floor.

Answered by Dana Dorsett
Posted Jun 15, 2016 4:23 PM ET


Response to Chris (Comment #28):

Q: "Is there an alternative form of insulation that would be good for below grade, that provides as good R value but does not require more depth of thickness than spray foam?"

A. The interior side of below-grade concrete walls can be insulated with rigid foam. For more information on this work, see How to Insulate a Basement Wall.

Answered by Martin Holladay
Posted Jun 16, 2016 1:01 AM ET

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